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Linux/kernel/relay.c

  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         *per_cpu_ptr(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  *      @work: contains the channel buffer
332  *
333  *      This is the function used to defer reader waking
334  */
335 static void wakeup_readers(struct irq_work *work)
336 {
337         struct rchan_buf *buf;
338 
339         buf = container_of(work, struct rchan_buf, wakeup_work);
340         wake_up_interruptible(&buf->read_wait);
341 }
342 
343 /**
344  *      __relay_reset - reset a channel buffer
345  *      @buf: the channel buffer
346  *      @init: 1 if this is a first-time initialization
347  *
348  *      See relay_reset() for description of effect.
349  */
350 static void __relay_reset(struct rchan_buf *buf, unsigned int init)
351 {
352         size_t i;
353 
354         if (init) {
355                 init_waitqueue_head(&buf->read_wait);
356                 kref_init(&buf->kref);
357                 init_irq_work(&buf->wakeup_work, wakeup_readers);
358         } else {
359                 irq_work_sync(&buf->wakeup_work);
360         }
361 
362         buf->subbufs_produced = 0;
363         buf->subbufs_consumed = 0;
364         buf->bytes_consumed = 0;
365         buf->finalized = 0;
366         buf->data = buf->start;
367         buf->offset = 0;
368 
369         for (i = 0; i < buf->chan->n_subbufs; i++)
370                 buf->padding[i] = 0;
371 
372         buf->chan->cb->subbuf_start(buf, buf->data, NULL, 0);
373 }
374 
375 /**
376  *      relay_reset - reset the channel
377  *      @chan: the channel
378  *
379  *      This has the effect of erasing all data from all channel buffers
380  *      and restarting the channel in its initial state.  The buffers
381  *      are not freed, so any mappings are still in effect.
382  *
383  *      NOTE. Care should be taken that the channel isn't actually
384  *      being used by anything when this call is made.
385  */
386 void relay_reset(struct rchan *chan)
387 {
388         struct rchan_buf *buf;
389         unsigned int i;
390 
391         if (!chan)
392                 return;
393 
394         if (chan->is_global && (buf = *per_cpu_ptr(chan->buf, 0))) {
395                 __relay_reset(buf, 0);
396                 return;
397         }
398 
399         mutex_lock(&relay_channels_mutex);
400         for_each_possible_cpu(i)
401                 if ((buf = *per_cpu_ptr(chan->buf, i)))
402                         __relay_reset(buf, 0);
403         mutex_unlock(&relay_channels_mutex);
404 }
405 EXPORT_SYMBOL_GPL(relay_reset);
406 
407 static inline void relay_set_buf_dentry(struct rchan_buf *buf,
408                                         struct dentry *dentry)
409 {
410         buf->dentry = dentry;
411         d_inode(buf->dentry)->i_size = buf->early_bytes;
412 }
413 
414 static struct dentry *relay_create_buf_file(struct rchan *chan,
415                                             struct rchan_buf *buf,
416                                             unsigned int cpu)
417 {
418         struct dentry *dentry;
419         char *tmpname;
420 
421         tmpname = kzalloc(NAME_MAX + 1, GFP_KERNEL);
422         if (!tmpname)
423                 return NULL;
424         snprintf(tmpname, NAME_MAX, "%s%d", chan->base_filename, cpu);
425 
426         /* Create file in fs */
427         dentry = chan->cb->create_buf_file(tmpname, chan->parent,
428                                            S_IRUSR, buf,
429                                            &chan->is_global);
430 
431         kfree(tmpname);
432 
433         return dentry;
434 }
435 
436 /*
437  *      relay_open_buf - create a new relay channel buffer
438  *
439  *      used by relay_open() and CPU hotplug.
440  */
441 static struct rchan_buf *relay_open_buf(struct rchan *chan, unsigned int cpu)
442 {
443         struct rchan_buf *buf = NULL;
444         struct dentry *dentry;
445 
446         if (chan->is_global)
447                 return *per_cpu_ptr(chan->buf, 0);
448 
449         buf = relay_create_buf(chan);
450         if (!buf)
451                 return NULL;
452 
453         if (chan->has_base_filename) {
454                 dentry = relay_create_buf_file(chan, buf, cpu);
455                 if (!dentry)
456                         goto free_buf;
457                 relay_set_buf_dentry(buf, dentry);
458         } else {
459                 /* Only retrieve global info, nothing more, nothing less */
460                 dentry = chan->cb->create_buf_file(NULL, NULL,
461                                                    S_IRUSR, buf,
462                                                    &chan->is_global);
463                 if (WARN_ON(dentry))
464                         goto free_buf;
465         }
466 
467         buf->cpu = cpu;
468         __relay_reset(buf, 1);
469 
470         if(chan->is_global) {
471                 *per_cpu_ptr(chan->buf, 0) = buf;
472                 buf->cpu = 0;
473         }
474 
475         return buf;
476 
477 free_buf:
478         relay_destroy_buf(buf);
479         return NULL;
480 }
481 
482 /**
483  *      relay_close_buf - close a channel buffer
484  *      @buf: channel buffer
485  *
486  *      Marks the buffer finalized and restores the default callbacks.
