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TOMOYO Linux Cross Reference
Linux/kernel/relay.c

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  1 /*
  2  * Public API and common code for kernel->userspace relay file support.
  3  *
  4  * See Documentation/filesystems/relay.txt for an overview.
  5  *
  6  * Copyright (C) 2002-2005 - Tom Zanussi (zanussi@us.ibm.com), IBM Corp
  7  * Copyright (C) 1999-2005 - Karim Yaghmour (karim@opersys.com)
  8  *
  9  * Moved to kernel/relay.c by Paul Mundt, 2006.
 10  * November 2006 - CPU hotplug support by Mathieu Desnoyers
 11  *      (mathieu.desnoyers@polymtl.ca)
 12  *
 13  * This file is released under the GPL.
 14  */
 15 #include <linux/errno.h>
 16 #include <linux/stddef.h>
 17 #include <linux/slab.h>
 18 #include <linux/export.h>
 19 #include <linux/string.h>
 20 #include <linux/relay.h>
 21 #include <linux/vmalloc.h>
 22 #include <linux/mm.h>
 23 #include <linux/cpu.h>
 24 #include <linux/splice.h>
 25 
 26 /* list of open channels, for cpu hotplug */
 27 static DEFINE_MUTEX(relay_channels_mutex);
 28 static LIST_HEAD(relay_channels);
 29 
 30 /*
 31  * close() vm_op implementation for relay file mapping.
 32  */
 33 static void relay_file_mmap_close(struct vm_area_struct *vma)
 34 {
 35         struct rchan_buf *buf = vma->vm_private_data;
 36         buf->chan->cb->buf_unmapped(buf, vma->vm_file);
 37 }
 38 
 39 /*
 40  * fault() vm_op implementation for relay file mapping.
 41  */
 42 static int relay_buf_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
 43 {
 44         struct page *page;
 45         struct rchan_buf *buf = vma->vm_private_data;
 46         pgoff_t pgoff = vmf->pgoff;
 47 
 48         if (!buf)
 49                 return VM_FAULT_OOM;
 50 
 51         page = vmalloc_to_page(buf->start + (pgoff << PAGE_SHIFT));
 52         if (!page)
 53                 return VM_FAULT_SIGBUS;
 54         get_page(page);
 55         vmf->page = page;
 56 
 57         return 0;
 58 }
 59 
 60 /*
 61  * vm_ops for relay file mappings.
 62  */
 63 static const struct vm_operations_struct relay_file_mmap_ops = {
 64         .fault = relay_buf_fault,
 65         .close = relay_file_mmap_close,
 66 };
 67 
 68 /*
 69  * allocate an array of pointers of struct page
 70  */
 71 static struct page **relay_alloc_page_array(unsigned int n_pages)
 72 {
 73         const size_t pa_size = n_pages * sizeof(struct page *);
 74         if (pa_size > PAGE_SIZE)
 75                 return vzalloc(pa_size);
 76         return kzalloc(pa_size, GFP_KERNEL);
 77 }
 78 
 79 /*
 80  * free an array of pointers of struct page
 81  */
 82 static void relay_free_page_array(struct page **array)
 83 {
 84         kvfree(array);
 85 }
 86 
 87 /**
 88  *      relay_mmap_buf: - mmap channel buffer to process address space
 89  *      @buf: relay channel buffer
 90  *      @vma: vm_area_struct describing memory to be mapped
 91  *
 92  *      Returns 0 if ok, negative on error
 93  *
 94  *      Caller should already have grabbed mmap_sem.
 95  */
 96 static int relay_mmap_buf(struct rchan_buf *buf, struct vm_area_struct *vma)
 97 {
 98         unsigned long length = vma->vm_end - vma->vm_start;
 99         struct file *filp = vma->vm_file;
100 
101         if (!buf)
102                 return -EBADF;
103 
104         if (length != (unsigned long)buf->chan->alloc_size)
105                 return -EINVAL;
106 
107         vma->vm_ops = &relay_file_mmap_ops;
108         vma->vm_flags |= VM_DONTEXPAND;
109         vma->vm_private_data = buf;
110         buf->chan->cb->buf_mapped(buf, filp);
111 
112         return 0;
113 }
114 
115 /**
116  *      relay_alloc_buf - allocate a channel buffer
117  *      @buf: the buffer struct
118  *      @size: total size of the buffer
119  *
120  *      Returns a pointer to the resulting buffer, %NULL if unsuccessful. The
121  *      passed in size will get page aligned, if it isn't already.
122  */
123 static void *relay_alloc_buf(struct rchan_buf *buf, size_t *size)
124 {
125         void *mem;
126         unsigned int i, j, n_pages;
127 
128         *size = PAGE_ALIGN(*size);
129         n_pages = *size >> PAGE_SHIFT;
130 
131         buf->page_array = relay_alloc_page_array(n_pages);
132         if (!buf->page_array)
133                 return NULL;
134 
135         for (i = 0; i < n_pages; i++) {
136                 buf->page_array[i] = alloc_page(GFP_KERNEL);
137                 if (unlikely(!buf->page_array[i]))
138                         goto depopulate;
139                 set_page_private(buf->page_array[i], (unsigned long)buf);
140         }
141         mem = vmap(buf->page_array, n_pages, VM_MAP, PAGE_KERNEL);
142         if (!mem)
143                 goto depopulate;
144 
145         memset(mem, 0, *size);
146         buf->page_count = n_pages;
147         return mem;
148 
149 depopulate:
150         for (j = 0; j < i; j++)
151                 __free_page(buf->page_array[j]);
152         relay_free_page_array(buf->page_array);
153         return NULL;
154 }
155 
156 /**
157  *      relay_create_buf - allocate and initialize a channel buffer
158  *      @chan: the relay channel
159  *
160  *      Returns channel buffer if successful, %NULL otherwise.
