[PATCH] kernel-doc for relay interface
[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 = kcalloc(1, 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(void *private)
312 {
313         struct rchan_buf *buf = private;
314         wake_up_interruptible(&buf->read_wait);
315 }
316
317 /**
318  *      __relay_reset - reset a channel buffer
319  *      @buf: the channel buffer
320  *      @init: 1 if this is a first-time initialization
321  *
322  *      See relay_reset for description of effect.
323  */
324 static inline void __relay_reset(struct rchan_buf *buf, unsigned int init)
325 {
326         size_t i;
327
328         if (init) {
329                 init_waitqueue_head(&buf->read_wait);
330                 kref_init(&buf->kref);
331                 INIT_WORK(&buf->wake_readers, NULL, NULL);
332         } else {
333                 cancel_delayed_work(&buf->wake_readers);
334                 flush_scheduled_work();
335         }
336
337         buf->subbufs_produced = 0;
338         buf->subbufs_consumed = 0;
339         buf->bytes_consumed = 0;
340         buf->finalized = 0;
341         buf->data = buf->start;
342         buf->offset = 0;
343
344         for (i = 0; i < buf->chan->n_subbufs; i++)
345                 buf->padding[i] = 0;
346
347         buf->chan->cb->subbuf_start(buf, buf->data, NULL, 0);
348 }
349
350 /**
351  *      relay_reset - reset the channel
352  *      @chan: the channel
353  *
354  *      This has the effect of erasing all data from all channel buffers
355  *      and restarting the channel in its initial state.  The buffers
356  *      are not freed, so any mappings are still in effect.
357  *
358  *      NOTE: Care should be taken that the channel isn't actually
359  *      being used by anything when this call is made.
360  */
361 void relay_reset(struct rchan *chan)
362 {
363         unsigned int i;
364         struct rchan_buf *prev = NULL;
365
366         if (!chan)
367                 return;
368
369         for (i = 0; i < NR_CPUS; i++) {
370                 if (!chan->buf[i] || chan->buf[i] == prev)
371                         break;
372                 __relay_reset(chan->buf[i], 0);
373                 prev = chan->buf[i];
374         }
375 }
376 EXPORT_SYMBOL_GPL(relay_reset);
377
378 /*
379  *      relay_open_buf - create a new relay channel buffer
380  *
381  *      Internal - used by relay_open().
382  */
383 static struct rchan_buf *relay_open_buf(struct rchan *chan,
384                                         const char *filename,
385                                         struct dentry *parent,
386                                         int *is_global)
387 {
388         struct rchan_buf *buf;
389         struct dentry *dentry;
390
391         if (*is_global)
392                 return chan->buf[0];
393
394         buf = relay_create_buf(chan);
395         if (!buf)
396                 return NULL;
397
398         /* Create file in fs */
399         dentry = chan->cb->create_buf_file(filename, parent, S_IRUSR,
400                                            buf, is_global);
401         if (!dentry) {
402                 relay_destroy_buf(buf);
403                 return NULL;
404         }
405
406         buf->dentry = dentry;
407         __relay_reset(buf, 1);
408
409         return buf;
410 }
411
412 /**
413  *      relay_close_buf - close a channel buffer
414  *      @buf: channel buffer
415  *
416  *      Marks the buffer finalized and restores the default callbacks.
417  *      The channel buffer and channel buffer data structure are then freed
418  *      automatically when the last reference is given up.