487  *      The channel buffer and channel buffer data structure are then freed
488  *      automatically when the last reference is given up.
489  */
490 static void relay_close_buf(struct rchan_buf *buf)
491 {
492         buf->finalized = 1;
493         irq_work_sync(&buf->wakeup_work);
494         buf->chan->cb->remove_buf_file(buf->dentry);
495         kref_put(&buf->kref, relay_remove_buf);
496 }
497 
498 static void setup_callbacks(struct rchan *chan,
499                                    struct rchan_callbacks *cb)
500 {
501         if (!cb) {
502                 chan->cb = &default_channel_callbacks;
503                 return;
504         }
505 
506         if (!cb->subbuf_start)
507                 cb->subbuf_start = subbuf_start_default_callback;
508         if (!cb->buf_mapped)
509                 cb->buf_mapped = buf_mapped_default_callback;
510         if (!cb->buf_unmapped)
511                 cb->buf_unmapped = buf_unmapped_default_callback;
512         if (!cb->create_buf_file)
513                 cb->create_buf_file = create_buf_file_default_callback;
514         if (!cb->remove_buf_file)
515                 cb->remove_buf_file = remove_buf_file_default_callback;
516         chan->cb = cb;
517 }
518 
519 int relay_prepare_cpu(unsigned int cpu)
520 {
521         struct rchan *chan;
522         struct rchan_buf *buf;
523 
524         mutex_lock(&relay_channels_mutex);
525         list_for_each_entry(chan, &relay_channels, list) {
526                 if ((buf = *per_cpu_ptr(chan->buf, cpu)))
527                         continue;
528                 buf = relay_open_buf(chan, cpu);
529                 if (!buf) {
530                         pr_err("relay: cpu %d buffer creation failed\n", cpu);
531                         mutex_unlock(&relay_channels_mutex);
532                         return -ENOMEM;
533                 }
534                 *per_cpu_ptr(chan->buf, cpu) = buf;
535         }
536         mutex_unlock(&relay_channels_mutex);
537         return 0;
538 }
539 
540 /**
541  *      relay_open - create a new relay channel
542  *      @base_filename: base name of files to create, %NULL for buffering only
543  *      @parent: dentry of parent directory, %NULL for root directory or buffer
544  *      @subbuf_size: size of sub-buffers
545  *      @n_subbufs: number of sub-buffers
546  *      @cb: client callback functions
547  *      @private_data: user-defined data
548  *
549  *      Returns channel pointer if successful, %NULL otherwise.
550  *
551  *      Creates a channel buffer for each cpu using the sizes and
552  *      attributes specified.  The created channel buffer files
553  *      will be named base_filename0...base_filenameN-1.  File
554  *      permissions will be %S_IRUSR.
555  *
556  *      If opening a buffer (@parent = NULL) that you later wish to register
557  *      in a filesystem, call relay_late_setup_files() once the @parent dentry
558  *      is available.
