Root/kernel/relay.c

1/*
2 * Public API and common code for kernel->userspace relay file support.
3 *
4 * See Documentation/filesystems/relay.txt for an overview.
5 *
6 * Copyright (C) 2002-2005 - Tom Zanussi (zanussi@us.ibm.com), IBM Corp
7 * Copyright (C) 1999-2005 - Karim Yaghmour (karim@opersys.com)
8 *
9 * Moved to kernel/relay.c by Paul Mundt, 2006.
10 * November 2006 - CPU hotplug support by Mathieu Desnoyers
11 * (mathieu.desnoyers@polymtl.ca)
12 *
13 * This file is released under the GPL.
14 */
15#include <linux/errno.h>
16#include <linux/stddef.h>
17#include <linux/slab.h>
18#include <linux/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#include <linux/splice.h>
25
26/* list of open channels, for cpu hotplug */
27static DEFINE_MUTEX(relay_channels_mutex);
28static LIST_HEAD(relay_channels);
29
30/*
31 * close() vm_op implementation for relay file mapping.
32 */
33static void relay_file_mmap_close(struct vm_area_struct *vma)
34{
35    struct rchan_buf *buf = vma->vm_private_data;
36    buf->chan->cb->buf_unmapped(buf, vma->vm_file);
37}
38
39/*
40 * fault() vm_op implementation for relay file mapping.
41 */
42static int relay_buf_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
43{
44    struct page *page;
45    struct rchan_buf *buf = vma->vm_private_data;
46    pgoff_t pgoff = vmf->pgoff;
47
48    if (!buf)
49        return VM_FAULT_OOM;
50
51    page = vmalloc_to_page(buf->start + (pgoff << PAGE_SHIFT));
52    if (!page)
53        return VM_FAULT_SIGBUS;
54    get_page(page);
55    vmf->page = page;
56
57    return 0;
58}
59
60/*
61 * vm_ops for relay file mappings.
62 */
63static const struct vm_operations_struct relay_file_mmap_ops = {
64    .fault = relay_buf_fault,
65    .close = relay_file_mmap_close,
66};
67
68/*
69 * allocate an array of pointers of struct page
70 */
71static struct page **relay_alloc_page_array(unsigned int n_pages)
72{
73    struct page **array;
74    size_t pa_size = n_pages * sizeof(struct page *);
75
76    if (pa_size > PAGE_SIZE) {
77        array = vmalloc(pa_size);
78        if (array)
79            memset(array, 0, pa_size);
80    } else {
81        array = kzalloc(pa_size, GFP_KERNEL);
82    }
83    return array;
84}
85
86/*
87 * free an array of pointers of struct page
88 */
89static void relay_free_page_array(struct page **array)
90{
91    if (is_vmalloc_addr(array))
92        vfree(array);
93    else
94        kfree(array);
95}
96
97/**
98 * relay_mmap_buf: - mmap channel buffer to process address space
99 * @buf: relay channel buffer
100 * @vma: vm_area_struct describing memory to be mapped
101 *
102 * Returns 0 if ok, negative on error
103 *
104 * Caller should already have grabbed mmap_sem.
105 */
106static int relay_mmap_buf(struct rchan_buf *buf, struct vm_area_struct *vma)
107{
108    unsigned long length = vma->vm_end - vma->vm_start;
109    struct file *filp = vma->vm_file;
110
111    if (!buf)
112        return -EBADF;
113
114    if (length != (unsigned long)buf->chan->alloc_size)
115        return -EINVAL;
116
117    vma->vm_ops = &relay_file_mmap_ops;
118    vma->vm_flags |= VM_DONTEXPAND;
119    vma->vm_private_data = buf;
120    buf->chan->cb->buf_mapped(buf, filp);
121
122    return 0;
123}
124
125/**
126 * relay_alloc_buf - allocate a channel buffer
127 * @buf: the buffer struct
128 * @size: total size of the buffer
129 *
130 * Returns a pointer to the resulting buffer, %NULL if unsuccessful. The
131 * passed in size will get page aligned, if it isn't already.
132 */
133static void *relay_alloc_buf(struct rchan_buf *buf, size_t *size)
134{
135    void *mem;
136    unsigned int i, j, n_pages;
137
138    *size = PAGE_ALIGN(*size);
139    n_pages = *size >> PAGE_SHIFT;
140
141    buf->page_array = relay_alloc_page_array(n_pages);
142    if (!buf->page_array)
143        return NULL;
144
145    for (i = 0; i < n_pages; i++) {
146        buf->page_array[i] = alloc_page(GFP_KERNEL);
147        if (unlikely(!buf->page_array[i]))
148            goto depopulate;
149        set_page_private(buf->page_array[i], (unsigned long)buf);
150    }
151    mem = vmap(buf->page_array, n_pages, VM_MAP, PAGE_KERNEL);
152    if (!mem)
153        goto depopulate;
154
155    memset(mem, 0, *size);
156    buf->page_count = n_pages;
157    return mem;
158
159depopulate:
160    for (j = 0; j < i; j++)
161        __free_page(buf->page_array[j]);
162    relay_free_page_array(buf->page_array);
163    return NULL;
164}
165
166/**
167 * relay_create_buf - allocate and initialize a channel buffer
168 * @chan: the relay channel
169 *
170 * Returns channel buffer if successful, %NULL otherwise.