419  */
420 static inline void relay_close_buf(struct rchan_buf *buf)
421 {
422         buf->finalized = 1;
423         cancel_delayed_work(&buf->wake_readers);
424         flush_scheduled_work();
425         kref_put(&buf->kref, relay_remove_buf);
426 }
427
428 static inline void setup_callbacks(struct rchan *chan,
429                                    struct rchan_callbacks *cb)
430 {
431         if (!cb) {
432                 chan->cb = &default_channel_callbacks;
433                 return;
434         }
435
436         if (!cb->subbuf_start)
437                 cb->subbuf_start = subbuf_start_default_callback;
438         if (!cb->buf_mapped)
439                 cb->buf_mapped = buf_mapped_default_callback;
440         if (!cb->buf_unmapped)
441                 cb->buf_unmapped = buf_unmapped_default_callback;
442         if (!cb->create_buf_file)
443                 cb->create_buf_file = create_buf_file_default_callback;
444         if (!cb->remove_buf_file)
445                 cb->remove_buf_file = remove_buf_file_default_callback;
446         chan->cb = cb;
447 }
448
449 /**
450  *      relay_open - create a new relay channel
451  *      @base_filename: base name of files to create
452  *      @parent: dentry of parent directory, %NULL for root directory
453  *      @subbuf_size: size of sub-buffers
454  *      @n_subbufs: number of sub-buffers
455  *      @cb: client callback functions
456  *
457  *      Returns channel pointer if successful, %NULL otherwise.
458  *
459  *      Creates a channel buffer for each cpu using the sizes and
460  *      attributes specified.  The created channel buffer files
461  *      will be named base_filename0...base_filenameN-1.  File
462  *      permissions will be S_IRUSR.
463  */
464 struct rchan *relay_open(const char *base_filename,
465                          struct dentry *parent,
466                          size_t subbuf_size,
467                          size_t n_subbufs,
468                          struct rchan_callbacks *cb)
469 {
470         unsigned int i;
471         struct rchan *chan;
472         char *tmpname;
473         int is_global = 0;
474
475         if (!base_filename)
476                 return NULL;
477
478         if (!(subbuf_size && n_subbufs))
479                 return NULL;
480
481         chan = kcalloc(1, sizeof(struct rchan), GFP_KERNEL);
482         if (!chan)
483                 return NULL;
484
485         chan->version = RELAYFS_CHANNEL_VERSION;
486         chan->n_subbufs = n_subbufs;
487         chan->subbuf_size = subbuf_size;
488         chan->alloc_size = FIX_SIZE(subbuf_size * n_subbufs);
489         setup_callbacks(chan, cb);
490         kref_init(&chan->kref);
491
492         tmpname = kmalloc(NAME_MAX + 1, GFP_KERNEL);
493         if (!tmpname)
494                 goto free_chan;
495
496         for_each_online_cpu(i) {
497                 sprintf(tmpname, "%s%d", base_filename, i);
498                 chan->buf[i] = relay_open_buf(chan, tmpname, parent,
499                                               &is_global);
500                 if (!chan->buf[i])
501                         goto free_bufs;
502
503                 chan->buf[i]->cpu = i;
504         }
505
506         kfree(tmpname);
507         return chan;
508
509 free_bufs:
510         for (i = 0; i < NR_CPUS; i++) {
511                 if (!chan->buf[i])
512                         break;
513                 relay_close_buf(chan->buf[i]);
514                 if (is_global)
515                         break;
516         }
517         kfree(tmpname);
518
519 free_chan:
520         kref_put(&chan->kref, relay_destroy_channel);
521         return NULL;
522 }
523 EXPORT_SYMBOL_GPL(relay_open);
524
525 /**
526  *      relay_switch_subbuf - switch to a new sub-buffer
527  *      @buf: channel buffer
528  *      @length: size of current event
529  *
530  *      Returns either the length passed in or 0 if full.
531  *
532  *      Performs sub-buffer-switch tasks such as invoking callbacks,
533  *      updating padding counts, waking up readers, etc.
