Re: [PATCH bpf-next v4 3/6] bpf: Dynptr support for ring buffers

[David Vernet <void@manifault.com>]

On Mon, May 09, 2022 at 03:42:54PM -0700, Joanne Koong wrote:
> Currently, our only way of writing dynamically-sized data into a ring
> buffer is through bpf_ringbuf_output but this incurs an extra memcpy
> cost. bpf_ringbuf_reserve + bpf_ringbuf_commit avoids this extra
> memcpy, but it can only safely support reservation sizes that are
> statically known since the verifier cannot guarantee that the bpf
> program won’t access memory outside the reserved space.
> 
> The bpf_dynptr abstraction allows for dynamically-sized ring buffer
> reservations without the extra memcpy.
> 
> There are 3 new APIs:
> 
> long bpf_ringbuf_reserve_dynptr(void *ringbuf, u32 size, u64 flags, struct bpf_dynptr *ptr);
> void bpf_ringbuf_submit_dynptr(struct bpf_dynptr *ptr, u64 flags);
> void bpf_ringbuf_discard_dynptr(struct bpf_dynptr *ptr, u64 flags);
> 
> These closely follow the functionalities of the original ringbuf APIs.
> For example, all ringbuffer dynptrs that have been reserved must be
> either submitted or discarded before the program exits.
> 
> Signed-off-by: Joanne Koong <joannelkoong@gmail.com>

Looks good!

Acked-by: David Vernet <void@manifault.com>