171 */
172static struct rchan_buf *relay_create_buf(struct rchan *chan)
173{
174    struct rchan_buf *buf = kzalloc(sizeof(struct rchan_buf), GFP_KERNEL);
175    if (!buf)
176        return NULL;
177
178    buf->padding = kmalloc(chan->n_subbufs * sizeof(size_t *), GFP_KERNEL);
179    if (!buf->padding)
180        goto free_buf;
181
182    buf->start = relay_alloc_buf(buf, &chan->alloc_size);
183    if (!buf->start)
184        goto free_buf;
185
186    buf->chan = chan;
187    kref_get(&buf->chan->kref);
188    return buf;
189
190free_buf:
191    kfree(buf->padding);
192    kfree(buf);
193    return NULL;
194}
195
196/**
197 * relay_destroy_channel - free the channel struct
198 * @kref: target kernel reference that contains the relay channel
199 *
200 * Should only be called from kref_put().
201 */
202static void relay_destroy_channel(struct kref *kref)
203{
204    struct rchan *chan = container_of(kref, struct rchan, kref);
205    kfree(chan);
206}
207
208/**
209 * relay_destroy_buf - destroy an rchan_buf struct and associated buffer
210 * @buf: the buffer struct
211 */
212static void relay_destroy_buf(struct rchan_buf *buf)
213{
214    struct rchan *chan = buf->chan;
215    unsigned int i;
216
217    if (likely(buf->start)) {
218        vunmap(buf->start);
219        for (i = 0; i < buf->page_count; i++)
220            __free_page(buf->page_array[i]);
221        relay_free_page_array(buf->page_array);
222    }
223    chan->buf[buf->cpu] = NULL;
224    kfree(buf->padding);
225    kfree(buf);
226    kref_put(&chan->kref, relay_destroy_channel);
227}
228
229/**
230 * relay_remove_buf - remove a channel buffer
231 * @kref: target kernel reference that contains the relay buffer
232 *
233 * Removes the file from the fileystem, which also frees the
234 * rchan_buf_struct and the channel buffer. Should only be called from
235 * kref_put().
236 */
237static void relay_remove_buf(struct kref *kref)
238{
239    struct rchan_buf *buf = container_of(kref, struct rchan_buf, kref);
240    buf->chan->cb->remove_buf_file(buf->dentry);
241    relay_destroy_buf(buf);
242}
243
244/**
245 * relay_buf_empty - boolean, is the channel buffer empty?
246 * @buf: channel buffer
247 *
248 * Returns 1 if the buffer is empty, 0 otherwise.
249 */
250static int relay_buf_empty(struct rchan_buf *buf)
251{
252    return (buf->subbufs_produced - buf->subbufs_consumed) ? 0 : 1;
253}
254
255/**
256 * relay_buf_full - boolean, is the channel buffer full?
257 * @buf: channel buffer
258 *
259 * Returns 1 if the buffer is full, 0 otherwise.
260 */
261int relay_buf_full(struct rchan_buf *buf)
262{
263    size_t ready = buf->subbufs_produced - buf->subbufs_consumed;
264    return (ready >= buf->chan->n_subbufs) ? 1 : 0;
265}
266EXPORT_SYMBOL_GPL(relay_buf_full);
267
268/*
269 * High-level relay kernel API and associated functions.
270 */
271
272/*
273 * rchan_callback implementations defining default channel behavior. Used
274 * in place of corresponding NULL values in client callback struct.
275 */
276
277/*
278 * subbuf_start() default callback. Does nothing.
279 */
280static int subbuf_start_default_callback (struct rchan_buf *buf,
281                      void *subbuf,
282                      void *prev_subbuf,
283                      size_t prev_padding)
284{
285    if (relay_buf_full(buf))
286        return 0;
287
288    return 1;
289}
290
291/*
292 * buf_mapped() default callback. Does nothing.
293 */
294static void buf_mapped_default_callback(struct rchan_buf *buf,
295                    struct file *filp)
296{
297}
298
299/*
300 * buf_unmapped() default callback. Does nothing.
301 */
302static void buf_unmapped_default_callback(struct rchan_buf *buf,
303                      struct file *filp)
304{
305}
306
307/*
308 * create_buf_file_create() default callback. Does nothing.
309 */
310static struct dentry *create_buf_file_default_callback(const char *filename,
311                               struct dentry *parent,
312                               int mode,
313                               struct rchan_buf *buf,
314                               int *is_global)
315{
316    return NULL;
317}
318
319/*
320 * remove_buf_file() default callback. Does nothing.
321 */
322static int remove_buf_file_default_callback(struct dentry *dentry)
323{
324    return -EINVAL;
325}
326
327/* relay channel default callbacks */
328static struct rchan_callbacks default_channel_callbacks = {
329    .subbuf_start = subbuf_start_default_callback,
330    .buf_mapped = buf_mapped_default_callback,
331    .buf_unmapped = buf_unmapped_default_callback,
332    .create_buf_file = create_buf_file_default_callback,
333    .remove_buf_file = remove_buf_file_default_callback,
334};
335
336/**
337 * wakeup_readers - wake up readers waiting on a channel
338 * @data: contains the channel buffer
339 *
340 * This is the timer function used to defer reader waking.
341 */
342static void wakeup_readers(unsigned long data)
343{
344    struct rchan_buf *buf = (struct rchan_buf *)data;
345    wake_up_interruptible(&buf->read_wait);
346}
347
348/**
349 * __relay_reset - reset a channel buffer
350 * @buf: the channel buffer
351 * @init: 1 if this is a first-time initialization
352 *
353 * See relay_reset() for description of effect.
