On Wed, Dec 27, 2023 at 2:01 AM Philo Lu <lulie@xxxxxxxxxxxxxxxxx> wrote:
>
> +__bpf_kfunc int bpf_relay_output(struct bpf_map *map,
> + void *data, u64 data__sz, u32 flags)
> +{
> + struct bpf_relay_map *rmap;
> +
> + /* not support any flag now */
> + if (unlikely(!map || flags))
> + return -EINVAL;
> +
> + rmap = container_of(map, struct bpf_relay_map, map);
> + if (!rmap->relay_chan->has_base_filename)
> + return -ENOENT;
> +
> + relay_write(rmap->relay_chan, data, data__sz);
> + return 0;
This just opens a can of worms.
Above is not nmi safe. relay_write() can be used only out of
known context which effectively makes it unusable out of bpf tracing
progs that can kprobe attach anywhere in the kernel.
perf_event buffer is the only sure way to deliver events to user
space with overwrite.
bpf ringbuf is a best effort due to
if (in_nmi()) if (!spin_trylock_irqsave
Sorry, but it's a nack to allow bpf progs interface with relay.
