xref: /openbmc/linux/kernel/relay.c (revision 799a545b)
1  /*
2   * Public API and common code for kernel->userspace relay file support.
3   *
4   * See Documentation/filesystems/relay.txt for an overview.
5   *
6   * Copyright (C) 2002-2005 - Tom Zanussi (zanussi@us.ibm.com), IBM Corp
7   * Copyright (C) 1999-2005 - Karim Yaghmour (karim@opersys.com)
8   *
9   * Moved to kernel/relay.c by Paul Mundt, 2006.
10   * November 2006 - CPU hotplug support by Mathieu Desnoyers
11   * 	(mathieu.desnoyers@polymtl.ca)
12   *
13   * This file is released under the GPL.
14   */
15  #include <linux/errno.h>
16  #include <linux/stddef.h>
17  #include <linux/slab.h>
18  #include <linux/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   * close() vm_op implementation for relay file mapping.
32   */
33  static void relay_file_mmap_close(struct vm_area_struct *vma)
34  {
35  	struct rchan_buf *buf = vma->vm_private_data;
36  	buf->chan->cb->buf_unmapped(buf, vma->vm_file);
37  }
38  
39  /*
40   * fault() vm_op implementation for relay file mapping.
41   */
42  static int relay_buf_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
43  {
44  	struct page *page;
45  	struct rchan_buf *buf = vma->vm_private_data;
46  	pgoff_t pgoff = vmf->pgoff;
47  
48  	if (!buf)
49  		return VM_FAULT_OOM;
50  
51  	page = vmalloc_to_page(buf->start + (pgoff << PAGE_SHIFT));
52  	if (!page)
53  		return VM_FAULT_SIGBUS;
54  	get_page(page);
55  	vmf->page = page;
56  
57  	return 0;
58  }
59  
60  /*
61   * vm_ops for relay file mappings.
62   */
63  static const struct vm_operations_struct relay_file_mmap_ops = {
64  	.fault = relay_buf_fault,
65  	.close = relay_file_mmap_close,
66  };
67  
68  /*
69   * allocate an array of pointers of struct page
70   */
71  static struct page **relay_alloc_page_array(unsigned int n_pages)
72  {
73  	const size_t pa_size = n_pages * sizeof(struct page *);
74  	if (pa_size > PAGE_SIZE)
75  		return vzalloc(pa_size);
76  	return kzalloc(pa_size, GFP_KERNEL);
77  }
78  
79  /*
80   * free an array of pointers of struct page
81   */
82  static void relay_free_page_array(struct page **array)
83  {
84  	kvfree(array);
85  }
86  
87  /**
88   *	relay_mmap_buf: - mmap channel buffer to process address space
89   *	@buf: relay channel buffer
90   *	@vma: vm_area_struct describing memory to be mapped
91   *
92   *	Returns 0 if ok, negative on error
93   *
94   *	Caller should already have grabbed mmap_sem.
95   */
96  static int relay_mmap_buf(struct rchan_buf *buf, struct vm_area_struct *vma)
97  {
98  	unsigned long length = vma->vm_end - vma->vm_start;
99  	struct file *filp = vma->vm_file;
100  
101  	if (!buf)
102  		return -EBADF;
103  
104  	if (length != (unsigned long)buf->chan->alloc_size)
105  		return -EINVAL;
106  
107  	vma->vm_ops = &relay_file_mmap_ops;
108  	vma->vm_flags |= VM_DONTEXPAND;
109  	vma->vm_private_data = buf;
110  	buf->chan->cb->buf_mapped(buf, filp);
111  
112  	return 0;
113  }
114  
115  /**
116   *	relay_alloc_buf - allocate a channel buffer
117   *	@buf: the buffer struct
118   *	@size: total size of the buffer
119   *
120   *	Returns a pointer to the resulting buffer, %NULL if unsuccessful. The
121   *	passed in size will get page aligned, if it isn't already.
122   */
123  static void *relay_alloc_buf(struct rchan_buf *buf, size_t *size)
124  {
125  	void *mem;
126  	unsigned int i, j, n_pages;
127  
128  	*size = PAGE_ALIGN(*size);
129  	n_pages = *size >> PAGE_SHIFT;
130  
131  	buf->page_array = relay_alloc_page_array(n_pages);
132  	if (!buf->page_array)
133  		return NULL;
134  
135  	for (i = 0; i < n_pages; i++) {
136  		buf->page_array[i] = alloc_page(GFP_KERNEL);
137  		if (unlikely(!buf->page_array[i]))
138  			goto depopulate;
139  		set_page_private(buf->page_array[i], (unsigned long)buf);
140  	}
141  	mem = vmap(buf->page_array, n_pages, VM_MAP, PAGE_KERNEL);
142  	if (!mem)
143  		goto depopulate;
144  
145  	memset(mem, 0, *size);
146  	buf->page_count = n_pages;
147  	return mem;
148  
149  depopulate:
150  	for (j = 0; j < i; j++)
151  		__free_page(buf->page_array[j]);
152  	relay_free_page_array(buf->page_array);
153  	return NULL;
154  }
155  
156  /**
157   *	relay_create_buf - allocate and initialize a channel buffer
158   *	@chan: the relay channel
159   *
160   *	Returns channel buffer if successful, %NULL otherwise.
161   */
162  static struct rchan_buf *relay_create_buf(struct rchan *chan)
163  {
164  	struct rchan_buf *buf;
165  
166  	if (chan->n_subbufs > UINT_MAX / sizeof(size_t *))
167  		return NULL;
168  
169  	buf = kzalloc(sizeof(struct rchan_buf), GFP_KERNEL);
170  	if (!buf)
171  		return NULL;
172  	buf->padding = kmalloc(chan->n_subbufs * sizeof(size_t *), GFP_KERNEL);
173  	if (!buf->padding)
174  		goto free_buf;
175  
176  	buf->start = relay_alloc_buf(buf, &chan->alloc_size);
177  	if (!buf->start)
178  		goto free_buf;
179  
180  	buf->chan = chan;
181  	kref_get(&buf->chan->kref);
182  	return buf;
183  
184  free_buf:
185  	kfree(buf->padding);
186  	kfree(buf);
187  	return NULL;
188  }
189  
190  /**
191   *	relay_destroy_channel - free the channel struct
192   *	@kref: target kernel reference that contains the relay channel
193   *
194   *	Should only be called from kref_put().