559  */
560 struct rchan *relay_open(const char *base_filename,
561                          struct dentry *parent,
562                          size_t subbuf_size,
563                          size_t n_subbufs,
564                          struct rchan_callbacks *cb,
565                          void *private_data)
566 {
567         unsigned int i;
568         struct rchan *chan;
569         struct rchan_buf *buf;
570 
571         if (!(subbuf_size && n_subbufs))
572                 return NULL;
573         if (subbuf_size > UINT_MAX / n_subbufs)
574                 return NULL;
575 
576         chan = kzalloc(sizeof(struct rchan), GFP_KERNEL);
577         if (!chan)
578                 return NULL;
579 
580         chan->buf = alloc_percpu(struct rchan_buf *);
581         chan->version = RELAYFS_CHANNEL_VERSION;
582         chan->n_subbufs = n_subbufs;
583         chan->subbuf_size = subbuf_size;
584         chan->alloc_size = PAGE_ALIGN(subbuf_size * n_subbufs);
585         chan->parent = parent;
586         chan->private_data = private_data;
587         if (base_filename) {
588                 chan->has_base_filename = 1;
589                 strlcpy(chan->base_filename, base_filename, NAME_MAX);
590         }
591         setup_callbacks(chan, cb);
592         kref_init(&chan->kref);
593 
594         mutex_lock(&relay_channels_mutex);
595         for_each_online_cpu(i) {
596                 buf = relay_open_buf(chan, i);
597                 if (!buf)
598                         goto free_bufs;
599                 *per_cpu_ptr(chan->buf, i) = buf;
600         }
601         list_add(&chan->list, &relay_channels);
602         mutex_unlock(&relay_channels_mutex);
603 
604         return chan;
605 
606 free_bufs:
607         for_each_possible_cpu(i) {
608                 if ((buf = *per_cpu_ptr(chan->buf, i)))
609                         relay_close_buf(buf);
610         }
611 
612         kref_put(&chan->kref, relay_destroy_channel);
613         mutex_unlock(&relay_channels_mutex);
614         kfree(chan);
615         return NULL;
616 }
617 EXPORT_SYMBOL_GPL(relay_open);
618 
619 struct rchan_percpu_buf_dispatcher {
620         struct rchan_buf *buf;
621         struct dentry *dentry;
622 };
623 
624 /* Called in atomic context. */
625 static void __relay_set_buf_dentry(void *info)
626 {
627         struct rchan_percpu_buf_dispatcher *p = info;
628 
629         relay_set_buf_dentry(p->buf, p->dentry);
630 }
631 
632 /**
633  *      relay_late_setup_files - triggers file creation
634  *      @chan: channel to operate on
635  *      @base_filename: base name of files to create
636  *      @parent: dentry of parent directory, %NULL for root directory
637  *
638  *      Returns 0 if successful, non-zero otherwise.
639  *
640  *      Use to setup files for a previously buffer-only channel created
641  *      by relay_open() with a NULL parent dentry.
642  *
643  *      For example, this is useful for perfomring early tracing in kernel,
644  *      before VFS is up and then exposing the early results once the dentry
645  *      is available.
646  */
647 int relay_late_setup_files(struct rchan *chan,
648                            const char *base_filename,
649                            struct dentry *parent)
650 {
651         int err = 0;
652         unsigned int i, curr_cpu;
653         unsigned long flags;
654         struct dentry *dentry;
655         struct rchan_buf *buf;
656         struct rchan_percpu_buf_dispatcher disp;
657 
658         if (!chan || !base_filename)
659                 return -EINVAL;
660 
661         strlcpy(chan->base_filename, base_filename, NAME_MAX);
662 
663         mutex_lock(&relay_channels_mutex);
664         /* Is chan already set up? */
665         if (unlikely(chan->has_base_filename)) {
666                 mutex_unlock(&relay_channels_mutex);
667                 return -EEXIST;
668         }
669         chan->has_base_filename = 1;
670         chan->parent = parent;
671 
672         if (chan->is_global) {
673                 err = -EINVAL;
674                 buf = *per_cpu_ptr(chan->buf, 0);
675                 if (!WARN_ON_ONCE(!buf)) {
676                         dentry = relay_create_buf_file(chan, buf, 0);
677                         if (dentry && !WARN_ON_ONCE(!chan->is_global)) {
678                                 relay_set_buf_dentry(buf, dentry);
679                                 err = 0;
680                         }
681                 }
682                 mutex_unlock(&relay_channels_mutex);
683                 return err;
684         }
685 
686         curr_cpu = get_cpu();
687         /*
688          * The CPU hotplug notifier ran before us and created buffers with
689          * no files associated. So it's safe to call relay_setup_buf_file()
690          * on all currently online CPUs.
691          */
692         for_each_online_cpu(i) {
693                 buf = *per_cpu_ptr(chan->buf, i);
694                 if (unlikely(!buf)) {
695                         WARN_ONCE(1, KERN_ERR "CPU has no buffer!\n");
696                         err = -EINVAL;
697                         break;
698                 }
699 
700                 dentry = relay_create_buf_file(chan, buf, i);
701                 if (unlikely(!dentry)) {
702                         err = -EINVAL;
703                         break;
704                 }
705 
706                 if (curr_cpu == i) {
707                         local_irq_save(flags);
708                         relay_set_buf_dentry(buf, dentry);
709                         local_irq_restore(flags);
710                 } else {
711                         disp.buf = buf;
712                         disp.dentry = dentry;
713                         smp_mb();
714                         /* relay_channels_mutex must be held, so wait. */
715                         err = smp_call_function_single(i,
716                                                        __relay_set_buf_dentry,
717                                                        &disp, 1);
718                 }
719                 if (unlikely(err))
720                         break;
721         }
722         put_cpu();
723         mutex_unlock(&relay_channels_mutex);
724 
725         return err;
726 }
727 EXPORT_SYMBOL_GPL(relay_late_setup_files);
728 
729 /**
730  *      relay_switch_subbuf - switch to a new sub-buffer
731  *      @buf: channel buffer
732  *      @length: size of current event
733  *
734  *      Returns either the length passed in or 0 if full.