161  */
162 static struct rchan_buf *relay_create_buf(struct rchan *chan)
163 {
164         struct rchan_buf *buf;
165 
166         if (chan->n_subbufs > UINT_MAX / sizeof(size_t *))
167                 return NULL;
168 
169         buf = kzalloc(sizeof(struct rchan_buf), GFP_KERNEL);
170         if (!buf)
171                 return NULL;
172         buf->padding = kmalloc(chan->n_subbufs * sizeof(size_t *), GFP_KERNEL);
173         if (!buf->padding)
174                 goto free_buf;
175 
176         buf->start = relay_alloc_buf(buf, &chan->alloc_size);
177         if (!buf->start)
178                 goto free_buf;
179 
180         buf->chan = chan;
181         kref_get(&buf->chan->kref);
182         return buf;
183 
184 free_buf:
185         kfree(buf->padding);
186         kfree(buf);
187         return NULL;
188 }
189 
190 /**
191  *      relay_destroy_channel - free the channel struct
192  *      @kref: target kernel reference that contains the relay channel
193  *
194  *      Should only be called from kref_put().
195  */
196 static void relay_destroy_channel(struct kref *kref)
197 {
198         struct rchan *chan = container_of(kref, struct rchan, kref);
199         kfree(chan);
200 }
201 
202 /**
203  *      relay_destroy_buf - destroy an rchan_buf struct and associated buffer
204  *      @buf: the buffer struct
205  */
206 static void relay_destroy_buf(struct rchan_buf *buf)
207 {
208         struct rchan *chan = buf->chan;
209         unsigned int i;
210 
211         if (likely(buf->start)) {
212                 vunmap(buf->start);
213                 for (i = 0; i < buf->page_count; i++)
214                         __free_page(buf->page_array[i]);
215                 relay_free_page_array(buf->page_array);
216         }
217         chan->buf[buf->cpu] = NULL;
218         kfree(buf->padding);
219         kfree(buf);
220         kref_put(&chan->kref, relay_destroy_channel);
221 }
222 
223 /**
224  *      relay_remove_buf - remove a channel buffer
225  *      @kref: target kernel reference that contains the relay buffer
226  *
227  *      Removes the file from the filesystem, which also frees the
228  *      rchan_buf_struct and the channel buffer.  Should only be called from
229  *      kref_put().
230  */
231 static void relay_remove_buf(struct kref *kref)
232 {
233         struct rchan_buf *buf = container_of(kref, struct rchan_buf, kref);
234         relay_destroy_buf(buf);
235 }
236 
237 /**
238  *      relay_buf_empty - boolean, is the channel buffer empty?
239  *      @buf: channel buffer
240  *
241  *      Returns 1 if the buffer is empty, 0 otherwise.
242  */
243 static int relay_buf_empty(struct rchan_buf *buf)
244 {
245         return (buf->subbufs_produced - buf->subbufs_consumed) ? 0 : 1;
246 }
247 
248 /**
249  *      relay_buf_full - boolean, is the channel buffer full?
250  *      @buf: channel buffer
251  *
252  *      Returns 1 if the buffer is full, 0 otherwise.
253  */
254 int relay_buf_full(struct rchan_buf *buf)
255 {
256         size_t ready = buf->subbufs_produced - buf->subbufs_consumed;
257         return (ready >= buf->chan->n_subbufs) ? 1 : 0;
258 }
259 EXPORT_SYMBOL_GPL(relay_buf_full);
260 
261 /*
262  * High-level relay kernel API and associated functions.
263  */
264 
265 /*
266  * rchan_callback implementations defining default channel behavior.  Used
267  * in place of corresponding NULL values in client callback struct.
268  */
269 
270 /*
271  * subbuf_start() default callback.  Does nothing.
272  */
273 static int subbuf_start_default_callback (struct rchan_buf *buf,
274                                           void *subbuf,
275                                           void *prev_subbuf,
276                                           size_t prev_padding)
277 {
278         if (relay_buf_full(buf))
279                 return 0;
280 
281         return 1;
282 }
283 
284 /*
285  * buf_mapped() default callback.  Does nothing.
286  */
287 static void buf_mapped_default_callback(struct rchan_buf *buf,
288                                         struct file *filp)
289 {
290 }
291 
292 /*
293  * buf_unmapped() default callback.  Does nothing.
294  */
295 static void buf_unmapped_default_callback(struct rchan_buf *buf,
296                                           struct file *filp)
297 {
298 }
299 
300 /*
301  * create_buf_file_create() default callback.  Does nothing.
302  */
303 static struct dentry *create_buf_file_default_callback(const char *filename,
304                                                        struct dentry *parent,
305                                                        umode_t mode,
306                                                        struct rchan_buf *buf,
307                                                        int *is_global)
308 {
309         return NULL;
310 }
311 
312 /*
313  * remove_buf_file() default callback.  Does nothing.
314  */
315 static int remove_buf_file_default_callback(struct dentry *dentry)
316 {
317         return -EINVAL;
318 }
319 
320 /* relay channel default callbacks */
321 static struct rchan_callbacks default_channel_callbacks = {
322         .subbuf_start = subbuf_start_default_callback,
323         .buf_mapped = buf_mapped_default_callback,
324         .buf_unmapped = buf_unmapped_default_callback,
325         .create_buf_file = create_buf_file_default_callback,
326         .remove_buf_file = remove_buf_file_default_callback,
327 };
328 
329 /**
330  *      wakeup_readers - wake up readers waiting on a channel
331  *      @data: contains the channel buffer
332  *
333  *      This is the timer function used to defer reader waking.
334  */
335 static void wakeup_readers(unsigned long data)
336 {
337         struct rchan_buf *buf = (struct rchan_buf *)data;
338         wake_up_interruptible(&buf->read_wait);
339 }
340 
341 /**
342  *      __relay_reset - reset a channel buffer
343  *      @buf: the channel buffer
344  *      @init: 1 if this is a first-time initialization
345  *
346  *      See relay_reset() for description of effect.
