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// SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
/*
* Ring buffer operations.
*
* Copyright (C) 2020 Facebook, Inc.
*/
#ifndef _GNU_SOURCE
#define _GNU_SOURCE
#endif
#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <unistd.h>
#include <linux/err.h>
#include <linux/bpf.h>
#include <asm/barrier.h>
#include <sys/mman.h>
#include <sys/epoll.h>
#include "libbpf.h"
#include "libbpf_internal.h"
#include "bpf.h"
struct ring {
ring_buffer_sample_fn sample_cb;
void *ctx;
void *data;
unsigned long *consumer_pos;
unsigned long *producer_pos;
unsigned long mask;
int map_fd;
};
struct ring_buffer {
struct epoll_event *events;
struct ring *rings;
size_t page_size;
int epoll_fd;
int ring_cnt;
};
static void ringbuf_unmap_ring(struct ring_buffer *rb, struct ring *r)
{
if (r->consumer_pos) {
munmap(r->consumer_pos, rb->page_size);
r->consumer_pos = NULL;
}
if (r->producer_pos) {
munmap(r->producer_pos, rb->page_size + 2 * (r->mask + 1));
r->producer_pos = NULL;
}
}
/* Add extra RINGBUF maps to this ring buffer manager */
int ring_buffer__add(struct ring_buffer *rb, int map_fd,
ring_buffer_sample_fn sample_cb, void *ctx)
{
struct bpf_map_info info;
__u32 len = sizeof(info);
struct epoll_event *e;
struct ring *r;
void *tmp;
int err;
memset(&info, 0, sizeof(info));
err = bpf_obj_get_info_by_fd(map_fd, &info, &len);
if (err) {
err = -errno;
pr_warn("ringbuf: failed to get map info for fd=%d: %d\n",
map_fd, err);
return err;
}
if (info.type != BPF_MAP_TYPE_RINGBUF) {
pr_warn("ringbuf: map fd=%d is not BPF_MAP_TYPE_RINGBUF\n",
map_fd);
return -EINVAL;
}
tmp = libbpf_reallocarray(rb->rings, rb->ring_cnt + 1, sizeof(*rb->rings));
if (!tmp)
return -ENOMEM;
rb->rings = tmp;
tmp = libbpf_reallocarray(rb->events, rb->ring_cnt + 1, sizeof(*rb->events));
if (!tmp)
return -ENOMEM;
rb->events = tmp;
r = &rb->rings[rb->ring_cnt];
memset(r, 0, sizeof(*r));
r->map_fd = map_fd;
r->sample_cb = sample_cb;
r->ctx = ctx;
r->mask = info.max_entries - 1;
/* Map writable consumer page */
tmp = mmap(NULL, rb->page_size, PROT_READ | PROT_WRITE, MAP_SHARED,
map_fd, 0);
if (tmp == MAP_FAILED) {
err = -errno;
pr_warn("ringbuf: failed to mmap consumer page for map fd=%d: %d\n",
map_fd, err);
return err;
}
r->consumer_pos = tmp;
/* Map read-only producer page and data pages. We map twice as big
* data size to allow simple reading of samples that wrap around the
* end of a ring buffer. See kernel implementation for details.