735  *
736  *      Performs sub-buffer-switch tasks such as invoking callbacks,
737  *      updating padding counts, waking up readers, etc.
738  */
739 size_t relay_switch_subbuf(struct rchan_buf *buf, size_t length)
740 {
741         void *old, *new;
742         size_t old_subbuf, new_subbuf;
743 
744         if (unlikely(length > buf->chan->subbuf_size))
745                 goto toobig;
746 
747         if (buf->offset != buf->chan->subbuf_size + 1) {
748                 buf->prev_padding = buf->chan->subbuf_size - buf->offset;
749                 old_subbuf = buf->subbufs_produced % buf->chan->n_subbufs;
750                 buf->padding[old_subbuf] = buf->prev_padding;
751                 buf->subbufs_produced++;
752                 if (buf->dentry)
753                         d_inode(buf->dentry)->i_size +=
754                                 buf->chan->subbuf_size -
755                                 buf->padding[old_subbuf];
756                 else
757                         buf->early_bytes += buf->chan->subbuf_size -
758                                             buf->padding[old_subbuf];
759                 smp_mb();
760                 if (waitqueue_active(&buf->read_wait)) {
761                         /*
762                          * Calling wake_up_interruptible() from here
763                          * will deadlock if we happen to be logging
764                          * from the scheduler (trying to re-grab
765                          * rq->lock), so defer it.
766                          */
767                         irq_work_queue(&buf->wakeup_work);
768                 }
769         }
770 
771         old = buf->data;
772         new_subbuf = buf->subbufs_produced % buf->chan->n_subbufs;
773         new = buf->start + new_subbuf * buf->chan->subbuf_size;
774         buf->offset = 0;
775         if (!buf->chan->cb->subbuf_start(buf, new, old, buf->prev_padding)) {
776                 buf->offset = buf->chan->subbuf_size + 1;
777                 return 0;
778         }
779         buf->data = new;
780         buf->padding[new_subbuf] = 0;
781 
782         if (unlikely(length + buf->offset > buf->chan->subbuf_size))
783                 goto toobig;
784 
785         return length;
786 
787 toobig:
788         buf->chan->last_toobig = length;
789         return 0;
790 }
791 EXPORT_SYMBOL_GPL(relay_switch_subbuf);
792 
793 /**
794  *      relay_subbufs_consumed - update the buffer's sub-buffers-consumed count
795  *      @chan: the channel
796  *      @cpu: the cpu associated with the channel buffer to update
797  *      @subbufs_consumed: number of sub-buffers to add to current buf's count
798  *
799  *      Adds to the channel buffer's consumed sub-buffer count.
800  *      subbufs_consumed should be the number of sub-buffers newly consumed,
801  *      not the total consumed.
802  *
803  *      NOTE. Kernel clients don't need to call this function if the channel
804  *      mode is 'overwrite'.
805  */
806 void relay_subbufs_consumed(struct rchan *chan,
807                             unsigned int cpu,
808                             size_t subbufs_consumed)
809 {
810         struct rchan_buf *buf;
811 
812         if (!chan || cpu >= NR_CPUS)
813                 return;
814 
815         buf = *per_cpu_ptr(chan->buf, cpu);
816         if (!buf || subbufs_consumed > chan->n_subbufs)
817                 return;
818 
819         if (subbufs_consumed > buf->subbufs_produced - buf->subbufs_consumed)
820                 buf->subbufs_consumed = buf->subbufs_produced;
821         else
822                 buf->subbufs_consumed += subbufs_consumed;
823 }
824 EXPORT_SYMBOL_GPL(relay_subbufs_consumed);
825 
826 /**
827  *      relay_close - close the channel
828  *      @chan: the channel
829  *
830  *      Closes all channel buffers and frees the channel.