195   */
196  static void relay_destroy_channel(struct kref *kref)
197  {
198  	struct rchan *chan = container_of(kref, struct rchan, kref);
199  	kfree(chan);
200  }
201  
202  /**
203   *	relay_destroy_buf - destroy an rchan_buf struct and associated buffer
204   *	@buf: the buffer struct
205   */
206  static void relay_destroy_buf(struct rchan_buf *buf)
207  {
208  	struct rchan *chan = buf->chan;
209  	unsigned int i;
210  
211  	if (likely(buf->start)) {
212  		vunmap(buf->start);
213  		for (i = 0; i < buf->page_count; i++)
214  			__free_page(buf->page_array[i]);
215  		relay_free_page_array(buf->page_array);
216  	}
217  	chan->buf[buf->cpu] = NULL;
218  	kfree(buf->padding);
219  	kfree(buf);
220  	kref_put(&chan->kref, relay_destroy_channel);
221  }
222  
223  /**
224   *	relay_remove_buf - remove a channel buffer
225   *	@kref: target kernel reference that contains the relay buffer
226   *
227   *	Removes the file from the filesystem, which also frees the
228   *	rchan_buf_struct and the channel buffer.  Should only be called from
229   *	kref_put().
230   */
231  static void relay_remove_buf(struct kref *kref)
232  {
233  	struct rchan_buf *buf = container_of(kref, struct rchan_buf, kref);
234  	relay_destroy_buf(buf);
235  }
236  
237  /**
238   *	relay_buf_empty - boolean, is the channel buffer empty?
239   *	@buf: channel buffer
240   *
241   *	Returns 1 if the buffer is empty, 0 otherwise.
242   */
243  static int relay_buf_empty(struct rchan_buf *buf)
244  {
245  	return (buf->subbufs_produced - buf->subbufs_consumed) ? 0 : 1;
246  }
247  
248  /**
249   *	relay_buf_full - boolean, is the channel buffer full?
250   *	@buf: channel buffer
251   *
252   *	Returns 1 if the buffer is full, 0 otherwise.
253   */
254  int relay_buf_full(struct rchan_buf *buf)
255  {
256  	size_t ready = buf->subbufs_produced - buf->subbufs_consumed;
257  	return (ready >= buf->chan->n_subbufs) ? 1 : 0;
258  }
259  EXPORT_SYMBOL_GPL(relay_buf_full);
260  
261  /*
262   * High-level relay kernel API and associated functions.
263   */
264  
265  /*
266   * rchan_callback implementations defining default channel behavior.  Used
267   * in place of corresponding NULL values in client callback struct.
268   */
269  
270  /*
271   * subbuf_start() default callback.  Does nothing.
272   */
273  static int subbuf_start_default_callback (struct rchan_buf *buf,
274  					  void *subbuf,
275  					  void *prev_subbuf,
276  					  size_t prev_padding)
277  {
278  	if (relay_buf_full(buf))
279  		return 0;
280  
281  	return 1;
282  }
283  
284  /*
285   * buf_mapped() default callback.  Does nothing.
286   */
287  static void buf_mapped_default_callback(struct rchan_buf *buf,
288  					struct file *filp)
289  {
290  }
291  
292  /*
293   * buf_unmapped() default callback.  Does nothing.
294   */
295  static void buf_unmapped_default_callback(struct rchan_buf *buf,
296  					  struct file *filp)
297  {
298  }
299  
300  /*
301   * create_buf_file_create() default callback.  Does nothing.
302   */
303  static struct dentry *create_buf_file_default_callback(const char *filename,
304  						       struct dentry *parent,
305  						       umode_t mode,
306  						       struct rchan_buf *buf,
307  						       int *is_global)
308  {
309  	return NULL;
310  }
311  
312  /*
313   * remove_buf_file() default callback.  Does nothing.
314   */
315  static int remove_buf_file_default_callback(struct dentry *dentry)
316  {
317  	return -EINVAL;
318  }
319  
320  /* relay channel default callbacks */
321  static struct rchan_callbacks default_channel_callbacks = {
322  	.subbuf_start = subbuf_start_default_callback,
323  	.buf_mapped = buf_mapped_default_callback,
324  	.buf_unmapped = buf_unmapped_default_callback,
325  	.create_buf_file = create_buf_file_default_callback,
326  	.remove_buf_file = remove_buf_file_default_callback,
327  };
328  
329  /**
330   *	wakeup_readers - wake up readers waiting on a channel
331   *	@data: contains the channel buffer
332   *
333   *	This is the timer function used to defer reader waking.
334   */
335  static void wakeup_readers(unsigned long data)
336  {
337  	struct rchan_buf *buf = (struct rchan_buf *)data;
338  	wake_up_interruptible(&buf->read_wait);
339  }
340  
341  /**
342   *	__relay_reset - reset a channel buffer
343   *	@buf: the channel buffer
344   *	@init: 1 if this is a first-time initialization
345   *
346   *	See relay_reset() for description of effect.
347   */
348  static void __relay_reset(struct rchan_buf *buf, unsigned int init)
349  {
350  	size_t i;
351  
352  	if (init) {
353  		init_waitqueue_head(&buf->read_wait);
354  		kref_init(&buf->kref);
355  		setup_timer(&buf->timer, wakeup_readers, (unsigned long)buf);
356  	} else
357  		del_timer_sync(&buf->timer);
358  
359  	buf->subbufs_produced = 0;
360  	buf->subbufs_consumed = 0;
361  	buf->bytes_consumed = 0;
362  	buf->finalized = 0;
363  	buf->data = buf->start;
364  	buf->offset = 0;
365  
366  	for (i = 0; i < buf->chan->n_subbufs; i++)
367  		buf->padding[i] = 0;
368  
369  	buf->chan->cb->subbuf_start(buf, buf->data, NULL, 0);
370  }
371  
372  /**
373   *	relay_reset - reset the channel
374   *	@chan: the channel
375   *
376   *	This has the effect of erasing all data from all channel buffers
377   *	and restarting the channel in its initial state.  The buffers
378   *	are not freed, so any mappings are still in effect.