347  */
348 static void __relay_reset(struct rchan_buf *buf, unsigned int init)
349 {
350         size_t i;
351 
352         if (init) {
353                 init_waitqueue_head(&buf->read_wait);
354                 kref_init(&buf->kref);
355                 setup_timer(&buf->timer, wakeup_readers, (unsigned long)buf);
356         } else
357                 del_timer_sync(&buf->timer);
358 
359         buf->subbufs_produced = 0;
360         buf->subbufs_consumed = 0;
361         buf->bytes_consumed = 0;
362         buf->finalized = 0;
363         buf->data = buf->start;
364         buf->offset = 0;
365 
366         for (i = 0; i < buf->chan->n_subbufs; i++)
367                 buf->padding[i] = 0;
368 
369         buf->chan->cb->subbuf_start(buf, buf->data, NULL, 0);
370 }
371 
372 /**
373  *      relay_reset - reset the channel
374  *      @chan: the channel
375  *
376  *      This has the effect of erasing all data from all channel buffers
377  *      and restarting the channel in its initial state.  The buffers
378  *      are not freed, so any mappings are still in effect.
379  *
380  *      NOTE. Care should be taken that the channel isn't actually
381  *      being used by anything when this call is made.
382  */
383 void relay_reset(struct rchan *chan)
384 {
385         unsigned int i;
386 
387         if (!chan)
388                 return;
389 
390         if (chan->is_global && chan->buf[0]) {
391                 __relay_reset(chan->buf[0], 0);
392                 return;
393         }
394 
395         mutex_lock(&relay_channels_mutex);
396         for_each_possible_cpu(i)
397                 if (chan->buf[i])
398                         __relay_reset(chan->buf[i], 0);
399         mutex_unlock(&relay_channels_mutex);
400 }
401 EXPORT_SYMBOL_GPL(relay_reset);
402 
403 static inline void relay_set_buf_dentry(struct rchan_buf *buf,
404                                         struct dentry *dentry)
405 {
406         buf->dentry = dentry;
407         d_inode(buf->dentry)->i_size = buf->early_bytes;
408 }
409 
410 static struct dentry *relay_create_buf_file(struct rchan *chan,
411                                             struct rchan_buf *buf,
412                                             unsigned int cpu)
413 {
414         struct dentry *dentry;
415         char *tmpname;
416 
417         tmpname = kzalloc(NAME_MAX + 1, GFP_KERNEL);
418         if (!tmpname)
419                 return NULL;
420         snprintf(tmpname, NAME_MAX, "%s%d", chan->base_filename, cpu);
421 
422         /* Create file in fs */
423         dentry = chan->cb->create_buf_file(tmpname, chan->parent,
424                                            S_IRUSR, buf,
425                                            &chan->is_global);
426 
427         kfree(tmpname);
428 
429         return dentry;
430 }
431 
432 /*
433  *      relay_open_buf - create a new relay channel buffer
434  *
435  *      used by relay_open() and CPU hotplug.
436  */
437 static struct rchan_buf *relay_open_buf(struct rchan *chan, unsigned int cpu)
438 {
439         struct rchan_buf *buf = NULL;
440         struct dentry *dentry;
441 
442         if (chan->is_global)
443                 return chan->buf[0];
444 
445         buf = relay_create_buf(chan);
446         if (!buf)
447                 return NULL;
448 
449         if (chan->has_base_filename) {
450                 dentry = relay_create_buf_file(chan, buf, cpu);
451                 if (!dentry)
452                         goto free_buf;
453                 relay_set_buf_dentry(buf, dentry);
454         }
455 
456         buf->cpu = cpu;
457         __relay_reset(buf, 1);
458 
459         if(chan->is_global) {
460                 chan->buf[0] = buf;
461                 buf->cpu = 0;
462         }
463 
464         return buf;
465 
466 free_buf:
467         relay_destroy_buf(buf);
468         return NULL;
469 }
470 
471 /**
472  *      relay_close_buf - close a channel buffer
473  *      @buf: channel buffer
474  *
475  *      Marks the buffer finalized and restores the default callbacks.
476  *      The channel buffer and channel buffer data structure are then freed
477  *      automatically when the last reference is given up.
478  */
479 static void relay_close_buf(struct rchan_buf *buf)
480 {
481         buf->finalized = 1;
482         del_timer_sync(&buf->timer);
483         buf->chan->cb->remove_buf_file(buf->dentry);
484         kref_put(&buf->kref, relay_remove_buf);
485 }
486 
487 static void setup_callbacks(struct rchan *chan,
488                                    struct rchan_callbacks *cb)
489 {
490         if (!cb) {
491                 chan->cb = &default_channel_callbacks;
492                 return;
493         }
494 
495         if (!cb->subbuf_start)
496                 cb->subbuf_start = subbuf_start_default_callback;
497         if (!cb->buf_mapped)
498                 cb->buf_mapped = buf_mapped_default_callback;
499         if (!cb->buf_unmapped)
500                 cb->buf_unmapped = buf_unmapped_default_callback;
501         if (!cb->create_buf_file)
502                 cb->create_buf_file = create_buf_file_default_callback;
503         if (!cb->remove_buf_file)
504                 cb->remove_buf_file = remove_buf_file_default_callback;
505         chan->cb = cb;
506 }
507 
508 /**
509  *      relay_hotcpu_callback - CPU hotplug callback
510  *      @nb: notifier block
511  *      @action: hotplug action to take
512  *      @hcpu: CPU number
513  *
514  *      Returns the success/failure of the operation. (%NOTIFY_OK, %NOTIFY_BAD)
515  */
516 static int relay_hotcpu_callback(struct notifier_block *nb,
517                                 unsigned long action,
518                                 void *hcpu)
519 {
520         unsigned int hotcpu = (unsigned long)hcpu;
521         struct rchan *chan;
522 
523         switch(action) {
524         case CPU_UP_PREPARE:
525         case CPU_UP_PREPARE_FROZEN:
526                 mutex_lock(&relay_channels_mutex);
527                 list_for_each_entry(chan, &relay_channels, list) {
528                         if (chan->buf[hotcpu])
529                                 continue;
530                         chan->buf[hotcpu] = relay_open_buf(chan, hotcpu);
531                         if(!chan->buf[hotcpu]) {
532                                 printk(KERN_ERR
533                                         "relay_hotcpu_callback: cpu %d buffer "
534                                         "creation failed\n", hotcpu);
535                                 mutex_unlock(&relay_channels_mutex);
536                                 return notifier_from_errno(-ENOMEM);
537                         }
538                 }
539                 mutex_unlock(&relay_channels_mutex);
540                 break;
541         case CPU_DEAD:
542         case CPU_DEAD_FROZEN:
543                 /* No need to flush the cpu : will be flushed upon
544                  * final relay_flush() call. */
545                 break;
546         }
547         return NOTIFY_OK;
548 }
549 
550 /**
551  *      relay_open - create a new relay channel
552  *      @base_filename: base name of files to create, %NULL for buffering only
553  *      @parent: dentry of parent directory, %NULL for root directory or buffer
554  *      @subbuf_size: size of sub-buffers
555  *      @n_subbufs: number of sub-buffers
556  *      @cb: client callback functions
557  *      @private_data: user-defined data
558  *
559  *      Returns channel pointer if successful, %NULL otherwise.
