Introduce ring__consume_n() and ring_buffer__consume_n() API to partially consume items from one (or more) ringbuffer(s). This can be useful, for example, to consume just a single item or when we need to copy multiple items to a limited user-space buffer from the ringbuffer callback. Practical example (where this API can be used): https://github.com/sched-ext/scx/blob/b7c06b9ed9f72cad83c31e39e9c4e2cfd8683a55/rust/scx_rustland_core/src/bpf.rs#L217 See also: https://lore.kernel.org/lkml/20240310154726.734289-1-andrea.righi@xxxxxxxxxxxxx/T/#u [ Note: I haven't implemented the special case of n == 0 as "no limit", because we still need to add a bunch of extra checks for INT_MAX, making the code less readable and, from a performance perspective, it seems that we may get more downsides than benefits, but I can try to look more at this if you think it's worth it ] v3: - rename ring__consume_max() -> ring__consume_n() and ring_buffer__consume_max() -> ring_buffer__consume_n() - add new API to a new 1.5.0 cycle - fixed minor nits / comments v2: - introduce a new API instead of changing the callback's retcode behavior Andrea Righi (2): libbpf: ringbuf: allow to consume up to a certain amount of items libbpf: Add ring__consume_n / ring_buffer__consume_n tools/lib/bpf/libbpf.h | 12 ++++++++++ tools/lib/bpf/libbpf.map | 6 +++++ tools/lib/bpf/ringbuf.c | 59 ++++++++++++++++++++++++++++++++++++++++-------- 3 files changed, 67 insertions(+), 10 deletions(-)
