ef923f6de2e7c17660ce569760cc70c28ef9ac18
[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  * 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/module.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
25 /* list of open channels, for cpu hotplug */
26 static DEFINE_MUTEX(relay_channels_mutex);
27 static LIST_HEAD(relay_channels);
28
29 /*
30  * close() vm_op implementation for relay file mapping.
31  */
32 static void relay_file_mmap_close(struct vm_area_struct *vma)
33 {
34         struct rchan_buf *buf = vma->vm_private_data;
35         buf->chan->cb->buf_unmapped(buf, vma->vm_file);
36 }
37
38 /*
39  * nopage() vm_op implementation for relay file mapping.
40  */
41 static struct page *relay_buf_nopage(struct vm_area_struct *vma,
42                                      unsigned long address,
43                                      int *type)
44 {
45         struct page *page;
46         struct rchan_buf *buf = vma->vm_private_data;
47         unsigned long offset = address - vma->vm_start;
48
49         if (address > vma->vm_end)
50                 return NOPAGE_SIGBUS; /* Disallow mremap */
51         if (!buf)
52                 return NOPAGE_OOM;
53
54         page = vmalloc_to_page(buf->start + offset);
55         if (!page)
56                 return NOPAGE_OOM;
57         get_page(page);
58
59         if (type)
60                 *type = VM_FAULT_MINOR;
61
62         return page;
63 }
64
65 /*
66  * vm_ops for relay file mappings.
67  */
68 static struct vm_operations_struct relay_file_mmap_ops = {
69         .nopage = relay_buf_nopage,
70         .close = relay_file_mmap_close,
71 };
72
73 /**
74  *      relay_mmap_buf: - mmap channel buffer to process address space
75  *      @buf: relay channel buffer
76  *      @vma: vm_area_struct describing memory to be mapped
77  *
78  *      Returns 0 if ok, negative on error
79  *
80  *      Caller should already have grabbed mmap_sem.
81  */
82 int relay_mmap_buf(struct rchan_buf *buf, struct vm_area_struct *vma)
83 {
84         unsigned long length = vma->vm_end - vma->vm_start;
85         struct file *filp = vma->vm_file;
86
87         if (!buf)
88                 return -EBADF;
89
90         if (length != (unsigned long)buf->chan->alloc_size)
91                 return -EINVAL;
92
93         vma->vm_ops = &relay_file_mmap_ops;
94         vma->vm_private_data = buf;
95         buf->chan->cb->buf_mapped(buf, filp);
96
97         return 0;
98 }
99
100 /**
101  *      relay_alloc_buf - allocate a channel buffer
102  *      @buf: the buffer struct
103  *      @size: total size of the buffer
104  *
105  *      Returns a pointer to the resulting buffer, %NULL if unsuccessful. The
106  *      passed in size will get page aligned, if it isn't already.
107  */
108 static void *relay_alloc_buf(struct rchan_buf *buf, size_t *size)
109 {
110         void *mem;
111         unsigned int i, j, n_pages;
112
113         *size = PAGE_ALIGN(*size);
114         n_pages = *size >> PAGE_SHIFT;
115
116         buf->page_array = kcalloc(n_pages, sizeof(struct page *), GFP_KERNEL);
117         if (!buf->page_array)
118                 return NULL;
119
120         for (i = 0; i < n_pages; i++) {
121                 buf->page_array[i] = alloc_page(GFP_KERNEL);
122                 if (unlikely(!buf->page_array[i]))
123                         goto depopulate;
124         }
125         mem = vmap(buf->page_array, n_pages, VM_MAP, PAGE_KERNEL);
126         if (!mem)
127                 goto depopulate;
128
129         memset(mem, 0, *size);
130         buf->page_count = n_pages;
131         return mem;
132
133 depopulate:
134         for (j = 0; j < i; j++)
135                 __free_page(buf->page_array[j]);
136         kfree(buf->page_array);
137         return NULL;
138 }
139
140 /**
141  *      relay_create_buf - allocate and initialize a channel buffer
142  *      @chan: the relay channel
143  *
144  *      Returns channel buffer if successful, %NULL otherwise.
145  */
146 struct rchan_buf *relay_create_buf(struct rchan *chan)
147 {
148         struct rchan_buf *buf = kzalloc(sizeof(struct rchan_buf), GFP_KERNEL);
149         if (!buf)
150                 return NULL;
151
152         buf->padding = kmalloc(chan->n_subbufs * sizeof(size_t *), GFP_KERNEL);
153         if (!buf->padding)
154                 goto free_buf;
155
156         buf->start = relay_alloc_buf(buf, &chan->alloc_size);
157         if (!buf->start)
158                 goto free_buf;
159
160         buf->chan = chan;
161         kref_get(&buf->chan->kref);
162         return buf;
163
164 free_buf:
165         kfree(buf->padding);
166         kfree(buf);
167         return NULL;
168 }
169
170 /**
171  *      relay_destroy_channel - free the channel struct
172  *      @kref: target kernel reference that contains the relay channel
173  *
174  *      Should only be called from kref_put().