560  *
561  *      Creates a channel buffer for each cpu using the sizes and
562  *      attributes specified.  The created channel buffer files
563  *      will be named base_filename0...base_filenameN-1.  File
564  *      permissions will be %S_IRUSR.
565  */
566 struct rchan *relay_open(const char *base_filename,
567                          struct dentry *parent,
568                          size_t subbuf_size,
569                          size_t n_subbufs,
570                          struct rchan_callbacks *cb,
571                          void *private_data)
572 {
573         unsigned int i;
574         struct rchan *chan;
575 
576         if (!(subbuf_size && n_subbufs))
577                 return NULL;
578         if (subbuf_size > UINT_MAX / n_subbufs)
579                 return NULL;
580 
581         chan = kzalloc(sizeof(struct rchan), GFP_KERNEL);
582         if (!chan)
583                 return NULL;
584 
585         chan->version = RELAYFS_CHANNEL_VERSION;
586         chan->n_subbufs = n_subbufs;
587         chan->subbuf_size = subbuf_size;
588         chan->alloc_size = PAGE_ALIGN(subbuf_size * n_subbufs);
589         chan->parent = parent;
590         chan->private_data = private_data;
591         if (base_filename) {
592                 chan->has_base_filename = 1;
593                 strlcpy(chan->base_filename, base_filename, NAME_MAX);
594         }
595         setup_callbacks(chan, cb);
596         kref_init(&chan->kref);
597 
598         mutex_lock(&relay_channels_mutex);
599         for_each_online_cpu(i) {
600                 chan->buf[i] = relay_open_buf(chan, i);
601                 if (!chan->buf[i])
602                         goto free_bufs;
603         }
604         list_add(&chan->list, &relay_channels);
605         mutex_unlock(&relay_channels_mutex);
606 
607         return chan;
608 
609 free_bufs:
610         for_each_possible_cpu(i) {
611                 if (chan->buf[i])
612                         relay_close_buf(chan->buf[i]);
613         }
614 
615         kref_put(&chan->kref, relay_destroy_channel);
616         mutex_unlock(&relay_channels_mutex);
617         return NULL;
618 }
619 EXPORT_SYMBOL_GPL(relay_open);
620 
621 struct rchan_percpu_buf_dispatcher {
622         struct rchan_buf *buf;
623         struct dentry *dentry;
624 };
625 
626 /* Called in atomic context. */
627 static void __relay_set_buf_dentry(void *info)
628 {
629         struct rchan_percpu_buf_dispatcher *p = info;
630 
631         relay_set_buf_dentry(p->buf, p->dentry);
632 }
633 
634 /**
635  *      relay_late_setup_files - triggers file creation
636  *      @chan: channel to operate on
637  *      @base_filename: base name of files to create
638  *      @parent: dentry of parent directory, %NULL for root directory
639  *
640  *      Returns 0 if successful, non-zero otherwise.
641  *
642  *      Use to setup files for a previously buffer-only channel.
643  *      Useful to do early tracing in kernel, before VFS is up, for example.
644  */
645 int relay_late_setup_files(struct rchan *chan,
646                            const char *base_filename,
647                            struct dentry *parent)
648 {
649         int err = 0;
650         unsigned int i, curr_cpu;
651         unsigned long flags;
652         struct dentry *dentry;
653         struct rchan_percpu_buf_dispatcher disp;
654 
655         if (!chan || !base_filename)
656                 return -EINVAL;
657 
658         strlcpy(chan->base_filename, base_filename, NAME_MAX);
659 
660         mutex_lock(&relay_channels_mutex);
661         /* Is chan already set up? */
662         if (unlikely(chan->has_base_filename)) {
663                 mutex_unlock(&relay_channels_mutex);
664                 return -EEXIST;
665         }
666         chan->has_base_filename = 1;
667         chan->parent = parent;
668         curr_cpu = get_cpu();
669         /*
670          * The CPU hotplug notifier ran before us and created buffers with
671          * no files associated. So it's safe to call relay_setup_buf_file()
672          * on all currently online CPUs.
673          */
674         for_each_online_cpu(i) {
675                 if (unlikely(!chan->buf[i])) {
676                         WARN_ONCE(1, KERN_ERR "CPU has no buffer!\n");
677                         err = -EINVAL;
678                         break;
679                 }
680 
681                 dentry = relay_create_buf_file(chan, chan->buf[i], i);
682                 if (unlikely(!dentry)) {
683                         err = -EINVAL;
684                         break;
685                 }
686 
687                 if (curr_cpu == i) {
688                         local_irq_save(flags);
689                         relay_set_buf_dentry(chan->buf[i], dentry);
690                         local_irq_restore(flags);
691                 } else {
692                         disp.buf = chan->buf[i];
693                         disp.dentry = dentry;
694                         smp_mb();
695                         /* relay_channels_mutex must be held, so wait. */
696                         err = smp_call_function_single(i,
697                                                        __relay_set_buf_dentry,
698                                                        &disp, 1);
699                 }
700                 if (unlikely(err))
701                         break;
702         }
703         put_cpu();
704         mutex_unlock(&relay_channels_mutex);
705 
706         return err;
707 }
708 
709 /**
710  *      relay_switch_subbuf - switch to a new sub-buffer
711  *      @buf: channel buffer
712  *      @length: size of current event
713  *
714  *      Returns either the length passed in or 0 if full.