831  */
832 void relay_close(struct rchan *chan)
833 {
834         struct rchan_buf *buf;
835         unsigned int i;
836 
837         if (!chan)
838                 return;
839 
840         mutex_lock(&relay_channels_mutex);
841         if (chan->is_global && (buf = *per_cpu_ptr(chan->buf, 0)))
842                 relay_close_buf(buf);
843         else
844                 for_each_possible_cpu(i)
845                         if ((buf = *per_cpu_ptr(chan->buf, i)))
846                                 relay_close_buf(buf);
847 
848         if (chan->last_toobig)
849                 printk(KERN_WARNING "relay: one or more items not logged "
850                        "[item size (%Zd) > sub-buffer size (%Zd)]\n",
851                        chan->last_toobig, chan->subbuf_size);
852 
853         list_del(&chan->list);
854         kref_put(&chan->kref, relay_destroy_channel);
855         mutex_unlock(&relay_channels_mutex);
856 }
857 EXPORT_SYMBOL_GPL(relay_close);
858 
859 /**
860  *      relay_flush - close the channel
861  *      @chan: the channel
862  *
863  *      Flushes all channel buffers, i.e. forces buffer switch.
864  */
865 void relay_flush(struct rchan *chan)
866 {
867         struct rchan_buf *buf;
868         unsigned int i;
869 
870         if (!chan)
871                 return;
872 
873         if (chan->is_global && (buf = *per_cpu_ptr(chan->buf, 0))) {
874                 relay_switch_subbuf(buf, 0);
875                 return;
876         }
877 
878         mutex_lock(&relay_channels_mutex);
879         for_each_possible_cpu(i)
880                 if ((buf = *per_cpu_ptr(chan->buf, i)))
881                         relay_switch_subbuf(buf, 0);
882         mutex_unlock(&relay_channels_mutex);
883 }
884 EXPORT_SYMBOL_GPL(relay_flush);
885 
886 /**
887  *      relay_file_open - open file op for relay files
888  *      @inode: the inode
889  *      @filp: the file
890  *
891  *      Increments the channel buffer refcount.
892  */
893 static int relay_file_open(struct inode *inode, struct file *filp)
894 {
895         struct rchan_buf *buf = inode->i_private;
896         kref_get(&buf->kref);
897         filp->private_data = buf;
898 
899         return nonseekable_open(inode, filp);
900 }
901 
902 /**
903  *      relay_file_mmap - mmap file op for relay files
904  *      @filp: the file
905  *      @vma: the vma describing what to map
906  *
907  *      Calls upon relay_mmap_buf() to map the file into user space.
908  */
909 static int relay_file_mmap(struct file *filp, struct vm_area_struct *vma)
910 {
911         struct rchan_buf *buf = filp->private_data;
912         return relay_mmap_buf(buf, vma);
913 }
914 
915 /**
916  *      relay_file_poll - poll file op for relay files
917  *      @filp: the file
918  *      @wait: poll table
919  *
920  *      Poll implemention.
921  */
922 static unsigned int relay_file_poll(struct file *filp, poll_table *wait)
923 {
924         unsigned int mask = 0;
925         struct rchan_buf *buf = filp->private_data;
926 
927         if (buf->finalized)
928                 return POLLERR;
929 
930         if (filp->f_mode & FMODE_READ) {
931                 poll_wait(filp, &buf->read_wait, wait);
932                 if (!relay_buf_empty(buf))
933                         mask |= POLLIN | POLLRDNORM;
934         }
935 
936         return mask;
937 }
938 
939 /**
940  *      relay_file_release - release file op for relay files
941  *      @inode: the inode
942  *      @filp: the file
943  *
944  *      Decrements the channel refcount, as the filesystem is
945  *      no longer using it.
946  */
947 static int relay_file_release(struct inode *inode, struct file *filp)
948 {
949         struct rchan_buf *buf = filp->private_data;
950         kref_put(&buf->kref, relay_remove_buf);
951 
952         return 0;
953 }
954 
955 /*
956  *      relay_file_read_consume - update the consumed count for the buffer
957  */
958 static void relay_file_read_consume(struct rchan_buf *buf,
959                                     size_t read_pos,
960                                     size_t bytes_consumed)
961 {
962         size_t subbuf_size = buf->chan->subbuf_size;
963         size_t n_subbufs = buf->chan->n_subbufs;
964         size_t read_subbuf;
965 
966         if (buf->subbufs_produced == buf->subbufs_consumed &&
967             buf->offset == buf->bytes_consumed)
968                 return;
969 
970         if (buf->bytes_consumed + bytes_consumed > subbuf_size) {
971                 relay_subbufs_consumed(buf->chan, buf->cpu, 1);
972                 buf->bytes_consumed = 0;
973         }
974 
975         buf->bytes_consumed += bytes_consumed;
976         if (!read_pos)
977                 read_subbuf = buf->subbufs_consumed % n_subbufs;
978         else
979                 read_subbuf = read_pos / buf->chan->subbuf_size;
980         if (buf->bytes_consumed + buf->padding[read_subbuf] == subbuf_size) {
981                 if ((read_subbuf == buf->subbufs_produced % n_subbufs) &&
982                     (buf->offset == subbuf_size))
983                         return;
984                 relay_subbufs_consumed(buf->chan, buf->cpu, 1);
985                 buf->bytes_consumed = 0;
986         }
987 }
988 
989 /*
990  *      relay_file_read_avail - boolean, are there unconsumed bytes available?