354 */
355static void __relay_reset(struct rchan_buf *buf, unsigned int init)
356{
357    size_t i;
358
359    if (init) {
360        init_waitqueue_head(&buf->read_wait);
361        kref_init(&buf->kref);
362        setup_timer(&buf->timer, wakeup_readers, (unsigned long)buf);
363    } else
364        del_timer_sync(&buf->timer);
365
366    buf->subbufs_produced = 0;
367    buf->subbufs_consumed = 0;
368    buf->bytes_consumed = 0;
369    buf->finalized = 0;
370    buf->data = buf->start;
371    buf->offset = 0;
372
373    for (i = 0; i < buf->chan->n_subbufs; i++)
374        buf->padding[i] = 0;
375
376    buf->chan->cb->subbuf_start(buf, buf->data, NULL, 0);
377}
378
379/**
380 * relay_reset - reset the channel
381 * @chan: the channel
382 *
383 * This has the effect of erasing all data from all channel buffers
384 * and restarting the channel in its initial state. The buffers
385 * are not freed, so any mappings are still in effect.
386 *
387 * NOTE. Care should be taken that the channel isn't actually
388 * being used by anything when this call is made.
389 */
390void relay_reset(struct rchan *chan)
391{
392    unsigned int i;
393
394    if (!chan)
395        return;
396
397    if (chan->is_global && chan->buf[0]) {
398        __relay_reset(chan->buf[0], 0);
399        return;
400    }
401
402    mutex_lock(&relay_channels_mutex);
403    for_each_possible_cpu(i)
404        if (chan->buf[i])
405            __relay_reset(chan->buf[i], 0);
406    mutex_unlock(&relay_channels_mutex);
407}
408EXPORT_SYMBOL_GPL(relay_reset);
409
410static inline void relay_set_buf_dentry(struct rchan_buf *buf,
411                    struct dentry *dentry)
412{
413    buf->dentry = dentry;
414    buf->dentry->d_inode->i_size = buf->early_bytes;
415}
416
417static struct dentry *relay_create_buf_file(struct rchan *chan,
418                        struct rchan_buf *buf,
419                        unsigned int cpu)
420{
421    struct dentry *dentry;
422    char *tmpname;
423
424    tmpname = kzalloc(NAME_MAX + 1, GFP_KERNEL);
425    if (!tmpname)
426        return NULL;
427    snprintf(tmpname, NAME_MAX, "%s%d", chan->base_filename, cpu);
428
429    /* Create file in fs */
430    dentry = chan->cb->create_buf_file(tmpname, chan->parent,
431                       S_IRUSR, buf,
432                       &chan->is_global);
433
434    kfree(tmpname);
435
436    return dentry;
437}
438
439/*
440 * relay_open_buf - create a new relay channel buffer
441 *
442 * used by relay_open() and CPU hotplug.
443 */
444static struct rchan_buf *relay_open_buf(struct rchan *chan, unsigned int cpu)
445{
446     struct rchan_buf *buf = NULL;
447    struct dentry *dentry;
448
449     if (chan->is_global)
450        return chan->buf[0];
451
452    buf = relay_create_buf(chan);
453    if (!buf)
454        return NULL;
455
456    if (chan->has_base_filename) {
457        dentry = relay_create_buf_file(chan, buf, cpu);
458        if (!dentry)
459            goto free_buf;
460        relay_set_buf_dentry(buf, dentry);
461    }
462
463     buf->cpu = cpu;
464     __relay_reset(buf, 1);
465
466     if(chan->is_global) {
467         chan->buf[0] = buf;
468         buf->cpu = 0;
469      }
470
471    return buf;
472
473free_buf:
474     relay_destroy_buf(buf);
475    return NULL;
476}
477
478/**
479 * relay_close_buf - close a channel buffer
480 * @buf: channel buffer
481 *
482 * Marks the buffer finalized and restores the default callbacks.
483 * The channel buffer and channel buffer data structure are then freed
484 * automatically when the last reference is given up.
485 */
486static void relay_close_buf(struct rchan_buf *buf)
487{
488    buf->finalized = 1;
489    del_timer_sync(&buf->timer);
490    kref_put(&buf->kref, relay_remove_buf);
491}
492
493static void setup_callbacks(struct rchan *chan,
494                   struct rchan_callbacks *cb)
495{
496    if (!cb) {
497        chan->cb = &default_channel_callbacks;
498        return;
499    }
500
501    if (!cb->subbuf_start)
502        cb->subbuf_start = subbuf_start_default_callback;
503    if (!cb->buf_mapped)
504        cb->buf_mapped = buf_mapped_default_callback;
505    if (!cb->buf_unmapped)
506        cb->buf_unmapped = buf_unmapped_default_callback;
507    if (!cb->create_buf_file)
508        cb->create_buf_file = create_buf_file_default_callback;
509    if (!cb->remove_buf_file)
510        cb->remove_buf_file = remove_buf_file_default_callback;
511    chan->cb = cb;
512}
513
514/**
515 * relay_hotcpu_callback - CPU hotplug callback
516 * @nb: notifier block
517 * @action: hotplug action to take
518 * @hcpu: CPU number
519 *
520 * Returns the success/failure of the operation. (%NOTIFY_OK, %NOTIFY_BAD)
521 */
522static int __cpuinit relay_hotcpu_callback(struct notifier_block *nb,
523                unsigned long action,
524                void *hcpu)
525{
526    unsigned int hotcpu = (unsigned long)hcpu;
527    struct rchan *chan;
528
529    switch(action) {
530    case CPU_UP_PREPARE:
531    case CPU_UP_PREPARE_FROZEN:
532        mutex_lock(&relay_channels_mutex);
533        list_for_each_entry(chan, &relay_channels, list) {
534            if (chan->buf[hotcpu])
535                continue;
536            chan->buf[hotcpu] = relay_open_buf(chan, hotcpu);
537            if(!chan->buf[hotcpu]) {
538                printk(KERN_ERR
539                    "relay_hotcpu_callback: cpu %d buffer "
540                    "creation failed\n", hotcpu);
541                mutex_unlock(&relay_channels_mutex);
542                return notifier_from_errno(-ENOMEM);
543            }
544        }
545        mutex_unlock(&relay_channels_mutex);
546        break;
547    case CPU_DEAD:
548    case CPU_DEAD_FROZEN:
549        /* No need to flush the cpu : will be flushed upon
550         * final relay_flush() call. */
551        break;
552    }
553    return NOTIFY_OK;
554}
555
556/**
557 * relay_open - create a new relay channel
558 * @base_filename: base name of files to create, %NULL for buffering only
559 * @parent: dentry of parent directory, %NULL for root directory or buffer
560 * @subbuf_size: size of sub-buffers
561 * @n_subbufs: number of sub-buffers
562 * @cb: client callback functions
563 * @private_data: user-defined data
564 *
565 * Returns channel pointer if successful, %NULL otherwise.