715  *
716  *      Performs sub-buffer-switch tasks such as invoking callbacks,
717  *      updating padding counts, waking up readers, etc.
718  */
719 size_t relay_switch_subbuf(struct rchan_buf *buf, size_t length)
720 {
721         void *old, *new;
722         size_t old_subbuf, new_subbuf;
723 
724         if (unlikely(length > buf->chan->subbuf_size))
725                 goto toobig;
726 
727         if (buf->offset != buf->chan->subbuf_size + 1) {
728                 buf->prev_padding = buf->chan->subbuf_size - buf->offset;
729                 old_subbuf = buf->subbufs_produced % buf->chan->n_subbufs;
730                 buf->padding[old_subbuf] = buf->prev_padding;
731                 buf->subbufs_produced++;
732                 if (buf->dentry)
733                         d_inode(buf->dentry)->i_size +=
734                                 buf->chan->subbuf_size -
735                                 buf->padding[old_subbuf];
736                 else
737                         buf->early_bytes += buf->chan->subbuf_size -
738                                             buf->padding[old_subbuf];
739                 smp_mb();
740                 if (waitqueue_active(&buf->read_wait))
741                         /*
742                          * Calling wake_up_interruptible() from here
743                          * will deadlock if we happen to be logging
744                          * from the scheduler (trying to re-grab
745                          * rq->lock), so defer it.
746                          */
747                         mod_timer(&buf->timer, jiffies + 1);
748         }
749 
750         old = buf->data;
751         new_subbuf = buf->subbufs_produced % buf->chan->n_subbufs;
752         new = buf->start + new_subbuf * buf->chan->subbuf_size;
753         buf->offset = 0;
754         if (!buf->chan->cb->subbuf_start(buf, new, old, buf->prev_padding)) {
755                 buf->offset = buf->chan->subbuf_size + 1;
756                 return 0;
757         }
758         buf->data = new;
759         buf->padding[new_subbuf] = 0;
760 
761         if (unlikely(length + buf->offset > buf->chan->subbuf_size))
762                 goto toobig;
763 
764         return length;
765 
766 toobig:
767         buf->chan->last_toobig = length;
768         return 0;
769 }
770 EXPORT_SYMBOL_GPL(relay_switch_subbuf);
771 
772 /**
773  *      relay_subbufs_consumed - update the buffer's sub-buffers-consumed count
774  *      @chan: the channel
775  *      @cpu: the cpu associated with the channel buffer to update
776  *      @subbufs_consumed: number of sub-buffers to add to current buf's count
777  *
778  *      Adds to the channel buffer's consumed sub-buffer count.
779  *      subbufs_consumed should be the number of sub-buffers newly consumed,
780  *      not the total consumed.
781  *
782  *      NOTE. Kernel clients don't need to call this function if the channel
783  *      mode is 'overwrite'.
784  */
785 void relay_subbufs_consumed(struct rchan *chan,
786                             unsigned int cpu,
787                             size_t subbufs_consumed)
788 {
789         struct rchan_buf *buf;
790 
791         if (!chan)
792                 return;
793 
794         if (cpu >= NR_CPUS || !chan->buf[cpu] ||
795                                         subbufs_consumed > chan->n_subbufs)
796                 return;
797 
798         buf = chan->buf[cpu];
799         if (subbufs_consumed > buf->subbufs_produced - buf->subbufs_consumed)
800                 buf->subbufs_consumed = buf->subbufs_produced;
801         else
802                 buf->subbufs_consumed += subbufs_consumed;
803 }
804 EXPORT_SYMBOL_GPL(relay_subbufs_consumed);
805 
806 /**
807  *      relay_close - close the channel
808  *      @chan: the channel
809  *
810  *      Closes all channel buffers and frees the channel.
811  */
812 void relay_close(struct rchan *chan)
813 {
814         unsigned int i;
815 
816         if (!chan)
817                 return;
818 
819         mutex_lock(&relay_channels_mutex);
820         if (chan->is_global && chan->buf[0])
821                 relay_close_buf(chan->buf[0]);
822         else
823                 for_each_possible_cpu(i)
824                         if (chan->buf[i])
825                                 relay_close_buf(chan->buf[i]);
826 
827         if (chan->last_toobig)
828                 printk(KERN_WARNING "relay: one or more items not logged "
829                        "[item size (%Zd) > sub-buffer size (%Zd)]\n",
830                        chan->last_toobig, chan->subbuf_size);
831 
832         list_del(&chan->list);
833         kref_put(&chan->kref, relay_destroy_channel);
834         mutex_unlock(&relay_channels_mutex);
835 }
836 EXPORT_SYMBOL_GPL(relay_close);
837 
838 /**
839  *      relay_flush - close the channel
840  *      @chan: the channel
841  *
842  *      Flushes all channel buffers, i.e. forces buffer switch.
843  */
844 void relay_flush(struct rchan *chan)
845 {
846         unsigned int i;
847 
848         if (!chan)
849                 return;
850 
851         if (chan->is_global && chan->buf[0]) {
852                 relay_switch_subbuf(chan->buf[0], 0);
853                 return;
854         }
855 
856         mutex_lock(&relay_channels_mutex);
857         for_each_possible_cpu(i)
858                 if (chan->buf[i])
859                         relay_switch_subbuf(chan->buf[i], 0);
860         mutex_unlock(&relay_channels_mutex);
861 }
862 EXPORT_SYMBOL_GPL(relay_flush);
863 
864 /**
865  *      relay_file_open - open file op for relay files
866  *      @inode: the inode
867  *      @filp: the file
868  *
869  *      Increments the channel buffer refcount.
