[PATCH] Fix numerous kcalloc() calls, convert to kzalloc()
[linux-2.6.git] / kernel / relay.c
1 /*
2  * Public API and common code for kernel->userspace relay file support.
3  *
4  * See Documentation/filesystems/relayfs.txt for an overview of relayfs.
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  *
11  * This file is released under the GPL.
12  */
13 #include <linux/errno.h>
14 #include <linux/stddef.h>
15 #include <linux/slab.h>
16 #include <linux/module.h>
17 #include <linux/string.h>
18 #include <linux/relay.h>
19 #include <linux/vmalloc.h>
20 #include <linux/mm.h>
21
22 /*
23  * close() vm_op implementation for relay file mapping.
24  */
25 static void relay_file_mmap_close(struct vm_area_struct *vma)
26 {
27         struct rchan_buf *buf = vma->vm_private_data;
28         buf->chan->cb->buf_unmapped(buf, vma->vm_file);
29 }
30
31 /*
32  * nopage() vm_op implementation for relay file mapping.
33  */
34 static struct page *relay_buf_nopage(struct vm_area_struct *vma,
35                                      unsigned long address,
36                                      int *type)
37 {
38         struct page *page;
39         struct rchan_buf *buf = vma->vm_private_data;
40         unsigned long offset = address - vma->vm_start;
41
42         if (address > vma->vm_end)
43                 return NOPAGE_SIGBUS; /* Disallow mremap */
44         if (!buf)
45                 return NOPAGE_OOM;
46
47         page = vmalloc_to_page(buf->start + offset);
48         if (!page)
49                 return NOPAGE_OOM;
50         get_page(page);
51
52         if (type)
53                 *type = VM_FAULT_MINOR;
54
55         return page;
56 }
57
58 /*
59  * vm_ops for relay file mappings.
60  */
61 static struct vm_operations_struct relay_file_mmap_ops = {
62         .nopage = relay_buf_nopage,
63         .close = relay_file_mmap_close,
64 };
65
66 /**
67  *      relay_mmap_buf: - mmap channel buffer to process address space
68  *      @buf: relay channel buffer
69  *      @vma: vm_area_struct describing memory to be mapped
70  *
71  *      Returns 0 if ok, negative on error
72  *
73  *      Caller should already have grabbed mmap_sem.
74  */
75 int relay_mmap_buf(struct rchan_buf *buf, struct vm_area_struct *vma)
76 {
77         unsigned long length = vma->vm_end - vma->vm_start;
78         struct file *filp = vma->vm_file;
79
80         if (!buf)
81                 return -EBADF;
82
83         if (length != (unsigned long)buf->chan->alloc_size)
84                 return -EINVAL;
85
86         vma->vm_ops = &relay_file_mmap_ops;
87         vma->vm_private_data = buf;
88         buf->chan->cb->buf_mapped(buf, filp);
89
90         return 0;
91 }
92
93 /**
94  *      relay_alloc_buf - allocate a channel buffer
95  *      @buf: the buffer struct
96  *      @size: total size of the buffer
97  *
98  *      Returns a pointer to the resulting buffer, %NULL if unsuccessful. The
99  *      passed in size will get page aligned, if it isn't already.
100  */
101 static void *relay_alloc_buf(struct rchan_buf *buf, size_t *size)
102 {
103         void *mem;
104         unsigned int i, j, n_pages;
105
106         *size = PAGE_ALIGN(*size);
107         n_pages = *size >> PAGE_SHIFT;
108
109         buf->page_array = kcalloc(n_pages, sizeof(struct page *), GFP_KERNEL);
110         if (!buf->page_array)
111                 return NULL;
112
113         for (i = 0; i < n_pages; i++) {
114                 buf->page_array[i] = alloc_page(GFP_KERNEL);
115                 if (unlikely(!buf->page_array[i]))
116                         goto depopulate;
117         }
118         mem = vmap(buf->page_array, n_pages, VM_MAP, PAGE_KERNEL);
119         if (!mem)
120                 goto depopulate;
121
122         memset(mem, 0, *size);
123         buf->page_count = n_pages;
124         return mem;
125
126 depopulate:
127         for (j = 0; j < i; j++)
128                 __free_page(buf->page_array[j]);
129         kfree(buf->page_array);
130         return NULL;
131 }
132
133 /**
134  *      relay_create_buf - allocate and initialize a channel buffer
135  *      @chan: the relay channel
136  *
137  *      Returns channel buffer if successful, %NULL otherwise.