566 *
567 * Creates a channel buffer for each cpu using the sizes and
568 * attributes specified. The created channel buffer files
569 * will be named base_filename0...base_filenameN-1. File
570 * permissions will be %S_IRUSR.
571 */
572struct rchan *relay_open(const char *base_filename,
573             struct dentry *parent,
574             size_t subbuf_size,
575             size_t n_subbufs,
576             struct rchan_callbacks *cb,
577             void *private_data)
578{
579    unsigned int i;
580    struct rchan *chan;
581
582    if (!(subbuf_size && n_subbufs))
583        return NULL;
584
585    chan = kzalloc(sizeof(struct rchan), GFP_KERNEL);
586    if (!chan)
587        return NULL;
588
589    chan->version = RELAYFS_CHANNEL_VERSION;
590    chan->n_subbufs = n_subbufs;
591    chan->subbuf_size = subbuf_size;
592    chan->alloc_size = FIX_SIZE(subbuf_size * n_subbufs);
593    chan->parent = parent;
594    chan->private_data = private_data;
595    if (base_filename) {
596        chan->has_base_filename = 1;
597        strlcpy(chan->base_filename, base_filename, NAME_MAX);
598    }
599    setup_callbacks(chan, cb);
600    kref_init(&chan->kref);
601
602    mutex_lock(&relay_channels_mutex);
603    for_each_online_cpu(i) {
604        chan->buf[i] = relay_open_buf(chan, i);
605        if (!chan->buf[i])
606            goto free_bufs;
607    }
608    list_add(&chan->list, &relay_channels);
609    mutex_unlock(&relay_channels_mutex);
610
611    return chan;
612
613free_bufs:
614    for_each_possible_cpu(i) {
615        if (chan->buf[i])
616            relay_close_buf(chan->buf[i]);
617    }
618
619    kref_put(&chan->kref, relay_destroy_channel);
620    mutex_unlock(&relay_channels_mutex);
621    return NULL;
622}
623EXPORT_SYMBOL_GPL(relay_open);
624
625struct rchan_percpu_buf_dispatcher {
626    struct rchan_buf *buf;
627    struct dentry *dentry;
628};
629
630/* Called in atomic context. */
631static void __relay_set_buf_dentry(void *info)
632{
633    struct rchan_percpu_buf_dispatcher *p = info;
634
635    relay_set_buf_dentry(p->buf, p->dentry);
636}
637
638/**
639 * relay_late_setup_files - triggers file creation
640 * @chan: channel to operate on
641 * @base_filename: base name of files to create
642 * @parent: dentry of parent directory, %NULL for root directory
643 *
644 * Returns 0 if successful, non-zero otherwise.
645 *
646 * Use to setup files for a previously buffer-only channel.
647 * Useful to do early tracing in kernel, before VFS is up, for example.
648 */
649int relay_late_setup_files(struct rchan *chan,
650               const char *base_filename,
651               struct dentry *parent)
652{
653    int err = 0;
654    unsigned int i, curr_cpu;
655    unsigned long flags;
656    struct dentry *dentry;
657    struct rchan_percpu_buf_dispatcher disp;
658
659    if (!chan || !base_filename)
660        return -EINVAL;
661
662    strlcpy(chan->base_filename, base_filename, NAME_MAX);
663
664    mutex_lock(&relay_channels_mutex);
665    /* Is chan already set up? */
666    if (unlikely(chan->has_base_filename)) {
667        mutex_unlock(&relay_channels_mutex);
668        return -EEXIST;
669    }
670    chan->has_base_filename = 1;
671    chan->parent = parent;
672    curr_cpu = get_cpu();
673    /*
674     * The CPU hotplug notifier ran before us and created buffers with
675     * no files associated. So it's safe to call relay_setup_buf_file()
676     * on all currently online CPUs.
677     */
678    for_each_online_cpu(i) {
679        if (unlikely(!chan->buf[i])) {
680            WARN_ONCE(1, KERN_ERR "CPU has no buffer!\n");
681            err = -EINVAL;
682            break;
683        }
684
685        dentry = relay_create_buf_file(chan, chan->buf[i], i);
686        if (unlikely(!dentry)) {
687            err = -EINVAL;
688            break;
689        }
690
691        if (curr_cpu == i) {
692            local_irq_save(flags);
693            relay_set_buf_dentry(chan->buf[i], dentry);
694            local_irq_restore(flags);
695        } else {
696            disp.buf = chan->buf[i];
697            disp.dentry = dentry;
698            smp_mb();
699            /* relay_channels_mutex must be held, so wait. */
700            err = smp_call_function_single(i,
701                               __relay_set_buf_dentry,
702                               &disp, 1);
703        }
704        if (unlikely(err))
705            break;
706    }
707    put_cpu();
708    mutex_unlock(&relay_channels_mutex);
709
710    return err;
711}
712
713/**
714 * relay_switch_subbuf - switch to a new sub-buffer
715 * @buf: channel buffer
716 * @length: size of current event
717 *
718 * Returns either the length passed in or 0 if full.