870  */
871 static int relay_file_open(struct inode *inode, struct file *filp)
872 {
873         struct rchan_buf *buf = inode->i_private;
874         kref_get(&buf->kref);
875         filp->private_data = buf;
876 
877         return nonseekable_open(inode, filp);
878 }
879 
880 /**
881  *      relay_file_mmap - mmap file op for relay files
882  *      @filp: the file
883  *      @vma: the vma describing what to map
884  *
885  *      Calls upon relay_mmap_buf() to map the file into user space.
886  */
887 static int relay_file_mmap(struct file *filp, struct vm_area_struct *vma)
888 {
889         struct rchan_buf *buf = filp->private_data;
890         return relay_mmap_buf(buf, vma);
891 }
892 
893 /**
894  *      relay_file_poll - poll file op for relay files
895  *      @filp: the file
896  *      @wait: poll table
897  *
898  *      Poll implemention.
899  */
900 static unsigned int relay_file_poll(struct file *filp, poll_table *wait)
901 {
902         unsigned int mask = 0;
903         struct rchan_buf *buf = filp->private_data;
904 
905         if (buf->finalized)
906                 return POLLERR;
907 
908         if (filp->f_mode & FMODE_READ) {
909                 poll_wait(filp, &buf->read_wait, wait);
910                 if (!relay_buf_empty(buf))
911                         mask |= POLLIN | POLLRDNORM;
912         }
913 
914         return mask;
915 }
916 
917 /**
918  *      relay_file_release - release file op for relay files
919  *      @inode: the inode
920  *      @filp: the file
921  *
922  *      Decrements the channel refcount, as the filesystem is
923  *      no longer using it.
924  */
925 static int relay_file_release(struct inode *inode, struct file *filp)
926 {
927         struct rchan_buf *buf = filp->private_data;
928         kref_put(&buf->kref, relay_remove_buf);
929 
930         return 0;
931 }
932 
933 /*
934  *      relay_file_read_consume - update the consumed count for the buffer
935  */
936 static void relay_file_read_consume(struct rchan_buf *buf,
937                                     size_t read_pos,
938                                     size_t bytes_consumed)
939 {
940         size_t subbuf_size = buf->chan->subbuf_size;
941         size_t n_subbufs = buf->chan->n_subbufs;
942         size_t read_subbuf;
943 
944         if (buf->subbufs_produced == buf->subbufs_consumed &&
945             buf->offset == buf->bytes_consumed)
946                 return;
947 
948         if (buf->bytes_consumed + bytes_consumed > subbuf_size) {
949                 relay_subbufs_consumed(buf->chan, buf->cpu, 1);
950                 buf->bytes_consumed = 0;
951         }
952 
953         buf->bytes_consumed += bytes_consumed;
954         if (!read_pos)
955                 read_subbuf = buf->subbufs_consumed % n_subbufs;
956         else
957                 read_subbuf = read_pos / buf->chan->subbuf_size;
958         if (buf->bytes_consumed + buf->padding[read_subbuf] == subbuf_size) {
959                 if ((read_subbuf == buf->subbufs_produced % n_subbufs) &&
960                     (buf->offset == subbuf_size))
961                         return;
962                 relay_subbufs_consumed(buf->chan, buf->cpu, 1);
963                 buf->bytes_consumed = 0;
964         }
965 }
966 
967 /*
968  *      relay_file_read_avail - boolean, are there unconsumed bytes available?
969  */
970 static int relay_file_read_avail(struct rchan_buf *buf, size_t read_pos)
971 {
972         size_t subbuf_size = buf->chan->subbuf_size;
973         size_t n_subbufs = buf->chan->n_subbufs;
974         size_t produced = buf->subbufs_produced;
975         size_t consumed = buf->subbufs_consumed;
976 
977         relay_file_read_consume(buf, read_pos, 0);
978 
979         consumed = buf->subbufs_consumed;
980 
981         if (unlikely(buf->offset > subbuf_size)) {
982                 if (produced == consumed)
983                         return 0;
984                 return 1;
985         }
986 
987         if (unlikely(produced - consumed >= n_subbufs)) {
988                 consumed = produced - n_subbufs + 1;
989                 buf->subbufs_consumed = consumed;
990                 buf->bytes_consumed = 0;
991         }
992 
993         produced = (produced % n_subbufs) * subbuf_size + buf->offset;
994         consumed = (consumed % n_subbufs) * subbuf_size + buf->bytes_consumed;
995 
996         if (consumed > produced)
997                 produced += n_subbufs * subbuf_size;
998 
999         if (consumed == produced) {
1000                 if (buf->offset == subbuf_size &&
1001                     buf->subbufs_produced > buf->subbufs_consumed)
1002                         return 1;
1003                 return 0;
1004         }
1005 
1006         return 1;
1007 }
1008 
1009 /**
1010  *      relay_file_read_subbuf_avail - return bytes available in sub-buffer
1011  *      @read_pos: file read position
1012  *      @buf: relay channel buffer
1013  */
1014 static size_t relay_file_read_subbuf_avail(size_t read_pos,
1015                                            struct rchan_buf *buf)
1016 {
1017         size_t padding, avail = 0;
1018         size_t read_subbuf, read_offset, write_subbuf, write_offset;
1019         size_t subbuf_size = buf->chan->subbuf_size;
1020 
1021         write_subbuf = (buf->data - buf->start) / subbuf_size;
1022         write_offset = buf->offset > subbuf_size ? subbuf_size : buf->offset;
1023         read_subbuf = read_pos / subbuf_size;
1024         read_offset = read_pos % subbuf_size;
1025         padding = buf->padding[read_subbuf];
1026 
1027         if (read_subbuf == write_subbuf) {
1028                 if (read_offset + padding < write_offset)
1029                         avail = write_offset - (read_offset + padding);
1030         } else
1031                 avail = (subbuf_size - padding) - read_offset;
1032 
1033         return avail;
1034 }
1035 
1036 /**
1037  *      relay_file_read_start_pos - find the first available byte to read
1038  *      @read_pos: file read position
1039  *      @buf: relay channel buffer
1040  *
1041  *      If the @read_pos is in the middle of padding, return the
1042  *      position of the first actually available byte, otherwise
1043  *      return the original value.
