From b66ccae01f1ddce47fe2c7f393a3a5c5ab3d7f06 Mon Sep 17 00:00:00 2001 From: David Vernet Date: Mon, 19 Sep 2022 19:00:59 -0500 Subject: bpf: Add libbpf logic for user-space ring buffer 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 Signed-off-by: Andrii Nakryiko Link: https://lore.kernel.org/bpf/20220920000100.477320-4-void@manifault.com --- tools/lib/bpf/libbpf.h | 107 +++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 107 insertions(+) (limited to 'tools/lib/bpf/libbpf.h') diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h index 88a1ac34b12a..e2d8c17f2e85 100644 --- a/tools/lib/bpf/libbpf.h +++ b/tools/lib/bpf/libbpf.h @@ -1011,6 +1011,7 @@ LIBBPF_API int bpf_tc_query(const struct bpf_tc_hook *hook, /* Ring buffer APIs */ struct ring_buffer; +struct user_ring_buffer; typedef int (*ring_buffer_sample_fn)(void *ctx, void *data, size_t size); @@ -1030,6 +1031,112 @@ LIBBPF_API int ring_buffer__poll(struct ring_buffer *rb, int timeout_ms); LIBBPF_API int ring_buffer__consume(struct ring_buffer *rb); LIBBPF_API int ring_buffer__epoll_fd(const struct ring_buffer *rb); +struct user_ring_buffer_opts { + size_t sz; /* size of this struct, for forward/backward compatibility */ +}; + +#define user_ring_buffer_opts__last_field sz + +/* @brief **user_ring_buffer__new()** creates a new instance of a user ring + * buffer. + * + * @param map_fd A file descriptor to a BPF_MAP_TYPE_USER_RINGBUF map. + * @param opts Options for how the ring buffer should be created. + * @return A user ring buffer on success; NULL and errno being set on a + * failure. + */ +LIBBPF_API struct user_ring_buffer * +user_ring_buffer__new(int map_fd, const struct user_ring_buffer_opts *opts); + +/* @brief **user_ring_buffer__reserve()** reserves a pointer to a sample in the + * user ring buffer. + * @param rb A pointer to a user ring buffer. + * @param size The size of the sample, in bytes. + * @return A pointer to an 8-byte aligned reserved region of the user ring + * buffer; NULL, and errno being set if a sample could not be reserved. + * + * This function is *not* thread safe, and callers must synchronize accessing + * this function if there are multiple producers. If a size is requested that + * is larger than the size of the entire ring buffer, errno will be set to + * E2BIG and NULL is returned. If the ring buffer could accommodate the size, + * but currently does not have enough space, errno is set to ENOSPC and NULL is + * returned. + * + * After initializing the sample, callers must invoke + * **user_ring_buffer__submit()** to post the sample to the kernel. Otherwise, + * the sample must be freed with **user_ring_buffer__discard()**. + */ +LIBBPF_API void *user_ring_buffer__reserve(struct user_ring_buffer *rb, __u32 size); + +/* @brief **user_ring_buffer__reserve_blocking()** reserves a record in the + * ring buffer, possibly blocking for up to @timeout_ms until a sample becomes + * available. + * @param rb The user ring buffer. + * @param size The size of the sample, in bytes. + * @param timeout_ms The amount of time, in milliseconds, for which the caller + * should block when waiting for a sample. -1 causes the caller to block + * indefinitely. + * @return A pointer to an 8-byte aligned reserved region of the user ring + * buffer; NULL, and errno being set if a sample could not be reserved. + * + * This function is *not* thread safe, and callers must synchronize + * accessing this function if there are multiple producers + * + * If **timeout_ms** is -1, the function will block indefinitely until a sample + * becomes available. Otherwise, **timeout_ms** must be non-negative, or errno + * is set to EINVAL, and NULL is returned. If **timeout_ms** is 0, no blocking + * will occur and the function will return immediately after attempting to + * reserve a sample. + * + * If **size** is larger than the size of the entire ring buffer, errno is set + * to E2BIG and NULL is returned. If the ring buffer could accommodate + * **size**, but currently does not have enough space, the caller will block + * until at most **timeout_ms** has elapsed. If insufficient space is available + * at that time, errno is set to ENOSPC, and NULL is returned. + * + * The kernel guarantees that it will wake up this thread to check if + * sufficient space is available in the ring buffer at least once per + * invocation of the **bpf_ringbuf_drain()** helper function, provided that at + * least one sample is consumed, and the BPF program did not invoke the + * function with BPF_RB_NO_WAKEUP. A wakeup may occur sooner than that, but the + * kernel does not guarantee this. If the helper function is invoked with + * BPF_RB_FORCE_WAKEUP, a wakeup event will be sent even if no sample is + * consumed. + * + * When a sample of size **size** is found within **timeout_ms**, a pointer to + * the sample is returned. After initializing the sample, callers must invoke + * **user_ring_buffer__submit()** to post the sample to the ring buffer. + * Otherwise, the sample must be freed with **user_ring_buffer__discard()**. + */ +LIBBPF_API void *user_ring_buffer__reserve_blocking(struct user_ring_buffer *rb, + __u32 size, + int timeout_ms); + +/* @brief **user_ring_buffer__submit()** submits a previously reserved sample + * into the ring buffer. + * @param rb The user ring buffer. + * @param sample A reserved sample. + * + * It is not necessary to synchronize amongst multiple producers when invoking + * this function. + */ +LIBBPF_API void user_ring_buffer__submit(struct user_ring_buffer *rb, void *sample); + +/* @brief **user_ring_buffer__discard()** discards a previously reserved sample. + * @param rb The user ring buffer. + * @param sample A reserved sample. + * + * It is not necessary to synchronize amongst multiple producers when invoking + * this function. + */ +LIBBPF_API void user_ring_buffer__discard(struct user_ring_buffer *rb, void *sample); + +/* @brief **user_ring_buffer__free()** frees a ring buffer that was previously + * created with **user_ring_buffer__new()**. + * @param rb The user ring buffer being freed. + */ +LIBBPF_API void user_ring_buffer__free(struct user_ring_buffer *rb); + /* Perf buffer APIs */ struct perf_buffer; -- cgit