991  */
992 static int relay_file_read_avail(struct rchan_buf *buf, size_t read_pos)
993 {
994         size_t subbuf_size = buf->chan->subbuf_size;
995         size_t n_subbufs = buf->chan->n_subbufs;
996         size_t produced = buf->subbufs_produced;
997         size_t consumed = buf->subbufs_consumed;
998 
999         relay_file_read_consume(buf, read_pos, 0);
1000 
1001         consumed = buf->subbufs_consumed;
1002 
1003         if (unlikely(buf->offset > subbuf_size)) {
1004                 if (produced == consumed)
1005                         return 0;
1006                 return 1;
1007         }
1008 
1009         if (unlikely(produced - consumed >= n_subbufs)) {
1010                 consumed = produced - n_subbufs + 1;
1011                 buf->subbufs_consumed = consumed;
1012                 buf->bytes_consumed = 0;
1013         }
1014 
1015         produced = (produced % n_subbufs) * subbuf_size + buf->offset;
1016         consumed = (consumed % n_subbufs) * subbuf_size + buf->bytes_consumed;
1017 
1018         if (consumed > produced)
1019                 produced += n_subbufs * subbuf_size;
1020 
1021         if (consumed == produced) {
1022                 if (buf->offset == subbuf_size &&
1023                     buf->subbufs_produced > buf->subbufs_consumed)
1024                         return 1;
1025                 return 0;
1026         }
1027 
1028         return 1;
1029 }
1030 
1031 /**
1032  *      relay_file_read_subbuf_avail - return bytes available in sub-buffer
1033  *      @read_pos: file read position
1034  *      @buf: relay channel buffer
1035  */
1036 static size_t relay_file_read_subbuf_avail(size_t read_pos,
1037                                            struct rchan_buf *buf)
1038 {
1039         size_t padding, avail = 0;
1040         size_t read_subbuf, read_offset, write_subbuf, write_offset;
1041         size_t subbuf_size = buf->chan->subbuf_size;
1042 
1043         write_subbuf = (buf->data - buf->start) / subbuf_size;
1044         write_offset = buf->offset > subbuf_size ? subbuf_size : buf->offset;
1045         read_subbuf = read_pos / subbuf_size;
1046         read_offset = read_pos % subbuf_size;
1047         padding = buf->padding[read_subbuf];
1048 
1049         if (read_subbuf == write_subbuf) {
1050                 if (read_offset + padding < write_offset)
1051                         avail = write_offset - (read_offset + padding);
1052         } else
1053                 avail = (subbuf_size - padding) - read_offset;
1054 
1055         return avail;
1056 }
1057 
1058 /**
1059  *      relay_file_read_start_pos - find the first available byte to read
1060  *      @read_pos: file read position
1061  *      @buf: relay channel buffer
1062  *
1063  *      If the @read_pos is in the middle of padding, return the
1064  *      position of the first actually available byte, otherwise
1065  *      return the original value.
