tools/perf/util/mmap.c - linux - Git at Google

 /*
  * Copyright (C) 2011-2017, Red Hat Inc, Arnaldo Carvalho de Melo <acme@redhat.com>
  *
  * Parts came from evlist.c builtin-{top,stat,record}.c, see those files for further
  * copyright notes.
  *
  * Released under the GPL v2. (and only v2, not any later version)
  */

 #include <sys/mman.h>
 #include <inttypes.h>
 #include <asm/bug.h>
 #include "debug.h"
 #include "event.h"
 #include "mmap.h"
 #include "util.h" /* page_size */

 size_t perf_mmap__mmap_len(struct perf_mmap *map)
 {
 	return map->mask + 1 + page_size;
 }

 /* When check_messup is true, 'end' must points to a good entry */
 static union perf_event *perf_mmap__read(struct perf_mmap *map, bool check_messup,
 					 u64 start, u64 end, u64 *prev)
 {
 	unsigned char *data = map->base + page_size;
 	union perf_event *event = NULL;
 	int diff = end - start;

 	if (check_messup) {
 		/*
 		 * If we're further behind than half the buffer, there's a chance
 		 * the writer will bite our tail and mess up the samples under us.
 		 *
 		 * If we somehow ended up ahead of the 'end', we got messed up.
 		 *
 		 * In either case, truncate and restart at 'end'.
 		 */
 		if (diff > map->mask / 2 || diff < 0) {
 			fprintf(stderr, "WARNING: failed to keep up with mmap data.\n");

 			/*
 			 * 'end' points to a known good entry, start there.
 			 */
 			start = end;
 			diff = 0;
 		}
 	}

 	if (diff >= (int)sizeof(event->header)) {
 		size_t size;

 		event = (union perf_event *)&data[start & map->mask];
 		size = event->header.size;

 		if (size < sizeof(event->header) || diff < (int)size) {
 			event = NULL;
 			goto broken_event;
 		}

 		/*
 		 * Event straddles the mmap boundary -- header should always
 		 * be inside due to u64 alignment of output.
 		 */
 		if ((start & map->mask) + size != ((start + size) & map->mask)) {
 			unsigned int offset = start;
 			unsigned int len = min(sizeof(*event), size), cpy;
 			void *dst = map->event_copy;

 			do {
 				cpy = min(map->mask + 1 - (offset & map->mask), len);
 				memcpy(dst, &data[offset & map->mask], cpy);
 				offset += cpy;
 				dst += cpy;
 				len -= cpy;
 			} while (len);

 			event = (union perf_event *)map->event_copy;
 		}

 		start += size;
 	}

 broken_event:
 	if (prev)
 		*prev = start;

 	return event;
 }

 union perf_event *perf_mmap__read_forward(struct perf_mmap *map, bool check_messup)
 {
 	u64 head;
 	u64 old = map->prev;

 	/*
 	 * Check if event was unmapped due to a POLLHUP/POLLERR.
 	 */
 	if (!refcount_read(&map->refcnt))
 		return NULL;

 	head = perf_mmap__read_head(map);

 	return perf_mmap__read(map, check_messup, old, head, &map->prev);
 }

 union perf_event *perf_mmap__read_backward(struct perf_mmap *map)
 {
 	u64 head, end;
 	u64 start = map->prev;

 	/*
 	 * Check if event was unmapped due to a POLLHUP/POLLERR.
 	 */
 	if (!refcount_read(&map->refcnt))
 		return NULL;

 	head = perf_mmap__read_head(map);
 	if (!head)
 		return NULL;

 	/*
 	 * 'head' pointer starts from 0. Kernel minus sizeof(record) form
 	 * it each time when kernel writes to it, so in fact 'head' is
 	 * negative. 'end' pointer is made manually by adding the size of
 	 * the ring buffer to 'head' pointer, means the validate data can
 	 * read is the whole ring buffer. If 'end' is positive, the ring
 	 * buffer has not fully filled, so we must adjust 'end' to 0.
 	 *
 	 * However, since both 'head' and 'end' is unsigned, we can't
 	 * simply compare 'end' against 0. Here we compare '-head' and
 	 * the size of the ring buffer, where -head is the number of bytes
 	 * kernel write to the ring buffer.
 	 */
 	if (-head < (u64)(map->mask + 1))
 		end = 0;
 	else
 		end = head + map->mask + 1;