719 *
720 * Performs sub-buffer-switch tasks such as invoking callbacks,
721 * updating padding counts, waking up readers, etc.
722 */
723size_t relay_switch_subbuf(struct rchan_buf *buf, size_t length)
724{
725    void *old, *new;
726    size_t old_subbuf, new_subbuf;
727
728    if (unlikely(length > buf->chan->subbuf_size))
729        goto toobig;
730
731    if (buf->offset != buf->chan->subbuf_size + 1) {
732        buf->prev_padding = buf->chan->subbuf_size - buf->offset;
733        old_subbuf = buf->subbufs_produced % buf->chan->n_subbufs;
734        buf->padding[old_subbuf] = buf->prev_padding;
735        buf->subbufs_produced++;
736        if (buf->dentry)
737            buf->dentry->d_inode->i_size +=
738                buf->chan->subbuf_size -
739                buf->padding[old_subbuf];
740        else
741            buf->early_bytes += buf->chan->subbuf_size -
742                        buf->padding[old_subbuf];
743        smp_mb();
744        if (waitqueue_active(&buf->read_wait))
745            /*
746             * Calling wake_up_interruptible() from here
747             * will deadlock if we happen to be logging
748             * from the scheduler (trying to re-grab
749             * rq->lock), so defer it.
750             */
751            mod_timer(&buf->timer, jiffies + 1);
752    }
753
754    old = buf->data;
755    new_subbuf = buf->subbufs_produced % buf->chan->n_subbufs;
756    new = buf->start + new_subbuf * buf->chan->subbuf_size;
757    buf->offset = 0;
758    if (!buf->chan->cb->subbuf_start(buf, new, old, buf->prev_padding)) {
759        buf->offset = buf->chan->subbuf_size + 1;
760        return 0;
761    }
762    buf->data = new;
763    buf->padding[new_subbuf] = 0;
764
765    if (unlikely(length + buf->offset > buf->chan->subbuf_size))
766        goto toobig;
767
768    return length;
769
770toobig:
771    buf->chan->last_toobig = length;
772    return 0;
773}
774EXPORT_SYMBOL_GPL(relay_switch_subbuf);
775
776/**
777 * relay_subbufs_consumed - update the buffer's sub-buffers-consumed count
778 * @chan: the channel
779 * @cpu: the cpu associated with the channel buffer to update
780 * @subbufs_consumed: number of sub-buffers to add to current buf's count
781 *
782 * Adds to the channel buffer's consumed sub-buffer count.
783 * subbufs_consumed should be the number of sub-buffers newly consumed,
784 * not the total consumed.
785 *
786 * NOTE. Kernel clients don't need to call this function if the channel
787 * mode is 'overwrite'.
788 */
789void relay_subbufs_consumed(struct rchan *chan,
790                unsigned int cpu,
791                size_t subbufs_consumed)
792{
793    struct rchan_buf *buf;
794
795    if (!chan)
796        return;
797
798    if (cpu >= NR_CPUS || !chan->buf[cpu] ||
799                    subbufs_consumed > chan->n_subbufs)
800        return;
801
802    buf = chan->buf[cpu];
803    if (subbufs_consumed > buf->subbufs_produced - buf->subbufs_consumed)
804        buf->subbufs_consumed = buf->subbufs_produced;
805    else
806        buf->subbufs_consumed += subbufs_consumed;
807}
808EXPORT_SYMBOL_GPL(relay_subbufs_consumed);
809
810/**
811 * relay_close - close the channel
812 * @chan: the channel
813 *
814 * Closes all channel buffers and frees the channel.
815 */
816void relay_close(struct rchan *chan)
817{
818    unsigned int i;
819
820    if (!chan)
821        return;
822
823    mutex_lock(&relay_channels_mutex);
824    if (chan->is_global && chan->buf[0])
825        relay_close_buf(chan->buf[0]);
826    else
827        for_each_possible_cpu(i)
828            if (chan->buf[i])
829                relay_close_buf(chan->buf[i]);
830
831    if (chan->last_toobig)
832        printk(KERN_WARNING "relay: one or more items not logged "
833               "[item size (%Zd) > sub-buffer size (%Zd)]\n",
834               chan->last_toobig, chan->subbuf_size);
835
836    list_del(&chan->list);
837    kref_put(&chan->kref, relay_destroy_channel);
838    mutex_unlock(&relay_channels_mutex);
839}
840EXPORT_SYMBOL_GPL(relay_close);
841
842/**
843 * relay_flush - close the channel
844 * @chan: the channel
845 *
846 * Flushes all channel buffers, i.e. forces buffer switch.
847 */
848void relay_flush(struct rchan *chan)
849{
850    unsigned int i;
851
852    if (!chan)
853        return;
854
855    if (chan->is_global && chan->buf[0]) {
856        relay_switch_subbuf(chan->buf[0], 0);
857        return;
858    }
859
860    mutex_lock(&relay_channels_mutex);
861    for_each_possible_cpu(i)
862        if (chan->buf[i])
863            relay_switch_subbuf(chan->buf[i], 0);
864    mutex_unlock(&relay_channels_mutex);
865}
866EXPORT_SYMBOL_GPL(relay_flush);
867
868/**
869 * relay_file_open - open file op for relay files
870 * @inode: the inode
871 * @filp: the file
872 *
873 * Increments the channel buffer refcount.
874 */
875static int relay_file_open(struct inode *inode, struct file *filp)
876{
877    struct rchan_buf *buf = inode->i_private;
878    kref_get(&buf->kref);
879    filp->private_data = buf;
880
881    return nonseekable_open(inode, filp);
882}
883
884/**
885 * relay_file_mmap - mmap file op for relay files
886 * @filp: the file
887 * @vma: the vma describing what to map
888 *
889 * Calls upon relay_mmap_buf() to map the file into user space.
