TOMOYO Linux Cross Reference
Linux/tools/lguest/lguest.c

   /*P:100
    * This is the Launcher code, a simple program which lays out the "physical"
    * memory for the new Guest by mapping the kernel image and the virtual
    * devices, then opens /dev/lguest to tell the kernel about the Guest and
    * control it.
   :*/
   #define _LARGEFILE64_SOURCE
   #define _GNU_SOURCE
   #include <stdio.h>
  #include <string.h>
  #include <unistd.h>
  #include <err.h>
  #include <stdint.h>
  #include <stdlib.h>
  #include <elf.h>
  #include <sys/mman.h>
  #include <sys/param.h>
  #include <sys/types.h>
  #include <sys/stat.h>
  #include <sys/wait.h>
  #include <sys/eventfd.h>
  #include <fcntl.h>
  #include <stdbool.h>
  #include <errno.h>
  #include <ctype.h>
  #include <sys/socket.h>
  #include <sys/ioctl.h>
  #include <sys/time.h>
  #include <time.h>
  #include <netinet/in.h>
  #include <net/if.h>
  #include <linux/sockios.h>
  #include <linux/if_tun.h>
  #include <sys/uio.h>
  #include <termios.h>
  #include <getopt.h>
  #include <assert.h>
  #include <sched.h>
  #include <limits.h>
  #include <stddef.h>
  #include <signal.h>
  #include <pwd.h>
  #include <grp.h>
  #include <sys/user.h>
  #include <linux/pci_regs.h>
  
  #ifndef VIRTIO_F_ANY_LAYOUT
  #define VIRTIO_F_ANY_LAYOUT             27
  #endif
  
  /*L:110
   * We can ignore the 43 include files we need for this program, but I do want
   * to draw attention to the use of kernel-style types.
   *
   * As Linus said, "C is a Spartan language, and so should your naming be."  I
   * like these abbreviations, so we define them here.  Note that u64 is always
   * unsigned long long, which works on all Linux systems: this means that we can
   * use %llu in printf for any u64.
   */
  typedef unsigned long long u64;
  typedef uint32_t u32;
  typedef uint16_t u16;
  typedef uint8_t u8;
  /*:*/
  
  #define VIRTIO_CONFIG_NO_LEGACY
  #define VIRTIO_PCI_NO_LEGACY
  #define VIRTIO_BLK_NO_LEGACY
  #define VIRTIO_NET_NO_LEGACY
  
  /* Use in-kernel ones, which defines VIRTIO_F_VERSION_1 */
  #include "../../include/uapi/linux/virtio_config.h"
  #include "../../include/uapi/linux/virtio_net.h"
  #include "../../include/uapi/linux/virtio_blk.h"
  #include "../../include/uapi/linux/virtio_console.h"
  #include "../../include/uapi/linux/virtio_rng.h"
  #include <linux/virtio_ring.h>
  #include "../../include/uapi/linux/virtio_pci.h"
  #include <asm/bootparam.h>
  #include "../../include/linux/lguest_launcher.h"
  
  #define BRIDGE_PFX "bridge:"
  #ifndef SIOCBRADDIF
  #define SIOCBRADDIF     0x89a2          /* add interface to bridge      */
  #endif
  /* We can have up to 256 pages for devices. */
  #define DEVICE_PAGES 256
  /* This will occupy 3 pages: it must be a power of 2. */
  #define VIRTQUEUE_NUM 256
  
  /*L:120
   * verbose is both a global flag and a macro.  The C preprocessor allows
   * this, and although I wouldn't recommend it, it works quite nicely here.
   */
  static bool verbose;
  #define verbose(args...) \
          do { if (verbose) printf(args); } while(0)
  /*:*/
  
 /* The pointer to the start of guest memory. */
 static void *guest_base;
 /* The maximum guest physical address allowed, and maximum possible. */
 static unsigned long guest_limit, guest_max, guest_mmio;
 /* The /dev/lguest file descriptor. */
 static int lguest_fd;
 
 /* a per-cpu variable indicating whose vcpu is currently running */
 static unsigned int __thread cpu_id;
 
 /* 5 bit device number in the PCI_CONFIG_ADDR => 32 only */
 #define MAX_PCI_DEVICES 32
 
 /* This is our list of devices. */
 struct device_list {
         /* Counter to assign interrupt numbers. */
         unsigned int next_irq;
 
         /* Counter to print out convenient device numbers. */
         unsigned int device_num;
 
         /* PCI devices. */
         struct device *pci[MAX_PCI_DEVICES];
 };
 
 /* The list of Guest devices, based on command line arguments. */
 static struct device_list devices;
 
 /*
  * Just like struct virtio_pci_cfg_cap in uapi/linux/virtio_pci.h,
  * but uses a u32 explicitly for the data.
  */
 struct virtio_pci_cfg_cap_u32 {
         struct virtio_pci_cap cap;
         u32 pci_cfg_data; /* Data for BAR access. */
 };
 
 struct virtio_pci_mmio {
         struct virtio_pci_common_cfg cfg;
         u16 notify;
         u8 isr;
         u8 padding;
         /* Device-specific configuration follows this. */
 };
 
 /* This is the layout (little-endian) of the PCI config space. */
 struct pci_config {
         u16 vendor_id, device_id;
         u16 command, status;
         u8 revid, prog_if, subclass, class;
         u8 cacheline_size, lat_timer, header_type, bist;
         u32 bar[6];
         u32 cardbus_cis_ptr;
         u16 subsystem_vendor_id, subsystem_device_id;
         u32 expansion_rom_addr;
         u8 capabilities, reserved1[3];
         u32 reserved2;
         u8 irq_line, irq_pin, min_grant, max_latency;
 
         /* Now, this is the linked capability list. */
         struct virtio_pci_cap common;
         struct virtio_pci_notify_cap notify;
         struct virtio_pci_cap isr;
         struct virtio_pci_cap device;
         struct virtio_pci_cfg_cap_u32 cfg_access;
 };
 
 /* The device structure describes a single device. */
 struct device {
         /* The name of this device, for --verbose. */
         const char *name;
 
         /* Any queues attached to this device */
         struct virtqueue *vq;
 
         /* Is it operational */
         bool running;
 
         /* Has it written FEATURES_OK but not re-checked it? */
         bool wrote_features_ok;
 
         /* PCI configuration */
         union {
                 struct pci_config config;
                 u32 config_words[sizeof(struct pci_config) / sizeof(u32)];
         };
 
         /* Features we offer, and those accepted. */
         u64 features, features_accepted;
 
         /* Device-specific config hangs off the end of this. */
         struct virtio_pci_mmio *mmio;
 
         /* PCI MMIO resources (all in BAR0) */
         size_t mmio_size;
         u32 mmio_addr;
 
         /* Device-specific data. */
         void *priv;
 };
 
 /* The virtqueue structure describes a queue attached to a device. */
 struct virtqueue {
         struct virtqueue *next;
 
         /* Which device owns me. */
         struct device *dev;
 
         /* Name for printing errors. */
         const char *name;
 
         /* The actual ring of buffers. */
         struct vring vring;
 
         /* The information about this virtqueue (we only use queue_size on) */
         struct virtio_pci_common_cfg pci_config;
 
         /* Last available index we saw. */
         u16 last_avail_idx;
 
         /* How many are used since we sent last irq? */
         unsigned int pending_used;
 
         /* Eventfd where Guest notifications arrive. */
         int eventfd;
 
         /* Function for the thread which is servicing this virtqueue. */
         void (*service)(struct virtqueue *vq);
         pid_t thread;
 };
 
 /* Remember the arguments to the program so we can "reboot" */
 static char **main_args;
 
 /* The original tty settings to restore on exit. */
 static struct termios orig_term;
 
 /*
  * We have to be careful with barriers: our devices are all run in separate
  * threads and so we need to make sure that changes visible to the Guest happen
  * in precise order.
  */
 #define wmb() __asm__ __volatile__("" : : : "memory")
 #define rmb() __asm__ __volatile__("lock; addl $0,0(%%esp)" : : : "memory")
 #define mb() __asm__ __volatile__("lock; addl $0,0(%%esp)" : : : "memory")
 
 /* Wrapper for the last available index.  Makes it easier to change. */
 #define lg_last_avail(vq)       ((vq)->last_avail_idx)
 
 /*
  * The virtio configuration space is defined to be little-endian.  x86 is
  * little-endian too, but it's nice to be explicit so we have these helpers.
  */
 #define cpu_to_le16(v16) (v16)
 #define cpu_to_le32(v32) (v32)
 #define cpu_to_le64(v64) (v64)
 #define le16_to_cpu(v16) (v16)
 #define le32_to_cpu(v32) (v32)
 #define le64_to_cpu(v64) (v64)
 
 /*
  * A real device would ignore weird/non-compliant driver behaviour.  We
  * stop and flag it, to help debugging Linux problems.
  */
 #define bad_driver(d, fmt, ...) \
         errx(1, "%s: bad driver: " fmt, (d)->name, ## __VA_ARGS__)
 #define bad_driver_vq(vq, fmt, ...)                            \
         errx(1, "%s vq %s: bad driver: " fmt, (vq)->dev->name, \
              vq->name, ## __VA_ARGS__)
 
 /* Is this iovec empty? */
 static bool iov_empty(const struct iovec iov[], unsigned int num_iov)
 {
         unsigned int i;
 
         for (i = 0; i < num_iov; i++)
                 if (iov[i].iov_len)
                         return false;
         return true;
 }
 
 /* Take len bytes from the front of this iovec. */
 static void iov_consume(struct device *d,
                         struct iovec iov[], unsigned num_iov,
                         void *dest, unsigned len)
 {
         unsigned int i;
 
         for (i = 0; i < num_iov; i++) {
                 unsigned int used;
 
                 used = iov[i].iov_len < len ? iov[i].iov_len : len;
                 if (dest) {
                         memcpy(dest, iov[i].iov_base, used);
                         dest += used;
                 }
                 iov[i].iov_base += used;
                 iov[i].iov_len -= used;
                 len -= used;
         }
         if (len != 0)
                 bad_driver(d, "iovec too short!");
 }
 
 /*L:100
  * The Launcher code itself takes us out into userspace, that scary place where
  * pointers run wild and free!  Unfortunately, like most userspace programs,
  * it's quite boring (which is why everyone likes to hack on the kernel!).
  * Perhaps if you make up an Lguest Drinking Game at this point, it will get
  * you through this section.  Or, maybe not.
  *
  * The Launcher sets up a big chunk of memory to be the Guest's "physical"
  * memory and stores it in "guest_base".  In other words, Guest physical ==
  * Launcher virtual with an offset.
  *
  * This can be tough to get your head around, but usually it just means that we
  * use these trivial conversion functions when the Guest gives us its
  * "physical" addresses:
  */
 static void *from_guest_phys(unsigned long addr)
 {
         return guest_base + addr;
 }
 
 static unsigned long to_guest_phys(const void *addr)
 {
         return (addr - guest_base);
 }
 
 /*L:130
  * Loading the Kernel.
  *
  * We start with couple of simple helper routines.  open_or_die() avoids
  * error-checking code cluttering the callers:
  */
 static int open_or_die(const char *name, int flags)
 {
         int fd = open(name, flags);
         if (fd < 0)
                 err(1, "Failed to open %s", name);
         return fd;
 }
 
 /* map_zeroed_pages() takes a number of pages. */
 static void *map_zeroed_pages(unsigned int num)
 {
         int fd = open_or_die("/dev/zero", O_RDONLY);
         void *addr;
 
         /*
          * We use a private mapping (ie. if we write to the page, it will be
          * copied). We allocate an extra two pages PROT_NONE to act as guard
          * pages against read/write attempts that exceed allocated space.
          */
         addr = mmap(NULL, getpagesize() * (num+2),
                     PROT_NONE, MAP_PRIVATE, fd, 0);
 
         if (addr == MAP_FAILED)
                 err(1, "Mmapping %u pages of /dev/zero", num);
 
         if (mprotect(addr + getpagesize(), getpagesize() * num,
                      PROT_READ|PROT_WRITE) == -1)
                 err(1, "mprotect rw %u pages failed", num);
 
         /*
          * One neat mmap feature is that you can close the fd, and it
          * stays mapped.
          */
         close(fd);
 
         /* Return address after PROT_NONE page */
         return addr + getpagesize();
 }
 
 /* Get some bytes which won't be mapped into the guest. */
 static unsigned long get_mmio_region(size_t size)
 {
         unsigned long addr = guest_mmio;
         size_t i;
 
         if (!size)
                 return addr;
 
         /* Size has to be a power of 2 (and multiple of 16) */
         for (i = 1; i < size; i <<= 1);
 
         guest_mmio += i;
 
         return addr;
 }
 
 /*
  * This routine is used to load the kernel or initrd.  It tries mmap, but if
  * that fails (Plan 9's kernel file isn't nicely aligned on page boundaries),
  * it falls back to reading the memory in.
  */
 static void map_at(int fd, void *addr, unsigned long offset, unsigned long len)
 {
         ssize_t r;
 
         /*
          * We map writable even though for some segments are marked read-only.
          * The kernel really wants to be writable: it patches its own
          * instructions.
          *
          * MAP_PRIVATE means that the page won't be copied until a write is
          * done to it.  This allows us to share untouched memory between
          * Guests.
          */
         if (mmap(addr, len, PROT_READ|PROT_WRITE,
                  MAP_FIXED|MAP_PRIVATE, fd, offset) != MAP_FAILED)
                 return;
 
         /* pread does a seek and a read in one shot: saves a few lines. */
         r = pread(fd, addr, len, offset);
         if (r != len)
                 err(1, "Reading offset %lu len %lu gave %zi", offset, len, r);
 }
 
 /*
  * This routine takes an open vmlinux image, which is in ELF, and maps it into
  * the Guest memory.  ELF = Embedded Linking Format, which is the format used
  * by all modern binaries on Linux including the kernel.
  *
  * The ELF headers give *two* addresses: a physical address, and a virtual
  * address.  We use the physical address; the Guest will map itself to the
  * virtual address.
  *
  * We return the starting address.
  */
 static unsigned long map_elf(int elf_fd, const Elf32_Ehdr *ehdr)
 {
         Elf32_Phdr phdr[ehdr->e_phnum];
         unsigned int i;
 
         /*
          * Sanity checks on the main ELF header: an x86 executable with a
          * reasonable number of correctly-sized program headers.
          */
         if (ehdr->e_type != ET_EXEC
             || ehdr->e_machine != EM_386
             || ehdr->e_phentsize != sizeof(Elf32_Phdr)
             || ehdr->e_phnum < 1 || ehdr->e_phnum > 65536U/sizeof(Elf32_Phdr))
                 errx(1, "Malformed elf header");
 
         /*
          * An ELF executable contains an ELF header and a number of "program"
          * headers which indicate which parts ("segments") of the program to
          * load where.
          */
 
