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