890 */
891static int relay_file_mmap(struct file *filp, struct vm_area_struct *vma)
892{
893    struct rchan_buf *buf = filp->private_data;
894    return relay_mmap_buf(buf, vma);
895}
896
897/**
898 * relay_file_poll - poll file op for relay files
899 * @filp: the file
900 * @wait: poll table
901 *
902 * Poll implemention.
903 */
904static unsigned int relay_file_poll(struct file *filp, poll_table *wait)
905{
906    unsigned int mask = 0;
907    struct rchan_buf *buf = filp->private_data;
908
909    if (buf->finalized)
910        return POLLERR;
911
912    if (filp->f_mode & FMODE_READ) {
913        poll_wait(filp, &buf->read_wait, wait);
914        if (!relay_buf_empty(buf))
915            mask |= POLLIN | POLLRDNORM;
916    }
917
918    return mask;
919}
920
921/**
922 * relay_file_release - release file op for relay files
923 * @inode: the inode
924 * @filp: the file
925 *
926 * Decrements the channel refcount, as the filesystem is
927 * no longer using it.
928 */
929static int relay_file_release(struct inode *inode, struct file *filp)
930{
931    struct rchan_buf *buf = filp->private_data;
932    kref_put(&buf->kref, relay_remove_buf);
933
934    return 0;
935}
936
937/*
938 * relay_file_read_consume - update the consumed count for the buffer
939 */
940static void relay_file_read_consume(struct rchan_buf *buf,
941                    size_t read_pos,
942                    size_t bytes_consumed)
943{
944    size_t subbuf_size = buf->chan->subbuf_size;
945    size_t n_subbufs = buf->chan->n_subbufs;
946    size_t read_subbuf;
947
948    if (buf->subbufs_produced == buf->subbufs_consumed &&
949        buf->offset == buf->bytes_consumed)
950        return;
951
952    if (buf->bytes_consumed + bytes_consumed > subbuf_size) {
953        relay_subbufs_consumed(buf->chan, buf->cpu, 1);
954        buf->bytes_consumed = 0;
955    }
956
957    buf->bytes_consumed += bytes_consumed;
958    if (!read_pos)
959        read_subbuf = buf->subbufs_consumed % n_subbufs;
960    else
961        read_subbuf = read_pos / buf->chan->subbuf_size;
962    if (buf->bytes_consumed + buf->padding[read_subbuf] == subbuf_size) {
963        if ((read_subbuf == buf->subbufs_produced % n_subbufs) &&
964            (buf->offset == subbuf_size))
965            return;
966        relay_subbufs_consumed(buf->chan, buf->cpu, 1);
967        buf->bytes_consumed = 0;
968    }
969}
970
971/*
972 * relay_file_read_avail - boolean, are there unconsumed bytes available?
973 */
974static int relay_file_read_avail(struct rchan_buf *buf, size_t read_pos)
975{
976    size_t subbuf_size = buf->chan->subbuf_size;
977    size_t n_subbufs = buf->chan->n_subbufs;
978    size_t produced = buf->subbufs_produced;
979    size_t consumed = buf->subbufs_consumed;
980
981    relay_file_read_consume(buf, read_pos, 0);
982
983    consumed = buf->subbufs_consumed;
984
985    if (unlikely(buf->offset > subbuf_size)) {
986        if (produced == consumed)
987            return 0;
988        return 1;
989    }
990
991    if (unlikely(produced - consumed >= n_subbufs)) {
992        consumed = produced - n_subbufs + 1;
993        buf->subbufs_consumed = consumed;
994        buf->bytes_consumed = 0;
995    }
996
997    produced = (produced % n_subbufs) * subbuf_size + buf->offset;
998    consumed = (consumed % n_subbufs) * subbuf_size + buf->bytes_consumed;
999
1000    if (consumed > produced)
1001        produced += n_subbufs * subbuf_size;
1002
1003    if (consumed == produced) {
1004        if (buf->offset == subbuf_size &&
1005            buf->subbufs_produced > buf->subbufs_consumed)
1006            return 1;
1007        return 0;
1008    }
1009
1010    return 1;
1011}
1012
1013/**
1014 * relay_file_read_subbuf_avail - return bytes available in sub-buffer
1015 * @read_pos: file read position
1016 * @buf: relay channel buffer
1017 */
1018static size_t relay_file_read_subbuf_avail(size_t read_pos,
1019                       struct rchan_buf *buf)
1020{
1021    size_t padding, avail = 0;
1022    size_t read_subbuf, read_offset, write_subbuf, write_offset;
1023    size_t subbuf_size = buf->chan->subbuf_size;
1024
1025    write_subbuf = (buf->data - buf->start) / subbuf_size;
1026    write_offset = buf->offset > subbuf_size ? subbuf_size : buf->offset;
1027    read_subbuf = read_pos / subbuf_size;
1028    read_offset = read_pos % subbuf_size;
1029    padding = buf->padding[read_subbuf];
1030
1031    if (read_subbuf == write_subbuf) {
1032        if (read_offset + padding < write_offset)
1033            avail = write_offset - (read_offset + padding);
1034    } else
1035        avail = (subbuf_size - padding) - read_offset;
1036
1037    return avail;
1038}
1039
1040/**
1041 * relay_file_read_start_pos - find the first available byte to read
1042 * @read_pos: file read position
1043 * @buf: relay channel buffer
1044 *
1045 * If the @read_pos is in the middle of padding, return the
1046 * position of the first actually available byte, otherwise
1047 * return the original value.