         /* We read in all the program headers at once: */
         if (lseek(elf_fd, ehdr->e_phoff, SEEK_SET) < 0)
                 err(1, "Seeking to program headers");
         if (read(elf_fd, phdr, sizeof(phdr)) != sizeof(phdr))
                 err(1, "Reading program headers");
 
         /*
          * Try all the headers: there are usually only three.  A read-only one,
          * a read-write one, and a "note" section which we don't load.
          */
         for (i = 0; i < ehdr->e_phnum; i++) {
                 /* If this isn't a loadable segment, we ignore it */
                 if (phdr[i].p_type != PT_LOAD)
                         continue;
 
                 verbose("Section %i: size %i addr %p\n",
                         i, phdr[i].p_memsz, (void *)phdr[i].p_paddr);
 
                 /* We map this section of the file at its physical address. */
                 map_at(elf_fd, from_guest_phys(phdr[i].p_paddr),
                        phdr[i].p_offset, phdr[i].p_filesz);
         }
 
         /* The entry point is given in the ELF header. */
         return ehdr->e_entry;
 }
 
 /*L:150
  * A bzImage, unlike an ELF file, is not meant to be loaded.  You're supposed
  * to jump into it and it will unpack itself.  We used to have to perform some
  * hairy magic because the unpacking code scared me.
  *
  * Fortunately, Jeremy Fitzhardinge convinced me it wasn't that hard and wrote
  * a small patch to jump over the tricky bits in the Guest, so now we just read
  * the funky header so we know where in the file to load, and away we go!
  */
 static unsigned long load_bzimage(int fd)
 {
         struct boot_params boot;
         int r;
         /* Modern bzImages get loaded at 1M. */
         void *p = from_guest_phys(0x100000);
 
         /*
          * Go back to the start of the file and read the header.  It should be
          * a Linux boot header (see Documentation/x86/boot.txt)
          */
         lseek(fd, 0, SEEK_SET);
         read(fd, &boot, sizeof(boot));
 
         /* Inside the setup_hdr, we expect the magic "HdrS" */
         if (memcmp(&boot.hdr.header, "HdrS", 4) != 0)
                 errx(1, "This doesn't look like a bzImage to me");
 
         /* Skip over the extra sectors of the header. */
         lseek(fd, (boot.hdr.setup_sects+1) * 512, SEEK_SET);
 
         /* Now read everything into memory. in nice big chunks. */
         while ((r = read(fd, p, 65536)) > 0)
                 p += r;
 
         /* Finally, code32_start tells us where to enter the kernel. */
         return boot.hdr.code32_start;
 }
 
 /*L:140
  * Loading the kernel is easy when it's a "vmlinux", but most kernels
  * come wrapped up in the self-decompressing "bzImage" format.  With a little
  * work, we can load those, too.
  */
 static unsigned long load_kernel(int fd)
 {
         Elf32_Ehdr hdr;
 
         /* Read in the first few bytes. */
         if (read(fd, &hdr, sizeof(hdr)) != sizeof(hdr))
                 err(1, "Reading kernel");
 
         /* If it's an ELF file, it starts with "\177ELF" */
         if (memcmp(hdr.e_ident, ELFMAG, SELFMAG) == 0)
                 return map_elf(fd, &hdr);
 
         /* Otherwise we assume it's a bzImage, and try to load it. */
         return load_bzimage(fd);
 }
 
 /*
  * This is a trivial little helper to align pages.  Andi Kleen hated it because
  * it calls getpagesize() twice: "it's dumb code."
  *
  * Kernel guys get really het up about optimization, even when it's not
  * necessary.  I leave this code as a reaction against that.
  */
 static inline unsigned long page_align(unsigned long addr)
 {
         /* Add upwards and truncate downwards. */
         return ((addr + getpagesize()-1) & ~(getpagesize()-1));
 }
 
 /*L:180
  * An "initial ram disk" is a disk image loaded into memory along with the
  * kernel which the kernel can use to boot from without needing any drivers.
  * Most distributions now use this as standard: the initrd contains the code to
  * load the appropriate driver modules for the current machine.
  *
  * Importantly, James Morris works for RedHat, and Fedora uses initrds for its
  * kernels.  He sent me this (and tells me when I break it).
  */
 static unsigned long load_initrd(const char *name, unsigned long mem)
 {
         int ifd;
         struct stat st;
         unsigned long len;
 
         ifd = open_or_die(name, O_RDONLY);
         /* fstat() is needed to get the file size. */
         if (fstat(ifd, &st) < 0)
                 err(1, "fstat() on initrd '%s'", name);
 
         /*
          * We map the initrd at the top of memory, but mmap wants it to be
          * page-aligned, so we round the size up for that.
          */
         len = page_align(st.st_size);
         map_at(ifd, from_guest_phys(mem - len), 0, st.st_size);
         /*
          * Once a file is mapped, you can close the file descriptor.  It's a
          * little odd, but quite useful.
          */
         close(ifd);
         verbose("mapped initrd %s size=%lu @ %p\n", name, len, (void*)mem-len);
 
         /* We return the initrd size. */
         return len;
 }
 /*:*/
 
 /*
  * Simple routine to roll all the commandline arguments together with spaces
  * between them.
  */
 static void concat(char *dst, char *args[])
 {
         unsigned int i, len = 0;
 
         for (i = 0; args[i]; i++) {
                 if (i) {
                         strcat(dst+len, " ");
                         len++;
                 }
                 strcpy(dst+len, args[i]);
                 len += strlen(args[i]);
         }
         /* In case it's empty. */
         dst[len] = '\0';
 }
 
 /*L:185
  * This is where we actually tell the kernel to initialize the Guest.  We
  * saw the arguments it expects when we looked at initialize() in lguest_user.c:
  * the base of Guest "physical" memory, the top physical page to allow and the
  * entry point for the Guest.
  */
 static void tell_kernel(unsigned long start)
 {
         unsigned long args[] = { LHREQ_INITIALIZE,
                                  (unsigned long)guest_base,
                                  guest_limit / getpagesize(), start,
                                  (guest_mmio+getpagesize()-1) / getpagesize() };
         verbose("Guest: %p - %p (%#lx, MMIO %#lx)\n",
                 guest_base, guest_base + guest_limit,
                 guest_limit, guest_mmio);
         lguest_fd = open_or_die("/dev/lguest", O_RDWR);
         if (write(lguest_fd, args, sizeof(args)) < 0)
                 err(1, "Writing to /dev/lguest");
 }
 /*:*/
 
 /*L:200
  * Device Handling.
  *
  * When the Guest gives us a buffer, it sends an array of addresses and sizes.
  * We need to make sure it's not trying to reach into the Launcher itself, so
  * we have a convenient routine which checks it and exits with an error message
  * if something funny is going on:
  */
 static void *_check_pointer(struct device *d,
                             unsigned long addr, unsigned int size,
                             unsigned int line)
 {
         /*
          * Check if the requested address and size exceeds the allocated memory,
          * or addr + size wraps around.
          */
         if ((addr + size) > guest_limit || (addr + size) < addr)
                 bad_driver(d, "%s:%i: Invalid address %#lx",
                            __FILE__, line, addr);
         /*
          * We return a pointer for the caller's convenience, now we know it's
          * safe to use.
          */
         return from_guest_phys(addr);
 }
 /* A macro which transparently hands the line number to the real function. */
 #define check_pointer(d,addr,size) _check_pointer(d, addr, size, __LINE__)
 
 /*
  * Each buffer in the virtqueues is actually a chain of descriptors.  This
  * function returns the next descriptor in the chain, or vq->vring.num if we're
  * at the end.
  */
 static unsigned next_desc(struct device *d, struct vring_desc *desc,
                           unsigned int i, unsigned int max)
 {
         unsigned int next;
 
         /* If this descriptor says it doesn't chain, we're done. */
         if (!(desc[i].flags & VRING_DESC_F_NEXT))
                 return max;
 
         /* Check they're not leading us off end of descriptors. */
         next = desc[i].next;
         /* Make sure compiler knows to grab that: we don't want it changing! */
         wmb();
 
         if (next >= max)
                 bad_driver(d, "Desc next is %u", next);
 
         return next;
 }
 
 /*
  * This actually sends the interrupt for this virtqueue, if we've used a
  * buffer.
  */
 static void trigger_irq(struct virtqueue *vq)
 {
         unsigned long buf[] = { LHREQ_IRQ, vq->dev->config.irq_line };
 
         /* Don't inform them if nothing used. */
         if (!vq->pending_used)
                 return;
         vq->pending_used = 0;
 
         /*
          * 2.4.7.1:
          *
          *  If the VIRTIO_F_EVENT_IDX feature bit is not negotiated:
          *    The driver MUST set flags to 0 or 1. 
          */
         if (vq->vring.avail->flags > 1)
                 bad_driver_vq(vq, "avail->flags = %u\n", vq->vring.avail->flags);
 
         /*
          * 2.4.7.2:
          *
          *  If the VIRTIO_F_EVENT_IDX feature bit is not negotiated:
          *
          *     - The device MUST ignore the used_event value.
          *     - After the device writes a descriptor index into the used ring:
          *         - If flags is 1, the device SHOULD NOT send an interrupt.
          *         - If flags is 0, the device MUST send an interrupt.
          */
         if (vq->vring.avail->flags & VRING_AVAIL_F_NO_INTERRUPT) {
                 return;
         }
 
         /*
          * 4.1.4.5.1:
          *
          *  If MSI-X capability is disabled, the device MUST set the Queue
          *  Interrupt bit in ISR status before sending a virtqueue notification
          *  to the driver.
          */
         vq->dev->mmio->isr = 0x1;
 
         /* Send the Guest an interrupt tell them we used something up. */
         if (write(lguest_fd, buf, sizeof(buf)) != 0)
                 err(1, "Triggering irq %i", vq->dev->config.irq_line);
 }
 
 /*
  * This looks in the virtqueue for the first available buffer, and converts
  * it to an iovec for convenient access.  Since descriptors consist of some
  * number of output then some number of input descriptors, it's actually two
  * iovecs, but we pack them into one and note how many of each there were.
  *
  * This function waits if necessary, and returns the descriptor number found.
  */
 static unsigned wait_for_vq_desc(struct virtqueue *vq,
                                  struct iovec iov[],
                                  unsigned int *out_num, unsigned int *in_num)
 {
         unsigned int i, head, max;
         struct vring_desc *desc;
         u16 last_avail = lg_last_avail(vq);
 
         /*
          * 2.4.7.1:
          *
          *   The driver MUST handle spurious interrupts from the device.
          *
          * That's why this is a while loop.
          */
 
         /* There's nothing available? */
         while (last_avail == vq->vring.avail->idx) {
                 u64 event;
 
                 /*
                  * Since we're about to sleep, now is a good time to tell the
                  * Guest about what we've used up to now.
                  */
                 trigger_irq(vq);
 
                 /* OK, now we need to know about added descriptors. */
                 vq->vring.used->flags &= ~VRING_USED_F_NO_NOTIFY;
 
                 /*
                  * They could have slipped one in as we were doing that: make
                  * sure it's written, then check again.
                  */
                 mb();
                 if (last_avail != vq->vring.avail->idx) {
                         vq->vring.used->flags |= VRING_USED_F_NO_NOTIFY;
                         break;
                 }
 
                 /* Nothing new?  Wait for eventfd to tell us they refilled. */
                 if (read(vq->eventfd, &event, sizeof(event)) != sizeof(event))
                         errx(1, "Event read failed?");
 
                 /* We don't need to be notified again. */
                 vq->vring.used->flags |= VRING_USED_F_NO_NOTIFY;
         }
 
         /* Check it isn't doing very strange things with descriptor numbers. */
         if ((u16)(vq->vring.avail->idx - last_avail) > vq->vring.num)
                 bad_driver_vq(vq, "Guest moved used index from %u to %u",
                               last_avail, vq->vring.avail->idx);
 
         /* 
          * Make sure we read the descriptor number *after* we read the ring
          * update; don't let the cpu or compiler change the order.
          */
         rmb();
 
         /*
          * Grab the next descriptor number they're advertising, and increment
          * the index we've seen.
          */
         head = vq->vring.avail->ring[last_avail % vq->vring.num];
         lg_last_avail(vq)++;
 
         /* If their number is silly, that's a fatal mistake. */
         if (head >= vq->vring.num)
                 bad_driver_vq(vq, "Guest says index %u is available", head);
 
         /* When we start there are none of either input nor output. */
         *out_num = *in_num = 0;
 
         max = vq->vring.num;
         desc = vq->vring.desc;
         i = head;
 
         /*
          * We have to read the descriptor after we read the descriptor number,
          * but there's a data dependency there so the CPU shouldn't reorder
          * that: no rmb() required.
          */
 
         do {
                 /*
                  * If this is an indirect entry, then this buffer contains a
                  * descriptor table which we handle as if it's any normal
                  * descriptor chain.
                  */
                 if (desc[i].flags & VRING_DESC_F_INDIRECT) {
                         /* 2.4.5.3.1:
                          *
                          *  The driver MUST NOT set the VIRTQ_DESC_F_INDIRECT
                          *  flag unless the VIRTIO_F_INDIRECT_DESC feature was
                          *  negotiated.
                          */
                         if (!(vq->dev->features_accepted &
                               (1<<VIRTIO_RING_F_INDIRECT_DESC)))
                                 bad_driver_vq(vq, "vq indirect not negotiated");
 
                         /*
                          * 2.4.5.3.1:
                          *
                          *   The driver MUST NOT set the VIRTQ_DESC_F_INDIRECT
                          *   flag within an indirect descriptor (ie. only one
                          *   table per descriptor).
                          */
                         if (desc != vq->vring.desc)
                                 bad_driver_vq(vq, "Indirect within indirect");
 
                         /*
                          * Proposed update VIRTIO-134 spells this out:
                          *
                          *   A driver MUST NOT set both VIRTQ_DESC_F_INDIRECT
                          *   and VIRTQ_DESC_F_NEXT in flags.
                          */
                         if (desc[i].flags & VRING_DESC_F_NEXT)
                                 bad_driver_vq(vq, "indirect and next together");
 
                         if (desc[i].len % sizeof(struct vring_desc))
                                 bad_driver_vq(vq,
                                               "Invalid size for indirect table");
                         /*
                          * 2.4.5.3.2:
                          *
                          *  The device MUST ignore the write-only flag
                          *  (flags&VIRTQ_DESC_F_WRITE) in the descriptor that
                          *  refers to an indirect table.
                          *
                          * We ignore it here: :)
                          */
 
                         max = desc[i].len / sizeof(struct vring_desc);
                         desc = check_pointer(vq->dev, desc[i].addr, desc[i].len);
                         i = 0;
 
                         /* 2.4.5.3.1:
                          *
                          *  A driver MUST NOT create a descriptor chain longer
                          *  than the Queue Size of the device.
                          */
                         if (max > vq->pci_config.queue_size)
                                 bad_driver_vq(vq,
                                               "indirect has too many entries");
                 }
 