 	return perf_mmap__read(map, false, start, end, &map->prev);
 }

 void perf_mmap__read_catchup(struct perf_mmap *map)
 {
 	u64 head;

 	if (!refcount_read(&map->refcnt))
 		return;

 	head = perf_mmap__read_head(map);
 	map->prev = head;
 }

 static bool perf_mmap__empty(struct perf_mmap *map)
 {
 	return perf_mmap__read_head(map) == map->prev && !map->auxtrace_mmap.base;
 }

 void perf_mmap__get(struct perf_mmap *map)
 {
 	refcount_inc(&map->refcnt);
 }

 void perf_mmap__put(struct perf_mmap *map)
 {
 	BUG_ON(map->base && refcount_read(&map->refcnt) == 0);

 	if (refcount_dec_and_test(&map->refcnt))
 		perf_mmap__munmap(map);
 }

 void perf_mmap__consume(struct perf_mmap *map, bool overwrite)
 {
 	if (!overwrite) {
 		u64 old = map->prev;

 		perf_mmap__write_tail(map, old);
 	}

 	if (refcount_read(&map->refcnt) == 1 && perf_mmap__empty(map))
 		perf_mmap__put(map);
 }

 int __weak auxtrace_mmap__mmap(struct auxtrace_mmap *mm __maybe_unused,
 			       struct auxtrace_mmap_params *mp __maybe_unused,
 			       void *userpg __maybe_unused,
 			       int fd __maybe_unused)
 {
 	return 0;
 }

 void __weak auxtrace_mmap__munmap(struct auxtrace_mmap *mm __maybe_unused)
 {
 }

 void __weak auxtrace_mmap_params__init(struct auxtrace_mmap_params *mp __maybe_unused,
 				       off_t auxtrace_offset __maybe_unused,
 				       unsigned int auxtrace_pages __maybe_unused,
 				       bool auxtrace_overwrite __maybe_unused)
 {
 }

 void __weak auxtrace_mmap_params__set_idx(struct auxtrace_mmap_params *mp __maybe_unused,
 					  struct perf_evlist *evlist __maybe_unused,
 					  int idx __maybe_unused,
 					  bool per_cpu __maybe_unused)
 {
 }

 void perf_mmap__munmap(struct perf_mmap *map)
 {
 	if (map->base != NULL) {
 		munmap(map->base, perf_mmap__mmap_len(map));
 		map->base = NULL;
 		map->fd = -1;
 		refcount_set(&map->refcnt, 0);
 	}
 	auxtrace_mmap__munmap(&map->auxtrace_mmap);
 }

 int perf_mmap__mmap(struct perf_mmap *map, struct mmap_params *mp, int fd)
 {
 	/*
 	 * The last one will be done at perf_evlist__mmap_consume(), so that we
 	 * make sure we don't prevent tools from consuming every last event in
 	 * the ring buffer.
 	 *
 	 * I.e. we can get the POLLHUP meaning that the fd doesn't exist
 	 * anymore, but the last events for it are still in the ring buffer,
 	 * waiting to be consumed.
 	 *
 	 * Tools can chose to ignore this at their own discretion, but the
 	 * evlist layer can't just drop it when filtering events in
 	 * perf_evlist__filter_pollfd().
 	 */
 	refcount_set(&map->refcnt, 2);
 	map->prev = 0;
 	map->mask = mp->mask;
 	map->base = mmap(NULL, perf_mmap__mmap_len(map), mp->prot,
 			 MAP_SHARED, fd, 0);
 	if (map->base == MAP_FAILED) {
 		pr_debug2("failed to mmap perf event ring buffer, error %d\n",
 			  errno);
 		map->base = NULL;
 		return -1;
 	}
 	map->fd = fd;

 	if (auxtrace_mmap__mmap(&map->auxtrace_mmap,
 				&mp->auxtrace_mp, map->base, fd))
 		return -1;

 	return 0;
 }

 static int backward_rb_find_range(void *buf, int mask, u64 head, u64 *start, u64 *end)
 {
 	struct perf_event_header *pheader;
 	u64 evt_head = head;
 	int size = mask + 1;