175  */
176 void relay_destroy_channel(struct kref *kref)
177 {
178         struct rchan *chan = container_of(kref, struct rchan, kref);
179         kfree(chan);
180 }
181
182 /**
183  *      relay_destroy_buf - destroy an rchan_buf struct and associated buffer
184  *      @buf: the buffer struct
185  */
186 void relay_destroy_buf(struct rchan_buf *buf)
187 {
188         struct rchan *chan = buf->chan;
189         unsigned int i;
190
191         if (likely(buf->start)) {
192                 vunmap(buf->start);
193                 for (i = 0; i < buf->page_count; i++)
194                         __free_page(buf->page_array[i]);
195                 kfree(buf->page_array);
196         }
197         chan->buf[buf->cpu] = NULL;
198         kfree(buf->padding);
199         kfree(buf);
200         kref_put(&chan->kref, relay_destroy_channel);
201 }
202
203 /**
204  *      relay_remove_buf - remove a channel buffer
205  *      @kref: target kernel reference that contains the relay buffer
206  *
207  *      Removes the file from the fileystem, which also frees the
208  *      rchan_buf_struct and the channel buffer.  Should only be called from
209  *      kref_put().
210  */
211 void relay_remove_buf(struct kref *kref)
212 {
213         struct rchan_buf *buf = container_of(kref, struct rchan_buf, kref);
214         buf->chan->cb->remove_buf_file(buf->dentry);
215         relay_destroy_buf(buf);
216 }
217
218 /**
219  *      relay_buf_empty - boolean, is the channel buffer empty?
220  *      @buf: channel buffer
221  *
222  *      Returns 1 if the buffer is empty, 0 otherwise.
223  */
224 int relay_buf_empty(struct rchan_buf *buf)
225 {
226         return (buf->subbufs_produced - buf->subbufs_consumed) ? 0 : 1;
227 }
228 EXPORT_SYMBOL_GPL(relay_buf_empty);
229
230 /**
231  *      relay_buf_full - boolean, is the channel buffer full?
232  *      @buf: channel buffer
233  *
234  *      Returns 1 if the buffer is full, 0 otherwise.
235  */
236 int relay_buf_full(struct rchan_buf *buf)
237 {
238         size_t ready = buf->subbufs_produced - buf->subbufs_consumed;
239         return (ready >= buf->chan->n_subbufs) ? 1 : 0;
240 }
241 EXPORT_SYMBOL_GPL(relay_buf_full);
242
243 /*
244  * High-level relay kernel API and associated functions.
245  */
246
247 /*
248  * rchan_callback implementations defining default channel behavior.  Used
249  * in place of corresponding NULL values in client callback struct.
250  */
251
252 /*
253  * subbuf_start() default callback.  Does nothing.
254  */
255 static int subbuf_start_default_callback (struct rchan_buf *buf,
256                                           void *subbuf,
257                                           void *prev_subbuf,
258                                           size_t prev_padding)
259 {
260         if (relay_buf_full(buf))
261                 return 0;
262
263         return 1;
264 }
265
266 /*
267  * buf_mapped() default callback.  Does nothing.
268  */
269 static void buf_mapped_default_callback(struct rchan_buf *buf,
270                                         struct file *filp)
271 {
272 }
273
274 /*
275  * buf_unmapped() default callback.  Does nothing.
276  */
277 static void buf_unmapped_default_callback(struct rchan_buf *buf,
278                                           struct file *filp)
279 {
280 }
281
282 /*
283  * create_buf_file_create() default callback.  Does nothing.
284  */
285 static struct dentry *create_buf_file_default_callback(const char *filename,
286                                                        struct dentry *parent,
287                                                        int mode,
288                                                        struct rchan_buf *buf,
289                                                        int *is_global)
290 {
291         return NULL;
292 }
293
294 /*
295  * remove_buf_file() default callback.  Does nothing.
