xref: /openbmc/linux/kernel/relay.c (revision 1406f0f3)
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   */
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   */
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   */
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   */
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   */
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   */
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   */
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   */
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   */
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   */
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   */
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  
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   */
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   */
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   */
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  
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  
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   */
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   */
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  
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 ((buf = *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   */
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. */
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   */
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   */
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   */
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   */
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   */
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   */
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   */
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   */
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   */
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   */
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   */
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   */
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   */
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   */
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  
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  
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  
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  
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   */
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  
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