379   *
380   *	NOTE. Care should be taken that the channel isn't actually
381   *	being used by anything when this call is made.
382   */
383  void relay_reset(struct rchan *chan)
384  {
385  	unsigned int i;
386  
387  	if (!chan)
388  		return;
389  
390  	if (chan->is_global && chan->buf[0]) {
391  		__relay_reset(chan->buf[0], 0);
392  		return;
393  	}
394  
395  	mutex_lock(&relay_channels_mutex);
396  	for_each_possible_cpu(i)
397  		if (chan->buf[i])
398  			__relay_reset(chan->buf[i], 0);
399  	mutex_unlock(&relay_channels_mutex);
400  }
401  EXPORT_SYMBOL_GPL(relay_reset);
402  
403  static inline void relay_set_buf_dentry(struct rchan_buf *buf,
404  					struct dentry *dentry)
405  {
406  	buf->dentry = dentry;
407  	d_inode(buf->dentry)->i_size = buf->early_bytes;
408  }
409  
410  static struct dentry *relay_create_buf_file(struct rchan *chan,
411  					    struct rchan_buf *buf,
412  					    unsigned int cpu)
413  {
414  	struct dentry *dentry;
415  	char *tmpname;
416  
417  	tmpname = kzalloc(NAME_MAX + 1, GFP_KERNEL);
418  	if (!tmpname)
419  		return NULL;
420  	snprintf(tmpname, NAME_MAX, "%s%d", chan->base_filename, cpu);
421  
422  	/* Create file in fs */
423  	dentry = chan->cb->create_buf_file(tmpname, chan->parent,
424  					   S_IRUSR, buf,
425  					   &chan->is_global);
426  
427  	kfree(tmpname);
428  
429  	return dentry;
430  }
431  
432  /*
433   *	relay_open_buf - create a new relay channel buffer
434   *
435   *	used by relay_open() and CPU hotplug.
436   */
437  static struct rchan_buf *relay_open_buf(struct rchan *chan, unsigned int cpu)
438  {
439   	struct rchan_buf *buf = NULL;
440  	struct dentry *dentry;
441  
442   	if (chan->is_global)
443  		return chan->buf[0];
444  
445  	buf = relay_create_buf(chan);
446  	if (!buf)
447  		return NULL;
448  
449  	if (chan->has_base_filename) {
450  		dentry = relay_create_buf_file(chan, buf, cpu);
451  		if (!dentry)
452  			goto free_buf;
453  		relay_set_buf_dentry(buf, dentry);
454  	} else {
455  		/* Only retrieve global info, nothing more, nothing less */
456  		dentry = chan->cb->create_buf_file(NULL, NULL,
457  						   S_IRUSR, buf,
458  						   &chan->is_global);
459  		if (WARN_ON(dentry))
460  			goto free_buf;
461  	}
462  
463   	buf->cpu = cpu;
464   	__relay_reset(buf, 1);
465  
466   	if(chan->is_global) {
467   		chan->buf[0] = buf;
468   		buf->cpu = 0;
469    	}
470  
471  	return buf;
472  
473  free_buf:
474   	relay_destroy_buf(buf);
475  	return NULL;
476  }
477  
478  /**
479   *	relay_close_buf - close a channel buffer
480   *	@buf: channel buffer
481   *
482   *	Marks the buffer finalized and restores the default callbacks.
483   *	The channel buffer and channel buffer data structure are then freed
484   *	automatically when the last reference is given up.
485   */
486  static void relay_close_buf(struct rchan_buf *buf)
487  {
488  	buf->finalized = 1;
489  	del_timer_sync(&buf->timer);
490  	buf->chan->cb->remove_buf_file(buf->dentry);
491  	kref_put(&buf->kref, relay_remove_buf);
492  }
493  
494  static void setup_callbacks(struct rchan *chan,
495  				   struct rchan_callbacks *cb)
496  {
497  	if (!cb) {
498  		chan->cb = &default_channel_callbacks;
499  		return;
500  	}
501  
502  	if (!cb->subbuf_start)
503  		cb->subbuf_start = subbuf_start_default_callback;
504  	if (!cb->buf_mapped)
505  		cb->buf_mapped = buf_mapped_default_callback;
506  	if (!cb->buf_unmapped)
507  		cb->buf_unmapped = buf_unmapped_default_callback;
508  	if (!cb->create_buf_file)
509  		cb->create_buf_file = create_buf_file_default_callback;
510  	if (!cb->remove_buf_file)
511  		cb->remove_buf_file = remove_buf_file_default_callback;
512  	chan->cb = cb;
513  }
514  
515  /**
516   * 	relay_hotcpu_callback - CPU hotplug callback
517   * 	@nb: notifier block
518   * 	@action: hotplug action to take
519   * 	@hcpu: CPU number
520   *
521   * 	Returns the success/failure of the operation. (%NOTIFY_OK, %NOTIFY_BAD)
522   */
523  static int relay_hotcpu_callback(struct notifier_block *nb,
524  				unsigned long action,
525  				void *hcpu)
526  {
527  	unsigned int hotcpu = (unsigned long)hcpu;
528  	struct rchan *chan;
529  
530  	switch(action) {
531  	case CPU_UP_PREPARE:
532  	case CPU_UP_PREPARE_FROZEN:
533  		mutex_lock(&relay_channels_mutex);
534  		list_for_each_entry(chan, &relay_channels, list) {
535  			if (chan->buf[hotcpu])
536  				continue;
537  			chan->buf[hotcpu] = relay_open_buf(chan, hotcpu);
538  			if(!chan->buf[hotcpu]) {
539  				printk(KERN_ERR
540  					"relay_hotcpu_callback: cpu %d buffer "
541  					"creation failed\n", hotcpu);
542  				mutex_unlock(&relay_channels_mutex);
543  				return notifier_from_errno(-ENOMEM);
544  			}
545  		}
546  		mutex_unlock(&relay_channels_mutex);
547  		break;
548  	case CPU_DEAD:
549  	case CPU_DEAD_FROZEN:
550  		/* No need to flush the cpu : will be flushed upon
551  		 * final relay_flush() call. */
552  		break;
553  	}
554  	return NOTIFY_OK;
555  }
556  
557  /**
558   *	relay_open - create a new relay channel
559   *	@base_filename: base name of files to create, %NULL for buffering only
560   *	@parent: dentry of parent directory, %NULL for root directory or buffer
561   *	@subbuf_size: size of sub-buffers
562   *	@n_subbufs: number of sub-buffers
563   *	@cb: client callback functions
564   *	@private_data: user-defined data
565   *
566   *	Returns channel pointer if successful, %NULL otherwise.