                 /* Grab the first descriptor, and check it's OK. */
                 iov[*out_num + *in_num].iov_len = desc[i].len;
                 iov[*out_num + *in_num].iov_base
                         = check_pointer(vq->dev, desc[i].addr, desc[i].len);
                 /* If this is an input descriptor, increment that count. */
                 if (desc[i].flags & VRING_DESC_F_WRITE)
                         (*in_num)++;
                 else {
                         /*
                          * If it's an output descriptor, they're all supposed
                          * to come before any input descriptors.
                          */
                         if (*in_num)
                                 bad_driver_vq(vq,
                                               "Descriptor has out after in");
                         (*out_num)++;
                 }
 
                 /* If we've got too many, that implies a descriptor loop. */
                 if (*out_num + *in_num > max)
                         bad_driver_vq(vq, "Looped descriptor");
         } while ((i = next_desc(vq->dev, desc, i, max)) != max);
 
         return head;
 }
 
 /*
  * After we've used one of their buffers, we tell the Guest about it.  Sometime
  * later we'll want to send them an interrupt using trigger_irq(); note that
  * wait_for_vq_desc() does that for us if it has to wait.
  */
 static void add_used(struct virtqueue *vq, unsigned int head, int len)
 {
         struct vring_used_elem *used;
 
         /*
          * The virtqueue contains a ring of used buffers.  Get a pointer to the
          * next entry in that used ring.
          */
         used = &vq->vring.used->ring[vq->vring.used->idx % vq->vring.num];
         used->id = head;
         used->len = len;
         /* Make sure buffer is written before we update index. */
         wmb();
         vq->vring.used->idx++;
         vq->pending_used++;
 }
 
 /* And here's the combo meal deal.  Supersize me! */
 static void add_used_and_trigger(struct virtqueue *vq, unsigned head, int len)
 {
         add_used(vq, head, len);
         trigger_irq(vq);
 }
 
 /*
  * The Console
  *
  * We associate some data with the console for our exit hack.
  */
 struct console_abort {
         /* How many times have they hit ^C? */
         int count;
         /* When did they start? */
         struct timeval start;
 };
 
 /* This is the routine which handles console input (ie. stdin). */
 static void console_input(struct virtqueue *vq)
 {
         int len;
         unsigned int head, in_num, out_num;
         struct console_abort *abort = vq->dev->priv;
         struct iovec iov[vq->vring.num];
 
         /* Make sure there's a descriptor available. */
         head = wait_for_vq_desc(vq, iov, &out_num, &in_num);
         if (out_num)
                 bad_driver_vq(vq, "Output buffers in console in queue?");
 
         /* Read into it.  This is where we usually wait. */
         len = readv(STDIN_FILENO, iov, in_num);
         if (len <= 0) {
                 /* Ran out of input? */
                 warnx("Failed to get console input, ignoring console.");
                 /*
                  * For simplicity, dying threads kill the whole Launcher.  So
                  * just nap here.
                  */
                 for (;;)
                         pause();
         }
 
         /* Tell the Guest we used a buffer. */
         add_used_and_trigger(vq, head, len);
 
         /*
          * Three ^C within one second?  Exit.
          *
          * This is such a hack, but works surprisingly well.  Each ^C has to
          * be in a buffer by itself, so they can't be too fast.  But we check
          * that we get three within about a second, so they can't be too
          * slow.
          */
         if (len != 1 || ((char *)iov[0].iov_base)[0] != 3) {
                 abort->count = 0;
                 return;
         }
 
         abort->count++;
         if (abort->count == 1)
                 gettimeofday(&abort->start, NULL);
         else if (abort->count == 3) {
                 struct timeval now;
                 gettimeofday(&now, NULL);
                 /* Kill all Launcher processes with SIGINT, like normal ^C */
                 if (now.tv_sec <= abort->start.tv_sec+1)
                         kill(0, SIGINT);
                 abort->count = 0;
         }
 }
 
 /* This is the routine which handles console output (ie. stdout). */
 static void console_output(struct virtqueue *vq)
 {
         unsigned int head, out, in;
         struct iovec iov[vq->vring.num];
 
         /* We usually wait in here, for the Guest to give us something. */
         head = wait_for_vq_desc(vq, iov, &out, &in);
         if (in)
                 bad_driver_vq(vq, "Input buffers in console output queue?");
 
         /* writev can return a partial write, so we loop here. */
         while (!iov_empty(iov, out)) {
                 int len = writev(STDOUT_FILENO, iov, out);
                 if (len <= 0) {
                         warn("Write to stdout gave %i (%d)", len, errno);
                         break;
                 }
                 iov_consume(vq->dev, iov, out, NULL, len);
         }
 
         /*
          * We're finished with that buffer: if we're going to sleep,
          * wait_for_vq_desc() will prod the Guest with an interrupt.
          */
         add_used(vq, head, 0);
 }
 
 /*
  * The Network
  *
  * Handling output for network is also simple: we get all the output buffers
  * and write them to /dev/net/tun.
  */
 struct net_info {
         int tunfd;
 };
 
 static void net_output(struct virtqueue *vq)
 {
         struct net_info *net_info = vq->dev->priv;
         unsigned int head, out, in;
         struct iovec iov[vq->vring.num];
 
         /* We usually wait in here for the Guest to give us a packet. */
         head = wait_for_vq_desc(vq, iov, &out, &in);
         if (in)
                 bad_driver_vq(vq, "Input buffers in net output queue?");
         /*
          * Send the whole thing through to /dev/net/tun.  It expects the exact
          * same format: what a coincidence!
          */
         if (writev(net_info->tunfd, iov, out) < 0)
                 warnx("Write to tun failed (%d)?", errno);
 
         /*
          * Done with that one; wait_for_vq_desc() will send the interrupt if
          * all packets are processed.
          */
         add_used(vq, head, 0);
 }
 
 /*
  * Handling network input is a bit trickier, because I've tried to optimize it.
  *
  * First we have a helper routine which tells is if from this file descriptor
  * (ie. the /dev/net/tun device) will block:
  */
 static bool will_block(int fd)
 {
         fd_set fdset;
         struct timeval zero = { 0, 0 };
         FD_ZERO(&fdset);
         FD_SET(fd, &fdset);
         return select(fd+1, &fdset, NULL, NULL, &zero) != 1;
 }
 
 /*
  * This handles packets coming in from the tun device to our Guest.  Like all
  * service routines, it gets called again as soon as it returns, so you don't
  * see a while(1) loop here.
  */
 static void net_input(struct virtqueue *vq)
 {
         int len;
         unsigned int head, out, in;
         struct iovec iov[vq->vring.num];
         struct net_info *net_info = vq->dev->priv;
 
         /*
          * Get a descriptor to write an incoming packet into.  This will also
          * send an interrupt if they're out of descriptors.
          */
         head = wait_for_vq_desc(vq, iov, &out, &in);
         if (out)
                 bad_driver_vq(vq, "Output buffers in net input queue?");
 
         /*
          * If it looks like we'll block reading from the tun device, send them
          * an interrupt.
          */
         if (vq->pending_used && will_block(net_info->tunfd))
                 trigger_irq(vq);
 
         /*
          * Read in the packet.  This is where we normally wait (when there's no
          * incoming network traffic).
          */
         len = readv(net_info->tunfd, iov, in);
         if (len <= 0)
                 warn("Failed to read from tun (%d).", errno);
 
         /*
          * Mark that packet buffer as used, but don't interrupt here.  We want
          * to wait until we've done as much work as we can.
          */
         add_used(vq, head, len);
 }
 /*:*/
 
 /* This is the helper to create threads: run the service routine in a loop. */
 static int do_thread(void *_vq)
 {
         struct virtqueue *vq = _vq;
 
         for (;;)
                 vq->service(vq);
         return 0;
 }
 
 /*
  * When a child dies, we kill our entire process group with SIGTERM.  This
  * also has the side effect that the shell restores the console for us!
  */
 static void kill_launcher(int signal)
 {
         kill(0, SIGTERM);
 }
 
 static void reset_vq_pci_config(struct virtqueue *vq)
 {
         vq->pci_config.queue_size = VIRTQUEUE_NUM;
         vq->pci_config.queue_enable = 0;
 }
 
 static void reset_device(struct device *dev)
 {
         struct virtqueue *vq;
 
         verbose("Resetting device %s\n", dev->name);
 
         /* Clear any features they've acked. */
         dev->features_accepted = 0;
 
         /* We're going to be explicitly killing threads, so ignore them. */
         signal(SIGCHLD, SIG_IGN);
 
         /*
          * 4.1.4.3.1:
          *
          *   The device MUST present a 0 in queue_enable on reset. 
          *
          * This means we set it here, and reset the saved ones in every vq.
          */
         dev->mmio->cfg.queue_enable = 0;
 
         /* Get rid of the virtqueue threads */
         for (vq = dev->vq; vq; vq = vq->next) {
                 vq->last_avail_idx = 0;
                 reset_vq_pci_config(vq);
                 if (vq->thread != (pid_t)-1) {
                         kill(vq->thread, SIGTERM);
                         waitpid(vq->thread, NULL, 0);
                         vq->thread = (pid_t)-1;
                 }
         }
         dev->running = false;
         dev->wrote_features_ok = false;
 
         /* Now we care if threads die. */
         signal(SIGCHLD, (void *)kill_launcher);
 }
 
 static void cleanup_devices(void)
 {
         unsigned int i;
 
         for (i = 1; i < MAX_PCI_DEVICES; i++) {
                 struct device *d = devices.pci[i];
                 if (!d)
                         continue;
                 reset_device(d);
         }
 
         /* If we saved off the original terminal settings, restore them now. */
         if (orig_term.c_lflag & (ISIG|ICANON|ECHO))
                 tcsetattr(STDIN_FILENO, TCSANOW, &orig_term);
 }
 
 /*L:217
  * We do PCI.  This is mainly done to let us test the kernel virtio PCI
  * code.
  */
 
 /* Linux expects a PCI host bridge: ours is a dummy, and first on the bus. */
 static struct device pci_host_bridge;
 
 static void init_pci_host_bridge(void)
 {
         pci_host_bridge.name = "PCI Host Bridge";
         pci_host_bridge.config.class = 0x06; /* bridge */
         pci_host_bridge.config.subclass = 0; /* host bridge */
         devices.pci[0] = &pci_host_bridge;
 }
 
 /* The IO ports used to read the PCI config space. */
 #define PCI_CONFIG_ADDR 0xCF8
 #define PCI_CONFIG_DATA 0xCFC
 
 /*
  * Not really portable, but does help readability: this is what the Guest
  * writes to the PCI_CONFIG_ADDR IO port.
  */
 union pci_config_addr {
         struct {
                 unsigned mbz: 2;
                 unsigned offset: 6;
                 unsigned funcnum: 3;
                 unsigned devnum: 5;
                 unsigned busnum: 8;
                 unsigned reserved: 7;
                 unsigned enabled : 1;
         } bits;
         u32 val;
 };
 
 /*
  * We cache what they wrote to the address port, so we know what they're
  * talking about when they access the data port.
  */
 static union pci_config_addr pci_config_addr;
 
 static struct device *find_pci_device(unsigned int index)
 {
         return devices.pci[index];
 }
 
 /* PCI can do 1, 2 and 4 byte reads; we handle that here. */
 static void ioread(u16 off, u32 v, u32 mask, u32 *val)
 {
         assert(off < 4);
         assert(mask == 0xFF || mask == 0xFFFF || mask == 0xFFFFFFFF);
         *val = (v >> (off * 8)) & mask;
 }
 
 /* PCI can do 1, 2 and 4 byte writes; we handle that here. */
 static void iowrite(u16 off, u32 v, u32 mask, u32 *dst)
 {
         assert(off < 4);
         assert(mask == 0xFF || mask == 0xFFFF || mask == 0xFFFFFFFF);
         *dst &= ~(mask << (off * 8));
         *dst |= (v & mask) << (off * 8);
 }
 
 /*
  * Where PCI_CONFIG_DATA accesses depends on the previous write to
  * PCI_CONFIG_ADDR.
  */
 static struct device *dev_and_reg(u32 *reg)
 {
         if (!pci_config_addr.bits.enabled)
                 return NULL;
 
         if (pci_config_addr.bits.funcnum != 0)
                 return NULL;
 
         if (pci_config_addr.bits.busnum != 0)
                 return NULL;
 
         if (pci_config_addr.bits.offset * 4 >= sizeof(struct pci_config))
                 return NULL;
 
         *reg = pci_config_addr.bits.offset;
         return find_pci_device(pci_config_addr.bits.devnum);
 }
 
 /*
  * We can get invalid combinations of values while they're writing, so we
  * only fault if they try to write with some invalid bar/offset/length.
  */
 static bool valid_bar_access(struct device *d,
                              struct virtio_pci_cfg_cap_u32 *cfg_access)
 {
         /* We only have 1 bar (BAR0) */
         if (cfg_access->cap.bar != 0)
                 return false;
 
         /* Check it's within BAR0. */
         if (cfg_access->cap.offset >= d->mmio_size
             || cfg_access->cap.offset + cfg_access->cap.length > d->mmio_size)
                 return false;
 
         /* Check length is 1, 2 or 4. */
         if (cfg_access->cap.length != 1
             && cfg_access->cap.length != 2
             && cfg_access->cap.length != 4)
                 return false;
 
         /*
          * 4.1.4.7.2:
          *
          *  The driver MUST NOT write a cap.offset which is not a multiple of
          *  cap.length (ie. all accesses MUST be aligned).
          */
         if (cfg_access->cap.offset % cfg_access->cap.length != 0)
                 return false;
 
         /* Return pointer into word in BAR0. */
         return true;
 }
 
 /* Is this accessing the PCI config address port?. */
 static bool is_pci_addr_port(u16 port)
 {
         return port >= PCI_CONFIG_ADDR && port < PCI_CONFIG_ADDR + 4;
 }
 
 static bool pci_addr_iowrite(u16 port, u32 mask, u32 val)
 {
         iowrite(port - PCI_CONFIG_ADDR, val, mask,
                 &pci_config_addr.val);
         verbose("PCI%s: %#x/%x: bus %u dev %u func %u reg %u\n",
                 pci_config_addr.bits.enabled ? "" : " DISABLED",
                 val, mask,
                 pci_config_addr.bits.busnum,
                 pci_config_addr.bits.devnum,
                 pci_config_addr.bits.funcnum,
                 pci_config_addr.bits.offset);
         return true;
 }
 
 static void pci_addr_ioread(u16 port, u32 mask, u32 *val)
 {
         ioread(port - PCI_CONFIG_ADDR, pci_config_addr.val, mask, val);
 }
 