534  */
535 size_t relay_switch_subbuf(struct rchan_buf *buf, size_t length)
536 {
537         void *old, *new;
538         size_t old_subbuf, new_subbuf;
539
540         if (unlikely(length > buf->chan->subbuf_size))
541                 goto toobig;
542
543         if (buf->offset != buf->chan->subbuf_size + 1) {
544                 buf->prev_padding = buf->chan->subbuf_size - buf->offset;
545                 old_subbuf = buf->subbufs_produced % buf->chan->n_subbufs;
546                 buf->padding[old_subbuf] = buf->prev_padding;
547                 buf->subbufs_produced++;
548                 buf->dentry->d_inode->i_size += buf->chan->subbuf_size -
549                         buf->padding[old_subbuf];
550                 smp_mb();
551                 if (waitqueue_active(&buf->read_wait)) {
552                         PREPARE_WORK(&buf->wake_readers, wakeup_readers, buf);
553                         schedule_delayed_work(&buf->wake_readers, 1);
554                 }
555         }
556
557         old = buf->data;
558         new_subbuf = buf->subbufs_produced % buf->chan->n_subbufs;
559         new = buf->start + new_subbuf * buf->chan->subbuf_size;
560         buf->offset = 0;
561         if (!buf->chan->cb->subbuf_start(buf, new, old, buf->prev_padding)) {
562                 buf->offset = buf->chan->subbuf_size + 1;
563                 return 0;
564         }
565         buf->data = new;
566         buf->padding[new_subbuf] = 0;
567
568         if (unlikely(length + buf->offset > buf->chan->subbuf_size))
569                 goto toobig;
570
571         return length;
572
573 toobig:
574         buf->chan->last_toobig = length;
575         return 0;
576 }
577 EXPORT_SYMBOL_GPL(relay_switch_subbuf);
578
579 /**
580  *      relay_subbufs_consumed - update the buffer's sub-buffers-consumed count
581  *      @chan: the channel
582  *      @cpu: the cpu associated with the channel buffer to update
583  *      @subbufs_consumed: number of sub-buffers to add to current buf's count
584  *
585  *      Adds to the channel buffer's consumed sub-buffer count.
586  *      subbufs_consumed should be the number of sub-buffers newly consumed,
587  *      not the total consumed.
588  *
589  *      NOTE: Kernel clients don't need to call this function if the channel
590  *      mode is 'overwrite'.
591  */
592 void relay_subbufs_consumed(struct rchan *chan,
593                             unsigned int cpu,
594                             size_t subbufs_consumed)
595 {
596         struct rchan_buf *buf;
597
598         if (!chan)
599                 return;
600
601         if (cpu >= NR_CPUS || !chan->buf[cpu])
602                 return;
603
604         buf = chan->buf[cpu];
605         buf->subbufs_consumed += subbufs_consumed;
606         if (buf->subbufs_consumed > buf->subbufs_produced)
607                 buf->subbufs_consumed = buf->subbufs_produced;
608 }
609 EXPORT_SYMBOL_GPL(relay_subbufs_consumed);
610
611 /**
612  *      relay_close - close the channel
613  *      @chan: the channel
614  *
615  *      Closes all channel buffers and frees the channel.
616  */
617 void relay_close(struct rchan *chan)
618 {
619         unsigned int i;
620         struct rchan_buf *prev = NULL;
621
622         if (!chan)
623                 return;
624
625         for (i = 0; i < NR_CPUS; i++) {
626                 if (!chan->buf[i] || chan->buf[i] == prev)
627                         break;
628                 relay_close_buf(chan->buf[i]);
629                 prev = chan->buf[i];
630         }
631
632         if (chan->last_toobig)
633                 printk(KERN_WARNING "relay: one or more items not logged "
634                        "[item size (%Zd) > sub-buffer size (%Zd)]\n",
635                        chan->last_toobig, chan->subbuf_size);
636
637         kref_put(&chan->kref, relay_destroy_channel);
638 }
639 EXPORT_SYMBOL_GPL(relay_close);
640
641 /**
642  *      relay_flush - close the channel
643  *      @chan: the channel
644  *
645  *      Flushes all channel buffers, i.e. forces buffer switch.
646  */
647 void relay_flush(struct rchan *chan)
648 {
649         unsigned int i;
650         struct rchan_buf *prev = NULL;
651
652         if (!chan)
653                 return;
654
655         for (i = 0; i < NR_CPUS; i++) {
656                 if (!chan->buf[i] || chan->buf[i] == prev)
657                         break;
658                 relay_switch_subbuf(chan->buf[i], 0);
659                 prev = chan->buf[i];
660         }
661 }
662 EXPORT_SYMBOL_GPL(relay_flush);
663
664 /**
665  *      relay_file_open - open file op for relay files
666  *      @inode: the inode
667  *      @filp: the file
668  *
669  *      Increments the channel buffer refcount.