* */
tmp = mmap(NULL, rb->page_size + 2 * info.max_entries, PROT_READ,
MAP_SHARED, map_fd, rb->page_size);
if (tmp == MAP_FAILED) {
err = -errno;
ringbuf_unmap_ring(rb, r);
pr_warn("ringbuf: failed to mmap data pages for map fd=%d: %d\n",
map_fd, err);
return err;
}
r->producer_pos = tmp;
r->data = tmp + rb->page_size;
e = &rb->events[rb->ring_cnt];
memset(e, 0, sizeof(*e));
e->events = EPOLLIN;
e->data.fd = rb->ring_cnt;
if (epoll_ctl(rb->epoll_fd, EPOLL_CTL_ADD, map_fd, e) < 0) {
err = -errno;
ringbuf_unmap_ring(rb, r);
pr_warn("ringbuf: failed to epoll add map fd=%d: %d\n",
map_fd, err);
return err;
}
rb->ring_cnt++;
return 0;
}
void ring_buffer__free(struct ring_buffer *rb)
{
int i;
if (!rb)
return;
for (i = 0; i < rb->ring_cnt; ++i)
ringbuf_unmap_ring(rb, &rb->rings[i]);
if (rb->epoll_fd >= 0)
close(rb->epoll_fd);
free(rb->events);
free(rb->rings);
free(rb);
}
struct ring_buffer *
ring_buffer__new(int map_fd, ring_buffer_sample_fn sample_cb, void *ctx,
const struct ring_buffer_opts *opts)
{
struct ring_buffer *rb;
int err;
if (!OPTS_VALID(opts, ring_buffer_opts))
return NULL;
rb = calloc(1, sizeof(*rb));
if (!rb)
return NULL;
rb->page_size = getpagesize();
rb->epoll_fd = epoll_create1(EPOLL_CLOEXEC);
if (rb->epoll_fd < 0) {
err = -errno;
pr_warn("ringbuf: failed to create epoll instance: %d\n", err);
goto err_out;
}
err = ring_buffer__add(rb, map_fd, sample_cb, ctx);
if (err)
goto err_out;
return rb;
err_out:
ring_buffer__free(rb);
return NULL;
}
static inline int roundup_len(__u32 len)
{
/* clear out top 2 bits (discard and busy, if set) */
len <<= 2;
len >>= 2;
/* add length prefix */
len += BPF_RINGBUF_HDR_SZ;
/* round up to 8 byte alignment */
return (len + 7) / 8 * 8;
}
static int64_t ringbuf_process_ring(struct ring* r)
{
int *len_ptr, len, err;
/* 64-bit to avoid overflow in case of extreme application behavior */
int64_t cnt = 0;
unsigned long cons_pos, prod_pos;
bool got_new_data;
void *sample;
cons_pos = smp_load_acquire(r->consumer_pos);
do {
got_new_data = false;
prod_pos = smp_load_acquire(r->producer_pos);
while (cons_pos < prod_pos) {
len_ptr = r->data + (cons_pos & r->mask);
len = smp_load_acquire(len_ptr);
/* sample not committed yet, bail out for now */
if (len & BPF_RINGBUF_BUSY_BIT)
goto done;
got_new_data = true;
cons_pos += roundup_len(len);
if ((len & BPF_RINGBUF_DISCARD_BIT) == 0) {
sample = (void *)len_ptr + BPF_RINGBUF_HDR_SZ;
err = r->sample_cb(r->ctx, sample, len);
if (err < 0) {
/* update consumer pos and bail out */
smp_store_release(r->consumer_pos,
cons_pos);
return err;
}
cnt++;
}
smp_store_release(r->consumer_pos, cons_pos);
}
} while (got_new_data);
done:
return cnt;
}
/* Consume available ring buffer(s) data without event polling.
* Returns number of records consumed across all registered ring buffers (or
* INT_MAX, whichever is less), or negative number if any of the callbacks
* return error.
*/
int ring_buffer__consume(struct ring_buffer *rb)
{
int64_t err, res = 0;
int i;
for (i = 0; i < rb->ring_cnt; i++) {
struct ring *ring = &rb->rings[i];
err = ringbuf_process_ring(ring);
if (err < 0)
return err;
res += err;
}
if (res > INT_MAX)
return INT_MAX;
return res;
}
/* Poll for available data and consume records, if any are available.
* Returns number of records consumed (or INT_MAX, whichever is less), or
* negative number, if any of the registered callbacks returned error.
*/
int ring_buffer__poll(struct ring_buffer *rb, int timeout_ms)
{
int i, cnt;
int64_t err, res = 0;
cnt = epoll_wait(rb->epoll_fd, rb->events, rb->ring_cnt, timeout_ms);
if (cnt < 0)
return -errno;
for (i = 0; i < cnt; i++) {
__u32 ring_id = rb->events[i].data.fd;
struct ring *ring = &rb->rings[ring_id];
err = ringbuf_process_ring(ring);
if (err < 0)
return err;
res += err;
}
if (res > INT_MAX)
return INT_MAX;
return res;
}