 	pr_debug2("backward_rb_find_range: buf=%p, head=%"PRIx64"\n", buf, head);
 	pheader = (struct perf_event_header *)(buf + (head & mask));
 	*start = head;
 	while (true) {
 		if (evt_head - head >= (unsigned int)size) {
 			pr_debug("Finished reading backward ring buffer: rewind\n");
 			if (evt_head - head > (unsigned int)size)
 				evt_head -= pheader->size;
 			*end = evt_head;
 			return 0;
 		}

 		pheader = (struct perf_event_header *)(buf + (evt_head & mask));

 		if (pheader->size == 0) {
 			pr_debug("Finished reading backward ring buffer: get start\n");
 			*end = evt_head;
 			return 0;
 		}

 		evt_head += pheader->size;
 		pr_debug3("move evt_head: %"PRIx64"\n", evt_head);
 	}
 	WARN_ONCE(1, "Shouldn't get here\n");
 	return -1;
 }

 static int rb_find_range(void *data, int mask, u64 head, u64 old,
 			 u64 *start, u64 *end, bool backward)
 {
 	if (!backward) {
 		*start = old;
 		*end = head;
 		return 0;
 	}

 	return backward_rb_find_range(data, mask, head, start, end);
 }

 int perf_mmap__push(struct perf_mmap *md, bool overwrite, bool backward,
 		    void *to, int push(void *to, void *buf, size_t size))
 {
 	u64 head = perf_mmap__read_head(md);
 	u64 old = md->prev;
 	u64 end = head, start = old;
 	unsigned char *data = md->base + page_size;
 	unsigned long size;
 	void *buf;
 	int rc = 0;

 	if (rb_find_range(data, md->mask, head, old, &start, &end, backward))
 		return -1;

 	if (start == end)
 		return 0;

 	size = end - start;
 	if (size > (unsigned long)(md->mask) + 1) {
 		WARN_ONCE(1, "failed to keep up with mmap data. (warn only once)\n");

 		md->prev = head;
 		perf_mmap__consume(md, overwrite || backward);
 		return 0;
 	}

 	if ((start & md->mask) + size != (end & md->mask)) {
 		buf = &data[start & md->mask];
 		size = md->mask + 1 - (start & md->mask);
 		start += size;

 		if (push(to, buf, size) < 0) {
 			rc = -1;
 			goto out;
 		}
 	}

 	buf = &data[start & md->mask];
 	size = end - start;
 	start += size;

 	if (push(to, buf, size) < 0) {
 		rc = -1;
 		goto out;
 	}

 	md->prev = head;
 	perf_mmap__consume(md, overwrite || backward);
 out:
 	return rc;
 }
	/*
	* Copyright (C) 2011-2017, Red Hat Inc, Arnaldo Carvalho de Melo <acme@redhat.com>
	*
	* Parts came from evlist.c builtin-{top,stat,record}.c, see those files for further
	* copyright notes.
	*
	* Released under the GPL v2. (and only v2, not any later version)
	*/

	#include <sys/mman.h>
	#include <inttypes.h>
	#include <asm/bug.h>
	#include "debug.h"
	#include "event.h"
	#include "mmap.h"
	#include "util.h" /* page_size */

	size_t perf_mmap__mmap_len(struct perf_mmap *map)
	{
	return map->mask + 1 + page_size;
	}

	/* When check_messup is true, 'end' must points to a good entry */
	static union perf_event perf_mmap__read(struct perf_mmap map, bool check_messup,
	u64 start, u64 end, u64 *prev)
	{
	unsigned char *data = map->base + page_size;
	union perf_event *event = NULL;
	int diff = end - start;

	if (check_messup) {
	/*
	* If we're further behind than half the buffer, there's a chance
	* the writer will bite our tail and mess up the samples under us.
	*
	* If we somehow ended up ahead of the 'end', we got messed up.
	*
	* In either case, truncate and restart at 'end'.
	*/
	if (diff > map->mask / 2 \|\| diff < 0) {
	fprintf(stderr, "WARNING: failed to keep up with mmap data.\n");

	/*
	* 'end' points to a known good entry, start there.
	*/
	start = end;
	diff = 0;
	}
	}

	if (diff >= (int)sizeof(event->header)) {
	size_t size;

	event = (union perf_event *)&data[start & map->mask];
	size = event->header.size;

	if (size < sizeof(event->header) \|\| diff < (int)size) {
	event = NULL;
	goto broken_event;
	}