670  */
671 static int relay_file_open(struct inode *inode, struct file *filp)
672 {
673         struct rchan_buf *buf = inode->i_private;
674         kref_get(&buf->kref);
675         filp->private_data = buf;
676
677         return 0;
678 }
679
680 /**
681  *      relay_file_mmap - mmap file op for relay files
682  *      @filp: the file
683  *      @vma: the vma describing what to map
684  *
685  *      Calls upon relay_mmap_buf to map the file into user space.
686  */
687 static int relay_file_mmap(struct file *filp, struct vm_area_struct *vma)
688 {
689         struct rchan_buf *buf = filp->private_data;
690         return relay_mmap_buf(buf, vma);
691 }
692
693 /**
694  *      relay_file_poll - poll file op for relay files
695  *      @filp: the file
696  *      @wait: poll table
697  *
698  *      Poll implemention.
699  */
700 static unsigned int relay_file_poll(struct file *filp, poll_table *wait)
701 {
702         unsigned int mask = 0;
703         struct rchan_buf *buf = filp->private_data;
704
705         if (buf->finalized)
706                 return POLLERR;
707
708         if (filp->f_mode & FMODE_READ) {
709                 poll_wait(filp, &buf->read_wait, wait);
710                 if (!relay_buf_empty(buf))
711                         mask |= POLLIN | POLLRDNORM;
712         }
713
714         return mask;
715 }
716
717 /**
718  *      relay_file_release - release file op for relay files
719  *      @inode: the inode
720  *      @filp: the file
721  *
722  *      Decrements the channel refcount, as the filesystem is
723  *      no longer using it.
724  */
725 static int relay_file_release(struct inode *inode, struct file *filp)
726 {
727         struct rchan_buf *buf = filp->private_data;
728         kref_put(&buf->kref, relay_remove_buf);
729
730         return 0;
731 }
732
733 /*
734  *      relay_file_read_consume - update the consumed count for the buffer
735  */
736 static void relay_file_read_consume(struct rchan_buf *buf,
737                                     size_t read_pos,
738                                     size_t bytes_consumed)
739 {
740         size_t subbuf_size = buf->chan->subbuf_size;
741         size_t n_subbufs = buf->chan->n_subbufs;
742         size_t read_subbuf;
743
744         if (buf->bytes_consumed + bytes_consumed > subbuf_size) {
745                 relay_subbufs_consumed(buf->chan, buf->cpu, 1);
746                 buf->bytes_consumed = 0;
747         }
748
749         buf->bytes_consumed += bytes_consumed;
750         read_subbuf = read_pos / buf->chan->subbuf_size;
751         if (buf->bytes_consumed + buf->padding[read_subbuf] == subbuf_size) {
752                 if ((read_subbuf == buf->subbufs_produced % n_subbufs) &&
753                     (buf->offset == subbuf_size))
754                         return;
755                 relay_subbufs_consumed(buf->chan, buf->cpu, 1);
756                 buf->bytes_consumed = 0;
757         }
758 }
759
760 /*
761  *      relay_file_read_avail - boolean, are there unconsumed bytes available?
