// 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 <time.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;
};
struct user_ring_buffer {
struct epoll_event event;
unsigned long *consumer_pos;
unsigned long *producer_pos;
void *data;
unsigned long mask;
size_t page_size;
int map_fd;
int epoll_fd;
};
/* 8-byte ring buffer header structure */
struct ringbuf_hdr {
__u32 len;
__u32 pad;
};
static void ringbuf_free_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;
}
free(r);
}
/* 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;
__u64 mmap_sz;
void *tmp;
int err;
memset(&info, 0, sizeof(info));
err = bpf_map_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 libbpf_err(err);
}
if (info.type != BPF_MAP_TYPE_RINGBUF) {
pr_warn("ringbuf: map fd=%d is not BPF_MAP_TYPE_RINGBUF\n",
map_fd);
return libbpf_err(-EINVAL);
}
tmp = libbpf_reallocarray(rb->rings, rb->ring_cnt + 1, sizeof(*rb->rings));
if (!tmp)
return libbpf_err(-ENOMEM);
rb->rings = tmp;
tmp = libbpf_reallocarray(rb->events, rb->ring_cnt + 1, sizeof(*rb->events));
if (!tmp)
return libbpf_err(-ENOMEM);
rb->events = tmp;
r = calloc(1, sizeof(*r));
if (!r)
return libbpf_err(-ENOMEM);
rb->rings[rb->ring_cnt] = 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);
goto err_out;
}
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.
*/
mmap_sz = rb->page_size + 2 * (__u64)info.max_entries;
if (mmap_sz != (__u64)(size_t)mmap_sz) {
err = -E2BIG;
pr_warn("ringbuf: ring buffer size (%u) is too big\n", info.max_entries);
goto err_out;
}
tmp = mmap(NULL, (size_t)mmap_sz, PROT_READ, MAP_SHARED, map_fd, rb->page_size);
if (tmp == MAP_FAILED) {
err = -errno;
pr_warn("ringbuf: failed to mmap data pages for map fd=%d: %d\n",
map_fd, err);
goto err_out;
}
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;
pr_warn("ringbuf: failed to epoll add map fd=%d: %d\n",
map_fd, err);
goto err_out;
}
rb->ring_cnt++;
return 0;
err_out:
ringbuf_free_ring(rb, r);
return libbpf_err(err);
}
void ring_buffer__free(struct ring_buffer *rb)
{
int i;
if (!rb)
return;
for (i = 0; i < rb->ring_cnt; ++i)
ringbuf_free_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 errno = EINVAL, NULL;
rb = calloc(1, sizeof(*rb));
if (!rb)
return errno = ENOMEM, 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 errno = -err, 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, size_t n)
{
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);
if (cnt >= n)
goto done;
}
} while (got_new_data);
done:
return cnt;
}
/* Consume available ring buffer(s) data without event polling, up to n
* records.
*
* Returns number of records consumed across all registered ring buffers (or
* n, whichever is less), or negative number if any of the callbacks return
* error.
*/
int ring_buffer__consume_n(struct ring_buffer *rb, size_t n)
{
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, n);
if (err < 0)
return libbpf_err(err);
res += err;
n -= err;
if (n == 0)
break;
}
return res > INT_MAX ? INT_MAX : res;
}
/* 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, INT_MAX);
if (err < 0)
return libbpf_err(err);
res += err;
if (res > INT_MAX) {
res = INT_MAX;
break;
}
}
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 libbpf_err(-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, INT_MAX);
if (err < 0)
return libbpf_err(err);
res += err;
}
if (res > INT_MAX)
res = INT_MAX;
return res;
}
/* Get an fd that can be used to sleep until data is available in the ring(s) */
int ring_buffer__epoll_fd(const struct ring_buffer *rb)
{
return rb->epoll_fd;
}
struct ring *ring_buffer__ring(struct ring_buffer *rb, unsigned int idx)
{
if (idx >= rb->ring_cnt)
return errno = ERANGE, NULL;
return rb->rings[idx];
}
unsigned long ring__consumer_pos(const struct ring *r)
{
/* Synchronizes with smp_store_release() in ringbuf_process_ring(). */
return smp_load_acquire(r->consumer_pos);
}
unsigned long ring__producer_pos(const struct ring *r)
{
/* Synchronizes with smp_store_release() in __bpf_ringbuf_reserve() in
* the kernel.