1066  */
1067 static size_t relay_file_read_start_pos(size_t read_pos,
1068                                         struct rchan_buf *buf)
1069 {
1070         size_t read_subbuf, padding, padding_start, padding_end;
1071         size_t subbuf_size = buf->chan->subbuf_size;
1072         size_t n_subbufs = buf->chan->n_subbufs;
1073         size_t consumed = buf->subbufs_consumed % n_subbufs;
1074 
1075         if (!read_pos)
1076                 read_pos = consumed * subbuf_size + buf->bytes_consumed;
1077         read_subbuf = read_pos / subbuf_size;
1078         padding = buf->padding[read_subbuf];
1079         padding_start = (read_subbuf + 1) * subbuf_size - padding;
1080         padding_end = (read_subbuf + 1) * subbuf_size;
1081         if (read_pos >= padding_start && read_pos < padding_end) {
1082                 read_subbuf = (read_subbuf + 1) % n_subbufs;
1083                 read_pos = read_subbuf * subbuf_size;
1084         }
1085 
1086         return read_pos;
1087 }
1088 
1089 /**
1090  *      relay_file_read_end_pos - return the new read position
1091  *      @read_pos: file read position
1092  *      @buf: relay channel buffer
1093  *      @count: number of bytes to be read
1094  */
1095 static size_t relay_file_read_end_pos(struct rchan_buf *buf,
1096                                       size_t read_pos,
1097                                       size_t count)
1098 {
1099         size_t read_subbuf, padding, end_pos;
1100         size_t subbuf_size = buf->chan->subbuf_size;
1101         size_t n_subbufs = buf->chan->n_subbufs;
1102 
1103         read_subbuf = read_pos / subbuf_size;
1104         padding = buf->padding[read_subbuf];
1105         if (read_pos % subbuf_size + count + padding == subbuf_size)
1106                 end_pos = (read_subbuf + 1) * subbuf_size;
1107         else
1108                 end_pos = read_pos + count;
1109         if (end_pos >= subbuf_size * n_subbufs)
1110                 end_pos = 0;
1111 
1112         return end_pos;
1113 }
1114 
1115 static ssize_t relay_file_read(struct file *filp,
1116                                char __user *buffer,
1117                                size_t count,
1118                                loff_t *ppos)
1119 {
1120         struct rchan_buf *buf = filp->private_data;
1121         size_t read_start, avail;
1122         size_t written = 0;
1123         int ret;
1124 
1125         if (!count)
1126                 return 0;
1127 
1128         inode_lock(file_inode(filp));
1129         do {
1130                 void *from;
1131 
1132                 if (!relay_file_read_avail(buf, *ppos))
1133                         break;
1134 
1135                 read_start = relay_file_read_start_pos(*ppos, buf);
1136                 avail = relay_file_read_subbuf_avail(read_start, buf);
1137                 if (!avail)
1138                         break;
1139 
1140                 avail = min(count, avail);
1141                 from = buf->start + read_start;
1142                 ret = avail;
1143                 if (copy_to_user(buffer, from, avail))
1144                         break;
1145 
1146                 buffer += ret;
1147                 written += ret;
1148                 count -= ret;
1149 
1150                 relay_file_read_consume(buf, read_start, ret);
1151                 *ppos = relay_file_read_end_pos(buf, read_start, ret);
1152         } while (count);
1153         inode_unlock(file_inode(filp));
1154 
1155         return written;
1156 }
1157 
1158 static void relay_consume_bytes(struct rchan_buf *rbuf, int bytes_consumed)
1159 {
1160         rbuf->bytes_consumed += bytes_consumed;
1161 
1162         if (rbuf->bytes_consumed >= rbuf->chan->subbuf_size) {
1163                 relay_subbufs_consumed(rbuf->chan, rbuf->cpu, 1);
1164                 rbuf->bytes_consumed %= rbuf->chan->subbuf_size;
1165         }
1166 }
1167 
1168 static void relay_pipe_buf_release(struct pipe_inode_info *pipe,
1169                                    struct pipe_buffer *buf)
1170 {
1171         struct rchan_buf *rbuf;
1172 
1173         rbuf = (struct rchan_buf *)page_private(buf->page);
1174         relay_consume_bytes(rbuf, buf->private);
1175 }
1176 
1177 static const struct pipe_buf_operations relay_pipe_buf_ops = {
1178         .can_merge = 0,
1179         .confirm = generic_pipe_buf_confirm,
1180         .release = relay_pipe_buf_release,
1181         .steal = generic_pipe_buf_steal,
1182         .get = generic_pipe_buf_get,
1183 };
1184 
1185 static void relay_page_release(struct splice_pipe_desc *spd, unsigned int i)
1186 {
1187 }
1188 
1189 /*
1190  *      subbuf_splice_actor - splice up to one subbuf's worth of data
1191  */
1192 static ssize_t subbuf_splice_actor(struct file *in,
1193                                loff_t *ppos,
1194                                struct pipe_inode_info *pipe,
1195                                size_t len,
1196                                unsigned int flags,
1197                                int *nonpad_ret)
1198 {
1199         unsigned int pidx, poff, total_len, subbuf_pages, nr_pages;
1200         struct rchan_buf *rbuf = in->private_data;