762  */
763 static int relay_file_read_avail(struct rchan_buf *buf, size_t read_pos)
764 {
765         size_t subbuf_size = buf->chan->subbuf_size;
766         size_t n_subbufs = buf->chan->n_subbufs;
767         size_t produced = buf->subbufs_produced;
768         size_t consumed = buf->subbufs_consumed;
769
770         relay_file_read_consume(buf, read_pos, 0);
771
772         if (unlikely(buf->offset > subbuf_size)) {
773                 if (produced == consumed)
774                         return 0;
775                 return 1;
776         }
777
778         if (unlikely(produced - consumed >= n_subbufs)) {
779                 consumed = (produced / n_subbufs) * n_subbufs;
780                 buf->subbufs_consumed = consumed;
781         }
782         
783         produced = (produced % n_subbufs) * subbuf_size + buf->offset;
784         consumed = (consumed % n_subbufs) * subbuf_size + buf->bytes_consumed;
785
786         if (consumed > produced)
787                 produced += n_subbufs * subbuf_size;
788         
789         if (consumed == produced)
790                 return 0;
791
792         return 1;
793 }
794
795 /**
796  *      relay_file_read_subbuf_avail - return bytes available in sub-buffer
797  *      @read_pos: file read position
798  *      @buf: relay channel buffer
799  */
800 static size_t relay_file_read_subbuf_avail(size_t read_pos,
801                                            struct rchan_buf *buf)
802 {
803         size_t padding, avail = 0;
804         size_t read_subbuf, read_offset, write_subbuf, write_offset;
805         size_t subbuf_size = buf->chan->subbuf_size;
806
807         write_subbuf = (buf->data - buf->start) / subbuf_size;
808         write_offset = buf->offset > subbuf_size ? subbuf_size : buf->offset;
809         read_subbuf = read_pos / subbuf_size;
810         read_offset = read_pos % subbuf_size;
811         padding = buf->padding[read_subbuf];
812
813         if (read_subbuf == write_subbuf) {
814                 if (read_offset + padding < write_offset)
815                         avail = write_offset - (read_offset + padding);
816         } else
817                 avail = (subbuf_size - padding) - read_offset;
818
819         return avail;
820 }
821
822 /**
823  *      relay_file_read_start_pos - find the first available byte to read
824  *      @read_pos: file read position
825  *      @buf: relay channel buffer
826  *
827  *      If the read_pos is in the middle of padding, return the
828  *      position of the first actually available byte, otherwise
829  *      return the original value.
830  */
831 static size_t relay_file_read_start_pos(size_t read_pos,
832                                         struct rchan_buf *buf)
833 {
834         size_t read_subbuf, padding, padding_start, padding_end;
835         size_t subbuf_size = buf->chan->subbuf_size;
836         size_t n_subbufs = buf->chan->n_subbufs;
837
838         read_subbuf = read_pos / subbuf_size;
839         padding = buf->padding[read_subbuf];
840         padding_start = (read_subbuf + 1) * subbuf_size - padding;
841         padding_end = (read_subbuf + 1) * subbuf_size;
842         if (read_pos >= padding_start && read_pos < padding_end) {
843                 read_subbuf = (read_subbuf + 1) % n_subbufs;
844                 read_pos = read_subbuf * subbuf_size;
845         }
846
847         return read_pos;
848 }
849
850 /**
851  *      relay_file_read_end_pos - return the new read position
852  *      @read_pos: file read position
853  *      @buf: relay channel buffer
854  *      @count: number of bytes to be read
855  */
856 static size_t relay_file_read_end_pos(struct rchan_buf *buf,
857                                       size_t read_pos,
858                                       size_t count)
859 {
860         size_t read_subbuf, padding, end_pos;
861         size_t subbuf_size = buf->chan->subbuf_size;
862         size_t n_subbufs = buf->chan->n_subbufs;
863
864         read_subbuf = read_pos / subbuf_size;
865         padding = buf->padding[read_subbuf];
866         if (read_pos % subbuf_size + count + padding == subbuf_size)
867                 end_pos = (read_subbuf + 1) * subbuf_size;
868         else
869                 end_pos = read_pos + count;
870         if (end_pos >= subbuf_size * n_subbufs)
871                 end_pos = 0;
872
873         return end_pos;
874 }
875
876 /*
877  *      subbuf_read_actor - read up to one subbuf's worth of data
878  */
879 static int subbuf_read_actor(size_t read_start,
880                              struct rchan_buf *buf,
881                              size_t avail,
882                              read_descriptor_t *desc,
883                              read_actor_t actor)