1048 */
1049static size_t relay_file_read_start_pos(size_t read_pos,
1050                    struct rchan_buf *buf)
1051{
1052    size_t read_subbuf, padding, padding_start, padding_end;
1053    size_t subbuf_size = buf->chan->subbuf_size;
1054    size_t n_subbufs = buf->chan->n_subbufs;
1055    size_t consumed = buf->subbufs_consumed % n_subbufs;
1056
1057    if (!read_pos)
1058        read_pos = consumed * subbuf_size + buf->bytes_consumed;
1059    read_subbuf = read_pos / subbuf_size;
1060    padding = buf->padding[read_subbuf];
1061    padding_start = (read_subbuf + 1) * subbuf_size - padding;
1062    padding_end = (read_subbuf + 1) * subbuf_size;
1063    if (read_pos >= padding_start && read_pos < padding_end) {
1064        read_subbuf = (read_subbuf + 1) % n_subbufs;
1065        read_pos = read_subbuf * subbuf_size;
1066    }
1067
1068    return read_pos;
1069}
1070
1071/**
1072 * relay_file_read_end_pos - return the new read position
1073 * @read_pos: file read position
1074 * @buf: relay channel buffer
1075 * @count: number of bytes to be read
1076 */
1077static size_t relay_file_read_end_pos(struct rchan_buf *buf,
1078                      size_t read_pos,
1079                      size_t count)
1080{
1081    size_t read_subbuf, padding, end_pos;
1082    size_t subbuf_size = buf->chan->subbuf_size;
1083    size_t n_subbufs = buf->chan->n_subbufs;
1084
1085    read_subbuf = read_pos / subbuf_size;
1086    padding = buf->padding[read_subbuf];
1087    if (read_pos % subbuf_size + count + padding == subbuf_size)
1088        end_pos = (read_subbuf + 1) * subbuf_size;
1089    else
1090        end_pos = read_pos + count;
1091    if (end_pos >= subbuf_size * n_subbufs)
1092        end_pos = 0;
1093
1094    return end_pos;
1095}
1096
1097/*
1098 * subbuf_read_actor - read up to one subbuf's worth of data
1099 */
1100static int subbuf_read_actor(size_t read_start,
1101                 struct rchan_buf *buf,
1102                 size_t avail,
1103                 read_descriptor_t *desc,
1104                 read_actor_t actor)
1105{
1106    void *from;
1107    int ret = 0;
1108
1109    from = buf->start + read_start;
1110    ret = avail;
1111    if (copy_to_user(desc->arg.buf, from, avail)) {
1112        desc->error = -EFAULT;
1113        ret = 0;
1114    }
1115    desc->arg.data += ret;
1116    desc->written += ret;
1117    desc->count -= ret;
1118
1119    return ret;
1120}
1121
1122typedef int (*subbuf_actor_t) (size_t read_start,
1123                   struct rchan_buf *buf,
1124                   size_t avail,
1125                   read_descriptor_t *desc,
1126                   read_actor_t actor);
1127
1128/*
1129 * relay_file_read_subbufs - read count bytes, bridging subbuf boundaries
1130 */
1131static ssize_t relay_file_read_subbufs(struct file *filp, loff_t *ppos,
1132                    subbuf_actor_t subbuf_actor,
1133                    read_actor_t actor,
1134                    read_descriptor_t *desc)
1135{
1136    struct rchan_buf *buf = filp->private_data;
1137    size_t read_start, avail;
1138    int ret;
1139
1140    if (!desc->count)
1141        return 0;
1142
1143    mutex_lock(&filp->f_path.dentry->d_inode->i_mutex);
1144    do {
1145        if (!relay_file_read_avail(buf, *ppos))
1146            break;
1147
1148        read_start = relay_file_read_start_pos(*ppos, buf);
1149        avail = relay_file_read_subbuf_avail(read_start, buf);
1150        if (!avail)
1151            break;
1152
1153        avail = min(desc->count, avail);
1154        ret = subbuf_actor(read_start, buf, avail, desc, actor);
1155        if (desc->error < 0)
1156            break;
1157
1158        if (ret) {
1159            relay_file_read_consume(buf, read_start, ret);
1160            *ppos = relay_file_read_end_pos(buf, read_start, ret);
1161        }
1162    } while (desc->count && ret);
1163    mutex_unlock(&filp->f_path.dentry->d_inode->i_mutex);
1164
1165    return desc->written;
1166}
1167
1168static ssize_t relay_file_read(struct file *filp,
1169                   char __user *buffer,
1170                   size_t count,
1171                   loff_t *ppos)
1172{
1173    read_descriptor_t desc;
1174    desc.written = 0;
1175    desc.count = count;
1176    desc.arg.buf = buffer;
1177    desc.error = 0;
1178    return relay_file_read_subbufs(filp, ppos, subbuf_read_actor,
1179                       NULL, &desc);
1180}
1181
1182static void relay_consume_bytes(struct rchan_buf *rbuf, int bytes_consumed)
1183{
1184    rbuf->bytes_consumed += bytes_consumed;
1185
1186    if (rbuf->bytes_consumed >= rbuf->chan->subbuf_size) {
1187        relay_subbufs_consumed(rbuf->chan, rbuf->cpu, 1);
1188        rbuf->bytes_consumed %= rbuf->chan->subbuf_size;
1189    }
1190}
1191
1192static void relay_pipe_buf_release(struct pipe_inode_info *pipe,
1193                   struct pipe_buffer *buf)
1194{
1195    struct rchan_buf *rbuf;
1196
1197    rbuf = (struct rchan_buf *)page_private(buf->page);
1198    relay_consume_bytes(rbuf, buf->private);
1199}
1200
1201static const struct pipe_buf_operations relay_pipe_buf_ops = {
1202    .can_merge = 0,
1203    .map = generic_pipe_buf_map,