567   *
568   *	Creates a channel buffer for each cpu using the sizes and
569   *	attributes specified.  The created channel buffer files
570   *	will be named base_filename0...base_filenameN-1.  File
571   *	permissions will be %S_IRUSR.
572   *
573   *	If opening a buffer (@parent = NULL) that you later wish to register
574   *	in a filesystem, call relay_late_setup_files() once the @parent dentry
575   *	is available.
576   */
577  struct rchan *relay_open(const char *base_filename,
578  			 struct dentry *parent,
579  			 size_t subbuf_size,
580  			 size_t n_subbufs,
581  			 struct rchan_callbacks *cb,
582  			 void *private_data)
583  {
584  	unsigned int i;
585  	struct rchan *chan;
586  
587  	if (!(subbuf_size && n_subbufs))
588  		return NULL;
589  	if (subbuf_size > UINT_MAX / n_subbufs)
590  		return NULL;
591  
592  	chan = kzalloc(sizeof(struct rchan), GFP_KERNEL);
593  	if (!chan)
594  		return NULL;
595  
596  	chan->version = RELAYFS_CHANNEL_VERSION;
597  	chan->n_subbufs = n_subbufs;
598  	chan->subbuf_size = subbuf_size;
599  	chan->alloc_size = PAGE_ALIGN(subbuf_size * n_subbufs);
600  	chan->parent = parent;
601  	chan->private_data = private_data;
602  	if (base_filename) {
603  		chan->has_base_filename = 1;
604  		strlcpy(chan->base_filename, base_filename, NAME_MAX);
605  	}
606  	setup_callbacks(chan, cb);
607  	kref_init(&chan->kref);
608  
609  	mutex_lock(&relay_channels_mutex);
610  	for_each_online_cpu(i) {
611  		chan->buf[i] = relay_open_buf(chan, i);
612  		if (!chan->buf[i])
613  			goto free_bufs;
614  	}
615  	list_add(&chan->list, &relay_channels);
616  	mutex_unlock(&relay_channels_mutex);
617  
618  	return chan;
619  
620  free_bufs:
621  	for_each_possible_cpu(i) {
622  		if (chan->buf[i])
623  			relay_close_buf(chan->buf[i]);
624  	}
625  
626  	kref_put(&chan->kref, relay_destroy_channel);
627  	mutex_unlock(&relay_channels_mutex);
628  	kfree(chan);
629  	return NULL;
630  }
631  EXPORT_SYMBOL_GPL(relay_open);
632  
633  struct rchan_percpu_buf_dispatcher {
634  	struct rchan_buf *buf;
635  	struct dentry *dentry;
636  };
637  
638  /* Called in atomic context. */
639  static void __relay_set_buf_dentry(void *info)
640  {
641  	struct rchan_percpu_buf_dispatcher *p = info;
642  
643  	relay_set_buf_dentry(p->buf, p->dentry);
644  }
645  
646  /**
647   *	relay_late_setup_files - triggers file creation
648   *	@chan: channel to operate on
649   *	@base_filename: base name of files to create
650   *	@parent: dentry of parent directory, %NULL for root directory
651   *
652   *	Returns 0 if successful, non-zero otherwise.
653   *
654   *	Use to setup files for a previously buffer-only channel created
655   *	by relay_open() with a NULL parent dentry.
656   *
657   *	For example, this is useful for perfomring early tracing in kernel,
658   *	before VFS is up and then exposing the early results once the dentry
659   *	is available.
660   */
661  int relay_late_setup_files(struct rchan *chan,
662  			   const char *base_filename,
663  			   struct dentry *parent)
664  {
665  	int err = 0;
666  	unsigned int i, curr_cpu;
667  	unsigned long flags;
668  	struct dentry *dentry;
669  	struct rchan_percpu_buf_dispatcher disp;
670  
671  	if (!chan || !base_filename)
672  		return -EINVAL;
673  
674  	strlcpy(chan->base_filename, base_filename, NAME_MAX);
675  
676  	mutex_lock(&relay_channels_mutex);
677  	/* Is chan already set up? */
678  	if (unlikely(chan->has_base_filename)) {
679  		mutex_unlock(&relay_channels_mutex);
680  		return -EEXIST;
681  	}
682  	chan->has_base_filename = 1;
683  	chan->parent = parent;
684  
685  	if (chan->is_global) {
686  		err = -EINVAL;
687  		if (!WARN_ON_ONCE(!chan->buf[0])) {
688  			dentry = relay_create_buf_file(chan, chan->buf[0], 0);
689  			if (dentry && !WARN_ON_ONCE(!chan->is_global)) {
690  				relay_set_buf_dentry(chan->buf[0], dentry);
691  				err = 0;
692  			}
693  		}
694  		mutex_unlock(&relay_channels_mutex);
695  		return err;
696  	}
697  
698  	curr_cpu = get_cpu();
699  	/*
700  	 * The CPU hotplug notifier ran before us and created buffers with
701  	 * no files associated. So it's safe to call relay_setup_buf_file()
702  	 * on all currently online CPUs.
703  	 */
704  	for_each_online_cpu(i) {
705  		if (unlikely(!chan->buf[i])) {
706  			WARN_ONCE(1, KERN_ERR "CPU has no buffer!\n");
707  			err = -EINVAL;
708  			break;
709  		}
710  
711  		dentry = relay_create_buf_file(chan, chan->buf[i], i);
712  		if (unlikely(!dentry)) {
713  			err = -EINVAL;
714  			break;
715  		}
716  
717  		if (curr_cpu == i) {
718  			local_irq_save(flags);
719  			relay_set_buf_dentry(chan->buf[i], dentry);
720  			local_irq_restore(flags);
721  		} else {
722  			disp.buf = chan->buf[i];
723  			disp.dentry = dentry;
724  			smp_mb();
725  			/* relay_channels_mutex must be held, so wait. */
726  			err = smp_call_function_single(i,
727  						       __relay_set_buf_dentry,
728  						       &disp, 1);
729  		}
730  		if (unlikely(err))
731  			break;
732  	}
733  	put_cpu();
734  	mutex_unlock(&relay_channels_mutex);
735  
736  	return err;
737  }
738  EXPORT_SYMBOL_GPL(relay_late_setup_files);
739  
740  /**
741   *	relay_switch_subbuf - switch to a new sub-buffer
742   *	@buf: channel buffer
743   *	@length: size of current event
744   *
745   *	Returns either the length passed in or 0 if full.
