xref: /kernel/linux/linux-5.10/tools/lib/perf/mmap.c (revision 8c2ecf20) 
1// SPDX-License-Identifier: GPL-2.0
2#include <sys/mman.h>
3#include <inttypes.h>
4#include <asm/bug.h>
5#include <errno.h>
6#include <string.h>
7#include <linux/ring_buffer.h>
8#include <linux/perf_event.h>
9#include <perf/mmap.h>
10#include <perf/event.h>
11#include <internal/mmap.h>
12#include <internal/lib.h>
13#include <linux/kernel.h>
14#include "internal.h"
15
16void perf_mmap__init(struct perf_mmap *map, struct perf_mmap *prev,
17		     bool overwrite, libperf_unmap_cb_t unmap_cb)
18{
19	map->fd = -1;
20	map->overwrite = overwrite;
21	map->unmap_cb  = unmap_cb;
22	refcount_set(&map->refcnt, 0);
23	if (prev)
24		prev->next = map;
25}
26
27size_t perf_mmap__mmap_len(struct perf_mmap *map)
28{
29	return map->mask + 1 + page_size;
30}
31
32int perf_mmap__mmap(struct perf_mmap *map, struct perf_mmap_param *mp,
33		    int fd, int cpu)
34{
35	map->prev = 0;
36	map->mask = mp->mask;
37	map->base = mmap(NULL, perf_mmap__mmap_len(map), mp->prot,
38			 MAP_SHARED, fd, 0);
39	if (map->base == MAP_FAILED) {
40		map->base = NULL;
41		return -1;
42	}
43
44	map->fd  = fd;
45	map->cpu = cpu;
46	return 0;
47}
48
49void perf_mmap__munmap(struct perf_mmap *map)
50{
51	if (map && map->base != NULL) {
52		munmap(map->base, perf_mmap__mmap_len(map));
53		map->base = NULL;
54		map->fd = -1;
55		refcount_set(&map->refcnt, 0);
56	}
57	if (map && map->unmap_cb)
58		map->unmap_cb(map);
59}
60
61void perf_mmap__get(struct perf_mmap *map)
62{
63	refcount_inc(&map->refcnt);
64}
65
66void perf_mmap__put(struct perf_mmap *map)
67{
68	BUG_ON(map->base && refcount_read(&map->refcnt) == 0);
69
70	if (refcount_dec_and_test(&map->refcnt))
71		perf_mmap__munmap(map);
72}
73
74static inline void perf_mmap__write_tail(struct perf_mmap *md, u64 tail)
75{
76	ring_buffer_write_tail(md->base, tail);
77}
78
79u64 perf_mmap__read_head(struct perf_mmap *map)
80{
81	return ring_buffer_read_head(map->base);
82}
83
84static bool perf_mmap__empty(struct perf_mmap *map)
85{
86	struct perf_event_mmap_page *pc = map->base;
87
88	return perf_mmap__read_head(map) == map->prev && !pc->aux_size;
89}
90
91void perf_mmap__consume(struct perf_mmap *map)
92{
93	if (!map->overwrite) {
94		u64 old = map->prev;
95
96		perf_mmap__write_tail(map, old);
97	}
98
99	if (refcount_read(&map->refcnt) == 1 && perf_mmap__empty(map))
100		perf_mmap__put(map);
101}
102
103static int overwrite_rb_find_range(void *buf, int mask, u64 *start, u64 *end)
104{
105	struct perf_event_header *pheader;
106	u64 evt_head = *start;
107	int size = mask + 1;
108
109	pr_debug2("%s: buf=%p, start=%"PRIx64"\n", __func__, buf, *start);
110	pheader = (struct perf_event_header *)(buf + (*start & mask));
111	while (true) {
112		if (evt_head - *start >= (unsigned int)size) {
113			pr_debug("Finished reading overwrite ring buffer: rewind\n");
114			if (evt_head - *start > (unsigned int)size)
115				evt_head -= pheader->size;
116			*end = evt_head;
117			return 0;
118		}
119
120		pheader = (struct perf_event_header *)(buf + (evt_head & mask));
121
122		if (pheader->size == 0) {
123			pr_debug("Finished reading overwrite ring buffer: get start\n");
124			*end = evt_head;
125			return 0;
126		}
127
128		evt_head += pheader->size;
129		pr_debug3("move evt_head: %"PRIx64"\n", evt_head);
130	}
131	WARN_ONCE(1, "Shouldn't get here\n");
132	return -1;
133}
134
135/*
136 * Report the start and end of the available data in ringbuffer
137 */
138static int __perf_mmap__read_init(struct perf_mmap *md)
139{
140	u64 head = perf_mmap__read_head(md);
141	u64 old = md->prev;
142	unsigned char *data = md->base + page_size;
143	unsigned long size;
144
145	md->start = md->overwrite ? head : old;
146	md->end = md->overwrite ? old : head;
147
148	if ((md->end - md->start) < md->flush)
149		return -EAGAIN;
150
151	size = md->end - md->start;
152	if (size > (unsigned long)(md->mask) + 1) {
153		if (!md->overwrite) {
154			WARN_ONCE(1, "failed to keep up with mmap data. (warn only once)\n");
155
156			md->prev = head;
157			perf_mmap__consume(md);
158			return -EAGAIN;
159		}
160
161		/*
162		 * Backward ring buffer is full. We still have a chance to read
163		 * most of data from it.
