linux-kernel - Re: For review: pidfd

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Message-ID: <20190924073817.zb7vr5he4wbibl7j@wittgenstein>
Date:   Tue, 24 Sep 2019 09:38:18 +0200
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     Florian Weimer <fw@...eb.enyo.de>
Cc:     "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>,
        Jann Horn <jannh@...gle.com>,
        Daniel Colascione <dancol@...gle.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Linux API <linux-api@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        linux-man <linux-man@...r.kernel.org>,
        Oleg Nesterov <oleg@...hat.com>
Subject: Re: For review: pidfd_open(2) manual page

On Mon, Sep 23, 2019 at 10:41:19PM +0200, Florian Weimer wrote:
> * Michael Kerrisk:
> 
> >>>        static
> >>>        int pidfd_open(pid_t pid, unsigned int flags)
> >>>        {
> >>>            return syscall(__NR_pidfd_open, pid, flags);
> >>>        }
> >> 
> >> Please call this function something else (not pidfd_open), so that the
> >> example continues to work if glibc provides the system call wrapper.
> >
> > I figured that if the syscall does get added to glibc, then I would
> > modify the example. In the meantime, this does seem the most natural
> > way of doing things, since the example then uses the real syscall
> > name as it would be used if there were a wrapper function.
> 
> The problem is that programs do this as well, so they fail to build
> once they are built on a newer glibc version.
> 
> > But, this leads to the question: what do you think the likelihood
> > is that this system call will land in glibc?
> 
> Quite likely.  It's easy enough to document, there are no P&C issues,
> and it doesn't need any new types.

My previous mail probably didn't make it so here it is again: I think
especially with the recently established glibc consensus to provide
wrappers for all new system calls (with some sensible exceptions) I'd
expect this to be the case.

> 
> pidfd_send_signal is slightly more difficult because we probably need
> to add rt_sigqueueinfo first, for consistency.

Oh, huh. Somehow I thought we already provide that.

Christian