 /* Is this accessing the PCI config data port?. */
 static bool is_pci_data_port(u16 port)
 {
         return port >= PCI_CONFIG_DATA && port < PCI_CONFIG_DATA + 4;
 }
 
 static void emulate_mmio_write(struct device *d, u32 off, u32 val, u32 mask);
 
 static bool pci_data_iowrite(u16 port, u32 mask, u32 val)
 {
         u32 reg, portoff;
         struct device *d = dev_and_reg(&reg);
 
         /* Complain if they don't belong to a device. */
         if (!d)
                 return false;
 
         /* They can do 1 byte writes, etc. */
         portoff = port - PCI_CONFIG_DATA;
 
         /*
          * PCI uses a weird way to determine the BAR size: the OS
          * writes all 1's, and sees which ones stick.
          */
         if (&d->config_words[reg] == &d->config.bar[0]) {
                 int i;
 
                 iowrite(portoff, val, mask, &d->config.bar[0]);
                 for (i = 0; (1 << i) < d->mmio_size; i++)
                         d->config.bar[0] &= ~(1 << i);
                 return true;
         } else if ((&d->config_words[reg] > &d->config.bar[0]
                     && &d->config_words[reg] <= &d->config.bar[6])
                    || &d->config_words[reg] == &d->config.expansion_rom_addr) {
                 /* Allow writing to any other BAR, or expansion ROM */
                 iowrite(portoff, val, mask, &d->config_words[reg]);
                 return true;
                 /* We let them override latency timer and cacheline size */
         } else if (&d->config_words[reg] == (void *)&d->config.cacheline_size) {
                 /* Only let them change the first two fields. */
                 if (mask == 0xFFFFFFFF)
                         mask = 0xFFFF;
                 iowrite(portoff, val, mask, &d->config_words[reg]);
                 return true;
         } else if (&d->config_words[reg] == (void *)&d->config.command
                    && mask == 0xFFFF) {
                 /* Ignore command writes. */
                 return true;
         } else if (&d->config_words[reg]
                    == (void *)&d->config.cfg_access.cap.bar
                    || &d->config_words[reg]
                    == &d->config.cfg_access.cap.length
                    || &d->config_words[reg]
                    == &d->config.cfg_access.cap.offset) {
 
                 /*
                  * The VIRTIO_PCI_CAP_PCI_CFG capability
                  * provides a backdoor to access the MMIO
                  * regions without mapping them.  Weird, but
                  * useful.
                  */
                 iowrite(portoff, val, mask, &d->config_words[reg]);
                 return true;
         } else if (&d->config_words[reg] == &d->config.cfg_access.pci_cfg_data) {
                 u32 write_mask;
 
                 /*
                  * 4.1.4.7.1:
                  *
                  *  Upon detecting driver write access to pci_cfg_data, the
                  *  device MUST execute a write access at offset cap.offset at
                  *  BAR selected by cap.bar using the first cap.length bytes
                  *  from pci_cfg_data.
                  */
 
                 /* Must be bar 0 */
                 if (!valid_bar_access(d, &d->config.cfg_access))
                         return false;
 
                 iowrite(portoff, val, mask, &d->config.cfg_access.pci_cfg_data);
 
                 /*
                  * Now emulate a write.  The mask we use is set by
                  * len, *not* this write!
                  */
                 write_mask = (1ULL<<(8*d->config.cfg_access.cap.length)) - 1;
                 verbose("Window writing %#x/%#x to bar %u, offset %u len %u\n",
                         d->config.cfg_access.pci_cfg_data, write_mask,
                         d->config.cfg_access.cap.bar,
                         d->config.cfg_access.cap.offset,
                         d->config.cfg_access.cap.length);
 
                 emulate_mmio_write(d, d->config.cfg_access.cap.offset,
                                    d->config.cfg_access.pci_cfg_data,
                                    write_mask);
                 return true;
         }
 
         /*
          * 4.1.4.1:
          *
          *  The driver MUST NOT write into any field of the capability
          *  structure, with the exception of those with cap_type
          *  VIRTIO_PCI_CAP_PCI_CFG...
          */
         return false;
 }
 
 static u32 emulate_mmio_read(struct device *d, u32 off, u32 mask);
 
 static void pci_data_ioread(u16 port, u32 mask, u32 *val)
 {
         u32 reg;
         struct device *d = dev_and_reg(&reg);
 
         if (!d)
                 return;
 
         /* Read through the PCI MMIO access window is special */
         if (&d->config_words[reg] == &d->config.cfg_access.pci_cfg_data) {
                 u32 read_mask;
 
                 /*
                  * 4.1.4.7.1:
                  *
                  *  Upon detecting driver read access to pci_cfg_data, the
                  *  device MUST execute a read access of length cap.length at
                  *  offset cap.offset at BAR selected by cap.bar and store the
                  *  first cap.length bytes in pci_cfg_data.
                  */
                 /* Must be bar 0 */
                 if (!valid_bar_access(d, &d->config.cfg_access))
                         bad_driver(d,
                              "Invalid cfg_access to bar%u, offset %u len %u",
                              d->config.cfg_access.cap.bar,
                              d->config.cfg_access.cap.offset,
                              d->config.cfg_access.cap.length);
 
                 /*
                  * Read into the window.  The mask we use is set by
                  * len, *not* this read!
                  */
                 read_mask = (1ULL<<(8*d->config.cfg_access.cap.length))-1;
                 d->config.cfg_access.pci_cfg_data
                         = emulate_mmio_read(d,
                                             d->config.cfg_access.cap.offset,
                                             read_mask);
                 verbose("Window read %#x/%#x from bar %u, offset %u len %u\n",
                         d->config.cfg_access.pci_cfg_data, read_mask,
                         d->config.cfg_access.cap.bar,
                         d->config.cfg_access.cap.offset,
                         d->config.cfg_access.cap.length);
         }
         ioread(port - PCI_CONFIG_DATA, d->config_words[reg], mask, val);
 }
 
 /*L:216
  * This is where we emulate a handful of Guest instructions.  It's ugly
  * and we used to do it in the kernel but it grew over time.
  */
 
 /*
  * We use the ptrace syscall's pt_regs struct to talk about registers
  * to lguest: these macros convert the names to the offsets.
  */
 #define getreg(name) getreg_off(offsetof(struct user_regs_struct, name))
 #define setreg(name, val) \
         setreg_off(offsetof(struct user_regs_struct, name), (val))
 
 static u32 getreg_off(size_t offset)
 {
         u32 r;
         unsigned long args[] = { LHREQ_GETREG, offset };
 
         if (pwrite(lguest_fd, args, sizeof(args), cpu_id) < 0)
                 err(1, "Getting register %u", offset);
         if (pread(lguest_fd, &r, sizeof(r), cpu_id) != sizeof(r))
                 err(1, "Reading register %u", offset);
 
         return r;
 }
 
 static void setreg_off(size_t offset, u32 val)
 {
         unsigned long args[] = { LHREQ_SETREG, offset, val };
 
         if (pwrite(lguest_fd, args, sizeof(args), cpu_id) < 0)
                 err(1, "Setting register %u", offset);
 }
 
 /* Get register by instruction encoding */
 static u32 getreg_num(unsigned regnum, u32 mask)
 {
         /* 8 bit ops use regnums 4-7 for high parts of word */
         if (mask == 0xFF && (regnum & 0x4))
                 return getreg_num(regnum & 0x3, 0xFFFF) >> 8;
 
         switch (regnum) {
         case 0: return getreg(eax) & mask;
         case 1: return getreg(ecx) & mask;
         case 2: return getreg(edx) & mask;
         case 3: return getreg(ebx) & mask;
         case 4: return getreg(esp) & mask;
         case 5: return getreg(ebp) & mask;
         case 6: return getreg(esi) & mask;
         case 7: return getreg(edi) & mask;
         }
         abort();
 }
 
 /* Set register by instruction encoding */
 static void setreg_num(unsigned regnum, u32 val, u32 mask)
 {
         /* Don't try to set bits out of range */
         assert(~(val & ~mask));
 
         /* 8 bit ops use regnums 4-7 for high parts of word */
         if (mask == 0xFF && (regnum & 0x4)) {
                 /* Construct the 16 bits we want. */
                 val = (val << 8) | getreg_num(regnum & 0x3, 0xFF);
                 setreg_num(regnum & 0x3, val, 0xFFFF);
                 return;
         }
 
         switch (regnum) {
         case 0: setreg(eax, val | (getreg(eax) & ~mask)); return;
         case 1: setreg(ecx, val | (getreg(ecx) & ~mask)); return;
         case 2: setreg(edx, val | (getreg(edx) & ~mask)); return;
         case 3: setreg(ebx, val | (getreg(ebx) & ~mask)); return;
         case 4: setreg(esp, val | (getreg(esp) & ~mask)); return;
         case 5: setreg(ebp, val | (getreg(ebp) & ~mask)); return;
         case 6: setreg(esi, val | (getreg(esi) & ~mask)); return;
         case 7: setreg(edi, val | (getreg(edi) & ~mask)); return;
         }
         abort();
 }
 
 /* Get bytes of displacement appended to instruction, from r/m encoding */
 static u32 insn_displacement_len(u8 mod_reg_rm)
 {
         /* Switch on the mod bits */
         switch (mod_reg_rm >> 6) {
         case 0:
                 /* If mod == 0, and r/m == 101, 16-bit displacement follows */
                 if ((mod_reg_rm & 0x7) == 0x5)
                         return 2;
                 /* Normally, mod == 0 means no literal displacement */
                 return 0;
         case 1:
                 /* One byte displacement */
                 return 1;
         case 2:
                 /* Four byte displacement */
                 return 4;
         case 3:
                 /* Register mode */
                 return 0;
         }
         abort();
 }
 
 static void emulate_insn(const u8 insn[])
 {
         unsigned long args[] = { LHREQ_TRAP, 13 };
         unsigned int insnlen = 0, in = 0, small_operand = 0, byte_access;
         unsigned int eax, port, mask;
         /*
          * Default is to return all-ones on IO port reads, which traditionally
          * means "there's nothing there".
          */
         u32 val = 0xFFFFFFFF;
 
         /*
          * This must be the Guest kernel trying to do something, not userspace!
          * The bottom two bits of the CS segment register are the privilege
          * level.
          */
         if ((getreg(xcs) & 3) != 0x1)
                 goto no_emulate;
 
         /* Decoding x86 instructions is icky. */
 
         /*
          * Around 2.6.33, the kernel started using an emulation for the
          * cmpxchg8b instruction in early boot on many configurations.  This
          * code isn't paravirtualized, and it tries to disable interrupts.
          * Ignore it, which will Mostly Work.
          */
         if (insn[insnlen] == 0xfa) {
                 /* "cli", or Clear Interrupt Enable instruction.  Skip it. */
                 insnlen = 1;
                 goto skip_insn;
         }
 
         /*
          * 0x66 is an "operand prefix".  It means a 16, not 32 bit in/out.
          */
         if (insn[insnlen] == 0x66) {
                 small_operand = 1;
                 /* The instruction is 1 byte so far, read the next byte. */
                 insnlen = 1;
         }
 
         /* If the lower bit isn't set, it's a single byte access */
         byte_access = !(insn[insnlen] & 1);
 
         /*
          * Now we can ignore the lower bit and decode the 4 opcodes
          * we need to emulate.
          */
         switch (insn[insnlen] & 0xFE) {
         case 0xE4: /* in     <next byte>,%al */
                 port = insn[insnlen+1];
                 insnlen += 2;
                 in = 1;
                 break;
         case 0xEC: /* in     (%dx),%al */
                 port = getreg(edx) & 0xFFFF;
                 insnlen += 1;
                 in = 1;
                 break;
         case 0xE6: /* out    %al,<next byte> */
                 port = insn[insnlen+1];
                 insnlen += 2;
                 break;
         case 0xEE: /* out    %al,(%dx) */
                 port = getreg(edx) & 0xFFFF;
                 insnlen += 1;
                 break;
         default:
                 /* OK, we don't know what this is, can't emulate. */
                 goto no_emulate;
         }
 
         /* Set a mask of the 1, 2 or 4 bytes, depending on size of IO */
         if (byte_access)
                 mask = 0xFF;
         else if (small_operand)
                 mask = 0xFFFF;
         else
                 mask = 0xFFFFFFFF;
 
         /*
          * If it was an "IN" instruction, they expect the result to be read
          * into %eax, so we change %eax.
          */
         eax = getreg(eax);
 
         if (in) {
                 /* This is the PS/2 keyboard status; 1 means ready for output */
                 if (port == 0x64)
                         val = 1;
                 else if (is_pci_addr_port(port))
                         pci_addr_ioread(port, mask, &val);
                 else if (is_pci_data_port(port))
                         pci_data_ioread(port, mask, &val);
 
                 /* Clear the bits we're about to read */
                 eax &= ~mask;
                 /* Copy bits in from val. */
                 eax |= val & mask;
                 /* Now update the register. */
                 setreg(eax, eax);
         } else {
                 if (is_pci_addr_port(port)) {
                         if (!pci_addr_iowrite(port, mask, eax))
                                 goto bad_io;
                 } else if (is_pci_data_port(port)) {
                         if (!pci_data_iowrite(port, mask, eax))
                                 goto bad_io;
                 }
                 /* There are many other ports, eg. CMOS clock, serial
                  * and parallel ports, so we ignore them all. */
         }
 
         verbose("IO %s of %x to %u: %#08x\n",
                 in ? "IN" : "OUT", mask, port, eax);
 skip_insn:
         /* Finally, we've "done" the instruction, so move past it. */
         setreg(eip, getreg(eip) + insnlen);
         return;
 
 bad_io:
         warnx("Attempt to %s port %u (%#x mask)",
               in ? "read from" : "write to", port, mask);
 
 no_emulate:
         /* Inject trap into Guest. */
         if (write(lguest_fd, args, sizeof(args)) < 0)
                 err(1, "Reinjecting trap 13 for fault at %#x", getreg(eip));
 }
 
 static struct device *find_mmio_region(unsigned long paddr, u32 *off)
 {
         unsigned int i;
 
         for (i = 1; i < MAX_PCI_DEVICES; i++) {
                 struct device *d = devices.pci[i];
 
                 if (!d)
                         continue;
                 if (paddr < d->mmio_addr)
                         continue;
                 if (paddr >= d->mmio_addr + d->mmio_size)
                         continue;
                 *off = paddr - d->mmio_addr;
                 return d;
         }
         return NULL;
 }
 
 /* FIXME: Use vq array. */
 static struct virtqueue *vq_by_num(struct device *d, u32 num)
 {
         struct virtqueue *vq = d->vq;
 
         while (num-- && vq)
                 vq = vq->next;
 
         return vq;
 }
 
 static void save_vq_config(const struct virtio_pci_common_cfg *cfg,
                            struct virtqueue *vq)
 {
         vq->pci_config = *cfg;
 }
 
 static void restore_vq_config(struct virtio_pci_common_cfg *cfg,
                               struct virtqueue *vq)
 {
         /* Only restore the per-vq part */
         size_t off = offsetof(struct virtio_pci_common_cfg, queue_size);
 
         memcpy((void *)cfg + off, (void *)&vq->pci_config + off,
                sizeof(*cfg) - off);
 }
 