746   *
747   *	Performs sub-buffer-switch tasks such as invoking callbacks,
748   *	updating padding counts, waking up readers, etc.
749   */
750  size_t relay_switch_subbuf(struct rchan_buf *buf, size_t length)
751  {
752  	void *old, *new;
753  	size_t old_subbuf, new_subbuf;
754  
755  	if (unlikely(length > buf->chan->subbuf_size))
756  		goto toobig;
757  
758  	if (buf->offset != buf->chan->subbuf_size + 1) {
759  		buf->prev_padding = buf->chan->subbuf_size - buf->offset;
760  		old_subbuf = buf->subbufs_produced % buf->chan->n_subbufs;
761  		buf->padding[old_subbuf] = buf->prev_padding;
762  		buf->subbufs_produced++;
763  		if (buf->dentry)
764  			d_inode(buf->dentry)->i_size +=
765  				buf->chan->subbuf_size -
766  				buf->padding[old_subbuf];
767  		else
768  			buf->early_bytes += buf->chan->subbuf_size -
769  					    buf->padding[old_subbuf];
770  		smp_mb();
771  		if (waitqueue_active(&buf->read_wait))
772  			/*
773  			 * Calling wake_up_interruptible() from here
774  			 * will deadlock if we happen to be logging
775  			 * from the scheduler (trying to re-grab
776  			 * rq->lock), so defer it.
777  			 */
778  			mod_timer(&buf->timer, jiffies + 1);
779  	}
780  
781  	old = buf->data;
782  	new_subbuf = buf->subbufs_produced % buf->chan->n_subbufs;
783  	new = buf->start + new_subbuf * buf->chan->subbuf_size;
784  	buf->offset = 0;
785  	if (!buf->chan->cb->subbuf_start(buf, new, old, buf->prev_padding)) {
786  		buf->offset = buf->chan->subbuf_size + 1;
787  		return 0;
788  	}
789  	buf->data = new;
790  	buf->padding[new_subbuf] = 0;
791  
792  	if (unlikely(length + buf->offset > buf->chan->subbuf_size))
793  		goto toobig;
794  
795  	return length;
796  
797  toobig:
798  	buf->chan->last_toobig = length;
799  	return 0;
800  }
801  EXPORT_SYMBOL_GPL(relay_switch_subbuf);
802  
803  /**
804   *	relay_subbufs_consumed - update the buffer's sub-buffers-consumed count
805   *	@chan: the channel
806   *	@cpu: the cpu associated with the channel buffer to update
807   *	@subbufs_consumed: number of sub-buffers to add to current buf's count
808   *
809   *	Adds to the channel buffer's consumed sub-buffer count.
810   *	subbufs_consumed should be the number of sub-buffers newly consumed,
811   *	not the total consumed.
812   *
813   *	NOTE. Kernel clients don't need to call this function if the channel
814   *	mode is 'overwrite'.
815   */
816  void relay_subbufs_consumed(struct rchan *chan,
817  			    unsigned int cpu,
818  			    size_t subbufs_consumed)
819  {
820  	struct rchan_buf *buf;
821  
822  	if (!chan)
823  		return;
824  
825  	if (cpu >= NR_CPUS || !chan->buf[cpu] ||
826  					subbufs_consumed > chan->n_subbufs)
827  		return;
828  
829  	buf = chan->buf[cpu];
830  	if (subbufs_consumed > buf->subbufs_produced - buf->subbufs_consumed)
831  		buf->subbufs_consumed = buf->subbufs_produced;
832  	else
833  		buf->subbufs_consumed += subbufs_consumed;
834  }
835  EXPORT_SYMBOL_GPL(relay_subbufs_consumed);
836  
837  /**
838   *	relay_close - close the channel
839   *	@chan: the channel
840   *
841   *	Closes all channel buffers and frees the channel.
842   */
843  void relay_close(struct rchan *chan)
844  {
845  	unsigned int i;
846  
847  	if (!chan)
848  		return;
849  
850  	mutex_lock(&relay_channels_mutex);
851  	if (chan->is_global && chan->buf[0])
852  		relay_close_buf(chan->buf[0]);
853  	else
854  		for_each_possible_cpu(i)
855  			if (chan->buf[i])
856  				relay_close_buf(chan->buf[i]);
857  
858  	if (chan->last_toobig)
859  		printk(KERN_WARNING "relay: one or more items not logged "
860  		       "[item size (%Zd) > sub-buffer size (%Zd)]\n",
861  		       chan->last_toobig, chan->subbuf_size);
862  
863  	list_del(&chan->list);
864  	kref_put(&chan->kref, relay_destroy_channel);
865  	mutex_unlock(&relay_channels_mutex);
866  }
867  EXPORT_SYMBOL_GPL(relay_close);
868  
869  /**
870   *	relay_flush - close the channel
871   *	@chan: the channel
872   *
873   *	Flushes all channel buffers, i.e. forces buffer switch.
874   */
875  void relay_flush(struct rchan *chan)
876  {
877  	unsigned int i;
878  
879  	if (!chan)
880  		return;
881  
882  	if (chan->is_global && chan->buf[0]) {
883  		relay_switch_subbuf(chan->buf[0], 0);
884  		return;
885  	}
886  
887  	mutex_lock(&relay_channels_mutex);
888  	for_each_possible_cpu(i)
889  		if (chan->buf[i])
890  			relay_switch_subbuf(chan->buf[i], 0);
891  	mutex_unlock(&relay_channels_mutex);
892  }
893  EXPORT_SYMBOL_GPL(relay_flush);
894  
895  /**
896   *	relay_file_open - open file op for relay files
897   *	@inode: the inode
898   *	@filp: the file
899   *
900   *	Increments the channel buffer refcount.