138  */
139 struct rchan_buf *relay_create_buf(struct rchan *chan)
140 {
141         struct rchan_buf *buf = kzalloc(sizeof(struct rchan_buf), GFP_KERNEL);
142         if (!buf)
143                 return NULL;
144
145         buf->padding = kmalloc(chan->n_subbufs * sizeof(size_t *), GFP_KERNEL);
146         if (!buf->padding)
147                 goto free_buf;
148
149         buf->start = relay_alloc_buf(buf, &chan->alloc_size);
150         if (!buf->start)
151                 goto free_buf;
152
153         buf->chan = chan;
154         kref_get(&buf->chan->kref);
155         return buf;
156
157 free_buf:
158         kfree(buf->padding);
159         kfree(buf);
160         return NULL;
161 }
162
163 /**
164  *      relay_destroy_channel - free the channel struct
165  *      @kref: target kernel reference that contains the relay channel
166  *
167  *      Should only be called from kref_put().
168  */
169 void relay_destroy_channel(struct kref *kref)
170 {
171         struct rchan *chan = container_of(kref, struct rchan, kref);
172         kfree(chan);
173 }
174
175 /**
176  *      relay_destroy_buf - destroy an rchan_buf struct and associated buffer
177  *      @buf: the buffer struct
178  */
179 void relay_destroy_buf(struct rchan_buf *buf)
180 {
181         struct rchan *chan = buf->chan;
182         unsigned int i;
183
184         if (likely(buf->start)) {
185                 vunmap(buf->start);
186                 for (i = 0; i < buf->page_count; i++)
187                         __free_page(buf->page_array[i]);
188                 kfree(buf->page_array);
189         }
190         kfree(buf->padding);
191         kfree(buf);
192         kref_put(&chan->kref, relay_destroy_channel);
193 }
194
195 /**
196  *      relay_remove_buf - remove a channel buffer
197  *      @kref: target kernel reference that contains the relay buffer
198  *
199  *      Removes the file from the fileystem, which also frees the
200  *      rchan_buf_struct and the channel buffer.  Should only be called from
201  *      kref_put().
202  */
203 void relay_remove_buf(struct kref *kref)
204 {
205         struct rchan_buf *buf = container_of(kref, struct rchan_buf, kref);
206         buf->chan->cb->remove_buf_file(buf->dentry);
207         relay_destroy_buf(buf);
208 }
209
210 /**
211  *      relay_buf_empty - boolean, is the channel buffer empty?
212  *      @buf: channel buffer
213  *
214  *      Returns 1 if the buffer is empty, 0 otherwise.
215  */
216 int relay_buf_empty(struct rchan_buf *buf)
217 {
218         return (buf->subbufs_produced - buf->subbufs_consumed) ? 0 : 1;
219 }
220 EXPORT_SYMBOL_GPL(relay_buf_empty);
221
222 /**
223  *      relay_buf_full - boolean, is the channel buffer full?
224  *      @buf: channel buffer
225  *
226  *      Returns 1 if the buffer is full, 0 otherwise.
227  */
228 int relay_buf_full(struct rchan_buf *buf)
229 {
230         size_t ready = buf->subbufs_produced - buf->subbufs_consumed;
231         return (ready >= buf->chan->n_subbufs) ? 1 : 0;
232 }
233 EXPORT_SYMBOL_GPL(relay_buf_full);
234
235 /*
236  * High-level relay kernel API and associated functions.
237  */
238
239 /*
240  * rchan_callback implementations defining default channel behavior.  Used
241  * in place of corresponding NULL values in client callback struct.
242  */
243
244 /*
245  * subbuf_start() default callback.  Does nothing.
246  */
247 static int subbuf_start_default_callback (struct rchan_buf *buf,
248                                           void *subbuf,
249                                           void *prev_subbuf,
250                                           size_t prev_padding)
251 {
252         if (relay_buf_full(buf))
253                 return 0;
254
255         return 1;
256 }
257
258 /*
259  * buf_mapped() default callback.  Does nothing.
260  */
261 static void buf_mapped_default_callback(struct rchan_buf *buf,
262                                         struct file *filp)
263 {
264 }
265
266 /*
267  * buf_unmapped() default callback.  Does nothing.