296  */
297 static int remove_buf_file_default_callback(struct dentry *dentry)
298 {
299         return -EINVAL;
300 }
301
302 /* relay channel default callbacks */
303 static struct rchan_callbacks default_channel_callbacks = {
304         .subbuf_start = subbuf_start_default_callback,
305         .buf_mapped = buf_mapped_default_callback,
306         .buf_unmapped = buf_unmapped_default_callback,
307         .create_buf_file = create_buf_file_default_callback,
308         .remove_buf_file = remove_buf_file_default_callback,
309 };
310
311 /**
312  *      wakeup_readers - wake up readers waiting on a channel
313  *      @work: work struct that contains the the channel buffer
314  *
315  *      This is the work function used to defer reader waking.  The
316  *      reason waking is deferred is that calling directly from write
317  *      causes problems if you're writing from say the scheduler.
318  */
319 static void wakeup_readers(struct work_struct *work)
320 {
321         struct rchan_buf *buf =
322                 container_of(work, struct rchan_buf, wake_readers.work);
323         wake_up_interruptible(&buf->read_wait);
324 }
325
326 /**
327  *      __relay_reset - reset a channel buffer
328  *      @buf: the channel buffer
329  *      @init: 1 if this is a first-time initialization
330  *
331  *      See relay_reset for description of effect.
332  */
333 static void __relay_reset(struct rchan_buf *buf, unsigned int init)
334 {
335         size_t i;
336
337         if (init) {
338                 init_waitqueue_head(&buf->read_wait);
339                 kref_init(&buf->kref);
340                 INIT_DELAYED_WORK(&buf->wake_readers, NULL);
341         } else {
342                 cancel_delayed_work(&buf->wake_readers);
343                 flush_scheduled_work();
344         }
345
346         buf->subbufs_produced = 0;
347         buf->subbufs_consumed = 0;
348         buf->bytes_consumed = 0;
349         buf->finalized = 0;
350         buf->data = buf->start;
351         buf->offset = 0;
352
353         for (i = 0; i < buf->chan->n_subbufs; i++)
354                 buf->padding[i] = 0;
355
356         buf->chan->cb->subbuf_start(buf, buf->data, NULL, 0);
357 }
358
359 /**
360  *      relay_reset - reset the channel
361  *      @chan: the channel
362  *
363  *      This has the effect of erasing all data from all channel buffers
364  *      and restarting the channel in its initial state.  The buffers
365  *      are not freed, so any mappings are still in effect.
366  *
367  *      NOTE: Care should be taken that the channel isn't actually
368  *      being used by anything when this call is made.
369  */
370 void relay_reset(struct rchan *chan)
371 {
372         unsigned int i;
373
374         if (!chan)
375                 return;
376
377         if (chan->is_global && chan->buf[0]) {
378                 __relay_reset(chan->buf[0], 0);
379                 return;
380         }
381
382         mutex_lock(&relay_channels_mutex);
383         for_each_online_cpu(i)
384                 if (chan->buf[i])
385                         __relay_reset(chan->buf[i], 0);
386         mutex_unlock(&relay_channels_mutex);
387 }
388 EXPORT_SYMBOL_GPL(relay_reset);
389
390 /*
391  *      relay_open_buf - create a new relay channel buffer
392  *
393  *      used by relay_open() and CPU hotplug.
394  */
395 static struct rchan_buf *relay_open_buf(struct rchan *chan, unsigned int cpu)
396 {
397         struct rchan_buf *buf = NULL;
398         struct dentry *dentry;
399         char *tmpname;
400
401         if (chan->is_global)
402                 return chan->buf[0];
403
404         tmpname = kzalloc(NAME_MAX + 1, GFP_KERNEL);
405         if (!tmpname)
406                 goto end;
407         snprintf(tmpname, NAME_MAX, "%s%d", chan->base_filename, cpu);
408
409         buf = relay_create_buf(chan);
410         if (!buf)
411                 goto free_name;
412
413         buf->cpu = cpu;
414         __relay_reset(buf, 1);
415
416         /* Create file in fs */
417         dentry = chan->cb->create_buf_file(tmpname, chan->parent, S_IRUSR,
418                                            buf, &chan->is_global);
419         if (!dentry)
420                 goto free_buf;
421
422         buf->dentry = dentry;
423
424         if(chan->is_global) {
425                 chan->buf[0] = buf;
426                 buf->cpu = 0;
427         }
428
429         goto free_name;
430
431 free_buf:
432         relay_destroy_buf(buf);
433 free_name:
434         kfree(tmpname);
435 end:
436         return buf;
437 }
438
439 /**
440  *      relay_close_buf - close a channel buffer
441  *      @buf: channel buffer
442  *
443  *      Marks the buffer finalized and restores the default callbacks.
444  *      The channel buffer and channel buffer data structure are then freed
445  *      automatically when the last reference is given up.