*/
return smp_load_acquire(r->producer_pos);
}
size_t ring__avail_data_size(const struct ring *r)
{
unsigned long cons_pos, prod_pos;
cons_pos = ring__consumer_pos(r);
prod_pos = ring__producer_pos(r);
return prod_pos - cons_pos;
}
size_t ring__size(const struct ring *r)
{
return r->mask + 1;
}
int ring__map_fd(const struct ring *r)
{
return r->map_fd;
}
int ring__consume_n(struct ring *r, size_t n)
{
int64_t res;
res = ringbuf_process_ring(r, n);
if (res < 0)
return libbpf_err(res);
return res > INT_MAX ? INT_MAX : res;
}
int ring__consume(struct ring *r)
{
return ring__consume_n(r, INT_MAX);
}
static void user_ringbuf_unmap_ring(struct user_ring_buffer *rb)
{
if (rb->consumer_pos) {
munmap(rb->consumer_pos, rb->page_size);
rb->consumer_pos = NULL;
}
if (rb->producer_pos) {
munmap(rb->producer_pos, rb->page_size + 2 * (rb->mask + 1));
rb->producer_pos = NULL;
}
}
void user_ring_buffer__free(struct user_ring_buffer *rb)
{
if (!rb)
return;
user_ringbuf_unmap_ring(rb);
if (rb->epoll_fd >= 0)
close(rb->epoll_fd);
free(rb);
}
static int user_ringbuf_map(struct user_ring_buffer *rb, int map_fd)
{
struct bpf_map_info info;
__u32 len = sizeof(info);
__u64 mmap_sz;
void *tmp;
struct epoll_event *rb_epoll;
int err;
memset(&info, 0, sizeof(info));
err = bpf_map_get_info_by_fd(map_fd, &info, &len);
if (err) {
err = -errno;
pr_warn("user ringbuf: failed to get map info for fd=%d: %d\n", map_fd, err);
return err;
}
if (info.type != BPF_MAP_TYPE_USER_RINGBUF) {
pr_warn("user ringbuf: map fd=%d is not BPF_MAP_TYPE_USER_RINGBUF\n", map_fd);
return -EINVAL;
}
rb->map_fd = map_fd;
rb->mask = info.max_entries - 1;
/* Map read-only consumer page */
tmp = mmap(NULL, rb->page_size, PROT_READ, MAP_SHARED, map_fd, 0);
if (tmp == MAP_FAILED) {
err = -errno;
pr_warn("user ringbuf: failed to mmap consumer page for map fd=%d: %d\n",
map_fd, err);
return err;
}
rb->consumer_pos = tmp;
/* Map read-write the producer page and data pages. We map the data
* region as twice the total size of the ring buffer to allow the
* simple reading and writing of samples that wrap around the end of
* the buffer. See the kernel implementation for details.
*/
mmap_sz = rb->page_size + 2 * (__u64)info.max_entries;
if (mmap_sz != (__u64)(size_t)mmap_sz) {
pr_warn("user ringbuf: ring buf size (%u) is too big\n", info.max_entries);
return -E2BIG;
}
tmp = mmap(NULL, (size_t)mmap_sz, PROT_READ | PROT_WRITE, MAP_SHARED,
map_fd, rb->page_size);
if (tmp == MAP_FAILED) {
err = -errno;
pr_warn("user ringbuf: failed to mmap data pages for map fd=%d: %d\n",
map_fd, err);
return err;
}
rb->producer_pos = tmp;
rb->data = tmp + rb->page_size;
rb_epoll = &rb->event;
rb_epoll->events = EPOLLOUT;
if (epoll_ctl(rb->epoll_fd, EPOLL_CTL_ADD, map_fd, rb_epoll) < 0) {
err = -errno;
pr_warn("user ringbuf: failed to epoll add map fd=%d: %d\n", map_fd, err);
return err;
}
return 0;
}
struct user_ring_buffer *
user_ring_buffer__new(int map_fd, const struct user_ring_buffer_opts *opts)
{
struct user_ring_buffer *rb;
int err;
if (!OPTS_VALID(opts, user_ring_buffer_opts))
return errno = EINVAL, NULL;
rb = calloc(1, sizeof(*rb));
if (!rb)
return errno = ENOMEM, NULL;
rb->page_size = getpagesize();
rb->epoll_fd = epoll_create1(EPOLL_CLOEXEC);
if (rb->epoll_fd < 0) {
err = -errno;
pr_warn("user ringbuf: failed to create epoll instance: %d\n", err);
goto err_out;
}
err = user_ringbuf_map(rb, map_fd);
if (err)
goto err_out;
return rb;
err_out:
user_ring_buffer__free(rb);
return errno = -err, NULL;
}
static void user_ringbuf_commit(struct user_ring_buffer *rb, void *sample, bool discard)
{
__u32 new_len;
struct ringbuf_hdr *hdr;
uintptr_t hdr_offset;
hdr_offset = rb->mask + 1 + (sample - rb->data) - BPF_RINGBUF_HDR_SZ;
hdr = rb->data + (hdr_offset & rb->mask);
new_len = hdr->len & ~BPF_RINGBUF_BUSY_BIT;
if (discard)
new_len |= BPF_RINGBUF_DISCARD_BIT;
/* Synchronizes with smp_load_acquire() in __bpf_user_ringbuf_peek() in
* the kernel.
