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