tools/perf/lib/mmap.c

// SPDX-License-Identifier: GPL-2.0
#include <sys/mman.h>
#include <linux/ring_buffer.h>
#include <linux/perf_event.h>
#include <perf/mmap.h>
#include <internal/mmap.h>
#include <internal/lib.h>
#include <linux/kernel.h>

void perf_mmap__init(struct perf_mmap *map, bool overwrite,
		     libperf_unmap_cb_t unmap_cb)
{
	map->fd = -1;
	map->overwrite = overwrite;
	map->unmap_cb  = unmap_cb;
	refcount_set(&map->refcnt, 0);
}

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

int perf_mmap__mmap(struct perf_mmap *map, struct perf_mmap_param *mp,
		    int fd, int cpu)
{
	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) {
		map->base = NULL;
		return -1;
	}

	map->fd  = fd;
	map->cpu = cpu;
	return 0;
}

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

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);
}

static inline void perf_mmap__write_tail(struct perf_mmap *md, u64 tail)
{
	ring_buffer_write_tail(md->base, tail);
}

u64 perf_mmap__read_head(struct perf_mmap *map)
{
	return ring_buffer_read_head(map->base);
}

static bool perf_mmap__empty(struct perf_mmap *map)
{
	struct perf_event_mmap_page *pc = map->base;

	return perf_mmap__read_head(map) == map->prev && !pc->aux_size;
}

void perf_mmap__consume(struct perf_mmap *map)
{
	if (!map->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);
}