446  */
447 static void relay_close_buf(struct rchan_buf *buf)
448 {
449         buf->finalized = 1;
450         cancel_delayed_work(&buf->wake_readers);
451         flush_scheduled_work();
452         kref_put(&buf->kref, relay_remove_buf);
453 }
454
455 static void setup_callbacks(struct rchan *chan,
456                                    struct rchan_callbacks *cb)
457 {
458         if (!cb) {
459                 chan->cb = &default_channel_callbacks;
460                 return;
461         }
462
463         if (!cb->subbuf_start)
464                 cb->subbuf_start = subbuf_start_default_callback;
465         if (!cb->buf_mapped)
466                 cb->buf_mapped = buf_mapped_default_callback;
467         if (!cb->buf_unmapped)
468                 cb->buf_unmapped = buf_unmapped_default_callback;
469         if (!cb->create_buf_file)
470                 cb->create_buf_file = create_buf_file_default_callback;
471         if (!cb->remove_buf_file)
472                 cb->remove_buf_file = remove_buf_file_default_callback;
473         chan->cb = cb;
474 }
475
476 /**
477  *
478  *      relay_hotcpu_callback - CPU hotplug callback
479  *      @nb: notifier block
480  *      @action: hotplug action to take
481  *      @hcpu: CPU number
482  *
483  *      Returns the success/failure of the operation. (NOTIFY_OK, NOTIFY_BAD)
484  */
485 static int __cpuinit relay_hotcpu_callback(struct notifier_block *nb,
486                                 unsigned long action,
487                                 void *hcpu)
488 {
489         unsigned int hotcpu = (unsigned long)hcpu;
490         struct rchan *chan;
491
492         switch(action) {
493         case CPU_UP_PREPARE:
494                 mutex_lock(&relay_channels_mutex);
495                 list_for_each_entry(chan, &relay_channels, list) {
496                         if (chan->buf[hotcpu])
497                                 continue;
498                         chan->buf[hotcpu] = relay_open_buf(chan, hotcpu);
499                         if(!chan->buf[hotcpu]) {
500                                 printk(KERN_ERR
501                                         "relay_hotcpu_callback: cpu %d buffer "
502                                         "creation failed\n", hotcpu);
503                                 mutex_unlock(&relay_channels_mutex);
504                                 return NOTIFY_BAD;
505                         }
506                 }
507                 mutex_unlock(&relay_channels_mutex);
508                 break;
509         case CPU_DEAD:
510                 /* No need to flush the cpu : will be flushed upon
511                  * final relay_flush() call. */
512                 break;
513         }
514         return NOTIFY_OK;
515 }
516
517 /**
518  *      relay_open - create a new relay channel
519  *      @base_filename: base name of files to create
520  *      @parent: dentry of parent directory, %NULL for root directory
521  *      @subbuf_size: size of sub-buffers
522  *      @n_subbufs: number of sub-buffers
523  *      @cb: client callback functions
524  *      @private_data: user-defined data
525  *
526  *      Returns channel pointer if successful, %NULL otherwise.
527  *
528  *      Creates a channel buffer for each cpu using the sizes and
529  *      attributes specified.  The created channel buffer files
530  *      will be named base_filename0...base_filenameN-1.  File
531  *      permissions will be S_IRUSR.
532  */
533 struct rchan *relay_open(const char *base_filename,
534                          struct dentry *parent,
535                          size_t subbuf_size,
536                          size_t n_subbufs,
537                          struct rchan_callbacks *cb,
538                          void *private_data)
539 {
540         unsigned int i;
541         struct rchan *chan;
542         if (!base_filename)
543                 return NULL;
544
545         if (!(subbuf_size && n_subbufs))
546                 return NULL;
547
548         chan = kzalloc(sizeof(struct rchan), GFP_KERNEL);
549         if (!chan)
550                 return NULL;
551
552         chan->version = RELAYFS_CHANNEL_VERSION;
553         chan->n_subbufs = n_subbufs;
554         chan->subbuf_size = subbuf_size;
555         chan->alloc_size = FIX_SIZE(subbuf_size * n_subbufs);
556         chan->parent = parent;
557         chan->private_data = private_data;
558         strlcpy(chan->base_filename, base_filename, NAME_MAX);
559         setup_callbacks(chan, cb);
560         kref_init(&chan->kref);
561
562         mutex_lock(&relay_channels_mutex);
563         for_each_online_cpu(i) {
564                 chan->buf[i] = relay_open_buf(chan, i);
565                 if (!chan->buf[i])
566                         goto free_bufs;
567         }
568         list_add(&chan->list, &relay_channels);
569         mutex_unlock(&relay_channels_mutex);
570
571         return chan;
572
573 free_bufs:
574         for_each_online_cpu(i) {
575                 if (!chan->buf[i])
576                         break;
577                 relay_close_buf(chan->buf[i]);
578         }
579
580         kref_put(&chan->kref, relay_destroy_channel);
581         mutex_unlock(&relay_channels_mutex);
582         return NULL;
583 }
584 EXPORT_SYMBOL_GPL(relay_open);
585
586 /**
587  *      relay_switch_subbuf - switch to a new sub-buffer
588  *      @buf: channel buffer
589  *      @length: size of current event
590  *
591  *      Returns either the length passed in or 0 if full.