901   */
902  static int relay_file_open(struct inode *inode, struct file *filp)
903  {
904  	struct rchan_buf *buf = inode->i_private;
905  	kref_get(&buf->kref);
906  	filp->private_data = buf;
907  
908  	return nonseekable_open(inode, filp);
909  }
910  
911  /**
912   *	relay_file_mmap - mmap file op for relay files
913   *	@filp: the file
914   *	@vma: the vma describing what to map
915   *
916   *	Calls upon relay_mmap_buf() to map the file into user space.
917   */
918  static int relay_file_mmap(struct file *filp, struct vm_area_struct *vma)
919  {
920  	struct rchan_buf *buf = filp->private_data;
921  	return relay_mmap_buf(buf, vma);
922  }
923  
924  /**
925   *	relay_file_poll - poll file op for relay files
926   *	@filp: the file
927   *	@wait: poll table
928   *
929   *	Poll implemention.
930   */
931  static unsigned int relay_file_poll(struct file *filp, poll_table *wait)
932  {
933  	unsigned int mask = 0;
934  	struct rchan_buf *buf = filp->private_data;
935  
936  	if (buf->finalized)
937  		return POLLERR;
938  
939  	if (filp->f_mode & FMODE_READ) {
940  		poll_wait(filp, &buf->read_wait, wait);
941  		if (!relay_buf_empty(buf))
942  			mask |= POLLIN | POLLRDNORM;
943  	}
944  
945  	return mask;
946  }
947  
948  /**
949   *	relay_file_release - release file op for relay files
950   *	@inode: the inode
951   *	@filp: the file
952   *
953   *	Decrements the channel refcount, as the filesystem is
954   *	no longer using it.
955   */
956  static int relay_file_release(struct inode *inode, struct file *filp)
957  {
958  	struct rchan_buf *buf = filp->private_data;
959  	kref_put(&buf->kref, relay_remove_buf);
960  
961  	return 0;
962  }
963  
964  /*
965   *	relay_file_read_consume - update the consumed count for the buffer
966   */
967  static void relay_file_read_consume(struct rchan_buf *buf,
968  				    size_t read_pos,
969  				    size_t bytes_consumed)
970  {
971  	size_t subbuf_size = buf->chan->subbuf_size;
972  	size_t n_subbufs = buf->chan->n_subbufs;
973  	size_t read_subbuf;
974  
975  	if (buf->subbufs_produced == buf->subbufs_consumed &&
976  	    buf->offset == buf->bytes_consumed)
977  		return;
978  
979  	if (buf->bytes_consumed + bytes_consumed > subbuf_size) {
980  		relay_subbufs_consumed(buf->chan, buf->cpu, 1);
981  		buf->bytes_consumed = 0;
982  	}
983  
984  	buf->bytes_consumed += bytes_consumed;
985  	if (!read_pos)
986  		read_subbuf = buf->subbufs_consumed % n_subbufs;
987  	else
988  		read_subbuf = read_pos / buf->chan->subbuf_size;
989  	if (buf->bytes_consumed + buf->padding[read_subbuf] == subbuf_size) {
990  		if ((read_subbuf == buf->subbufs_produced % n_subbufs) &&
991  		    (buf->offset == subbuf_size))
992  			return;
993  		relay_subbufs_consumed(buf->chan, buf->cpu, 1);
994  		buf->bytes_consumed = 0;
995  	}
996  }
997  
998  /*
999   *	relay_file_read_avail - boolean, are there unconsumed bytes available?
1000   */
1001  static int relay_file_read_avail(struct rchan_buf *buf, size_t read_pos)
1002  {
1003  	size_t subbuf_size = buf->chan->subbuf_size;
1004  	size_t n_subbufs = buf->chan->n_subbufs;
1005  	size_t produced = buf->subbufs_produced;
1006  	size_t consumed = buf->subbufs_consumed;
1007  
1008  	relay_file_read_consume(buf, read_pos, 0);
1009  
1010  	consumed = buf->subbufs_consumed;
1011  
1012  	if (unlikely(buf->offset > subbuf_size)) {
1013  		if (produced == consumed)
1014  			return 0;
1015  		return 1;
1016  	}
1017  
1018  	if (unlikely(produced - consumed >= n_subbufs)) {
1019  		consumed = produced - n_subbufs + 1;
1020  		buf->subbufs_consumed = consumed;
1021  		buf->bytes_consumed = 0;
1022  	}
1023  
1024  	produced = (produced % n_subbufs) * subbuf_size + buf->offset;
1025  	consumed = (consumed % n_subbufs) * subbuf_size + buf->bytes_consumed;
1026  
1027  	if (consumed > produced)
1028  		produced += n_subbufs * subbuf_size;
1029  
1030  	if (consumed == produced) {
1031  		if (buf->offset == subbuf_size &&
1032  		    buf->subbufs_produced > buf->subbufs_consumed)
1033  			return 1;
1034  		return 0;
1035  	}
1036  
1037  	return 1;
1038  }
1039  
1040  /**
1041   *	relay_file_read_subbuf_avail - return bytes available in sub-buffer
1042   *	@read_pos: file read position
1043   *	@buf: relay channel buffer
1044   */
1045  static size_t relay_file_read_subbuf_avail(size_t read_pos,
1046  					   struct rchan_buf *buf)
1047  {
1048  	size_t padding, avail = 0;
1049  	size_t read_subbuf, read_offset, write_subbuf, write_offset;
1050  	size_t subbuf_size = buf->chan->subbuf_size;
1051  
1052  	write_subbuf = (buf->data - buf->start) / subbuf_size;
1053  	write_offset = buf->offset > subbuf_size ? subbuf_size : buf->offset;
1054  	read_subbuf = read_pos / subbuf_size;
1055  	read_offset = read_pos % subbuf_size;
1056  	padding = buf->padding[read_subbuf];
1057  
1058  	if (read_subbuf == write_subbuf) {
1059  		if (read_offset + padding < write_offset)
1060  			avail = write_offset - (read_offset + padding);
1061  	} else
1062  		avail = (subbuf_size - padding) - read_offset;
1063  
1064  	return avail;
1065  }
1066  
1067  /**
1068   *	relay_file_read_start_pos - find the first available byte to read
1069   *	@read_pos: file read position
1070   *	@buf: relay channel buffer
1071   *
1072   *	If the @read_pos is in the middle of padding, return the
1073   *	position of the first actually available byte, otherwise
1074   *	return the original value.