 /*
  * 4.1.4.3.2:
  *
  *  The driver MUST configure the other virtqueue fields before
  *  enabling the virtqueue with queue_enable.
  *
  * When they enable the virtqueue, we check that their setup is valid.
  */
 static void check_virtqueue(struct device *d, struct virtqueue *vq)
 {
         /* Because lguest is 32 bit, all the descriptor high bits must be 0 */
         if (vq->pci_config.queue_desc_hi
             || vq->pci_config.queue_avail_hi
             || vq->pci_config.queue_used_hi)
                 bad_driver_vq(vq, "invalid 64-bit queue address");
 
         /*
          * 2.4.1:
          *
          *  The driver MUST ensure that the physical address of the first byte
          *  of each virtqueue part is a multiple of the specified alignment
          *  value in the above table.
          */
         if (vq->pci_config.queue_desc_lo % 16
             || vq->pci_config.queue_avail_lo % 2
             || vq->pci_config.queue_used_lo % 4)
                 bad_driver_vq(vq, "invalid alignment in queue addresses");
 
         /* Initialize the virtqueue and check they're all in range. */
         vq->vring.num = vq->pci_config.queue_size;
         vq->vring.desc = check_pointer(vq->dev,
                                        vq->pci_config.queue_desc_lo,
                                        sizeof(*vq->vring.desc) * vq->vring.num);
         vq->vring.avail = check_pointer(vq->dev,
                                         vq->pci_config.queue_avail_lo,
                                         sizeof(*vq->vring.avail)
                                         + (sizeof(vq->vring.avail->ring[0])
                                            * vq->vring.num));
         vq->vring.used = check_pointer(vq->dev,
                                        vq->pci_config.queue_used_lo,
                                        sizeof(*vq->vring.used)
                                        + (sizeof(vq->vring.used->ring[0])
                                           * vq->vring.num));
 
         /*
          * 2.4.9.1:
          *
          *   The driver MUST initialize flags in the used ring to 0
          *   when allocating the used ring.
          */
         if (vq->vring.used->flags != 0)
                 bad_driver_vq(vq, "invalid initial used.flags %#x",
                               vq->vring.used->flags);
 }
 
 static void start_virtqueue(struct virtqueue *vq)
 {
         /*
          * Create stack for thread.  Since the stack grows upwards, we point
          * the stack pointer to the end of this region.
          */
         char *stack = malloc(32768);
 
         /* Create a zero-initialized eventfd. */
         vq->eventfd = eventfd(0, 0);
         if (vq->eventfd < 0)
                 err(1, "Creating eventfd");
 
         /*
          * CLONE_VM: because it has to access the Guest memory, and SIGCHLD so
          * we get a signal if it dies.
          */
         vq->thread = clone(do_thread, stack + 32768, CLONE_VM | SIGCHLD, vq);
         if (vq->thread == (pid_t)-1)
                 err(1, "Creating clone");
 }
 
 static void start_virtqueues(struct device *d)
 {
         struct virtqueue *vq;
 
         for (vq = d->vq; vq; vq = vq->next) {
                 if (vq->pci_config.queue_enable)
                         start_virtqueue(vq);
         }
 }
 
 static void emulate_mmio_write(struct device *d, u32 off, u32 val, u32 mask)
 {
         struct virtqueue *vq;
 
         switch (off) {
         case offsetof(struct virtio_pci_mmio, cfg.device_feature_select):
                 /*
                  * 4.1.4.3.1:
                  *
                  * The device MUST present the feature bits it is offering in
                  * device_feature, starting at bit device_feature_select ∗ 32
                  * for any device_feature_select written by the driver
                  */
                 if (val == 0)
                         d->mmio->cfg.device_feature = d->features;
                 else if (val == 1)
                         d->mmio->cfg.device_feature = (d->features >> 32);
                 else
                         d->mmio->cfg.device_feature = 0;
                 goto feature_write_through32;
         case offsetof(struct virtio_pci_mmio, cfg.guest_feature_select):
                 if (val > 1)
                         bad_driver(d, "Unexpected driver select %u", val);
                 goto feature_write_through32;
         case offsetof(struct virtio_pci_mmio, cfg.guest_feature):
                 if (d->mmio->cfg.guest_feature_select == 0) {
                         d->features_accepted &= ~((u64)0xFFFFFFFF);
                         d->features_accepted |= val;
                 } else {
                         assert(d->mmio->cfg.guest_feature_select == 1);
                         d->features_accepted &= 0xFFFFFFFF;
                         d->features_accepted |= ((u64)val) << 32;
                 }
                 /*
                  * 2.2.1:
                  *
                  *   The driver MUST NOT accept a feature which the device did
                  *   not offer
                  */
                 if (d->features_accepted & ~d->features)
                         bad_driver(d, "over-accepted features %#llx of %#llx",
                                    d->features_accepted, d->features);
                 goto feature_write_through32;
         case offsetof(struct virtio_pci_mmio, cfg.device_status): {
                 u8 prev;
 
                 verbose("%s: device status -> %#x\n", d->name, val);
                 /*
                  * 4.1.4.3.1:
                  * 
                  *  The device MUST reset when 0 is written to device_status,
                  *  and present a 0 in device_status once that is done.
                  */
                 if (val == 0) {
                         reset_device(d);
                         goto write_through8;
                 }
 
                 /* 2.1.1: The driver MUST NOT clear a device status bit. */
                 if (d->mmio->cfg.device_status & ~val)
                         bad_driver(d, "unset of device status bit %#x -> %#x",
                                    d->mmio->cfg.device_status, val);
 
                 /*
                  * 2.1.2:
                  *
                  *  The device MUST NOT consume buffers or notify the driver
                  *  before DRIVER_OK.
                  */
                 if (val & VIRTIO_CONFIG_S_DRIVER_OK
                     && !(d->mmio->cfg.device_status & VIRTIO_CONFIG_S_DRIVER_OK))
                         start_virtqueues(d);
 
                 /*
                  * 3.1.1:
                  *
                  *   The driver MUST follow this sequence to initialize a device:
                  *   - Reset the device.
                  *   - Set the ACKNOWLEDGE status bit: the guest OS has
                  *     notice the device.
                  *   - Set the DRIVER status bit: the guest OS knows how
                  *     to drive the device.
                  *   - Read device feature bits, and write the subset
                  *     of feature bits understood by the OS and driver
                  *     to the device. During this step the driver MAY
                  *     read (but MUST NOT write) the device-specific
                  *     configuration fields to check that it can
                  *     support the device before accepting it.
                  *   - Set the FEATURES_OK status bit.  The driver
                  *     MUST not accept new feature bits after this
                  *     step.
                  *   - Re-read device status to ensure the FEATURES_OK
                  *     bit is still set: otherwise, the device does
                  *     not support our subset of features and the
                  *     device is unusable.
                  *   - Perform device-specific setup, including
                  *     discovery of virtqueues for the device,
                  *     optional per-bus setup, reading and possibly
                  *     writing the device’s virtio configuration
                  *     space, and population of virtqueues.
                  *   - Set the DRIVER_OK status bit. At this point the
                  *     device is “live”.
                  */
                 prev = 0;
                 switch (val & ~d->mmio->cfg.device_status) {
                 case VIRTIO_CONFIG_S_DRIVER_OK:
                         prev |= VIRTIO_CONFIG_S_FEATURES_OK; /* fall thru */
                 case VIRTIO_CONFIG_S_FEATURES_OK:
                         prev |= VIRTIO_CONFIG_S_DRIVER; /* fall thru */
                 case VIRTIO_CONFIG_S_DRIVER:
                         prev |= VIRTIO_CONFIG_S_ACKNOWLEDGE; /* fall thru */
                 case VIRTIO_CONFIG_S_ACKNOWLEDGE:
                         break;
                 default:
                         bad_driver(d, "unknown device status bit %#x -> %#x",
                                    d->mmio->cfg.device_status, val);
                 }
                 if (d->mmio->cfg.device_status != prev)
                         bad_driver(d, "unexpected status transition %#x -> %#x",
                                    d->mmio->cfg.device_status, val);
 
                 /* If they just wrote FEATURES_OK, we make sure they read */
                 switch (val & ~d->mmio->cfg.device_status) {
                 case VIRTIO_CONFIG_S_FEATURES_OK:
                         d->wrote_features_ok = true;
                         break;
                 case VIRTIO_CONFIG_S_DRIVER_OK:
                         if (d->wrote_features_ok)
                                 bad_driver(d, "did not re-read FEATURES_OK");
                         break;
                 }
                 goto write_through8;
         }
         case offsetof(struct virtio_pci_mmio, cfg.queue_select):
                 vq = vq_by_num(d, val);
                 /*
                  * 4.1.4.3.1:
                  *
                  *  The device MUST present a 0 in queue_size if the virtqueue
                  *  corresponding to the current queue_select is unavailable.
                  */
                 if (!vq) {
                         d->mmio->cfg.queue_size = 0;
                         goto write_through16;
                 }
                 /* Save registers for old vq, if it was a valid vq */
                 if (d->mmio->cfg.queue_size)
                         save_vq_config(&d->mmio->cfg,
                                        vq_by_num(d, d->mmio->cfg.queue_select));
                 /* Restore the registers for the queue they asked for */
                 restore_vq_config(&d->mmio->cfg, vq);
                 goto write_through16;
         case offsetof(struct virtio_pci_mmio, cfg.queue_size):
                 /*
                  * 4.1.4.3.2:
                  *
                  *  The driver MUST NOT write a value which is not a power of 2
                  *  to queue_size.
                  */
                 if (val & (val-1))
                         bad_driver(d, "invalid queue size %u", val);
                 if (d->mmio->cfg.queue_enable)
                         bad_driver(d, "changing queue size on live device");
                 goto write_through16;
         case offsetof(struct virtio_pci_mmio, cfg.queue_msix_vector):
                 bad_driver(d, "attempt to set MSIX vector to %u", val);
         case offsetof(struct virtio_pci_mmio, cfg.queue_enable): {
                 struct virtqueue *vq = vq_by_num(d, d->mmio->cfg.queue_select);
 
                 /*
                  * 4.1.4.3.2:
                  *
                  *  The driver MUST NOT write a 0 to queue_enable.
                  */
                 if (val != 1)
                         bad_driver(d, "setting queue_enable to %u", val);
 
                 /*
                  * 3.1.1:
                  *
                  *  7. Perform device-specific setup, including discovery of
                  *     virtqueues for the device, optional per-bus setup,
                  *     reading and possibly writing the device’s virtio
                  *     configuration space, and population of virtqueues.
                  *  8. Set the DRIVER_OK status bit.
                  *
                  * All our devices require all virtqueues to be enabled, so
                  * they should have done that before setting DRIVER_OK.
                  */
                 if (d->mmio->cfg.device_status & VIRTIO_CONFIG_S_DRIVER_OK)
                         bad_driver(d, "enabling vq after DRIVER_OK");
 
                 d->mmio->cfg.queue_enable = val;
                 save_vq_config(&d->mmio->cfg, vq);
                 check_virtqueue(d, vq);
                 goto write_through16;
         }
         case offsetof(struct virtio_pci_mmio, cfg.queue_notify_off):
                 bad_driver(d, "attempt to write to queue_notify_off");
         case offsetof(struct virtio_pci_mmio, cfg.queue_desc_lo):
         case offsetof(struct virtio_pci_mmio, cfg.queue_desc_hi):
         case offsetof(struct virtio_pci_mmio, cfg.queue_avail_lo):
         case offsetof(struct virtio_pci_mmio, cfg.queue_avail_hi):
         case offsetof(struct virtio_pci_mmio, cfg.queue_used_lo):
         case offsetof(struct virtio_pci_mmio, cfg.queue_used_hi):
                 /*
                  * 4.1.4.3.2:
                  *
                  *  The driver MUST configure the other virtqueue fields before
                  *  enabling the virtqueue with queue_enable.
                  */
                 if (d->mmio->cfg.queue_enable)
                         bad_driver(d, "changing queue on live device");
 
                 /*
                  * 3.1.1:
                  *
                  *  The driver MUST follow this sequence to initialize a device:
                  *...
                  *  5. Set the FEATURES_OK status bit. The driver MUST not
                  *  accept new feature bits after this step.
                  */
                 if (!(d->mmio->cfg.device_status & VIRTIO_CONFIG_S_FEATURES_OK))
                         bad_driver(d, "setting up vq before FEATURES_OK");
 
                 /*
                  *  6. Re-read device status to ensure the FEATURES_OK bit is
                  *     still set...
                  */
                 if (d->wrote_features_ok)
                         bad_driver(d, "didn't re-read FEATURES_OK before setup");
 
                 goto write_through32;
         case offsetof(struct virtio_pci_mmio, notify):
                 vq = vq_by_num(d, val);
                 if (!vq)
                         bad_driver(d, "Invalid vq notification on %u", val);
                 /* Notify the process handling this vq by adding 1 to eventfd */
                 write(vq->eventfd, "\1\0\0\0\0\0\0\0", 8);
                 goto write_through16;
         case offsetof(struct virtio_pci_mmio, isr):
                 bad_driver(d, "Unexpected write to isr");
         /* Weird corner case: write to emerg_wr of console */
         case sizeof(struct virtio_pci_mmio)
                 + offsetof(struct virtio_console_config, emerg_wr):
                 if (strcmp(d->name, "console") == 0) {
                         char c = val;
                         write(STDOUT_FILENO, &c, 1);
                         goto write_through32;
                 }
                 /* Fall through... */
         default:
                 /*
                  * 4.1.4.3.2:
                  *
                  *   The driver MUST NOT write to device_feature, num_queues,
                  *   config_generation or queue_notify_off.
                  */
                 bad_driver(d, "Unexpected write to offset %u", off);
         }
 
 feature_write_through32:
         /*
          * 3.1.1:
          *
          *   The driver MUST follow this sequence to initialize a device:
          *...
          *   - Set the DRIVER status bit: the guest OS knows how
          *     to drive the device.
          *   - Read device feature bits, and write the subset
          *     of feature bits understood by the OS and driver
          *     to the device.
          *...
          *   - Set the FEATURES_OK status bit. The driver MUST not
          *     accept new feature bits after this step.
          */
         if (!(d->mmio->cfg.device_status & VIRTIO_CONFIG_S_DRIVER))
                 bad_driver(d, "feature write before VIRTIO_CONFIG_S_DRIVER");
         if (d->mmio->cfg.device_status & VIRTIO_CONFIG_S_FEATURES_OK)
                 bad_driver(d, "feature write after VIRTIO_CONFIG_S_FEATURES_OK");
 