268  */
269 static void buf_unmapped_default_callback(struct rchan_buf *buf,
270                                           struct file *filp)
271 {
272 }
273
274 /*
275  * create_buf_file_create() default callback.  Does nothing.
276  */
277 static struct dentry *create_buf_file_default_callback(const char *filename,
278                                                        struct dentry *parent,
279                                                        int mode,
280                                                        struct rchan_buf *buf,
281                                                        int *is_global)
282 {
283         return NULL;
284 }
285
286 /*
287  * remove_buf_file() default callback.  Does nothing.
288  */
289 static int remove_buf_file_default_callback(struct dentry *dentry)
290 {
291         return -EINVAL;
292 }
293
294 /* relay channel default callbacks */
295 static struct rchan_callbacks default_channel_callbacks = {
296         .subbuf_start = subbuf_start_default_callback,
297         .buf_mapped = buf_mapped_default_callback,
298         .buf_unmapped = buf_unmapped_default_callback,
299         .create_buf_file = create_buf_file_default_callback,
300         .remove_buf_file = remove_buf_file_default_callback,
301 };
302
303 /**
304  *      wakeup_readers - wake up readers waiting on a channel
305  *      @private: the channel buffer
306  *
307  *      This is the work function used to defer reader waking.  The
308  *      reason waking is deferred is that calling directly from write
309  *      causes problems if you're writing from say the scheduler.
310  */
311 static void wakeup_readers(struct work_struct *work)
312 {
313         struct rchan_buf *buf =
314                 container_of(work, struct rchan_buf, wake_readers.work);
315         wake_up_interruptible(&buf->read_wait);
316 }
317
318 /**
319  *      __relay_reset - reset a channel buffer
320  *      @buf: the channel buffer
321  *      @init: 1 if this is a first-time initialization
322  *
323  *      See relay_reset for description of effect.
324  */
325 static inline void __relay_reset(struct rchan_buf *buf, unsigned int init)
326 {
327         size_t i;
328
329         if (init) {
330                 init_waitqueue_head(&buf->read_wait);
331                 kref_init(&buf->kref);
332                 INIT_DELAYED_WORK(&buf->wake_readers, NULL);
333         } else {
334                 cancel_delayed_work(&buf->wake_readers);
335                 flush_scheduled_work();
336         }
337
338         buf->subbufs_produced = 0;
339         buf->subbufs_consumed = 0;
340         buf->bytes_consumed = 0;
341         buf->finalized = 0;
342         buf->data = buf->start;
343         buf->offset = 0;
344
345         for (i = 0; i < buf->chan->n_subbufs; i++)
346                 buf->padding[i] = 0;
347
348         buf->chan->cb->subbuf_start(buf, buf->data, NULL, 0);
349 }
350
351 /**
352  *      relay_reset - reset the channel
353  *      @chan: the channel
354  *
355  *      This has the effect of erasing all data from all channel buffers
356  *      and restarting the channel in its initial state.  The buffers
357  *      are not freed, so any mappings are still in effect.
358  *
359  *      NOTE: Care should be taken that the channel isn't actually
360  *      being used by anything when this call is made.
361  */
362 void relay_reset(struct rchan *chan)
363 {
364         unsigned int i;
365         struct rchan_buf *prev = NULL;
366
367         if (!chan)
368                 return;
369
370         for (i = 0; i < NR_CPUS; i++) {
371                 if (!chan->buf[i] || chan->buf[i] == prev)
372                         break;
373                 __relay_reset(chan->buf[i], 0);
374                 prev = chan->buf[i];
375         }
376 }
377 EXPORT_SYMBOL_GPL(relay_reset);
378
379 /*
380  *      relay_open_buf - create a new relay channel buffer
381  *
382  *      Internal - used by relay_open().
383  */
384 static struct rchan_buf *relay_open_buf(struct rchan *chan,
385                                         const char *filename,
386                                         struct dentry *parent,
387                                         int *is_global)
388 {
389         struct rchan_buf *buf;
390         struct dentry *dentry;
391
392         if (*is_global)
393                 return chan->buf[0];
394
395         buf = relay_create_buf(chan);
396         if (!buf)
397                 return NULL;
398
399         /* Create file in fs */
400         dentry = chan->cb->create_buf_file(filename, parent, S_IRUSR,
401                                            buf, is_global);
402         if (!dentry) {
403                 relay_destroy_buf(buf);
404                 return NULL;
405         }
406
407         buf->dentry = dentry;
408         __relay_reset(buf, 1);
409
410         return buf;
411 }
412
413 /**
414  *      relay_close_buf - close a channel buffer
415  *      @buf: channel buffer
416  *
417  *      Marks the buffer finalized and restores the default callbacks.
