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

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