         /*
          * 4.1.3.1:
          *
          *  The driver MUST access each field using the “natural” access
          *  method, i.e. 32-bit accesses for 32-bit fields, 16-bit accesses for
          *  16-bit fields and 8-bit accesses for 8-bit fields.
          */
 write_through32:
         if (mask != 0xFFFFFFFF) {
                 bad_driver(d, "non-32-bit write to offset %u (%#x)",
                            off, getreg(eip));
                 return;
         }
         memcpy((char *)d->mmio + off, &val, 4);
         return;
 
 write_through16:
         if (mask != 0xFFFF)
                 bad_driver(d, "non-16-bit write to offset %u (%#x)",
                            off, getreg(eip));
         memcpy((char *)d->mmio + off, &val, 2);
         return;
 
 write_through8:
         if (mask != 0xFF)
                 bad_driver(d, "non-8-bit write to offset %u (%#x)",
                            off, getreg(eip));
         memcpy((char *)d->mmio + off, &val, 1);
         return;
 }
 
 static u32 emulate_mmio_read(struct device *d, u32 off, u32 mask)
 {
         u8 isr;
         u32 val = 0;
 
         switch (off) {
         case offsetof(struct virtio_pci_mmio, cfg.device_feature_select):
         case offsetof(struct virtio_pci_mmio, cfg.device_feature):
         case offsetof(struct virtio_pci_mmio, cfg.guest_feature_select):
         case offsetof(struct virtio_pci_mmio, cfg.guest_feature):
                 /*
                  * 3.1.1:
                  *
                  *   The driver MUST follow this sequence to initialize a device:
                  *...
                  *   - Set the DRIVER status bit: the guest OS knows how
                  *     to drive the device.
                  *   - Read device feature bits, and write the subset
                  *     of feature bits understood by the OS and driver
                  *     to the device.
                  */
                 if (!(d->mmio->cfg.device_status & VIRTIO_CONFIG_S_DRIVER))
                         bad_driver(d,
                                    "feature read before VIRTIO_CONFIG_S_DRIVER");
                 goto read_through32;
         case offsetof(struct virtio_pci_mmio, cfg.msix_config):
                 bad_driver(d, "read of msix_config");
         case offsetof(struct virtio_pci_mmio, cfg.num_queues):
                 goto read_through16;
         case offsetof(struct virtio_pci_mmio, cfg.device_status):
                 /* As they did read, any write of FEATURES_OK is now fine. */
                 d->wrote_features_ok = false;
                 goto read_through8;
         case offsetof(struct virtio_pci_mmio, cfg.config_generation):
                 /*
                  * 4.1.4.3.1:
                  *
                  *  The device MUST present a changed config_generation after
                  *  the driver has read a device-specific configuration value
                  *  which has changed since any part of the device-specific
                  *  configuration was last read.
                  *
                  * This is simple: none of our devices change config, so this
                  * is always 0.
                  */
                 goto read_through8;
         case offsetof(struct virtio_pci_mmio, notify):
                 /*
                  * 3.1.1:
                  *
                  *   The driver MUST NOT notify the device before setting
                  *   DRIVER_OK.
                  */
                 if (!(d->mmio->cfg.device_status & VIRTIO_CONFIG_S_DRIVER_OK))
                         bad_driver(d, "notify before VIRTIO_CONFIG_S_DRIVER_OK");
                 goto read_through16;
         case offsetof(struct virtio_pci_mmio, isr):
                 if (mask != 0xFF)
                         bad_driver(d, "non-8-bit read from offset %u (%#x)",
                                    off, getreg(eip));
                 isr = d->mmio->isr;
                 /*
                  * 4.1.4.5.1:
                  *
                  *  The device MUST reset ISR status to 0 on driver read. 
                  */
                 d->mmio->isr = 0;
                 return isr;
         case offsetof(struct virtio_pci_mmio, padding):
                 bad_driver(d, "read from padding (%#x)", getreg(eip));
         default:
                 /* Read from device config space, beware unaligned overflow */
                 if (off > d->mmio_size - 4)
                         bad_driver(d, "read past end (%#x)", getreg(eip));
 
                 /*
                  * 3.1.1:
                  *  The driver MUST follow this sequence to initialize a device:
                  *...
                  *  3. Set the DRIVER status bit: the guest OS knows how to
                  *  drive the device.
                  *  4. Read device feature bits, and write the subset of
                  *  feature bits understood by the OS and driver to the
                  *  device. During this step the driver MAY read (but MUST NOT
                  *  write) the device-specific configuration fields to check
                  *  that it can support the device before accepting it.
                  */
                 if (!(d->mmio->cfg.device_status & VIRTIO_CONFIG_S_DRIVER))
                         bad_driver(d,
                                    "config read before VIRTIO_CONFIG_S_DRIVER");
 
                 if (mask == 0xFFFFFFFF)
                         goto read_through32;
                 else if (mask == 0xFFFF)
                         goto read_through16;
                 else
                         goto read_through8;
         }
 
         /*
          * 4.1.3.1:
          *
          *  The driver MUST access each field using the “natural” access
          *  method, i.e. 32-bit accesses for 32-bit fields, 16-bit accesses for
          *  16-bit fields and 8-bit accesses for 8-bit fields.
          */
 read_through32:
         if (mask != 0xFFFFFFFF)
                 bad_driver(d, "non-32-bit read to offset %u (%#x)",
                            off, getreg(eip));
         memcpy(&val, (char *)d->mmio + off, 4);
         return val;
 
 read_through16:
         if (mask != 0xFFFF)
                 bad_driver(d, "non-16-bit read to offset %u (%#x)",
                            off, getreg(eip));
         memcpy(&val, (char *)d->mmio + off, 2);
         return val;
 
 read_through8:
         if (mask != 0xFF)
                 bad_driver(d, "non-8-bit read to offset %u (%#x)",
                            off, getreg(eip));
         memcpy(&val, (char *)d->mmio + off, 1);
         return val;
 }
 
 static void emulate_mmio(unsigned long paddr, const u8 *insn)
 {
         u32 val, off, mask = 0xFFFFFFFF, insnlen = 0;
         struct device *d = find_mmio_region(paddr, &off);
         unsigned long args[] = { LHREQ_TRAP, 14 };
 
         if (!d) {
                 warnx("MMIO touching %#08lx (not a device)", paddr);
                 goto reinject;
         }
 
         /* Prefix makes it a 16 bit op */
         if (insn[0] == 0x66) {
                 mask = 0xFFFF;
                 insnlen++;
         }
 
         /* iowrite */
         if (insn[insnlen] == 0x89) {
                 /* Next byte is r/m byte: bits 3-5 are register. */
                 val = getreg_num((insn[insnlen+1] >> 3) & 0x7, mask);
                 emulate_mmio_write(d, off, val, mask);
                 insnlen += 2 + insn_displacement_len(insn[insnlen+1]);
         } else if (insn[insnlen] == 0x8b) { /* ioread */
                 /* Next byte is r/m byte: bits 3-5 are register. */
                 val = emulate_mmio_read(d, off, mask);
                 setreg_num((insn[insnlen+1] >> 3) & 0x7, val, mask);
                 insnlen += 2 + insn_displacement_len(insn[insnlen+1]);
         } else if (insn[0] == 0x88) { /* 8-bit iowrite */
                 mask = 0xff;
                 /* Next byte is r/m byte: bits 3-5 are register. */
                 val = getreg_num((insn[1] >> 3) & 0x7, mask);
                 emulate_mmio_write(d, off, val, mask);
                 insnlen = 2 + insn_displacement_len(insn[1]);
         } else if (insn[0] == 0x8a) { /* 8-bit ioread */
                 mask = 0xff;
                 val = emulate_mmio_read(d, off, mask);
                 setreg_num((insn[1] >> 3) & 0x7, val, mask);
                 insnlen = 2 + insn_displacement_len(insn[1]);
         } else {
                 warnx("Unknown MMIO instruction touching %#08lx:"
                      " %02x %02x %02x %02x at %u",
                      paddr, insn[0], insn[1], insn[2], insn[3], getreg(eip));
         reinject:
                 /* Inject trap into Guest. */
                 if (write(lguest_fd, args, sizeof(args)) < 0)
                         err(1, "Reinjecting trap 14 for fault at %#x",
                             getreg(eip));
                 return;
         }
 
         /* Finally, we've "done" the instruction, so move past it. */
         setreg(eip, getreg(eip) + insnlen);
 }
 
 /*L:190
  * Device Setup
  *
  * All devices need a descriptor so the Guest knows it exists, and a "struct
  * device" so the Launcher can keep track of it.  We have common helper
  * routines to allocate and manage them.
  */
 static void add_pci_virtqueue(struct device *dev,
                               void (*service)(struct virtqueue *),
                               const char *name)
 {
         struct virtqueue **i, *vq = malloc(sizeof(*vq));
 
         /* Initialize the virtqueue */
         vq->next = NULL;
         vq->last_avail_idx = 0;
         vq->dev = dev;
         vq->name = name;
 
         /*
          * This is the routine the service thread will run, and its Process ID
          * once it's running.
          */
         vq->service = service;
         vq->thread = (pid_t)-1;
 
         /* Initialize the configuration. */
         reset_vq_pci_config(vq);
         vq->pci_config.queue_notify_off = 0;
 
         /* Add one to the number of queues */
         vq->dev->mmio->cfg.num_queues++;
 
         /*
          * Add to tail of list, so dev->vq is first vq, dev->vq->next is
          * second.
          */
         for (i = &dev->vq; *i; i = &(*i)->next);
         *i = vq;
 }
 
 /* The Guest accesses the feature bits via the PCI common config MMIO region */
 static void add_pci_feature(struct device *dev, unsigned bit)
 {
         dev->features |= (1ULL << bit);
 }
 
 /* For devices with no config. */
 static void no_device_config(struct device *dev)
 {
         dev->mmio_addr = get_mmio_region(dev->mmio_size);
 
         dev->config.bar[0] = dev->mmio_addr;
         /* Bottom 4 bits must be zero */
         assert(~(dev->config.bar[0] & 0xF));
 }
 
 /* This puts the device config into BAR0 */
 static void set_device_config(struct device *dev, const void *conf, size_t len)
 {
         /* Set up BAR 0 */
         dev->mmio_size += len;
         dev->mmio = realloc(dev->mmio, dev->mmio_size);
         memcpy(dev->mmio + 1, conf, len);
 
         /*
          * 4.1.4.6:
          *
          *  The device MUST present at least one VIRTIO_PCI_CAP_DEVICE_CFG
          *  capability for any device type which has a device-specific
          *  configuration.
          */
         /* Hook up device cfg */
         dev->config.cfg_access.cap.cap_next
                 = offsetof(struct pci_config, device);
 
         /*
          * 4.1.4.6.1:
          *
          *  The offset for the device-specific configuration MUST be 4-byte
          *  aligned.
          */
         assert(dev->config.cfg_access.cap.cap_next % 4 == 0);
 
         /* Fix up device cfg field length. */
         dev->config.device.length = len;
 
         /* The rest is the same as the no-config case */
         no_device_config(dev);
 }
 
 static void init_cap(struct virtio_pci_cap *cap, size_t caplen, int type,
                      size_t bar_offset, size_t bar_bytes, u8 next)
 {
         cap->cap_vndr = PCI_CAP_ID_VNDR;
         cap->cap_next = next;
         cap->cap_len = caplen;
         cap->cfg_type = type;
         cap->bar = 0;
         memset(cap->padding, 0, sizeof(cap->padding));
         cap->offset = bar_offset;
         cap->length = bar_bytes;
 }
 
 /*
  * This sets up the pci_config structure, as defined in the virtio 1.0
  * standard (and PCI standard).
  */
 static void init_pci_config(struct pci_config *pci, u16 type,
                             u8 class, u8 subclass)
 {
         size_t bar_offset, bar_len;
 
         /*
          * 4.1.4.4.1:
          *
          *  The device MUST either present notify_off_multiplier as an even
          *  power of 2, or present notify_off_multiplier as 0.
          *
          * 2.1.2:
          *
          *   The device MUST initialize device status to 0 upon reset. 
          */
         memset(pci, 0, sizeof(*pci));
 
         /* 4.1.2.1: Devices MUST have the PCI Vendor ID 0x1AF4 */
         pci->vendor_id = 0x1AF4;
         /* 4.1.2.1: ... PCI Device ID calculated by adding 0x1040 ... */
         pci->device_id = 0x1040 + type;
 
         /*
          * PCI have specific codes for different types of devices.
          * Linux doesn't care, but it's a good clue for people looking
          * at the device.
          */
         pci->class = class;
         pci->subclass = subclass;
 
         /*
          * 4.1.2.1:
          *
          *  Non-transitional devices SHOULD have a PCI Revision ID of 1 or
          *  higher
          */
         pci->revid = 1;
 
         /*
          * 4.1.2.1:
          *
          *  Non-transitional devices SHOULD have a PCI Subsystem Device ID of
          *  0x40 or higher.
          */
         pci->subsystem_device_id = 0x40;
 
         /* We use our dummy interrupt controller, and irq_line is the irq */
         pci->irq_line = devices.next_irq++;
         pci->irq_pin = 0;
 
         /* Support for extended capabilities. */
         pci->status = (1 << 4);
 
         /* Link them in. */
         /*
          * 4.1.4.3.1:
          *
          *  The device MUST present at least one common configuration
          *  capability.
          */
         pci->capabilities = offsetof(struct pci_config, common);
 
         /* 4.1.4.3.1 ... offset MUST be 4-byte aligned. */
         assert(pci->capabilities % 4 == 0);
 
         bar_offset = offsetof(struct virtio_pci_mmio, cfg);
         bar_len = sizeof(((struct virtio_pci_mmio *)0)->cfg);
         init_cap(&pci->common, sizeof(pci->common), VIRTIO_PCI_CAP_COMMON_CFG,
                  bar_offset, bar_len,
                  offsetof(struct pci_config, notify));
 
         /*
          * 4.1.4.4.1:
          *
          *  The device MUST present at least one notification capability.
          */
         bar_offset += bar_len;
         bar_len = sizeof(((struct virtio_pci_mmio *)0)->notify);
 
         /*
          * 4.1.4.4.1:
          *
          *  The cap.offset MUST be 2-byte aligned.
          */
         assert(pci->common.cap_next % 2 == 0);
 
         /* FIXME: Use a non-zero notify_off, for per-queue notification? */
         /*
          * 4.1.4.4.1:
          *
          *  The value cap.length presented by the device MUST be at least 2 and
          *  MUST be large enough to support queue notification offsets for all
          *  supported queues in all possible configurations.
          */
         assert(bar_len >= 2);
 
         init_cap(&pci->notify.cap, sizeof(pci->notify),
                  VIRTIO_PCI_CAP_NOTIFY_CFG,
                  bar_offset, bar_len,
                  offsetof(struct pci_config, isr));
 
         bar_offset += bar_len;
         bar_len = sizeof(((struct virtio_pci_mmio *)0)->isr);
         /*
          * 4.1.4.5.1:
          *
          *  The device MUST present at least one VIRTIO_PCI_CAP_ISR_CFG
          *  capability.
          */
         init_cap(&pci->isr, sizeof(pci->isr),
                  VIRTIO_PCI_CAP_ISR_CFG,
                  bar_offset, bar_len,
                  offsetof(struct pci_config, cfg_access));
 