592  *
593  *      Performs sub-buffer-switch tasks such as invoking callbacks,
594  *      updating padding counts, waking up readers, etc.
595  */
596 size_t relay_switch_subbuf(struct rchan_buf *buf, size_t length)
597 {
598         void *old, *new;
599         size_t old_subbuf, new_subbuf;
600
601         if (unlikely(length > buf->chan->subbuf_size))
602                 goto toobig;
603
604         if (buf->offset != buf->chan->subbuf_size + 1) {
605                 buf->prev_padding = buf->chan->subbuf_size - buf->offset;
606                 old_subbuf = buf->subbufs_produced % buf->chan->n_subbufs;
607                 buf->padding[old_subbuf] = buf->prev_padding;
608                 buf->subbufs_produced++;
609                 buf->dentry->d_inode->i_size += buf->chan->subbuf_size -
610                         buf->padding[old_subbuf];
611                 smp_mb();
612                 if (waitqueue_active(&buf->read_wait)) {
613                         PREPARE_DELAYED_WORK(&buf->wake_readers,
614                                              wakeup_readers);
615                         schedule_delayed_work(&buf->wake_readers, 1);
616                 }
617         }
618
619         old = buf->data;
620         new_subbuf = buf->subbufs_produced % buf->chan->n_subbufs;
621         new = buf->start + new_subbuf * buf->chan->subbuf_size;
622         buf->offset = 0;
623         if (!buf->chan->cb->subbuf_start(buf, new, old, buf->prev_padding)) {
624                 buf->offset = buf->chan->subbuf_size + 1;
625                 return 0;
626         }
627         buf->data = new;
628         buf->padding[new_subbuf] = 0;
629
630         if (unlikely(length + buf->offset > buf->chan->subbuf_size))
631                 goto toobig;
632
633         return length;
634
635 toobig:
636         buf->chan->last_toobig = length;
637         return 0;
638 }
639 EXPORT_SYMBOL_GPL(relay_switch_subbuf);
640
641 /**
642  *      relay_subbufs_consumed - update the buffer's sub-buffers-consumed count
643  *      @chan: the channel
644  *      @cpu: the cpu associated with the channel buffer to update
645  *      @subbufs_consumed: number of sub-buffers to add to current buf's count
646  *
647  *      Adds to the channel buffer's consumed sub-buffer count.
648  *      subbufs_consumed should be the number of sub-buffers newly consumed,
649  *      not the total consumed.
650  *
651  *      NOTE: Kernel clients don't need to call this function if the channel
652  *      mode is 'overwrite'.
653  */
654 void relay_subbufs_consumed(struct rchan *chan,
655                             unsigned int cpu,
656                             size_t subbufs_consumed)
657 {
658         struct rchan_buf *buf;
659
660         if (!chan)
661                 return;
662
663         if (cpu >= NR_CPUS || !chan->buf[cpu])
664                 return;
665
666         buf = chan->buf[cpu];
667         buf->subbufs_consumed += subbufs_consumed;
668         if (buf->subbufs_consumed > buf->subbufs_produced)
669                 buf->subbufs_consumed = buf->subbufs_produced;
670 }
671 EXPORT_SYMBOL_GPL(relay_subbufs_consumed);
672
673 /**
674  *      relay_close - close the channel
675  *      @chan: the channel
676  *
677  *      Closes all channel buffers and frees the channel.
678  */
679 void relay_close(struct rchan *chan)
680 {
681         unsigned int i;
682
683         if (!chan)
684                 return;
685
686         mutex_lock(&relay_channels_mutex);
687         if (chan->is_global && chan->buf[0])
688                 relay_close_buf(chan->buf[0]);
689         else
690                 for_each_possible_cpu(i)
691                         if (chan->buf[i])
692                                 relay_close_buf(chan->buf[i]);
693
694         if (chan->last_toobig)
695                 printk(KERN_WARNING "relay: one or more items not logged "
696                        "[item size (%Zd) > sub-buffer size (%Zd)]\n",
697                        chan->last_toobig, chan->subbuf_size);
698
699         list_del(&chan->list);
700         kref_put(&chan->kref, relay_destroy_channel);
701         mutex_unlock(&relay_channels_mutex);
702 }
703 EXPORT_SYMBOL_GPL(relay_close);
704
705 /**
706  *      relay_flush - close the channel
707  *      @chan: the channel
708  *
709  *      Flushes all channel buffers, i.e. forces buffer switch.