1201         unsigned int subbuf_size = rbuf->chan->subbuf_size;
1202         uint64_t pos = (uint64_t) *ppos;
1203         uint32_t alloc_size = (uint32_t) rbuf->chan->alloc_size;
1204         size_t read_start = (size_t) do_div(pos, alloc_size);
1205         size_t read_subbuf = read_start / subbuf_size;
1206         size_t padding = rbuf->padding[read_subbuf];
1207         size_t nonpad_end = read_subbuf * subbuf_size + subbuf_size - padding;
1208         struct page *pages[PIPE_DEF_BUFFERS];
1209         struct partial_page partial[PIPE_DEF_BUFFERS];
1210         struct splice_pipe_desc spd = {
1211                 .pages = pages,
1212                 .nr_pages = 0,
1213                 .nr_pages_max = PIPE_DEF_BUFFERS,
1214                 .partial = partial,
1215                 .flags = flags,
1216                 .ops = &relay_pipe_buf_ops,
1217                 .spd_release = relay_page_release,
1218         };
1219         ssize_t ret;
1220 
1221         if (rbuf->subbufs_produced == rbuf->subbufs_consumed)
1222                 return 0;
1223         if (splice_grow_spd(pipe, &spd))
1224                 return -ENOMEM;
1225 
1226         /*
1227          * Adjust read len, if longer than what is available
1228          */
1229         if (len > (subbuf_size - read_start % subbuf_size))
1230                 len = subbuf_size - read_start % subbuf_size;
1231 
1232         subbuf_pages = rbuf->chan->alloc_size >> PAGE_SHIFT;
1233         pidx = (read_start / PAGE_SIZE) % subbuf_pages;
1234         poff = read_start & ~PAGE_MASK;
1235         nr_pages = min_t(unsigned int, subbuf_pages, spd.nr_pages_max);
1236 
1237         for (total_len = 0; spd.nr_pages < nr_pages; spd.nr_pages++) {
1238                 unsigned int this_len, this_end, private;
1239                 unsigned int cur_pos = read_start + total_len;
1240 
1241                 if (!len)
1242                         break;
1243 
1244                 this_len = min_t(unsigned long, len, PAGE_SIZE - poff);
1245                 private = this_len;
1246 
1247                 spd.pages[spd.nr_pages] = rbuf->page_array[pidx];
1248                 spd.partial[spd.nr_pages].offset = poff;
1249 
1250                 this_end = cur_pos + this_len;
1251                 if (this_end >= nonpad_end) {
1252                         this_len = nonpad_end - cur_pos;
1253                         private = this_len + padding;
1254                 }
1255                 spd.partial[spd.nr_pages].len = this_len;
1256                 spd.partial[spd.nr_pages].private = private;
1257 
1258                 len -= this_len;
1259                 total_len += this_len;
1260                 poff = 0;
1261                 pidx = (pidx + 1) % subbuf_pages;
1262 
1263                 if (this_end >= nonpad_end) {
1264                         spd.nr_pages++;
1265                         break;
1266                 }
1267         }
1268 
1269         ret = 0;
1270         if (!spd.nr_pages)
1271                 goto out;
1272 
1273         ret = *nonpad_ret = splice_to_pipe(pipe, &spd);
1274         if (ret < 0 || ret < total_len)
1275                 goto out;
1276 
1277         if (read_start + ret == nonpad_end)
1278                 ret += padding;
1279 
1280 out:
1281         splice_shrink_spd(&spd);
1282         return ret;
1283 }
1284 
1285 static ssize_t relay_file_splice_read(struct file *in,
1286                                       loff_t *ppos,
1287                                       struct pipe_inode_info *pipe,
1288                                       size_t len,
1289                                       unsigned int flags)
1290 {
1291         ssize_t spliced;
1292         int ret;
1293         int nonpad_ret = 0;
1294 
1295         ret = 0;
1296         spliced = 0;
1297 
1298         while (len && !spliced) {
1299                 ret = subbuf_splice_actor(in, ppos, pipe, len, flags, &nonpad_ret);
1300                 if (ret < 0)
1301                         break;
1302                 else if (!ret) {
1303                         if (flags & SPLICE_F_NONBLOCK)
1304                                 ret = -EAGAIN;
1305                         break;
1306                 }
1307 
1308                 *ppos += ret;
1309                 if (ret > len)
1310                         len = 0;
1311                 else
1312                         len -= ret;
1313                 spliced += nonpad_ret;
1314                 nonpad_ret = 0;
1315         }
1316 
1317         if (spliced)
1318                 return spliced;
1319 
1320         return ret;
1321 }
1322 
1323 const struct file_operations relay_file_operations = {
1324         .open           = relay_file_open,
1325         .poll           = relay_file_poll,
1326         .mmap           = relay_file_mmap,
1327         .read           = relay_file_read,
1328         .llseek         = no_llseek,
1329         .release        = relay_file_release,
1330         .splice_read    = relay_file_splice_read,
1331 };
1332 EXPORT_SYMBOL_GPL(relay_file_operations);
1333 

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