*/
__atomic_exchange_n(&hdr->len, new_len, __ATOMIC_ACQ_REL);
}
void user_ring_buffer__discard(struct user_ring_buffer *rb, void *sample)
{
user_ringbuf_commit(rb, sample, true);
}
void user_ring_buffer__submit(struct user_ring_buffer *rb, void *sample)
{
user_ringbuf_commit(rb, sample, false);
}
void *user_ring_buffer__reserve(struct user_ring_buffer *rb, __u32 size)
{
__u32 avail_size, total_size, max_size;
/* 64-bit to avoid overflow in case of extreme application behavior */
__u64 cons_pos, prod_pos;
struct ringbuf_hdr *hdr;
/* The top two bits are used as special flags */
if (size & (BPF_RINGBUF_BUSY_BIT | BPF_RINGBUF_DISCARD_BIT))
return errno = E2BIG, NULL;
/* Synchronizes with smp_store_release() in __bpf_user_ringbuf_peek() in
* the kernel.
*/
cons_pos = smp_load_acquire(rb->consumer_pos);
/* Synchronizes with smp_store_release() in user_ringbuf_commit() */
prod_pos = smp_load_acquire(rb->producer_pos);
max_size = rb->mask + 1;
avail_size = max_size - (prod_pos - cons_pos);
/* Round up total size to a multiple of 8. */
total_size = (size + BPF_RINGBUF_HDR_SZ + 7) / 8 * 8;
if (total_size > max_size)
return errno = E2BIG, NULL;
if (avail_size < total_size)
return errno = ENOSPC, NULL;
hdr = rb->data + (prod_pos & rb->mask);
hdr->len = size | BPF_RINGBUF_BUSY_BIT;
hdr->pad = 0;
/* Synchronizes with smp_load_acquire() in __bpf_user_ringbuf_peek() in
* the kernel.
*/
smp_store_release(rb->producer_pos, prod_pos + total_size);
return (void *)rb->data + ((prod_pos + BPF_RINGBUF_HDR_SZ) & rb->mask);
}
static __u64 ns_elapsed_timespec(const struct timespec *start, const struct timespec *end)
{
__u64 start_ns, end_ns, ns_per_s = 1000000000;
start_ns = (__u64)start->tv_sec * ns_per_s + start->tv_nsec;
end_ns = (__u64)end->tv_sec * ns_per_s + end->tv_nsec;
return end_ns - start_ns;
}
void *user_ring_buffer__reserve_blocking(struct user_ring_buffer *rb, __u32 size, int timeout_ms)
{
void *sample;
int err, ms_remaining = timeout_ms;
struct timespec start;
if (timeout_ms < 0 && timeout_ms != -1)
return errno = EINVAL, NULL;
if (timeout_ms != -1) {
err = clock_gettime(CLOCK_MONOTONIC, &start);
if (err)
return NULL;
}
do {
int cnt, ms_elapsed;
struct timespec curr;
__u64 ns_per_ms = 1000000;
sample = user_ring_buffer__reserve(rb, size);
if (sample)
return sample;
else if (errno != ENOSPC)
return NULL;
/* The kernel guarantees at least one event notification
* delivery whenever at least one sample is drained from the
* ring buffer in an invocation to bpf_ringbuf_drain(). Other
* additional events may be delivered at any time, but only one
* event is guaranteed per bpf_ringbuf_drain() invocation,
* provided that a sample is drained, and the BPF program did
* not pass BPF_RB_NO_WAKEUP to bpf_ringbuf_drain(). If
* BPF_RB_FORCE_WAKEUP is passed to bpf_ringbuf_drain(), a
* wakeup event will be delivered even if no samples are
* drained.
*/
cnt = epoll_wait(rb->epoll_fd, &rb->event, 1, ms_remaining);
if (cnt < 0)
return NULL;
if (timeout_ms == -1)
continue;
err = clock_gettime(CLOCK_MONOTONIC, &curr);
if (err)
return NULL;
ms_elapsed = ns_elapsed_timespec(&start, &curr) / ns_per_ms;
ms_remaining = timeout_ms - ms_elapsed;
} while (ms_remaining > 0);
/* Try one more time to reserve a sample after the specified timeout has elapsed. */
return user_ring_buffer__reserve(rb, size);
}
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