418  *      The channel buffer and channel buffer data structure are then freed
419  *      automatically when the last reference is given up.
420  */
421 static inline void relay_close_buf(struct rchan_buf *buf)
422 {
423         buf->finalized = 1;
424         cancel_delayed_work(&buf->wake_readers);
425         flush_scheduled_work();
426         kref_put(&buf->kref, relay_remove_buf);
427 }
428
429 static inline void setup_callbacks(struct rchan *chan,
430                                    struct rchan_callbacks *cb)
431 {
432         if (!cb) {
433                 chan->cb = &default_channel_callbacks;
434                 return;
435         }
436
437         if (!cb->subbuf_start)
438                 cb->subbuf_start = subbuf_start_default_callback;
439         if (!cb->buf_mapped)
440                 cb->buf_mapped = buf_mapped_default_callback;
441         if (!cb->buf_unmapped)
442                 cb->buf_unmapped = buf_unmapped_default_callback;
443         if (!cb->create_buf_file)
444                 cb->create_buf_file = create_buf_file_default_callback;
445         if (!cb->remove_buf_file)
446                 cb->remove_buf_file = remove_buf_file_default_callback;
447         chan->cb = cb;
448 }
449
450 /**
451  *      relay_open - create a new relay channel
452  *      @base_filename: base name of files to create
453  *      @parent: dentry of parent directory, %NULL for root directory
454  *      @subbuf_size: size of sub-buffers
455  *      @n_subbufs: number of sub-buffers
456  *      @cb: client callback functions
457  *
458  *      Returns channel pointer if successful, %NULL otherwise.
459  *
460  *      Creates a channel buffer for each cpu using the sizes and
461  *      attributes specified.  The created channel buffer files
462  *      will be named base_filename0...base_filenameN-1.  File
463  *      permissions will be S_IRUSR.
464  */
465 struct rchan *relay_open(const char *base_filename,
466                          struct dentry *parent,
467                          size_t subbuf_size,
468                          size_t n_subbufs,
469                          struct rchan_callbacks *cb)
470 {
471         unsigned int i;
472         struct rchan *chan;
473         char *tmpname;
474         int is_global = 0;
475
476         if (!base_filename)
477                 return NULL;
478
479         if (!(subbuf_size && n_subbufs))
480                 return NULL;
481
482         chan = kzalloc(sizeof(struct rchan), GFP_KERNEL);
483         if (!chan)
484                 return NULL;
485
486         chan->version = RELAYFS_CHANNEL_VERSION;
487         chan->n_subbufs = n_subbufs;
488         chan->subbuf_size = subbuf_size;
489         chan->alloc_size = FIX_SIZE(subbuf_size * n_subbufs);
490         setup_callbacks(chan, cb);
491         kref_init(&chan->kref);
492
493         tmpname = kmalloc(NAME_MAX + 1, GFP_KERNEL);
494         if (!tmpname)
495                 goto free_chan;
496
497         for_each_online_cpu(i) {
498                 sprintf(tmpname, "%s%d", base_filename, i);
499                 chan->buf[i] = relay_open_buf(chan, tmpname, parent,
500                                               &is_global);
501                 if (!chan->buf[i])
502                         goto free_bufs;
503
504                 chan->buf[i]->cpu = i;
505         }
506
507         kfree(tmpname);
508         return chan;
509
510 free_bufs:
511         for (i = 0; i < NR_CPUS; i++) {
512                 if (!chan->buf[i])
513                         break;
514                 relay_close_buf(chan->buf[i]);
515                 if (is_global)
516                         break;
517         }
518         kfree(tmpname);
519
520 free_chan:
521         kref_put(&chan->kref, relay_destroy_channel);
522         return NULL;
523 }
524 EXPORT_SYMBOL_GPL(relay_open);
525
526 /**
527  *      relay_switch_subbuf - switch to a new sub-buffer
528  *      @buf: channel buffer
529  *      @length: size of current event
530  *
531  *      Returns either the length passed in or 0 if full.