710  */
711 void relay_flush(struct rchan *chan)
712 {
713         unsigned int i;
714
715         if (!chan)
716                 return;
717
718         if (chan->is_global && chan->buf[0]) {
719                 relay_switch_subbuf(chan->buf[0], 0);
720                 return;
721         }
722
723         mutex_lock(&relay_channels_mutex);
724         for_each_possible_cpu(i)
725                 if (chan->buf[i])
726                         relay_switch_subbuf(chan->buf[i], 0);
727         mutex_unlock(&relay_channels_mutex);
728 }
729 EXPORT_SYMBOL_GPL(relay_flush);
730
731 /**
732  *      relay_file_open - open file op for relay files
733  *      @inode: the inode
734  *      @filp: the file
735  *
736  *      Increments the channel buffer refcount.
737  */
738 static int relay_file_open(struct inode *inode, struct file *filp)
739 {
740         struct rchan_buf *buf = inode->i_private;
741         kref_get(&buf->kref);
742         filp->private_data = buf;
743
744         return 0;
745 }
746
747 /**
748  *      relay_file_mmap - mmap file op for relay files
749  *      @filp: the file
750  *      @vma: the vma describing what to map
751  *
752  *      Calls upon relay_mmap_buf to map the file into user space.
753  */
754 static int relay_file_mmap(struct file *filp, struct vm_area_struct *vma)
755 {
756         struct rchan_buf *buf = filp->private_data;
757         return relay_mmap_buf(buf, vma);
758 }
759
760 /**
761  *      relay_file_poll - poll file op for relay files
762  *      @filp: the file
763  *      @wait: poll table
764  *
765  *      Poll implemention.
766  */
767 static unsigned int relay_file_poll(struct file *filp, poll_table *wait)
768 {
769         unsigned int mask = 0;
770         struct rchan_buf *buf = filp->private_data;
771
772         if (buf->finalized)
773                 return POLLERR;
774
775         if (filp->f_mode & FMODE_READ) {
776                 poll_wait(filp, &buf->read_wait, wait);
777                 if (!relay_buf_empty(buf))
778                         mask |= POLLIN | POLLRDNORM;
779         }
780
781         return mask;
782 }
783
784 /**
785  *      relay_file_release - release file op for relay files
786  *      @inode: the inode
787  *      @filp: the file
788  *
789  *      Decrements the channel refcount, as the filesystem is
790  *      no longer using it.
791  */
792 static int relay_file_release(struct inode *inode, struct file *filp)
793 {
794         struct rchan_buf *buf = filp->private_data;
795         kref_put(&buf->kref, relay_remove_buf);
796
797         return 0;
798 }
799
800 /*
801  *      relay_file_read_consume - update the consumed count for the buffer
802  */
803 static void relay_file_read_consume(struct rchan_buf *buf,
804                                     size_t read_pos,
805                                     size_t bytes_consumed)
806 {
807         size_t subbuf_size = buf->chan->subbuf_size;
808         size_t n_subbufs = buf->chan->n_subbufs;
809         size_t read_subbuf;
810
811         if (buf->bytes_consumed + bytes_consumed > subbuf_size) {
812                 relay_subbufs_consumed(buf->chan, buf->cpu, 1);
813                 buf->bytes_consumed = 0;
814         }
815
816         buf->bytes_consumed += bytes_consumed;
817         read_subbuf = read_pos / buf->chan->subbuf_size;
818         if (buf->bytes_consumed + buf->padding[read_subbuf] == subbuf_size) {
819                 if ((read_subbuf == buf->subbufs_produced % n_subbufs) &&
820                     (buf->offset == subbuf_size))
821                         return;
822                 relay_subbufs_consumed(buf->chan, buf->cpu, 1);
823                 buf->bytes_consumed = 0;
824         }
825 }
826
827 /*
828  *      relay_file_read_avail - boolean, are there unconsumed bytes available?