         /*
          * 4.1.4.7.1:
          *
          * The device MUST present at least one VIRTIO_PCI_CAP_PCI_CFG
          * capability.
          */
         /* This doesn't have any presence in the BAR */
         init_cap(&pci->cfg_access.cap, sizeof(pci->cfg_access),
                  VIRTIO_PCI_CAP_PCI_CFG,
                  0, 0, 0);
 
         bar_offset += bar_len + sizeof(((struct virtio_pci_mmio *)0)->padding);
         assert(bar_offset == sizeof(struct virtio_pci_mmio));
 
         /*
          * This gets sewn in and length set in set_device_config().
          * Some devices don't have a device configuration interface, so
          * we never expose this if we don't call set_device_config().
          */
         init_cap(&pci->device, sizeof(pci->device), VIRTIO_PCI_CAP_DEVICE_CFG,
                  bar_offset, 0, 0);
 }
 
 /*
  * This routine does all the creation and setup of a new device, but we don't
  * actually place the MMIO region until we know the size (if any) of the
  * device-specific config.  And we don't actually start the service threads
  * until later.
  *
  * See what I mean about userspace being boring?
  */
 static struct device *new_pci_device(const char *name, u16 type,
                                      u8 class, u8 subclass)
 {
         struct device *dev = malloc(sizeof(*dev));
 
         /* Now we populate the fields one at a time. */
         dev->name = name;
         dev->vq = NULL;
         dev->running = false;
         dev->wrote_features_ok = false;
         dev->mmio_size = sizeof(struct virtio_pci_mmio);
         dev->mmio = calloc(1, dev->mmio_size);
         dev->features = (u64)1 << VIRTIO_F_VERSION_1;
         dev->features_accepted = 0;
 
         if (devices.device_num + 1 >= MAX_PCI_DEVICES)
                 errx(1, "Can only handle 31 PCI devices");
 
         init_pci_config(&dev->config, type, class, subclass);
         assert(!devices.pci[devices.device_num+1]);
         devices.pci[++devices.device_num] = dev;
 
         return dev;
 }
 
 /*
  * Our first setup routine is the console.  It's a fairly simple device, but
  * UNIX tty handling makes it uglier than it could be.
  */
 static void setup_console(void)
 {
         struct device *dev;
         struct virtio_console_config conf;
 
         /* If we can save the initial standard input settings... */
         if (tcgetattr(STDIN_FILENO, &orig_term) == 0) {
                 struct termios term = orig_term;
                 /*
                  * Then we turn off echo, line buffering and ^C etc: We want a
                  * raw input stream to the Guest.
                  */
                 term.c_lflag &= ~(ISIG|ICANON|ECHO);
                 tcsetattr(STDIN_FILENO, TCSANOW, &term);
         }
 
         dev = new_pci_device("console", VIRTIO_ID_CONSOLE, 0x07, 0x00);
 
         /* We store the console state in dev->priv, and initialize it. */
         dev->priv = malloc(sizeof(struct console_abort));
         ((struct console_abort *)dev->priv)->count = 0;
 
         /*
          * The console needs two virtqueues: the input then the output.  When
          * they put something the input queue, we make sure we're listening to
          * stdin.  When they put something in the output queue, we write it to
          * stdout.
          */
         add_pci_virtqueue(dev, console_input, "input");
         add_pci_virtqueue(dev, console_output, "output");
 
         /* We need a configuration area for the emerg_wr early writes. */
         add_pci_feature(dev, VIRTIO_CONSOLE_F_EMERG_WRITE);
         set_device_config(dev, &conf, sizeof(conf));
 
         verbose("device %u: console\n", devices.device_num);
 }
 /*:*/
 
 /*M:010
  * Inter-guest networking is an interesting area.  Simplest is to have a
  * --sharenet=<name> option which opens or creates a named pipe.  This can be
  * used to send packets to another guest in a 1:1 manner.
  *
  * More sophisticated is to use one of the tools developed for project like UML
  * to do networking.
  *
  * Faster is to do virtio bonding in kernel.  Doing this 1:1 would be
  * completely generic ("here's my vring, attach to your vring") and would work
  * for any traffic.  Of course, namespace and permissions issues need to be
  * dealt with.  A more sophisticated "multi-channel" virtio_net.c could hide
  * multiple inter-guest channels behind one interface, although it would
  * require some manner of hotplugging new virtio channels.
  *
  * Finally, we could use a virtio network switch in the kernel, ie. vhost.
 :*/
 
 static u32 str2ip(const char *ipaddr)
 {
         unsigned int b[4];
 
         if (sscanf(ipaddr, "%u.%u.%u.%u", &b[0], &b[1], &b[2], &b[3]) != 4)
                 errx(1, "Failed to parse IP address '%s'", ipaddr);
         return (b[0] << 24) | (b[1] << 16) | (b[2] << 8) | b[3];
 }
 
 static void str2mac(const char *macaddr, unsigned char mac[6])
 {
         unsigned int m[6];
         if (sscanf(macaddr, "%02x:%02x:%02x:%02x:%02x:%02x",
                    &m[0], &m[1], &m[2], &m[3], &m[4], &m[5]) != 6)
                 errx(1, "Failed to parse mac address '%s'", macaddr);
         mac[0] = m[0];
         mac[1] = m[1];
         mac[2] = m[2];
         mac[3] = m[3];
         mac[4] = m[4];
         mac[5] = m[5];
 }
 
 /*
  * This code is "adapted" from libbridge: it attaches the Host end of the
  * network device to the bridge device specified by the command line.
  *
  * This is yet another James Morris contribution (I'm an IP-level guy, so I
  * dislike bridging), and I just try not to break it.
  */
 static void add_to_bridge(int fd, const char *if_name, const char *br_name)
 {
         int ifidx;
         struct ifreq ifr;
 
         if (!*br_name)
                 errx(1, "must specify bridge name");
 
         ifidx = if_nametoindex(if_name);
         if (!ifidx)
                 errx(1, "interface %s does not exist!", if_name);
 
         strncpy(ifr.ifr_name, br_name, IFNAMSIZ);
         ifr.ifr_name[IFNAMSIZ-1] = '\0';
         ifr.ifr_ifindex = ifidx;
         if (ioctl(fd, SIOCBRADDIF, &ifr) < 0)
                 err(1, "can't add %s to bridge %s", if_name, br_name);
 }
 
 /*
  * This sets up the Host end of the network device with an IP address, brings
  * it up so packets will flow, the copies the MAC address into the hwaddr
  * pointer.
  */
 static void configure_device(int fd, const char *tapif, u32 ipaddr)
 {
         struct ifreq ifr;
         struct sockaddr_in sin;
 
         memset(&ifr, 0, sizeof(ifr));
         strcpy(ifr.ifr_name, tapif);
 
         /* Don't read these incantations.  Just cut & paste them like I did! */
         sin.sin_family = AF_INET;
         sin.sin_addr.s_addr = htonl(ipaddr);
         memcpy(&ifr.ifr_addr, &sin, sizeof(sin));
         if (ioctl(fd, SIOCSIFADDR, &ifr) != 0)
                 err(1, "Setting %s interface address", tapif);
         ifr.ifr_flags = IFF_UP;
         if (ioctl(fd, SIOCSIFFLAGS, &ifr) != 0)
                 err(1, "Bringing interface %s up", tapif);
 }
 
 static int get_tun_device(char tapif[IFNAMSIZ])
 {
         struct ifreq ifr;
         int vnet_hdr_sz;
         int netfd;
 
         /* Start with this zeroed.  Messy but sure. */
         memset(&ifr, 0, sizeof(ifr));
 
         /*
          * We open the /dev/net/tun device and tell it we want a tap device.  A
          * tap device is like a tun device, only somehow different.  To tell
          * the truth, I completely blundered my way through this code, but it
          * works now!
          */
         netfd = open_or_die("/dev/net/tun", O_RDWR);
         ifr.ifr_flags = IFF_TAP | IFF_NO_PI | IFF_VNET_HDR;
         strcpy(ifr.ifr_name, "tap%d");
         if (ioctl(netfd, TUNSETIFF, &ifr) != 0)
                 err(1, "configuring /dev/net/tun");
 
         if (ioctl(netfd, TUNSETOFFLOAD,
                   TUN_F_CSUM|TUN_F_TSO4|TUN_F_TSO6|TUN_F_TSO_ECN) != 0)
                 err(1, "Could not set features for tun device");
 
         /*
          * We don't need checksums calculated for packets coming in this
          * device: trust us!
          */
         ioctl(netfd, TUNSETNOCSUM, 1);
 
         /*
          * In virtio before 1.0 (aka legacy virtio), we added a 16-bit
          * field at the end of the network header iff
          * VIRTIO_NET_F_MRG_RXBUF was negotiated.  For virtio 1.0,
          * that became the norm, but we need to tell the tun device
          * about our expanded header (which is called
          * virtio_net_hdr_mrg_rxbuf in the legacy system).
          */
         vnet_hdr_sz = sizeof(struct virtio_net_hdr_v1);
         if (ioctl(netfd, TUNSETVNETHDRSZ, &vnet_hdr_sz) != 0)
                 err(1, "Setting tun header size to %u", vnet_hdr_sz);
 
         memcpy(tapif, ifr.ifr_name, IFNAMSIZ);
         return netfd;
 }
 
 /*L:195
  * Our network is a Host<->Guest network.  This can either use bridging or
  * routing, but the principle is the same: it uses the "tun" device to inject
  * packets into the Host as if they came in from a normal network card.  We
  * just shunt packets between the Guest and the tun device.
  */
 static void setup_tun_net(char *arg)
 {
         struct device *dev;
         struct net_info *net_info = malloc(sizeof(*net_info));
         int ipfd;
         u32 ip = INADDR_ANY;
         bool bridging = false;
         char tapif[IFNAMSIZ], *p;
         struct virtio_net_config conf;
 
         net_info->tunfd = get_tun_device(tapif);
 
         /* First we create a new network device. */
         dev = new_pci_device("net", VIRTIO_ID_NET, 0x02, 0x00);
         dev->priv = net_info;
 
         /* Network devices need a recv and a send queue, just like console. */
         add_pci_virtqueue(dev, net_input, "rx");
         add_pci_virtqueue(dev, net_output, "tx");
 
         /*
          * We need a socket to perform the magic network ioctls to bring up the
          * tap interface, connect to the bridge etc.  Any socket will do!
          */
         ipfd = socket(PF_INET, SOCK_DGRAM, IPPROTO_IP);
         if (ipfd < 0)
                 err(1, "opening IP socket");
 
         /* If the command line was --tunnet=bridge:<name> do bridging. */
         if (!strncmp(BRIDGE_PFX, arg, strlen(BRIDGE_PFX))) {
                 arg += strlen(BRIDGE_PFX);
                 bridging = true;
         }
 
         /* A mac address may follow the bridge name or IP address */
         p = strchr(arg, ':');
         if (p) {
                 str2mac(p+1, conf.mac);
                 add_pci_feature(dev, VIRTIO_NET_F_MAC);
                 *p = '\0';
         }
 
         /* arg is now either an IP address or a bridge name */
         if (bridging)
                 add_to_bridge(ipfd, tapif, arg);
         else
                 ip = str2ip(arg);
 
         /* Set up the tun device. */
         configure_device(ipfd, tapif, ip);
 
         /* Expect Guest to handle everything except UFO */
         add_pci_feature(dev, VIRTIO_NET_F_CSUM);
         add_pci_feature(dev, VIRTIO_NET_F_GUEST_CSUM);
         add_pci_feature(dev, VIRTIO_NET_F_GUEST_TSO4);
         add_pci_feature(dev, VIRTIO_NET_F_GUEST_TSO6);
         add_pci_feature(dev, VIRTIO_NET_F_GUEST_ECN);
         add_pci_feature(dev, VIRTIO_NET_F_HOST_TSO4);
         add_pci_feature(dev, VIRTIO_NET_F_HOST_TSO6);
         add_pci_feature(dev, VIRTIO_NET_F_HOST_ECN);
         /* We handle indirect ring entries */
         add_pci_feature(dev, VIRTIO_RING_F_INDIRECT_DESC);
         set_device_config(dev, &conf, sizeof(conf));
 
         /* We don't need the socket any more; setup is done. */
         close(ipfd);
 
         if (bridging)
                 verbose("device %u: tun %s attached to bridge: %s\n",
                         devices.device_num, tapif, arg);
         else
                 verbose("device %u: tun %s: %s\n",
                         devices.device_num, tapif, arg);
 }
 /*:*/
 
 /* This hangs off device->priv. */
 struct vblk_info {
         /* The size of the file. */
         off64_t len;
 
         /* The file descriptor for the file. */
         int fd;
 
 };
 
 /*L:210
  * The Disk
  *
  * The disk only has one virtqueue, so it only has one thread.  It is really
  * simple: the Guest asks for a block number and we read or write that position
  * in the file.
  *
  * Before we serviced each virtqueue in a separate thread, that was unacceptably
  * slow: the Guest waits until the read is finished before running anything
  * else, even if it could have been doing useful work.
  *
  * We could have used async I/O, except it's reputed to suck so hard that
  * characters actually go missing from your code when you try to use it.
  */
 static void blk_request(struct virtqueue *vq)
 {
         struct vblk_info *vblk = vq->dev->priv;
         unsigned int head, out_num, in_num, wlen;
         int ret, i;
         u8 *in;
         struct virtio_blk_outhdr out;
         struct iovec iov[vq->vring.num];
         off64_t off;
 
         /*
          * Get the next request, where we normally wait.  It triggers the
          * interrupt to acknowledge previously serviced requests (if any).
          */
         head = wait_for_vq_desc(vq, iov, &out_num, &in_num);
 
         /* Copy the output header from the front of the iov (adjusts iov) */
         iov_consume(vq->dev, iov, out_num, &out, sizeof(out));
 
         /* Find and trim end of iov input array, for our status byte. */
         in = NULL;
         for (i = out_num + in_num - 1; i >= out_num; i--) {
                 if (iov[i].iov_len > 0) {
                         in = iov[i].iov_base + iov[i].iov_len - 1;
                         iov[i].iov_len--;
                         break;
                 }
         }
         if (!in)
                 bad_driver_vq(vq, "Bad virtblk cmd with no room for status");
 
         /*
          * For historical reasons, block operations are expressed in 512 byte
          * "sectors".
          */
         off = out.sector * 512;
 
         if (out.type & VIRTIO_BLK_T_OUT) {
                 /*
                  * Write
                  *
                  * Move to the right location in the block file.  This can fail
                  * if they try to write past end.
                  */
                 if (lseek64(vblk->fd, off, SEEK_SET) != off)
                         err(1, "Bad seek to sector %llu", out.sector);
 
                 ret = writev(vblk->fd, iov, out_num);
                 verbose("WRITE to sector %llu: %i\n", out.sector, ret);
 