532  *
533  *      Performs sub-buffer-switch tasks such as invoking callbacks,
534  *      updating padding counts, waking up readers, etc.
535  */
536 size_t relay_switch_subbuf(struct rchan_buf *buf, size_t length)
537 {
538         void *old, *new;
539         size_t old_subbuf, new_subbuf;
540
541         if (unlikely(length > buf->chan->subbuf_size))
542                 goto toobig;
543
544         if (buf->offset != buf->chan->subbuf_size + 1) {
545                 buf->prev_padding = buf->chan->subbuf_size - buf->offset;
546                 old_subbuf = buf->subbufs_produced % buf->chan->n_subbufs;
547                 buf->padding[old_subbuf] = buf->prev_padding;
548                 buf->subbufs_produced++;
549                 buf->dentry->d_inode->i_size += buf->chan->subbuf_size -
550                         buf->padding[old_subbuf];
551                 smp_mb();
552                 if (waitqueue_active(&buf->read_wait)) {
553                         PREPARE_DELAYED_WORK(&buf->wake_readers,
554                                              wakeup_readers);
555                         schedule_delayed_work(&buf->wake_readers, 1);
556                 }
557         }
558
559         old = buf->data;
560         new_subbuf = buf->subbufs_produced % buf->chan->n_subbufs;
561         new = buf->start + new_subbuf * buf->chan->subbuf_size;
562         buf->offset = 0;
563         if (!buf->chan->cb->subbuf_start(buf, new, old, buf->prev_padding)) {
564                 buf->offset = buf->chan->subbuf_size + 1;
565                 return 0;
566         }
567         buf->data = new;
568         buf->padding[new_subbuf] = 0;
569
570         if (unlikely(length + buf->offset > buf->chan->subbuf_size))
571                 goto toobig;
572
573         return length;
574
575 toobig:
576         buf->chan->last_toobig = length;
577         return 0;
578 }
579 EXPORT_SYMBOL_GPL(relay_switch_subbuf);
580
581 /**
582  *      relay_subbufs_consumed - update the buffer's sub-buffers-consumed count
583  *      @chan: the channel
584  *      @cpu: the cpu associated with the channel buffer to update
585  *      @subbufs_consumed: number of sub-buffers to add to current buf's count
586  *
587  *      Adds to the channel buffer's consumed sub-buffer count.
588  *      subbufs_consumed should be the number of sub-buffers newly consumed,
589  *      not the total consumed.
590  *
591  *      NOTE: Kernel clients don't need to call this function if the channel
592  *      mode is 'overwrite'.
593  */
594 void relay_subbufs_consumed(struct rchan *chan,
595                             unsigned int cpu,
596                             size_t subbufs_consumed)
597 {
598         struct rchan_buf *buf;
599
600         if (!chan)
601                 return;
602
603         if (cpu >= NR_CPUS || !chan->buf[cpu])
604                 return;
605
606         buf = chan->buf[cpu];
607         buf->subbufs_consumed += subbufs_consumed;
608         if (buf->subbufs_consumed > buf->subbufs_produced)
609                 buf->subbufs_consumed = buf->subbufs_produced;
610 }
611 EXPORT_SYMBOL_GPL(relay_subbufs_consumed);
612
613 /**
614  *      relay_close - close the channel
615  *      @chan: the channel
616  *
617  *      Closes all channel buffers and frees the channel.
618  */
619 void relay_close(struct rchan *chan)
620 {
621         unsigned int i;
622         struct rchan_buf *prev = NULL;
623
624         if (!chan)
625                 return;
626
627         for (i = 0; i < NR_CPUS; i++) {
628                 if (!chan->buf[i] || chan->buf[i] == prev)
629                         break;
630                 relay_close_buf(chan->buf[i]);
631                 prev = chan->buf[i];
632         }
633
634         if (chan->last_toobig)
635                 printk(KERN_WARNING "relay: one or more items not logged "
636                        "[item size (%Zd) > sub-buffer size (%Zd)]\n",
637                        chan->last_toobig, chan->subbuf_size);
638
639         kref_put(&chan->kref, relay_destroy_channel);
640 }
641 EXPORT_SYMBOL_GPL(relay_close);
642
643 /**
644  *      relay_flush - close the channel
645  *      @chan: the channel
646  *
647  *      Flushes all channel buffers, i.e. forces buffer switch.