1044  */
1045 static size_t relay_file_read_start_pos(size_t read_pos,
1046                                         struct rchan_buf *buf)
1047 {
1048         size_t read_subbuf, padding, padding_start, padding_end;
1049         size_t subbuf_size = buf->chan->subbuf_size;
1050         size_t n_subbufs = buf->chan->n_subbufs;
1051         size_t consumed = buf->subbufs_consumed % n_subbufs;
1052 
1053         if (!read_pos)
1054                 read_pos = consumed * subbuf_size + buf->bytes_consumed;
1055         read_subbuf = read_pos / subbuf_size;
1056         padding = buf->padding[read_subbuf];
1057         padding_start = (read_subbuf + 1) * subbuf_size - padding;
1058         padding_end = (read_subbuf + 1) * subbuf_size;
1059         if (read_pos >= padding_start && read_pos < padding_end) {
1060                 read_subbuf = (read_subbuf + 1) % n_subbufs;
1061                 read_pos = read_subbuf * subbuf_size;
1062         }
1063 
1064         return read_pos;
1065 }
1066 
1067 /**
1068  *      relay_file_read_end_pos - return the new read position
1069  *      @read_pos: file read position
1070  *      @buf: relay channel buffer
1071  *      @count: number of bytes to be read
1072  */
1073 static size_t relay_file_read_end_pos(struct rchan_buf *buf,
1074                                       size_t read_pos,
1075                                       size_t count)
1076 {
1077         size_t read_subbuf, padding, end_pos;
1078         size_t subbuf_size = buf->chan->subbuf_size;
1079         size_t n_subbufs = buf->chan->n_subbufs;
1080 
1081         read_subbuf = read_pos / subbuf_size;
1082         padding = buf->padding[read_subbuf];
1083         if (read_pos % subbuf_size + count + padding == subbuf_size)
1084                 end_pos = (read_subbuf + 1) * subbuf_size;
1085         else
1086                 end_pos = read_pos + count;
1087         if (end_pos >= subbuf_size * n_subbufs)
1088                 end_pos = 0;
1089 
1090         return end_pos;
1091 }
1092 
1093 /*
1094  *      subbuf_read_actor - read up to one subbuf's worth of data
1095  */
1096 static int subbuf_read_actor(size_t read_start,
1097                              struct rchan_buf *buf,
1098                              size_t avail,
1099                              read_descriptor_t *desc)
1100 {
1101         void *from;
1102         int ret = 0;
1103 
1104         from = buf->start + read_start;
1105         ret = avail;
1106         if (copy_to_user(desc->arg.buf, from, avail)) {
1107                 desc->error = -EFAULT;
1108                 ret = 0;
1109         }
1110         desc->arg.data += ret;
1111         desc->written += ret;
1112         desc->count -= ret;
1113 
1114         return ret;
1115 }
1116 
1117 typedef int (*subbuf_actor_t) (size_t read_start,
1118                                struct rchan_buf *buf,
1119                                size_t avail,
1120                                read_descriptor_t *desc);
1121 
1122 /*
1123  *      relay_file_read_subbufs - read count bytes, bridging subbuf boundaries
1124  */
1125 static ssize_t relay_file_read_subbufs(struct file *filp, loff_t *ppos,
1126                                         subbuf_actor_t subbuf_actor,
1127                                         read_descriptor_t *desc)
1128 {
1129         struct rchan_buf *buf = filp->private_data;
1130         size_t read_start, avail;
1131         int ret;
1132 
1133         if (!desc->count)
1134                 return 0;
1135 
1136         inode_lock(file_inode(filp));
1137         do {
1138                 if (!relay_file_read_avail(buf, *ppos))
1139                         break;
1140 
1141                 read_start = relay_file_read_start_pos(*ppos, buf);
1142                 avail = relay_file_read_subbuf_avail(read_start, buf);
1143                 if (!avail)
1144                         break;
1145 
1146                 avail = min(desc->count, avail);
1147                 ret = subbuf_actor(read_start, buf, avail, desc);
1148                 if (desc->error < 0)
1149                         break;
1150 
1151                 if (ret) {
1152                         relay_file_read_consume(buf, read_start, ret);
1153                         *ppos = relay_file_read_end_pos(buf, read_start, ret);
1154                 }
1155         } while (desc->count && ret);
1156         inode_unlock(file_inode(filp));
1157 
1158         return desc->written;
1159 }
1160 
1161 static ssize_t relay_file_read(struct file *filp,
1162                                char __user *buffer,
1163                                size_t count,
1164                                loff_t *ppos)
1165 {
1166         read_descriptor_t desc;
1167         desc.written = 0;
1168         desc.count = count;
1169         desc.arg.buf = buffer;
1170         desc.error = 0;
1171         return relay_file_read_subbufs(filp, ppos, subbuf_read_actor, &desc);
1172 }
1173 
1174 static void relay_consume_bytes(struct rchan_buf *rbuf, int bytes_consumed)
1175 {
1176         rbuf->bytes_consumed += bytes_consumed;
1177 
1178         if (rbuf->bytes_consumed >= rbuf->chan->subbuf_size) {
1179                 relay_subbufs_consumed(rbuf->chan, rbuf->cpu, 1);
1180                 rbuf->bytes_consumed %= rbuf->chan->subbuf_size;
1181         }
1182 }
1183 
1184 static void relay_pipe_buf_release(struct pipe_inode_info *pipe,
1185                                    struct pipe_buffer *buf)
1186 {
1187         struct rchan_buf *rbuf;
1188 
1189         rbuf = (struct rchan_buf *)page_private(buf->page);
1190         relay_consume_bytes(rbuf, buf->private);
1191 }
1192 
1193 static const struct pipe_buf_operations relay_pipe_buf_ops = {
1194         .can_merge = 0,
1195         .confirm = generic_pipe_buf_confirm,
1196         .release = relay_pipe_buf_release,
1197         .steal = generic_pipe_buf_steal,
1198         .get = generic_pipe_buf_get,
1199 };
1200 