164		 */
165		if (overwrite_rb_find_range(data, md->mask, &md->start, &md->end))
166			return -EINVAL;
167	}
168
169	return 0;
170}
171
172int perf_mmap__read_init(struct perf_mmap *map)
173{
174	/*
175	 * Check if event was unmapped due to a POLLHUP/POLLERR.
176	 */
177	if (!refcount_read(&map->refcnt))
178		return -ENOENT;
179
180	return __perf_mmap__read_init(map);
181}
182
183/*
184 * Mandatory for overwrite mode
185 * The direction of overwrite mode is backward.
186 * The last perf_mmap__read() will set tail to map->core.prev.
187 * Need to correct the map->core.prev to head which is the end of next read.
188 */
189void perf_mmap__read_done(struct perf_mmap *map)
190{
191	/*
192	 * Check if event was unmapped due to a POLLHUP/POLLERR.
193	 */
194	if (!refcount_read(&map->refcnt))
195		return;
196
197	map->prev = perf_mmap__read_head(map);
198}
199
200/* When check_messup is true, 'end' must points to a good entry */
201static union perf_event *perf_mmap__read(struct perf_mmap *map,
202					 u64 *startp, u64 end)
203{
204	unsigned char *data = map->base + page_size;
205	union perf_event *event = NULL;
206	int diff = end - *startp;
207
208	if (diff >= (int)sizeof(event->header)) {
209		size_t size;
210
211		event = (union perf_event *)&data[*startp & map->mask];
212		size = event->header.size;
213
214		if (size < sizeof(event->header) || diff < (int)size)
215			return NULL;
216
217		/*
218		 * Event straddles the mmap boundary -- header should always
219		 * be inside due to u64 alignment of output.
220		 */
221		if ((*startp & map->mask) + size != ((*startp + size) & map->mask)) {
222			unsigned int offset = *startp;
223			unsigned int len = min(sizeof(*event), size), cpy;
224			void *dst = map->event_copy;
225
226			do {
227				cpy = min(map->mask + 1 - (offset & map->mask), len);
228				memcpy(dst, &data[offset & map->mask], cpy);
229				offset += cpy;
230				dst += cpy;
231				len -= cpy;
232			} while (len);
233
234			event = (union perf_event *)map->event_copy;
235		}
236
237		*startp += size;
238	}
239
240	return event;
241}
242
243/*
244 * Read event from ring buffer one by one.
245 * Return one event for each call.
246 *
247 * Usage:
248 * perf_mmap__read_init()
249 * while(event = perf_mmap__read_event()) {
250 *	//process the event
251 *	perf_mmap__consume()
252 * }
253 * perf_mmap__read_done()
254 */
255union perf_event *perf_mmap__read_event(struct perf_mmap *map)
256{
257	union perf_event *event;
258
259	/*
260	 * Check if event was unmapped due to a POLLHUP/POLLERR.
261	 */
262	if (!refcount_read(&map->refcnt))
263		return NULL;
264
265	/* non-overwirte doesn't pause the ringbuffer */
266	if (!map->overwrite)
267		map->end = perf_mmap__read_head(map);
268
269	event = perf_mmap__read(map, &map->start, map->end);
270
271	if (!map->overwrite)
272		map->prev = map->start;
273
274	return event;
275}
276