linux-kernel - Re: [PATCH v2 2/4] exit: support non-blocking pidfds

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Message-ID: <20200903142241.GI4386@redhat.com>
Date:   Thu, 3 Sep 2020 16:22:42 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Christian Brauner <christian.brauner@...ntu.com>
Cc:     linux-kernel@...r.kernel.org,
        Christian Brauner <christian@...uner.io>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Kees Cook <keescook@...omium.org>,
        Sargun Dhillon <sargun@...gun.me>,
        Aleksa Sarai <cyphar@...har.com>,
        linux-kselftest@...r.kernel.org,
        Josh Triplett <josh@...htriplett.org>,
        Jens Axboe <axboe@...nel.dk>, linux-api@...r.kernel.org,
        Jann Horn <jannh@...gle.com>
Subject: Re: [PATCH v2 2/4] exit: support non-blocking pidfds

On 09/02, Christian Brauner wrote:
>
> It also makes the API more consistent and uniform. In essence, waitid() is
> treated like a read on a non-blocking pidfd or a recvmsg() on a non-blocking
> socket.
> With the addition of support for non-blocking pidfds we support the same
> functionality that sockets do. For sockets() recvmsg() supports MSG_DONTWAIT
> for pidfds waitid() supports WNOHANG.

What I personally do not like is that waitid(WNOHANG) returns zero or EAGAIN
depending on f_flags & O_NONBLOCK... This doesn't match recvmsg(MSG_DONTWAIT)
and doesn't look consistent to me.

Nevermind, the patch looks correct and if you think this can really help
user-space I won't argue.

Reviewed-by: Oleg Nesterov <oleg@...hat.com>