648  */
649 void relay_flush(struct rchan *chan)
650 {
651         unsigned int i;
652         struct rchan_buf *prev = NULL;
653
654         if (!chan)
655                 return;
656
657         for (i = 0; i < NR_CPUS; i++) {
658                 if (!chan->buf[i] || chan->buf[i] == prev)
659                         break;
660                 relay_switch_subbuf(chan->buf[i], 0);
661                 prev = chan->buf[i];
662         }
663 }
664 EXPORT_SYMBOL_GPL(relay_flush);
665
666 /**
667  *      relay_file_open - open file op for relay files
668  *      @inode: the inode
669  *      @filp: the file
670  *
671  *      Increments the channel buffer refcount.
672  */
673 static int relay_file_open(struct inode *inode, struct file *filp)
674 {
675         struct rchan_buf *buf = inode->i_private;
676         kref_get(&buf->kref);
677         filp->private_data = buf;
678
679         return 0;
680 }
681
682 /**
683  *      relay_file_mmap - mmap file op for relay files
684  *      @filp: the file
685  *      @vma: the vma describing what to map
686  *
687  *      Calls upon relay_mmap_buf to map the file into user space.
688  */
689 static int relay_file_mmap(struct file *filp, struct vm_area_struct *vma)
690 {
691         struct rchan_buf *buf = filp->private_data;
692         return relay_mmap_buf(buf, vma);
693 }
694
695 /**
696  *      relay_file_poll - poll file op for relay files
697  *      @filp: the file
698  *      @wait: poll table
699  *
700  *      Poll implemention.
701  */
702 static unsigned int relay_file_poll(struct file *filp, poll_table *wait)
703 {
704         unsigned int mask = 0;
705         struct rchan_buf *buf = filp->private_data;
706
707         if (buf->finalized)
708                 return POLLERR;
709
710         if (filp->f_mode & FMODE_READ) {
711                 poll_wait(filp, &buf->read_wait, wait);
712                 if (!relay_buf_empty(buf))
713                         mask |= POLLIN | POLLRDNORM;
714         }
715
716         return mask;
717 }
718
719 /**
720  *      relay_file_release - release file op for relay files
721  *      @inode: the inode
722  *      @filp: the file
723  *
724  *      Decrements the channel refcount, as the filesystem is
725  *      no longer using it.
726  */
727 static int relay_file_release(struct inode *inode, struct file *filp)
728 {
729         struct rchan_buf *buf = filp->private_data;
730         kref_put(&buf->kref, relay_remove_buf);
731
732         return 0;
733 }
734
735 /*
736  *      relay_file_read_consume - update the consumed count for the buffer
737  */
738 static void relay_file_read_consume(struct rchan_buf *buf,
739                                     size_t read_pos,
740                                     size_t bytes_consumed)
741 {
742         size_t subbuf_size = buf->chan->subbuf_size;
743         size_t n_subbufs = buf->chan->n_subbufs;
744         size_t read_subbuf;
745
746         if (buf->bytes_consumed + bytes_consumed > subbuf_size) {
747                 relay_subbufs_consumed(buf->chan, buf->cpu, 1);
748                 buf->bytes_consumed = 0;
749         }
750
751         buf->bytes_consumed += bytes_consumed;
752         read_subbuf = read_pos / buf->chan->subbuf_size;
753         if (buf->bytes_consumed + buf->padding[read_subbuf] == subbuf_size) {
754                 if ((read_subbuf == buf->subbufs_produced % n_subbufs) &&
755                     (buf->offset == subbuf_size))
756                         return;
757                 relay_subbufs_consumed(buf->chan, buf->cpu, 1);
758                 buf->bytes_consumed = 0;
759         }
760 }
761
762 /*
763  *      relay_file_read_avail - boolean, are there unconsumed bytes available?