	/*
	* Event straddles the mmap boundary -- header should always
	* be inside due to u64 alignment of output.
	*/
	if ((start & map->mask) + size != ((start + size) & map->mask)) {
	unsigned int offset = start;
	unsigned int len = min(sizeof(*event), size), cpy;
	void *dst = map->event_copy;

	do {
	cpy = min(map->mask + 1 - (offset & map->mask), len);
	memcpy(dst, &data[offset & map->mask], cpy);
	offset += cpy;
	dst += cpy;
	len -= cpy;
	} while (len);

	event = (union perf_event *)map->event_copy;
	}

	start += size;
	}

	broken_event:
	if (prev)
	*prev = start;

	return event;
	}

	union perf_event perf_mmap__read_forward(struct perf_mmap map, bool check_messup)
	{
	u64 head;
	u64 old = map->prev;

	/*
	* Check if event was unmapped due to a POLLHUP/POLLERR.
	*/
	if (!refcount_read(&map->refcnt))
	return NULL;

	head = perf_mmap__read_head(map);

	return perf_mmap__read(map, check_messup, old, head, &map->prev);
	}

	union perf_event perf_mmap__read_backward(struct perf_mmap map)
	{
	u64 head, end;
	u64 start = map->prev;

	/*
	* Check if event was unmapped due to a POLLHUP/POLLERR.
	*/
	if (!refcount_read(&map->refcnt))
	return NULL;

	head = perf_mmap__read_head(map);
	if (!head)
	return NULL;

	/*
	* 'head' pointer starts from 0. Kernel minus sizeof(record) form
	* it each time when kernel writes to it, so in fact 'head' is
	* negative. 'end' pointer is made manually by adding the size of
	* the ring buffer to 'head' pointer, means the validate data can
	* read is the whole ring buffer. If 'end' is positive, the ring
	* buffer has not fully filled, so we must adjust 'end' to 0.
	*
	* However, since both 'head' and 'end' is unsigned, we can't
	* simply compare 'end' against 0. Here we compare '-head' and
	* the size of the ring buffer, where -head is the number of bytes
	* kernel write to the ring buffer.
	*/
	if (-head < (u64)(map->mask + 1))
	end = 0;
	else
	end = head + map->mask + 1;

	return perf_mmap__read(map, false, start, end, &map->prev);
	}

	void perf_mmap__read_catchup(struct perf_mmap *map)
	{
	u64 head;

	if (!refcount_read(&map->refcnt))
	return;

	head = perf_mmap__read_head(map);
	map->prev = head;
	}

	static bool perf_mmap__empty(struct perf_mmap *map)
	{
	return perf_mmap__read_head(map) == map->prev && !map->auxtrace_mmap.base;
	}

	void perf_mmap__get(struct perf_mmap *map)
	{
	refcount_inc(&map->refcnt);
	}

	void perf_mmap__put(struct perf_mmap *map)
	{
	BUG_ON(map->base && refcount_read(&map->refcnt) == 0);

	if (refcount_dec_and_test(&map->refcnt))
	perf_mmap__munmap(map);
	}

	void perf_mmap__consume(struct perf_mmap *map, bool overwrite)
	{
	if (!overwrite) {
	u64 old = map->prev;

	perf_mmap__write_tail(map, old);
	}

	if (refcount_read(&map->refcnt) == 1 && perf_mmap__empty(map))
	perf_mmap__put(map);
	}

	int __weak auxtrace_mmap__mmap(struct auxtrace_mmap *mm __maybe_unused,
	struct auxtrace_mmap_params *mp __maybe_unused,
	void *userpg __maybe_unused,
	int fd __maybe_unused)
	{
	return 0;
	}

	void __weak auxtrace_mmap__munmap(struct auxtrace_mmap *mm __maybe_unused)
	{
	}

	void __weak auxtrace_mmap_params__init(struct auxtrace_mmap_params *mp __maybe_unused,
	off_t auxtrace_offset __maybe_unused,
	unsigned int auxtrace_pages __maybe_unused,
	bool auxtrace_overwrite __maybe_unused)
	{
	}

	void __weak auxtrace_mmap_params__set_idx(struct auxtrace_mmap_params *mp __maybe_unused,
	struct perf_evlist *evlist __maybe_unused,
	int idx __maybe_unused,
	bool per_cpu __maybe_unused)
	{
	}

