On Mon, Oct 12, 2020 at 1:30 PM Michael Kerrisk (man-pages)
<mtk.manpages@xxxxxxxxx> wrote:
>
> [CC += Davide]
I'm not sure how active Davide is any more..
> I don't think this is correct. The epoll(7) manual page
> sill carries the text written long ago by Davide Libenzi,
> the creator of epoll:
>
> Since even with edge-triggered epoll, multiple events can be gen‐
> erated upon receipt of multiple chunks of data, the caller has the
> option to specify the EPOLLONESHOT flag, to tell epoll to disable
> the associated file descriptor after the receipt of an event with
> epoll_wait(2).
>
> My reading of that text is that in the scenario that I describe a
> readiness notification should be generated at step 3 (and indeed
> should be generated whenever additional data bleeds into the channel).
Hmm.
That is unfortunate, because it basically exposes an internal wait
queue implementation decision, not actual real semantics.
I suspect it's easy enough to "fix" the regression with the attached
patch. It's pretty nonsensical, but I guess there's not a lot of
downside - if the pipe wasn't empty, there normally shouldn't be any
non-epoll readers anyway.
I'm busy merging, mind testing this odd patch out? It is _entirely_
untested, but from the symptoms I think it's the obvious fix.
I did the same thing for the "reader starting out from a full pipe" case too.
Linus
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