1075   */
1076  static size_t relay_file_read_start_pos(size_t read_pos,
1077  					struct rchan_buf *buf)
1078  {
1079  	size_t read_subbuf, padding, padding_start, padding_end;
1080  	size_t subbuf_size = buf->chan->subbuf_size;
1081  	size_t n_subbufs = buf->chan->n_subbufs;
1082  	size_t consumed = buf->subbufs_consumed % n_subbufs;
1083  
1084  	if (!read_pos)
1085  		read_pos = consumed * subbuf_size + buf->bytes_consumed;
1086  	read_subbuf = read_pos / subbuf_size;
1087  	padding = buf->padding[read_subbuf];
1088  	padding_start = (read_subbuf + 1) * subbuf_size - padding;
1089  	padding_end = (read_subbuf + 1) * subbuf_size;
1090  	if (read_pos >= padding_start && read_pos < padding_end) {
1091  		read_subbuf = (read_subbuf + 1) % n_subbufs;
1092  		read_pos = read_subbuf * subbuf_size;
1093  	}
1094  
1095  	return read_pos;
1096  }
1097  
1098  /**
1099   *	relay_file_read_end_pos - return the new read position
1100   *	@read_pos: file read position
1101   *	@buf: relay channel buffer
1102   *	@count: number of bytes to be read
1103   */
1104  static size_t relay_file_read_end_pos(struct rchan_buf *buf,
1105  				      size_t read_pos,
1106  				      size_t count)
1107  {
1108  	size_t read_subbuf, padding, end_pos;
1109  	size_t subbuf_size = buf->chan->subbuf_size;
1110  	size_t n_subbufs = buf->chan->n_subbufs;
1111  
1112  	read_subbuf = read_pos / subbuf_size;
1113  	padding = buf->padding[read_subbuf];
1114  	if (read_pos % subbuf_size + count + padding == subbuf_size)
1115  		end_pos = (read_subbuf + 1) * subbuf_size;
1116  	else
1117  		end_pos = read_pos + count;
1118  	if (end_pos >= subbuf_size * n_subbufs)
1119  		end_pos = 0;
1120  
1121  	return end_pos;
1122  }
1123  
1124  /*
1125   *	subbuf_read_actor - read up to one subbuf's worth of data
1126   */
1127  static int subbuf_read_actor(size_t read_start,
1128  			     struct rchan_buf *buf,
1129  			     size_t avail,
1130  			     read_descriptor_t *desc)
1131  {
1132  	void *from;
1133  	int ret = 0;
1134  
1135  	from = buf->start + read_start;
1136  	ret = avail;
1137  	if (copy_to_user(desc->arg.buf, from, avail)) {
1138  		desc->error = -EFAULT;
1139  		ret = 0;
1140  	}
1141  	desc->arg.data += ret;
1142  	desc->written += ret;
1143  	desc->count -= ret;
1144  
1145  	return ret;
1146  }
1147  
1148  typedef int (*subbuf_actor_t) (size_t read_start,
1149  			       struct rchan_buf *buf,
1150  			       size_t avail,
1151  			       read_descriptor_t *desc);
1152  
1153  /*
1154   *	relay_file_read_subbufs - read count bytes, bridging subbuf boundaries
1155   */
1156  static ssize_t relay_file_read_subbufs(struct file *filp, loff_t *ppos,
1157  					subbuf_actor_t subbuf_actor,
1158  					read_descriptor_t *desc)
1159  {
1160  	struct rchan_buf *buf = filp->private_data;
1161  	size_t read_start, avail;
1162  	int ret;
1163  
1164  	if (!desc->count)
1165  		return 0;
1166  
1167  	inode_lock(file_inode(filp));
1168  	do {
1169  		if (!relay_file_read_avail(buf, *ppos))
1170  			break;
1171  
1172  		read_start = relay_file_read_start_pos(*ppos, buf);
1173  		avail = relay_file_read_subbuf_avail(read_start, buf);
1174  		if (!avail)
1175  			break;
1176  
1177  		avail = min(desc->count, avail);
1178  		ret = subbuf_actor(read_start, buf, avail, desc);
1179  		if (desc->error < 0)
1180  			break;
1181  
1182  		if (ret) {
1183  			relay_file_read_consume(buf, read_start, ret);
1184  			*ppos = relay_file_read_end_pos(buf, read_start, ret);
1185  		}
1186  	} while (desc->count && ret);
1187  	inode_unlock(file_inode(filp));
1188  
1189  	return desc->written;
1190  }
1191  
1192  static ssize_t relay_file_read(struct file *filp,
1193  			       char __user *buffer,
1194  			       size_t count,
1195  			       loff_t *ppos)
1196  {
1197  	read_descriptor_t desc;
1198  	desc.written = 0;
1199  	desc.count = count;
1200  	desc.arg.buf = buffer;
1201  	desc.error = 0;
1202  	return relay_file_read_subbufs(filp, ppos, subbuf_read_actor, &desc);
1203  }
1204  
1205  static void relay_consume_bytes(struct rchan_buf *rbuf, int bytes_consumed)
1206  {
1207  	rbuf->bytes_consumed += bytes_consumed;
1208  
1209  	if (rbuf->bytes_consumed >= rbuf->chan->subbuf_size) {
1210  		relay_subbufs_consumed(rbuf->chan, rbuf->cpu, 1);
1211  		rbuf->bytes_consumed %= rbuf->chan->subbuf_size;
1212  	}
1213  }
1214  
1215  static void relay_pipe_buf_release(struct pipe_inode_info *pipe,
1216  				   struct pipe_buffer *buf)
1217  {
1218  	struct rchan_buf *rbuf;
1219  
1220  	rbuf = (struct rchan_buf *)page_private(buf->page);
1221  	relay_consume_bytes(rbuf, buf->private);
1222  }
1223  
1224  static const struct pipe_buf_operations relay_pipe_buf_ops = {
1225  	.can_merge = 0,
1226  	.confirm = generic_pipe_buf_confirm,