884 {
885         void *from;
886         int ret = 0;
887
888         from = buf->start + read_start;
889         ret = avail;
890         if (copy_to_user(desc->arg.data, from, avail)) {
891                 desc->error = -EFAULT;
892                 ret = 0;
893         }
894         desc->arg.data += ret;
895         desc->written += ret;
896         desc->count -= ret;
897
898         return ret;
899 }
900
901 /*
902  *      subbuf_send_actor - send up to one subbuf's worth of data
903  */
904 static int subbuf_send_actor(size_t read_start,
905                              struct rchan_buf *buf,
906                              size_t avail,
907                              read_descriptor_t *desc,
908                              read_actor_t actor)
909 {
910         unsigned long pidx, poff;
911         unsigned int subbuf_pages;
912         int ret = 0;
913
914         subbuf_pages = buf->chan->alloc_size >> PAGE_SHIFT;
915         pidx = (read_start / PAGE_SIZE) % subbuf_pages;
916         poff = read_start & ~PAGE_MASK;
917         while (avail) {
918                 struct page *p = buf->page_array[pidx];
919                 unsigned int len;
920
921                 len = PAGE_SIZE - poff;
922                 if (len > avail)
923                         len = avail;
924
925                 len = actor(desc, p, poff, len);
926                 if (desc->error)
927                         break;
928
929                 avail -= len;
930                 ret += len;
931                 poff = 0;
932                 pidx = (pidx + 1) % subbuf_pages;
933         }
934
935         return ret;
936 }
937
938 typedef int (*subbuf_actor_t) (size_t read_start,
939                                struct rchan_buf *buf,
940                                size_t avail,
941                                read_descriptor_t *desc,
942                                read_actor_t actor);
943
944 /*
945  *      relay_file_read_subbufs - read count bytes, bridging subbuf boundaries
946  */
947 static inline ssize_t relay_file_read_subbufs(struct file *filp,
948                                               loff_t *ppos,
949                                               size_t count,
950                                               subbuf_actor_t subbuf_actor,
951                                               read_actor_t actor,
952                                               void *target)
953 {
954         struct rchan_buf *buf = filp->private_data;
955         size_t read_start, avail;
956         read_descriptor_t desc;
957         int ret;
958
959         if (!count)
960                 return 0;
961
962         desc.written = 0;
963         desc.count = count;
964         desc.arg.data = target;
965         desc.error = 0;
966
967         mutex_lock(&filp->f_dentry->d_inode->i_mutex);
968         do {
969                 if (!relay_file_read_avail(buf, *ppos))
970                         break;
971
972                 read_start = relay_file_read_start_pos(*ppos, buf);
973                 avail = relay_file_read_subbuf_avail(read_start, buf);
974                 if (!avail)
975                         break;
976
977                 avail = min(desc.count, avail);
978                 ret = subbuf_actor(read_start, buf, avail, &desc, actor);
979                 if (desc.error < 0)
980                         break;
981
982                 if (ret) {
983                         relay_file_read_consume(buf, read_start, ret);
984                         *ppos = relay_file_read_end_pos(buf, read_start, ret);
985                 }
986         } while (desc.count && ret);
987         mutex_unlock(&filp->f_dentry->d_inode->i_mutex);
988
989         return desc.written;
990 }
991
992 static ssize_t relay_file_read(struct file *filp,
993                                char __user *buffer,
994                                size_t count,
995                                loff_t *ppos)
996 {
997         return relay_file_read_subbufs(filp, ppos, count, subbuf_read_actor,
998                                        NULL, buffer);
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         return relay_file_read_subbufs(filp, ppos, count, subbuf_send_actor,
1008                                        actor, target);
1009 }
1010
1011 struct file_operations relay_file_operations = {
1012         .open           = relay_file_open,
1013         .poll           = relay_file_poll,
1014         .mmap           = relay_file_mmap,
1015         .read           = relay_file_read,
1016         .llseek         = no_llseek,
1017         .release        = relay_file_release,
1018         .sendfile       = relay_file_sendfile,
1019 };
1020 EXPORT_SYMBOL_GPL(relay_file_operations);