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bpf: Add libbpf logic for user-space ring buffer

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Now that all of the logic is in place in the kernel to support user-space
produced ring buffers, we can add the user-space logic to libbpf. This
patch therefore adds the following public symbols to libbpf:

struct user_ring_buffer *
user_ring_buffer__new(int map_fd,
		      const struct user_ring_buffer_opts *opts);
void *user_ring_buffer__reserve(struct user_ring_buffer *rb, __u32 size);
void *user_ring_buffer__reserve_blocking(struct user_ring_buffer *rb,
                                         __u32 size, int timeout_ms);
void user_ring_buffer__submit(struct user_ring_buffer *rb, void *sample);
void user_ring_buffer__discard(struct user_ring_buffer *rb,
void user_ring_buffer__free(struct user_ring_buffer *rb);

A user-space producer must first create a struct user_ring_buffer * object
with user_ring_buffer__new(), and can then reserve samples in the
ring buffer using one of the following two symbols:

void *user_ring_buffer__reserve(struct user_ring_buffer *rb, __u32 size);
void *user_ring_buffer__reserve_blocking(struct user_ring_buffer *rb,
                                         __u32 size, int timeout_ms);

With user_ring_buffer__reserve(), a pointer to a 'size' region of the ring
buffer will be returned if sufficient space is available in the buffer.
user_ring_buffer__reserve_blocking() provides similar semantics, but will
block for up to 'timeout_ms' in epoll_wait if there is insufficient space
in the buffer. This function has the guarantee from the kernel that it will
receive at least one event-notification per invocation to
bpf_ringbuf_drain(), provided that at least one sample is drained, and the
BPF program did not pass the BPF_RB_NO_WAKEUP flag to bpf_ringbuf_drain().

Once a sample is reserved, it must either be committed to the ring buffer
with user_ring_buffer__submit(), or discarded with
user_ring_buffer__discard().

Signed-off-by: David Vernet <void@manifault.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20220920000100.477320-4-void@manifault.com
This commit is contained in:
David Vernet
2022-09-19 19:00:59 -05:00
committed by Andrii Nakryiko
parent 28903eb40e
commit 9e9bf46c92
6 changed files with 398 additions and 3 deletions
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10
src/libbpf.map
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@@ -368,3 +368,13 @@ LIBBPF_1.0.0 {
libbpf_bpf_prog_type_str;
perf_buffer__buffer;
};
LIBBPF_1.1.0 {
global:
user_ring_buffer__discard;
user_ring_buffer__free;
user_ring_buffer__new;
user_ring_buffer__reserve;
user_ring_buffer__reserve_blocking;
user_ring_buffer__submit;
} LIBBPF_1.0.0;