1204    .unmap = generic_pipe_buf_unmap,
1205    .confirm = generic_pipe_buf_confirm,
1206    .release = relay_pipe_buf_release,
1207    .steal = generic_pipe_buf_steal,
1208    .get = generic_pipe_buf_get,
1209};
1210
1211static void relay_page_release(struct splice_pipe_desc *spd, unsigned int i)
1212{
1213}
1214
1215/*
1216 * subbuf_splice_actor - splice up to one subbuf's worth of data
1217 */
1218static ssize_t subbuf_splice_actor(struct file *in,
1219                   loff_t *ppos,
1220                   struct pipe_inode_info *pipe,
1221                   size_t len,
1222                   unsigned int flags,
1223                   int *nonpad_ret)
1224{
1225    unsigned int pidx, poff, total_len, subbuf_pages, nr_pages;
1226    struct rchan_buf *rbuf = in->private_data;
1227    unsigned int subbuf_size = rbuf->chan->subbuf_size;
1228    uint64_t pos = (uint64_t) *ppos;
1229    uint32_t alloc_size = (uint32_t) rbuf->chan->alloc_size;
1230    size_t read_start = (size_t) do_div(pos, alloc_size);
1231    size_t read_subbuf = read_start / subbuf_size;
1232    size_t padding = rbuf->padding[read_subbuf];
1233    size_t nonpad_end = read_subbuf * subbuf_size + subbuf_size - padding;
1234    struct page *pages[PIPE_DEF_BUFFERS];
1235    struct partial_page partial[PIPE_DEF_BUFFERS];
1236    struct splice_pipe_desc spd = {
1237        .pages = pages,
1238        .nr_pages = 0,
1239        .partial = partial,
1240        .flags = flags,
1241        .ops = &relay_pipe_buf_ops,
1242        .spd_release = relay_page_release,
1243    };
1244    ssize_t ret;
1245
1246    if (rbuf->subbufs_produced == rbuf->subbufs_consumed)
1247        return 0;
1248    if (splice_grow_spd(pipe, &spd))
1249        return -ENOMEM;
1250
1251    /*
1252     * Adjust read len, if longer than what is available
1253     */
1254    if (len > (subbuf_size - read_start % subbuf_size))
1255        len = subbuf_size - read_start % subbuf_size;
1256
1257    subbuf_pages = rbuf->chan->alloc_size >> PAGE_SHIFT;
1258    pidx = (read_start / PAGE_SIZE) % subbuf_pages;
1259    poff = read_start & ~PAGE_MASK;
1260    nr_pages = min_t(unsigned int, subbuf_pages, pipe->buffers);
1261
1262    for (total_len = 0; spd.nr_pages < nr_pages; spd.nr_pages++) {
1263        unsigned int this_len, this_end, private;
1264        unsigned int cur_pos = read_start + total_len;
1265
1266        if (!len)
1267            break;
1268
1269        this_len = min_t(unsigned long, len, PAGE_SIZE - poff);
1270        private = this_len;
1271
1272        spd.pages[spd.nr_pages] = rbuf->page_array[pidx];
1273        spd.partial[spd.nr_pages].offset = poff;
1274
1275        this_end = cur_pos + this_len;
1276        if (this_end >= nonpad_end) {
1277            this_len = nonpad_end - cur_pos;
1278            private = this_len + padding;
1279        }
1280        spd.partial[spd.nr_pages].len = this_len;
1281        spd.partial[spd.nr_pages].private = private;
1282
1283        len -= this_len;
1284        total_len += this_len;
1285        poff = 0;
1286        pidx = (pidx + 1) % subbuf_pages;
1287
1288        if (this_end >= nonpad_end) {
1289            spd.nr_pages++;
1290            break;
1291        }
1292    }
1293
1294    ret = 0;
1295    if (!spd.nr_pages)
1296        goto out;
1297
1298    ret = *nonpad_ret = splice_to_pipe(pipe, &spd);
1299    if (ret < 0 || ret < total_len)
1300        goto out;
1301
1302        if (read_start + ret == nonpad_end)
1303                ret += padding;
1304
1305out:
1306    splice_shrink_spd(pipe, &spd);
1307        return ret;
1308}
1309
1310static ssize_t relay_file_splice_read(struct file *in,
1311                      loff_t *ppos,
1312                      struct pipe_inode_info *pipe,
1313                      size_t len,
1314                      unsigned int flags)
1315{
1316    ssize_t spliced;
1317    int ret;
1318    int nonpad_ret = 0;
1319
1320    ret = 0;
1321    spliced = 0;
1322
1323    while (len && !spliced) {
1324        ret = subbuf_splice_actor(in, ppos, pipe, len, flags, &nonpad_ret);
1325        if (ret < 0)
1326            break;
1327        else if (!ret) {
1328            if (flags & SPLICE_F_NONBLOCK)
1329                ret = -EAGAIN;
1330            break;
1331        }
1332
1333        *ppos += ret;
1334        if (ret > len)
1335            len = 0;
1336        else
1337            len -= ret;
1338        spliced += nonpad_ret;
1339        nonpad_ret = 0;
1340    }
1341
1342    if (spliced)
1343        return spliced;
1344
1345    return ret;
1346}
1347
1348const struct file_operations relay_file_operations = {
1349    .open = relay_file_open,
1350    .poll = relay_file_poll,
1351    .mmap = relay_file_mmap,
1352    .read = relay_file_read,
1353    .llseek = no_llseek,
1354    .release = relay_file_release,
1355    .splice_read = relay_file_splice_read,
1356};
1357EXPORT_SYMBOL_GPL(relay_file_operations);
1358
1359static __init int relay_init(void)
1360{
1361
1362    hotcpu_notifier(relay_hotcpu_callback, 0);
1363    return 0;
1364}
1365
1366early_initcall(relay_init);
1367

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