764  */
765 static int relay_file_read_avail(struct rchan_buf *buf, size_t read_pos)
766 {
767         size_t subbuf_size = buf->chan->subbuf_size;
768         size_t n_subbufs = buf->chan->n_subbufs;
769         size_t produced = buf->subbufs_produced;
770         size_t consumed = buf->subbufs_consumed;
771
772         relay_file_read_consume(buf, read_pos, 0);
773
774         if (unlikely(buf->offset > subbuf_size)) {
775                 if (produced == consumed)
776                         return 0;
777                 return 1;
778         }
779
780         if (unlikely(produced - consumed >= n_subbufs)) {
781                 consumed = (produced / n_subbufs) * n_subbufs;
782                 buf->subbufs_consumed = consumed;
783         }
784         
785         produced = (produced % n_subbufs) * subbuf_size + buf->offset;
786         consumed = (consumed % n_subbufs) * subbuf_size + buf->bytes_consumed;
787
788         if (consumed > produced)
789                 produced += n_subbufs * subbuf_size;
790         
791         if (consumed == produced)
792                 return 0;
793
794         return 1;
795 }
796
797 /**
798  *      relay_file_read_subbuf_avail - return bytes available in sub-buffer
799  *      @read_pos: file read position
800  *      @buf: relay channel buffer
801  */
802 static size_t relay_file_read_subbuf_avail(size_t read_pos,
803                                            struct rchan_buf *buf)
804 {
805         size_t padding, avail = 0;
806         size_t read_subbuf, read_offset, write_subbuf, write_offset;
807         size_t subbuf_size = buf->chan->subbuf_size;
808
809         write_subbuf = (buf->data - buf->start) / subbuf_size;
810         write_offset = buf->offset > subbuf_size ? subbuf_size : buf->offset;
811         read_subbuf = read_pos / subbuf_size;
812         read_offset = read_pos % subbuf_size;
813         padding = buf->padding[read_subbuf];
814
815         if (read_subbuf == write_subbuf) {
816                 if (read_offset + padding < write_offset)
817                         avail = write_offset - (read_offset + padding);
818         } else
819                 avail = (subbuf_size - padding) - read_offset;
820
821         return avail;
822 }
823
824 /**
825  *      relay_file_read_start_pos - find the first available byte to read
826  *      @read_pos: file read position
827  *      @buf: relay channel buffer
828  *
829  *      If the read_pos is in the middle of padding, return the
830  *      position of the first actually available byte, otherwise
831  *      return the original value.
832  */
833 static size_t relay_file_read_start_pos(size_t read_pos,
834                                         struct rchan_buf *buf)
835 {
836         size_t read_subbuf, padding, padding_start, padding_end;
837         size_t subbuf_size = buf->chan->subbuf_size;
838         size_t n_subbufs = buf->chan->n_subbufs;
839
840         read_subbuf = read_pos / subbuf_size;
841         padding = buf->padding[read_subbuf];
842         padding_start = (read_subbuf + 1) * subbuf_size - padding;
843         padding_end = (read_subbuf + 1) * subbuf_size;
844         if (read_pos >= padding_start && read_pos < padding_end) {
845                 read_subbuf = (read_subbuf + 1) % n_subbufs;
846                 read_pos = read_subbuf * subbuf_size;
847         }
848
849         return read_pos;
850 }
851
852 /**
853  *      relay_file_read_end_pos - return the new read position
854  *      @read_pos: file read position
855  *      @buf: relay channel buffer
856  *      @count: number of bytes to be read
857  */
858 static size_t relay_file_read_end_pos(struct rchan_buf *buf,
859                                       size_t read_pos,
860                                       size_t count)
861 {
862         size_t read_subbuf, padding, end_pos;
863         size_t subbuf_size = buf->chan->subbuf_size;
864         size_t n_subbufs = buf->chan->n_subbufs;
865
866         read_subbuf = read_pos / subbuf_size;
867         padding = buf->padding[read_subbuf];
868         if (read_pos % subbuf_size + count + padding == subbuf_size)
869                 end_pos = (read_subbuf + 1) * subbuf_size;
870         else
871                 end_pos = read_pos + count;
872         if (end_pos >= subbuf_size * n_subbufs)
873                 end_pos = 0;
874
875         return end_pos;
876 }
877
878 /*
879  *      subbuf_read_actor - read up to one subbuf's worth of data
880  */
881 static int subbuf_read_actor(size_t read_start,
882                              struct rchan_buf *buf,
883                              size_t avail,
884                              read_descriptor_t *desc,
885                              read_actor_t actor)
886 {
887         void *from;
888         int ret = 0;
889
890         from = buf->start + read_start;
891         ret = avail;
892         if (copy_to_user(desc->arg.buf, from, avail)) {
