linux/tools/lib/bpf/ringbuf.c
Andrii Nakryiko e9fc3ce99b libbpf: Streamline error reporting for high-level APIs
Implement changes to error reporting for high-level libbpf APIs to make them
less surprising and less error-prone to users:
  - in all the cases when error happens, errno is set to an appropriate error
    value;
  - in libbpf 1.0 mode, all pointer-returning APIs return NULL on error and
    error code is communicated through errno; this applies both to APIs that
    already returned NULL before (so now they communicate more detailed error
    codes), as well as for many APIs that used ERR_PTR() macro and encoded
    error numbers as fake pointers.
  - in legacy (default) mode, those APIs that were returning ERR_PTR(err),
    continue doing so, but still set errno.

With these changes, errno can be always used to extract actual error,
regardless of legacy or libbpf 1.0 modes. This is utilized internally in
libbpf in places where libbpf uses it's own high-level APIs.
libbpf_get_error() is adapted to handle both cases completely transparently to
end-users (and is used by libbpf consistently as well).

More context, justification, and discussion can be found in "Libbpf: the road
to v1.0" document ([0]).

  [0] https://docs.google.com/document/d/1UyjTZuPFWiPFyKk1tV5an11_iaRuec6U-ZESZ54nNTY

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Toke Høiland-Jørgensen <toke@redhat.com>
Link: https://lore.kernel.org/bpf/20210525035935.1461796-5-andrii@kernel.org
2021-05-25 17:32:35 -07:00

303 lines
6.8 KiB
C

// 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 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 = &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 libbpf_err(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 libbpf_err(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 libbpf_err(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 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)
{
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 libbpf_err(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 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);
if (err < 0)
return libbpf_err(err);
res += err;
}
if (res > INT_MAX)
return 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;
}