linux-kernel - pidfd and O

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Message-ID: <20200811181236.GA18763@localhost>
Date:   Tue, 11 Aug 2020 11:12:36 -0700
From:   Josh Triplett <josh@...htriplett.org>
To:     linux-kernel@...r.kernel.org
Cc:     Christian Brauner <christian@...uner.io>,
        Jens Axboe <axboe@...nel.dk>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        linux-doc@...r.kernel.org
Subject: pidfd and O_NONBLOCK

As far as I can tell, O_NONBLOCK has no effect on a pidfd. When calling
waitid on a pidfd for a running process, it always blocks unless you
provide WNOHANG.

I don't think anything depends on that behavior. Would it be possible to
make O_NONBLOCK on a pidfd cause waitid on a running process to return
EWOULDBLOCK?

This would make it easier to use pidfd in some non-blocking event loops.

- Josh Triplett