	void perf_mmap__munmap(struct perf_mmap *map)
	{
	if (map->base != NULL) {
	munmap(map->base, perf_mmap__mmap_len(map));
	map->base = NULL;
	map->fd = -1;
	refcount_set(&map->refcnt, 0);
	}
	auxtrace_mmap__munmap(&map->auxtrace_mmap);
	}

	int perf_mmap__mmap(struct perf_mmap map, struct mmap_params mp, int fd)
	{
	/*
	* The last one will be done at perf_evlist__mmap_consume(), so that we
	* make sure we don't prevent tools from consuming every last event in
	* the ring buffer.
	*
	* I.e. we can get the POLLHUP meaning that the fd doesn't exist
	* anymore, but the last events for it are still in the ring buffer,
	* waiting to be consumed.
	*
	* Tools can chose to ignore this at their own discretion, but the
	* evlist layer can't just drop it when filtering events in
	* perf_evlist__filter_pollfd().
	*/
	refcount_set(&map->refcnt, 2);
	map->prev = 0;
	map->mask = mp->mask;
	map->base = mmap(NULL, perf_mmap__mmap_len(map), mp->prot,
	MAP_SHARED, fd, 0);
	if (map->base == MAP_FAILED) {
	pr_debug2("failed to mmap perf event ring buffer, error %d\n",
	errno);
	map->base = NULL;
	return -1;
	}
	map->fd = fd;

	if (auxtrace_mmap__mmap(&map->auxtrace_mmap,
	&mp->auxtrace_mp, map->base, fd))
	return -1;

	return 0;
	}

	static int backward_rb_find_range(void buf, int mask, u64 head, u64 start, u64 *end)
	{
	struct perf_event_header *pheader;
	u64 evt_head = head;
	int size = mask + 1;

	pr_debug2("backward_rb_find_range: buf=%p, head=%"PRIx64"\n", buf, head);
	pheader = (struct perf_event_header *)(buf + (head & mask));
	*start = head;
	while (true) {
	if (evt_head - head >= (unsigned int)size) {
	pr_debug("Finished reading backward ring buffer: rewind\n");
	if (evt_head - head > (unsigned int)size)
	evt_head -= pheader->size;
	*end = evt_head;
	return 0;
	}

	pheader = (struct perf_event_header *)(buf + (evt_head & mask));

	if (pheader->size == 0) {
	pr_debug("Finished reading backward ring buffer: get start\n");
	*end = evt_head;
	return 0;
	}

	evt_head += pheader->size;
	pr_debug3("move evt_head: %"PRIx64"\n", evt_head);
	}
	WARN_ONCE(1, "Shouldn't get here\n");
	return -1;
	}

	static int rb_find_range(void *data, int mask, u64 head, u64 old,
	u64 start, u64 end, bool backward)
	{
	if (!backward) {
	*start = old;
	*end = head;
	return 0;
	}

	return backward_rb_find_range(data, mask, head, start, end);
	}

	int perf_mmap__push(struct perf_mmap *md, bool overwrite, bool backward,
	void to, int push(void to, void *buf, size_t size))
	{
	u64 head = perf_mmap__read_head(md);
	u64 old = md->prev;
	u64 end = head, start = old;
	unsigned char *data = md->base + page_size;
	unsigned long size;
	void *buf;
	int rc = 0;

	if (rb_find_range(data, md->mask, head, old, &start, &end, backward))
	return -1;

	if (start == end)
	return 0;

	size = end - start;
	if (size > (unsigned long)(md->mask) + 1) {
	WARN_ONCE(1, "failed to keep up with mmap data. (warn only once)\n");

	md->prev = head;
	perf_mmap__consume(md, overwrite \|\| backward);
	return 0;
	}

	if ((start & md->mask) + size != (end & md->mask)) {
	buf = &data[start & md->mask];
	size = md->mask + 1 - (start & md->mask);
	start += size;

	if (push(to, buf, size) < 0) {
	rc = -1;
	goto out;
	}
	}

	buf = &data[start & md->mask];
	size = end - start;
	start += size;

	if (push(to, buf, size) < 0) {
	rc = -1;
	goto out;
	}

	md->prev = head;
	perf_mmap__consume(md, overwrite \|\| backward);
	out:
	return rc;
	}