829  */
830 static int relay_file_read_avail(struct rchan_buf *buf, size_t read_pos)
831 {
832         size_t subbuf_size = buf->chan->subbuf_size;
833         size_t n_subbufs = buf->chan->n_subbufs;
834         size_t produced = buf->subbufs_produced;
835         size_t consumed = buf->subbufs_consumed;
836
837         relay_file_read_consume(buf, read_pos, 0);
838
839         if (unlikely(buf->offset > subbuf_size)) {
840                 if (produced == consumed)
841                         return 0;
842                 return 1;
843         }
844
845         if (unlikely(produced - consumed >= n_subbufs)) {
846                 consumed = (produced / n_subbufs) * n_subbufs;
847                 buf->subbufs_consumed = consumed;
848         }
849         
850         produced = (produced % n_subbufs) * subbuf_size + buf->offset;
851         consumed = (consumed % n_subbufs) * subbuf_size + buf->bytes_consumed;
852
853         if (consumed > produced)
854                 produced += n_subbufs * subbuf_size;
855         
856         if (consumed == produced)
857                 return 0;
858
859         return 1;
860 }
861
862 /**
863  *      relay_file_read_subbuf_avail - return bytes available in sub-buffer
864  *      @read_pos: file read position
865  *      @buf: relay channel buffer
866  */
867 static size_t relay_file_read_subbuf_avail(size_t read_pos,
868                                            struct rchan_buf *buf)
869 {
870         size_t padding, avail = 0;
871         size_t read_subbuf, read_offset, write_subbuf, write_offset;
872         size_t subbuf_size = buf->chan->subbuf_size;
873
874         write_subbuf = (buf->data - buf->start) / subbuf_size;
875         write_offset = buf->offset > subbuf_size ? subbuf_size : buf->offset;
876         read_subbuf = read_pos / subbuf_size;
877         read_offset = read_pos % subbuf_size;
878         padding = buf->padding[read_subbuf];
879
880         if (read_subbuf == write_subbuf) {
881                 if (read_offset + padding < write_offset)
882                         avail = write_offset - (read_offset + padding);
883         } else
884                 avail = (subbuf_size - padding) - read_offset;
885
886         return avail;
887 }
888
889 /**
890  *      relay_file_read_start_pos - find the first available byte to read
891  *      @read_pos: file read position
892  *      @buf: relay channel buffer
893  *
894  *      If the read_pos is in the middle of padding, return the
895  *      position of the first actually available byte, otherwise
896  *      return the original value.
897  */
898 static size_t relay_file_read_start_pos(size_t read_pos,
899                                         struct rchan_buf *buf)
900 {
901         size_t read_subbuf, padding, padding_start, padding_end;
902         size_t subbuf_size = buf->chan->subbuf_size;
903         size_t n_subbufs = buf->chan->n_subbufs;
904
905         read_subbuf = read_pos / subbuf_size;
906         padding = buf->padding[read_subbuf];
907         padding_start = (read_subbuf + 1) * subbuf_size - padding;
908         padding_end = (read_subbuf + 1) * subbuf_size;
909         if (read_pos >= padding_start && read_pos < padding_end) {
910                 read_subbuf = (read_subbuf + 1) % n_subbufs;
911                 read_pos = read_subbuf * subbuf_size;
912         }
913
914         return read_pos;
915 }
916
917 /**
918  *      relay_file_read_end_pos - return the new read position
919  *      @read_pos: file read position
920  *      @buf: relay channel buffer
921  *      @count: number of bytes to be read
922  */
923 static size_t relay_file_read_end_pos(struct rchan_buf *buf,
924                                       size_t read_pos,
925                                       size_t count)
926 {
927         size_t read_subbuf, padding, end_pos;
928         size_t subbuf_size = buf->chan->subbuf_size;
929         size_t n_subbufs = buf->chan->n_subbufs;
930
931         read_subbuf = read_pos / subbuf_size;
932         padding = buf->padding[read_subbuf];
933         if (read_pos % subbuf_size + count + padding == subbuf_size)
934                 end_pos = (read_subbuf + 1) * subbuf_size;
935         else
936                 end_pos = read_pos + count;
937         if (end_pos >= subbuf_size * n_subbufs)
938                 end_pos = 0;
939
940         return end_pos;
941 }
942
943 /*
944  *      subbuf_read_actor - read up to one subbuf's worth of data
945  */
946 static int subbuf_read_actor(size_t read_start,
947                              struct rchan_buf *buf,
948                              size_t avail,
949                              read_descriptor_t *desc,
950                              read_actor_t actor)
951 {
952         void *from;
953         int ret = 0;
954
955         from = buf->start + read_start;
956         ret = avail;
957         if (copy_to_user(desc->arg.buf, from, avail)) {
958                 desc->error = -EFAULT;
959                 ret = 0;
