mmap.c

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/*
 * 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,
                     u64 *startp, u64 end)
{
    unsigned char *data = map->base + page_size;
    union perf_event *event = NULL;
    int diff = end - *startp;

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

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

        if (size < sizeof(event->header) || diff < (int)size)
            return NULL;

        /*
         * Event straddles the mmap boundary -- header should always
         * be inside due to u64 alignment of output.
         */
        if ((*startp & map->mask) + size != ((*startp + size) & map->mask)) {
            unsigned int offset = *startp;
            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;
        }

        *startp += size;
    }

    return event;
}

/*
 * Read event from ring buffer one by one.
 * Return one event for each call.
 *
 * Usage:
 * perf_mmap__read_init()
 * while(event = perf_mmap__read_event()) {
 *  //process the event
 *  perf_mmap__consume()
 * }
 * perf_mmap__read_done()
 */
union perf_event *perf_mmap__read_event(struct perf_mmap *map)
{
    union perf_event *event;

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

    /* non-overwirte doesn't pause the ringbuffer */
    if (!map->overwrite)
        map->end = perf_mmap__read_head(map);

    event = perf_mmap__read(map, &map->start, map->end);

    if (!map->overwrite)
        map->prev = map->start;

    return event;
}

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)
{
    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);
}

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

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

/*
 * Report the start and end of the available data in ringbuffer
 */
static int __perf_mmap__read_init(struct perf_mmap *md)
{
    u64 head = perf_mmap__read_head(md);
    u64 old = md->prev;
    unsigned char *data = md->base + page_size;
    unsigned long size;

    md->start = md->overwrite ? head : old;
    md->end = md->overwrite ? old : head;

    if (md->start == md->end)
        return -EAGAIN;

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

            md->prev = head;
            perf_mmap__consume(md);
            return -EAGAIN;
        }

        /*
         * Backward ring buffer is full. We still have a chance to read
         * most of data from it.
         */
        if (overwrite_rb_find_range(data, md->mask, &md->start, &md->end))
            return -EINVAL;
    }

    return 0;
}

int perf_mmap__read_init(struct perf_mmap *map)
{
    /*
     * Check if event was unmapped due to a POLLHUP/POLLERR.
     */
    if (!refcount_read(&map->refcnt))
        return -ENOENT;

    return __perf_mmap__read_init(map);
}

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

    rc = perf_mmap__read_init(md);
    if (rc < 0)
        return (rc == -EAGAIN) ? 0 : -1;

    size = md->end - md->start;

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

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

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

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

    md->prev = head;
    perf_mmap__consume(md);
out:
    return rc;
}

/*
 * Mandatory for overwrite mode
 * The direction of overwrite mode is backward.
 * The last perf_mmap__read() will set tail to map->prev.
 * Need to correct the map->prev to head which is the end of next read.
 */
void perf_mmap__read_done(struct perf_mmap *map)
{
    /*
     * Check if event was unmapped due to a POLLHUP/POLLERR.
     */
    if (!refcount_read(&map->refcnt))
        return;

    map->prev = perf_mmap__read_head(map);
}