On Tue, May 4, 2021 at 2:01 AM Brendan Jackman <jackmanb@xxxxxxxxxx> wrote:
>
> On Mon, 3 May 2021 at 19:46, Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> wrote:
> >
> > On Mon, May 3, 2021 at 5:01 AM Brendan Jackman <jackmanb@xxxxxxxxxx> wrote:
> > >
> > > On Fri, 30 Apr 2021 at 18:31, Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> wrote:
>
> > So while doing that I noticed that you didn't fix ring_buffer__poll(),
> > so I had to fix it up a bit more extensively. Please check the end
> > result in bpf tree and let me know if there are any problems with it:
> >
> > 2a30f9440640 ("libbpf: Fix signed overflow in ringbuf_process_ring")
>
> Ah, thanks for that. Yep, the additional fix looks good to me.
>
> I think it actually fixes another very niche issue:
>
> int ring_buffer__poll(struct ring_buffer *rb, int timeout_ms)
> {
> - int i, cnt, err, res = 0;
> + int i, cnt;
> + int64_t err, res = 0;
>
> cnt = epoll_wait(rb->epoll_fd, rb->events, rb->ring_cnt, timeout_ms);
> + if (cnt < 0)
> + return -errno;
> +
> for (i = 0; i < cnt; i++) {
> __u32 ring_id = rb->events[i].data.fd;
> struct ring *ring = &rb->rings[ring_id];
> @@ -280,7 +290,9 @@ int ring_buffer__poll(struct ring_buffer *rb, int
> timeout_ms)
> return err;
> res += err;
> }
> - return cnt < 0 ? -errno : res;
>
> If the callback returns an error but errno is 0 this fails to report the error.
Yeah, there was no need to be clever about that. Explicit if (cnt < 0)
check is obvious and correct.
>
> errno(3) says "the value of errno is never set to zero by any system
> call or library function" but then describes a scenario where an
> application might usefully set it to zero itself. Maybe it can also be
> 0 in new threads, depending on your metaphysical interpretation of "by
> a system call or library function".
>
> + if (res > INT_MAX)
> + return INT_MAX;
> + return res;