893                 desc->error = -EFAULT;
894                 ret = 0;
895         }
896         desc->arg.data += ret;
897         desc->written += ret;
898         desc->count -= ret;
899
900         return ret;
901 }
902
903 /*
904  *      subbuf_send_actor - send up to one subbuf's worth of data
905  */
906 static int subbuf_send_actor(size_t read_start,
907                              struct rchan_buf *buf,
908                              size_t avail,
909                              read_descriptor_t *desc,
910                              read_actor_t actor)
911 {
912         unsigned long pidx, poff;
913         unsigned int subbuf_pages;
914         int ret = 0;
915
916         subbuf_pages = buf->chan->alloc_size >> PAGE_SHIFT;
917         pidx = (read_start / PAGE_SIZE) % subbuf_pages;
918         poff = read_start & ~PAGE_MASK;
919         while (avail) {
920                 struct page *p = buf->page_array[pidx];
921                 unsigned int len;
922
923                 len = PAGE_SIZE - poff;
924                 if (len > avail)
925                         len = avail;
926
927                 len = actor(desc, p, poff, len);
928                 if (desc->error)
929                         break;
930
931                 avail -= len;
932                 ret += len;
933                 poff = 0;
934                 pidx = (pidx + 1) % subbuf_pages;
935         }
936
937         return ret;
938 }
939
940 typedef int (*subbuf_actor_t) (size_t read_start,
941                                struct rchan_buf *buf,
942                                size_t avail,
943                                read_descriptor_t *desc,
944                                read_actor_t actor);
945
946 /*
947  *      relay_file_read_subbufs - read count bytes, bridging subbuf boundaries
948  */
949 static inline ssize_t relay_file_read_subbufs(struct file *filp,
950                                               loff_t *ppos,
951                                               subbuf_actor_t subbuf_actor,
952                                               read_actor_t actor,
953                                               read_descriptor_t *desc)
954 {
955         struct rchan_buf *buf = filp->private_data;
956         size_t read_start, avail;
957         int ret;
958
959         if (!desc->count)
960                 return 0;
961
962         mutex_lock(&filp->f_path.dentry->d_inode->i_mutex);
963         do {
964                 if (!relay_file_read_avail(buf, *ppos))
965                         break;
966
967                 read_start = relay_file_read_start_pos(*ppos, buf);
968                 avail = relay_file_read_subbuf_avail(read_start, buf);
969                 if (!avail)
970                         break;
971
972                 avail = min(desc->count, avail);
973                 ret = subbuf_actor(read_start, buf, avail, desc, actor);
974                 if (desc->error < 0)
975                         break;
976
977                 if (ret) {
978                         relay_file_read_consume(buf, read_start, ret);
979                         *ppos = relay_file_read_end_pos(buf, read_start, ret);
980                 }
981         } while (desc->count && ret);
982         mutex_unlock(&filp->f_path.dentry->d_inode->i_mutex);
983
984         return desc->written;
985 }
986
987 static ssize_t relay_file_read(struct file *filp,
988                                char __user *buffer,
989                                size_t count,
990                                loff_t *ppos)
991 {
992         read_descriptor_t desc;
993         desc.written = 0;
994         desc.count = count;
995         desc.arg.buf = buffer;
996         desc.error = 0;
997         return relay_file_read_subbufs(filp, ppos, subbuf_read_actor,
998                                        NULL, &desc);
999 }
1000
1001 static ssize_t relay_file_sendfile(struct file *filp,
1002                                    loff_t *ppos,
1003                                    size_t count,
1004                                    read_actor_t actor,
1005                                    void *target)
1006 {
1007         read_descriptor_t desc;
1008         desc.written = 0;
1009         desc.count = count;
1010         desc.arg.data = target;
1011         desc.error = 0;
1012         return relay_file_read_subbufs(filp, ppos, subbuf_send_actor,
1013                                        actor, &desc);
1014 }
1015
1016 const struct file_operations relay_file_operations = {
1017         .open           = relay_file_open,
1018         .poll           = relay_file_poll,
1019         .mmap           = relay_file_mmap,
1020         .read           = relay_file_read,
1021         .llseek         = no_llseek,
1022         .release        = relay_file_release,
1023         .sendfile       = relay_file_sendfile,
1024 };
1025 EXPORT_SYMBOL_GPL(relay_file_operations);