960         }
961         desc->arg.data += ret;
962         desc->written += ret;
963         desc->count -= ret;
964
965         return ret;
966 }
967
968 /*
969  *      subbuf_send_actor - send up to one subbuf's worth of data
970  */
971 static int subbuf_send_actor(size_t read_start,
972                              struct rchan_buf *buf,
973                              size_t avail,
974                              read_descriptor_t *desc,
975                              read_actor_t actor)
976 {
977         unsigned long pidx, poff;
978         unsigned int subbuf_pages;
979         int ret = 0;
980
981         subbuf_pages = buf->chan->alloc_size >> PAGE_SHIFT;
982         pidx = (read_start / PAGE_SIZE) % subbuf_pages;
983         poff = read_start & ~PAGE_MASK;
984         while (avail) {
985                 struct page *p = buf->page_array[pidx];
986                 unsigned int len;
987
988                 len = PAGE_SIZE - poff;
989                 if (len > avail)
990                         len = avail;
991
992                 len = actor(desc, p, poff, len);
993                 if (desc->error)
994                         break;
995
996                 avail -= len;
997                 ret += len;
998                 poff = 0;
999                 pidx = (pidx + 1) % subbuf_pages;
1000         }
1001
1002         return ret;
1003 }
1004
1005 typedef int (*subbuf_actor_t) (size_t read_start,
1006                                struct rchan_buf *buf,
1007                                size_t avail,
1008                                read_descriptor_t *desc,
1009                                read_actor_t actor);
1010
1011 /*
1012  *      relay_file_read_subbufs - read count bytes, bridging subbuf boundaries
1013  */
1014 static ssize_t relay_file_read_subbufs(struct file *filp, loff_t *ppos,
1015                                         subbuf_actor_t subbuf_actor,
1016                                         read_actor_t actor,
1017                                         read_descriptor_t *desc)
1018 {
1019         struct rchan_buf *buf = filp->private_data;
1020         size_t read_start, avail;
1021         int ret;
1022
1023         if (!desc->count)
1024                 return 0;
1025
1026         mutex_lock(&filp->f_path.dentry->d_inode->i_mutex);
1027         do {
1028                 if (!relay_file_read_avail(buf, *ppos))
1029                         break;
1030
1031                 read_start = relay_file_read_start_pos(*ppos, buf);
1032                 avail = relay_file_read_subbuf_avail(read_start, buf);
1033                 if (!avail)
1034                         break;
1035
1036                 avail = min(desc->count, avail);
1037                 ret = subbuf_actor(read_start, buf, avail, desc, actor);
1038                 if (desc->error < 0)
1039                         break;
1040
1041                 if (ret) {
1042                         relay_file_read_consume(buf, read_start, ret);
1043                         *ppos = relay_file_read_end_pos(buf, read_start, ret);
1044                 }
1045         } while (desc->count && ret);
1046         mutex_unlock(&filp->f_path.dentry->d_inode->i_mutex);
1047
1048         return desc->written;
1049 }
1050
1051 static ssize_t relay_file_read(struct file *filp,
1052                                char __user *buffer,
1053                                size_t count,
1054                                loff_t *ppos)
1055 {
1056         read_descriptor_t desc;
1057         desc.written = 0;
1058         desc.count = count;
1059         desc.arg.buf = buffer;
1060         desc.error = 0;
1061         return relay_file_read_subbufs(filp, ppos, subbuf_read_actor,
1062                                        NULL, &desc);
1063 }
1064
1065 static ssize_t relay_file_sendfile(struct file *filp,
1066                                    loff_t *ppos,
1067                                    size_t count,
1068                                    read_actor_t actor,
1069                                    void *target)
1070 {
1071         read_descriptor_t desc;
1072         desc.written = 0;
1073         desc.count = count;
1074         desc.arg.data = target;
1075         desc.error = 0;
1076         return relay_file_read_subbufs(filp, ppos, subbuf_send_actor,
1077                                        actor, &desc);
1078 }
1079
1080 const struct file_operations relay_file_operations = {
1081         .open           = relay_file_open,
1082         .poll           = relay_file_poll,
1083         .mmap           = relay_file_mmap,
1084         .read           = relay_file_read,
1085         .llseek         = no_llseek,
1086         .release        = relay_file_release,
1087         .sendfile       = relay_file_sendfile,
1088 };
1089 EXPORT_SYMBOL_GPL(relay_file_operations);
1090
1091 static __init int relay_init(void)
1092 {
1093
1094         hotcpu_notifier(relay_hotcpu_callback, 0);
1095         return 0;
1096 }
1097
1098 module_init(relay_init);