                 /*
                  * Grr... Now we know how long the descriptor they sent was, we
                  * make sure they didn't try to write over the end of the block
                  * file (possibly extending it).
                  */
                 if (ret > 0 && off + ret > vblk->len) {
                         /* Trim it back to the correct length */
                         ftruncate64(vblk->fd, vblk->len);
                         /* Die, bad Guest, die. */
                         bad_driver_vq(vq, "Write past end %llu+%u", off, ret);
                 }
 
                 wlen = sizeof(*in);
                 *in = (ret >= 0 ? VIRTIO_BLK_S_OK : VIRTIO_BLK_S_IOERR);
         } else if (out.type & VIRTIO_BLK_T_FLUSH) {
                 /* Flush */
                 ret = fdatasync(vblk->fd);
                 verbose("FLUSH fdatasync: %i\n", ret);
                 wlen = sizeof(*in);
                 *in = (ret >= 0 ? VIRTIO_BLK_S_OK : VIRTIO_BLK_S_IOERR);
         } else {
                 /*
                  * Read
                  *
                  * Move to the right location in the block file.  This can fail
                  * if they try to read past end.
                  */
                 if (lseek64(vblk->fd, off, SEEK_SET) != off)
                         err(1, "Bad seek to sector %llu", out.sector);
 
                 ret = readv(vblk->fd, iov + out_num, in_num);
                 if (ret >= 0) {
                         wlen = sizeof(*in) + ret;
                         *in = VIRTIO_BLK_S_OK;
                 } else {
                         wlen = sizeof(*in);
                         *in = VIRTIO_BLK_S_IOERR;
                 }
         }
 
         /* Finished that request. */
         add_used(vq, head, wlen);
 }
 
 /*L:198 This actually sets up a virtual block device. */
 static void setup_block_file(const char *filename)
 {
         struct device *dev;
         struct vblk_info *vblk;
         struct virtio_blk_config conf;
 
         /* Create the device. */
         dev = new_pci_device("block", VIRTIO_ID_BLOCK, 0x01, 0x80);
 
         /* The device has one virtqueue, where the Guest places requests. */
         add_pci_virtqueue(dev, blk_request, "request");
 
         /* Allocate the room for our own bookkeeping */
         vblk = dev->priv = malloc(sizeof(*vblk));
 
         /* First we open the file and store the length. */
         vblk->fd = open_or_die(filename, O_RDWR|O_LARGEFILE);
         vblk->len = lseek64(vblk->fd, 0, SEEK_END);
 
         /* Tell Guest how many sectors this device has. */
         conf.capacity = cpu_to_le64(vblk->len / 512);
 
         /*
          * Tell Guest not to put in too many descriptors at once: two are used
          * for the in and out elements.
          */
         add_pci_feature(dev, VIRTIO_BLK_F_SEG_MAX);
         conf.seg_max = cpu_to_le32(VIRTQUEUE_NUM - 2);
 
         set_device_config(dev, &conf, sizeof(struct virtio_blk_config));
 
         verbose("device %u: virtblock %llu sectors\n",
                 devices.device_num, le64_to_cpu(conf.capacity));
 }
 
 /*L:211
  * Our random number generator device reads from /dev/urandom into the Guest's
  * input buffers.  The usual case is that the Guest doesn't want random numbers
  * and so has no buffers although /dev/urandom is still readable, whereas
  * console is the reverse.
  *
  * The same logic applies, however.
  */
 struct rng_info {
         int rfd;
 };
 
 static void rng_input(struct virtqueue *vq)
 {
         int len;
         unsigned int head, in_num, out_num, totlen = 0;
         struct rng_info *rng_info = vq->dev->priv;
         struct iovec iov[vq->vring.num];
 
         /* First we need a buffer from the Guests's virtqueue. */
         head = wait_for_vq_desc(vq, iov, &out_num, &in_num);
         if (out_num)
                 bad_driver_vq(vq, "Output buffers in rng?");
 
         /*
          * Just like the console write, we loop to cover the whole iovec.
          * In this case, short reads actually happen quite a bit.
          */
         while (!iov_empty(iov, in_num)) {
                 len = readv(rng_info->rfd, iov, in_num);
                 if (len <= 0)
                         err(1, "Read from /dev/urandom gave %i", len);
                 iov_consume(vq->dev, iov, in_num, NULL, len);
                 totlen += len;
         }
 
         /* Tell the Guest about the new input. */
         add_used(vq, head, totlen);
 }
 
 /*L:199
  * This creates a "hardware" random number device for the Guest.
  */
 static void setup_rng(void)
 {
         struct device *dev;
         struct rng_info *rng_info = malloc(sizeof(*rng_info));
 
         /* Our device's private info simply contains the /dev/urandom fd. */
         rng_info->rfd = open_or_die("/dev/urandom", O_RDONLY);
 
         /* Create the new device. */
         dev = new_pci_device("rng", VIRTIO_ID_RNG, 0xff, 0);
         dev->priv = rng_info;
 
         /* The device has one virtqueue, where the Guest places inbufs. */
         add_pci_virtqueue(dev, rng_input, "input");
 
         /* We don't have any configuration space */
         no_device_config(dev);
 
         verbose("device %u: rng\n", devices.device_num);
 }
 /* That's the end of device setup. */
 
 /*L:230 Reboot is pretty easy: clean up and exec() the Launcher afresh. */
 static void __attribute__((noreturn)) restart_guest(void)
 {
         unsigned int i;
 
         /*
          * Since we don't track all open fds, we simply close everything beyond
          * stderr.
          */
         for (i = 3; i < FD_SETSIZE; i++)
                 close(i);
 
         /* Reset all the devices (kills all threads). */
         cleanup_devices();
 
         execv(main_args[0], main_args);
         err(1, "Could not exec %s", main_args[0]);
 }
 
 /*L:220
  * Finally we reach the core of the Launcher which runs the Guest, serves
  * its input and output, and finally, lays it to rest.
  */
 static void __attribute__((noreturn)) run_guest(void)
 {
         for (;;) {
                 struct lguest_pending notify;
                 int readval;
 
                 /* We read from the /dev/lguest device to run the Guest. */
                 readval = pread(lguest_fd, &notify, sizeof(notify), cpu_id);
                 if (readval == sizeof(notify)) {
                         if (notify.trap == 13) {
                                 verbose("Emulating instruction at %#x\n",
                                         getreg(eip));
                                 emulate_insn(notify.insn);
                         } else if (notify.trap == 14) {
                                 verbose("Emulating MMIO at %#x\n",
                                         getreg(eip));
                                 emulate_mmio(notify.addr, notify.insn);
                         } else
                                 errx(1, "Unknown trap %i addr %#08x\n",
                                      notify.trap, notify.addr);
                 /* ENOENT means the Guest died.  Reading tells us why. */
                 } else if (errno == ENOENT) {
                         char reason[1024] = { 0 };
                         pread(lguest_fd, reason, sizeof(reason)-1, cpu_id);
                         errx(1, "%s", reason);
                 /* ERESTART means that we need to reboot the guest */
                 } else if (errno == ERESTART) {
                         restart_guest();
                 /* Anything else means a bug or incompatible change. */
                 } else
                         err(1, "Running guest failed");
         }
 }
 /*L:240
  * This is the end of the Launcher.  The good news: we are over halfway
  * through!  The bad news: the most fiendish part of the code still lies ahead
  * of us.
  *
  * Are you ready?  Take a deep breath and join me in the core of the Host, in
  * "make Host".
 :*/
 
 static struct option opts[] = {
         { "verbose", 0, NULL, 'v' },
         { "tunnet", 1, NULL, 't' },
         { "block", 1, NULL, 'b' },
         { "rng", 0, NULL, 'r' },
         { "initrd", 1, NULL, 'i' },
         { "username", 1, NULL, 'u' },
         { "chroot", 1, NULL, 'c' },
         { NULL },
 };
 static void usage(void)
 {
         errx(1, "Usage: lguest [--verbose] "
              "[--tunnet=(<ipaddr>:<macaddr>|bridge:<bridgename>:<macaddr>)\n"
              "|--block=<filename>|--initrd=<filename>]...\n"
              "<mem-in-mb> vmlinux [args...]");
 }
 
 /*L:105 The main routine is where the real work begins: */
 int main(int argc, char *argv[])
 {
         /* Memory, code startpoint and size of the (optional) initrd. */
         unsigned long mem = 0, start, initrd_size = 0;
         /* Two temporaries. */
         int i, c;
         /* The boot information for the Guest. */
         struct boot_params *boot;
         /* If they specify an initrd file to load. */
         const char *initrd_name = NULL;
 
         /* Password structure for initgroups/setres[gu]id */
         struct passwd *user_details = NULL;
 
         /* Directory to chroot to */
         char *chroot_path = NULL;
 
         /* Save the args: we "reboot" by execing ourselves again. */
         main_args = argv;
 
         /*
          * First we initialize the device list.  We remember next interrupt
          * number to use for devices (1: remember that 0 is used by the timer).
          */
         devices.next_irq = 1;
 
         /* We're CPU 0.  In fact, that's the only CPU possible right now. */
         cpu_id = 0;
 
         /*
          * We need to know how much memory so we can set up the device
          * descriptor and memory pages for the devices as we parse the command
          * line.  So we quickly look through the arguments to find the amount
          * of memory now.
          */
         for (i = 1; i < argc; i++) {
                 if (argv[i][0] != '-') {
                         mem = atoi(argv[i]) * 1024 * 1024;
                         /*
                          * We start by mapping anonymous pages over all of
                          * guest-physical memory range.  This fills it with 0,
                          * and ensures that the Guest won't be killed when it
                          * tries to access it.
                          */
                         guest_base = map_zeroed_pages(mem / getpagesize()
                                                       + DEVICE_PAGES);
                         guest_limit = mem;
                         guest_max = guest_mmio = mem + DEVICE_PAGES*getpagesize();
                         break;
                 }
         }
 
         /* If we exit via err(), this kills all the threads, restores tty. */
         atexit(cleanup_devices);
 
         /* We always have a console device, and it's always device 1. */
         setup_console();
 
         /* The options are fairly straight-forward */
         while ((c = getopt_long(argc, argv, "v", opts, NULL)) != EOF) {
                 switch (c) {
                 case 'v':
                         verbose = true;
                         break;
                 case 't':
                         setup_tun_net(optarg);
                         break;
                 case 'b':
                         setup_block_file(optarg);
                         break;
                 case 'r':
                         setup_rng();
                         break;
                 case 'i':
                         initrd_name = optarg;
                         break;
                 case 'u':
                         user_details = getpwnam(optarg);
                         if (!user_details)
                                 err(1, "getpwnam failed, incorrect username?");
                         break;
                 case 'c':
                         chroot_path = optarg;
                         break;
                 default:
                         warnx("Unknown argument %s", argv[optind]);
                         usage();
                 }
         }
         /*
          * After the other arguments we expect memory and kernel image name,
          * followed by command line arguments for the kernel.
          */
         if (optind + 2 > argc)
                 usage();
 
         verbose("Guest base is at %p\n", guest_base);
 
         /* Initialize the (fake) PCI host bridge device. */
         init_pci_host_bridge();
 
         /* Now we load the kernel */
         start = load_kernel(open_or_die(argv[optind+1], O_RDONLY));
 
         /* Boot information is stashed at physical address 0 */
         boot = from_guest_phys(0);
 
         /* Map the initrd image if requested (at top of physical memory) */
         if (initrd_name) {
                 initrd_size = load_initrd(initrd_name, mem);
                 /*
                  * These are the location in the Linux boot header where the
                  * start and size of the initrd are expected to be found.
                  */
                 boot->hdr.ramdisk_image = mem - initrd_size;
                 boot->hdr.ramdisk_size = initrd_size;
                 /* The bootloader type 0xFF means "unknown"; that's OK. */
                 boot->hdr.type_of_loader = 0xFF;
         }
 
         /*
          * The Linux boot header contains an "E820" memory map: ours is a
          * simple, single region.
          */
         boot->e820_entries = 1;
         boot->e820_table[0] = ((struct e820_entry) { 0, mem, E820_TYPE_RAM });
         /*
          * The boot header contains a command line pointer: we put the command
          * line after the boot header.
          */
         boot->hdr.cmd_line_ptr = to_guest_phys(boot + 1);
         /* We use a simple helper to copy the arguments separated by spaces. */
         concat((char *)(boot + 1), argv+optind+2);
 
         /* Set kernel alignment to 16M (CONFIG_PHYSICAL_ALIGN) */
         boot->hdr.kernel_alignment = 0x1000000;
 
         /* Boot protocol version: 2.07 supports the fields for lguest. */
         boot->hdr.version = 0x207;
 
         /* X86_SUBARCH_LGUEST tells the Guest it's an lguest. */
         boot->hdr.hardware_subarch = X86_SUBARCH_LGUEST;
 
         /* Tell the entry path not to try to reload segment registers. */
         boot->hdr.loadflags |= KEEP_SEGMENTS;
 
         /* We don't support tboot: */
         boot->tboot_addr = 0;
 
         /* Ensure this is 0 to prevent APM from loading: */
         boot->apm_bios_info.version = 0;
 
         /* We tell the kernel to initialize the Guest. */
         tell_kernel(start);
 
         /* Ensure that we terminate if a device-servicing child dies. */
         signal(SIGCHLD, kill_launcher);
 
         /* If requested, chroot to a directory */
         if (chroot_path) {
                 if (chroot(chroot_path) != 0)
                         err(1, "chroot(\"%s\") failed", chroot_path);
 
                 if (chdir("/") != 0)
                         err(1, "chdir(\"/\") failed");
 
                 verbose("chroot done\n");
         }
 
         /* If requested, drop privileges */
         if (user_details) {
                 uid_t u;
                 gid_t g;
 
                 u = user_details->pw_uid;
                 g = user_details->pw_gid;
 
                 if (initgroups(user_details->pw_name, g) != 0)
                         err(1, "initgroups failed");
 
                 if (setresgid(g, g, g) != 0)
                         err(1, "setresgid failed");
 
                 if (setresuid(u, u, u) != 0)
                         err(1, "setresuid failed");
 
                 verbose("Dropping privileges completed\n");
         }
 
         /* Finally, run the Guest.  This doesn't return. */
         run_guest();
 }
 /*:*/
 
 /*M:999
  * Mastery is done: you now know everything I do.
  *
  * But surely you have seen code, features and bugs in your wanderings which
  * you now yearn to attack?  That is the real game, and I look forward to you
  * patching and forking lguest into the Your-Name-Here-visor.
  *
  * Farewell, and good coding!
  * Rusty Russell.
  */