1201 static void relay_page_release(struct splice_pipe_desc *spd, unsigned int i)
1202 {
1203 }
1204 
1205 /*
1206  *      subbuf_splice_actor - splice up to one subbuf's worth of data
1207  */
1208 static ssize_t subbuf_splice_actor(struct file *in,
1209                                loff_t *ppos,
1210                                struct pipe_inode_info *pipe,
1211                                size_t len,
1212                                unsigned int flags,
1213                                int *nonpad_ret)
1214 {
1215         unsigned int pidx, poff, total_len, subbuf_pages, nr_pages;
1216         struct rchan_buf *rbuf = in->private_data;
1217         unsigned int subbuf_size = rbuf->chan->subbuf_size;
1218         uint64_t pos = (uint64_t) *ppos;
1219         uint32_t alloc_size = (uint32_t) rbuf->chan->alloc_size;
1220         size_t read_start = (size_t) do_div(pos, alloc_size);
1221         size_t read_subbuf = read_start / subbuf_size;
1222         size_t padding = rbuf->padding[read_subbuf];
1223         size_t nonpad_end = read_subbuf * subbuf_size + subbuf_size - padding;
1224         struct page *pages[PIPE_DEF_BUFFERS];
1225         struct partial_page partial[PIPE_DEF_BUFFERS];
1226         struct splice_pipe_desc spd = {
1227                 .pages = pages,
1228                 .nr_pages = 0,
1229                 .nr_pages_max = PIPE_DEF_BUFFERS,
1230                 .partial = partial,
1231                 .flags = flags,
1232                 .ops = &relay_pipe_buf_ops,
1233                 .spd_release = relay_page_release,
1234         };
1235         ssize_t ret;
1236 
1237         if (rbuf->subbufs_produced == rbuf->subbufs_consumed)
1238                 return 0;
1239         if (splice_grow_spd(pipe, &spd))
1240                 return -ENOMEM;
1241 
1242         /*
1243          * Adjust read len, if longer than what is available
1244          */
1245         if (len > (subbuf_size - read_start % subbuf_size))
1246                 len = subbuf_size - read_start % subbuf_size;
1247 
1248         subbuf_pages = rbuf->chan->alloc_size >> PAGE_SHIFT;
1249         pidx = (read_start / PAGE_SIZE) % subbuf_pages;
1250         poff = read_start & ~PAGE_MASK;
1251         nr_pages = min_t(unsigned int, subbuf_pages, spd.nr_pages_max);
1252 
1253         for (total_len = 0; spd.nr_pages < nr_pages; spd.nr_pages++) {
1254                 unsigned int this_len, this_end, private;
1255                 unsigned int cur_pos = read_start + total_len;
1256 
1257                 if (!len)
1258                         break;
1259 
1260                 this_len = min_t(unsigned long, len, PAGE_SIZE - poff);
1261                 private = this_len;
1262 
1263                 spd.pages[spd.nr_pages] = rbuf->page_array[pidx];
1264                 spd.partial[spd.nr_pages].offset = poff;
1265 
1266                 this_end = cur_pos + this_len;
1267                 if (this_end >= nonpad_end) {
1268                         this_len = nonpad_end - cur_pos;
1269                         private = this_len + padding;
1270                 }
1271                 spd.partial[spd.nr_pages].len = this_len;
1272                 spd.partial[spd.nr_pages].private = private;
1273 
1274                 len -= this_len;
1275                 total_len += this_len;
1276                 poff = 0;
1277                 pidx = (pidx + 1) % subbuf_pages;
1278 
1279                 if (this_end >= nonpad_end) {
1280                         spd.nr_pages++;
1281                         break;
1282                 }
1283         }
1284 
1285         ret = 0;
1286         if (!spd.nr_pages)
1287                 goto out;
1288 
1289         ret = *nonpad_ret = splice_to_pipe(pipe, &spd);
1290         if (ret < 0 || ret < total_len)
1291                 goto out;
1292 
1293         if (read_start + ret == nonpad_end)
1294                 ret += padding;
1295 
1296 out:
1297         splice_shrink_spd(&spd);
1298         return ret;
1299 }
1300 
1301 static ssize_t relay_file_splice_read(struct file *in,
1302                                       loff_t *ppos,
1303                                       struct pipe_inode_info *pipe,
1304                                       size_t len,
1305                                       unsigned int flags)
1306 {
1307         ssize_t spliced;
1308         int ret;
1309         int nonpad_ret = 0;
1310 
1311         ret = 0;
1312         spliced = 0;
1313 
1314         while (len && !spliced) {
1315                 ret = subbuf_splice_actor(in, ppos, pipe, len, flags, &nonpad_ret);
1316                 if (ret < 0)
1317                         break;
1318                 else if (!ret) {
1319                         if (flags & SPLICE_F_NONBLOCK)
1320                                 ret = -EAGAIN;
1321                         break;
1322                 }
1323 
1324                 *ppos += ret;
1325                 if (ret > len)
1326                         len = 0;
1327                 else
1328                         len -= ret;
1329                 spliced += nonpad_ret;
1330                 nonpad_ret = 0;
1331         }
1332 
1333         if (spliced)
1334                 return spliced;
1335 
1336         return ret;
1337 }
1338 
1339 const struct file_operations relay_file_operations = {
1340         .open           = relay_file_open,
1341         .poll           = relay_file_poll,
1342         .mmap           = relay_file_mmap,
1343         .read           = relay_file_read,
1344         .llseek         = no_llseek,
1345         .release        = relay_file_release,
1346         .splice_read    = relay_file_splice_read,
1347 };
1348 EXPORT_SYMBOL_GPL(relay_file_operations);
1349 
1350 static __init int relay_init(void)
1351 {
1352 
1353         hotcpu_notifier(relay_hotcpu_callback, 0);
1354         return 0;
1355 }
1356 
1357 early_initcall(relay_init);
1358 

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