1227  	.release = relay_pipe_buf_release,
1228  	.steal = generic_pipe_buf_steal,
1229  	.get = generic_pipe_buf_get,
1230  };
1231  
1232  static void relay_page_release(struct splice_pipe_desc *spd, unsigned int i)
1233  {
1234  }
1235  
1236  /*
1237   *	subbuf_splice_actor - splice up to one subbuf's worth of data
1238   */
1239  static ssize_t subbuf_splice_actor(struct file *in,
1240  			       loff_t *ppos,
1241  			       struct pipe_inode_info *pipe,
1242  			       size_t len,
1243  			       unsigned int flags,
1244  			       int *nonpad_ret)
1245  {
1246  	unsigned int pidx, poff, total_len, subbuf_pages, nr_pages;
1247  	struct rchan_buf *rbuf = in->private_data;
1248  	unsigned int subbuf_size = rbuf->chan->subbuf_size;
1249  	uint64_t pos = (uint64_t) *ppos;
1250  	uint32_t alloc_size = (uint32_t) rbuf->chan->alloc_size;
1251  	size_t read_start = (size_t) do_div(pos, alloc_size);
1252  	size_t read_subbuf = read_start / subbuf_size;
1253  	size_t padding = rbuf->padding[read_subbuf];
1254  	size_t nonpad_end = read_subbuf * subbuf_size + subbuf_size - padding;
1255  	struct page *pages[PIPE_DEF_BUFFERS];
1256  	struct partial_page partial[PIPE_DEF_BUFFERS];
1257  	struct splice_pipe_desc spd = {
1258  		.pages = pages,
1259  		.nr_pages = 0,
1260  		.nr_pages_max = PIPE_DEF_BUFFERS,
1261  		.partial = partial,
1262  		.flags = flags,
1263  		.ops = &relay_pipe_buf_ops,
1264  		.spd_release = relay_page_release,
1265  	};
1266  	ssize_t ret;
1267  
1268  	if (rbuf->subbufs_produced == rbuf->subbufs_consumed)
1269  		return 0;
1270  	if (splice_grow_spd(pipe, &spd))
1271  		return -ENOMEM;
1272  
1273  	/*
1274  	 * Adjust read len, if longer than what is available
1275  	 */
1276  	if (len > (subbuf_size - read_start % subbuf_size))
1277  		len = subbuf_size - read_start % subbuf_size;
1278  
1279  	subbuf_pages = rbuf->chan->alloc_size >> PAGE_SHIFT;
1280  	pidx = (read_start / PAGE_SIZE) % subbuf_pages;
1281  	poff = read_start & ~PAGE_MASK;
1282  	nr_pages = min_t(unsigned int, subbuf_pages, spd.nr_pages_max);
1283  
1284  	for (total_len = 0; spd.nr_pages < nr_pages; spd.nr_pages++) {
1285  		unsigned int this_len, this_end, private;
1286  		unsigned int cur_pos = read_start + total_len;
1287  
1288  		if (!len)
1289  			break;
1290  
1291  		this_len = min_t(unsigned long, len, PAGE_SIZE - poff);
1292  		private = this_len;
1293  
1294  		spd.pages[spd.nr_pages] = rbuf->page_array[pidx];
1295  		spd.partial[spd.nr_pages].offset = poff;
1296  
1297  		this_end = cur_pos + this_len;
1298  		if (this_end >= nonpad_end) {
1299  			this_len = nonpad_end - cur_pos;
1300  			private = this_len + padding;
1301  		}
1302  		spd.partial[spd.nr_pages].len = this_len;
1303  		spd.partial[spd.nr_pages].private = private;
1304  
1305  		len -= this_len;
1306  		total_len += this_len;
1307  		poff = 0;
1308  		pidx = (pidx + 1) % subbuf_pages;
1309  
1310  		if (this_end >= nonpad_end) {
1311  			spd.nr_pages++;
1312  			break;
1313  		}
1314  	}
1315  
1316  	ret = 0;
1317  	if (!spd.nr_pages)
1318  		goto out;
1319  
1320  	ret = *nonpad_ret = splice_to_pipe(pipe, &spd);
1321  	if (ret < 0 || ret < total_len)
1322  		goto out;
1323  
1324          if (read_start + ret == nonpad_end)
1325                  ret += padding;
1326  
1327  out:
1328  	splice_shrink_spd(&spd);
1329  	return ret;
1330  }
1331  
1332  static ssize_t relay_file_splice_read(struct file *in,
1333  				      loff_t *ppos,
1334  				      struct pipe_inode_info *pipe,
1335  				      size_t len,
1336  				      unsigned int flags)
1337  {
1338  	ssize_t spliced;
1339  	int ret;
1340  	int nonpad_ret = 0;
1341  
1342  	ret = 0;
1343  	spliced = 0;
1344  
1345  	while (len && !spliced) {
1346  		ret = subbuf_splice_actor(in, ppos, pipe, len, flags, &nonpad_ret);
1347  		if (ret < 0)
1348  			break;
1349  		else if (!ret) {
1350  			if (flags & SPLICE_F_NONBLOCK)
1351  				ret = -EAGAIN;
1352  			break;
1353  		}
1354  
1355  		*ppos += ret;
1356  		if (ret > len)
1357  			len = 0;
1358  		else
1359  			len -= ret;
1360  		spliced += nonpad_ret;
1361  		nonpad_ret = 0;
1362  	}
1363  
1364  	if (spliced)
1365  		return spliced;
1366  
1367  	return ret;
1368  }
1369  
1370  const struct file_operations relay_file_operations = {
1371  	.open		= relay_file_open,
1372  	.poll		= relay_file_poll,
1373  	.mmap		= relay_file_mmap,
1374  	.read		= relay_file_read,
1375  	.llseek		= no_llseek,
1376  	.release	= relay_file_release,
1377  	.splice_read	= relay_file_splice_read,
1378  };
1379  EXPORT_SYMBOL_GPL(relay_file_operations);
1380  
1381  static __init int relay_init(void)
1382  {
1383  
1384  	hotcpu_notifier(relay_hotcpu_callback, 0);
1385  	return 0;
1386  }
1387  
1388  early_initcall(relay_init);
1389