linux-kernel - Re: [PATCH v9 2/4] pid: Implement pidfd

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Date:   Mon, 13 Jan 2020 15:58:07 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Sargun Dhillon <sargun@...gun.me>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Linux Containers <containers@...ts.linux-foundation.org>,
        Linux API <linux-api@...r.kernel.org>,
        Linux FS-devel Mailing List <linux-fsdevel@...r.kernel.org>,
        Tycho Andersen <tycho@...ho.ws>, Jann Horn <jannh@...gle.com>,
        Aleksa Sarai <cyphar@...har.com>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Andy Lutomirski <luto@...capital.net>,
        Al Viro <viro@...iv.linux.org.uk>,
        Gian-Carlo Pascutto <gpascutto@...illa.com>,
        Emilio Cobos Álvarez <ealvarez@...illa.com>,
        Florian Weimer <fweimer@...hat.com>,
        Jed Davis <jld@...illa.com>
Subject: Re: [PATCH v9 2/4] pid: Implement pidfd_getfd syscall

On Tue, Jan 7, 2020 at 6:59 PM Sargun Dhillon <sargun@...gun.me> wrote:
> +/**
> + * sys_pidfd_getfd() - Get a file descriptor from another process
> + *
> + * @pidfd:     the pidfd file descriptor of the process
> + * @fd:                the file descriptor number to get
> + * @flags:     flags on how to get the fd (reserved)
> + *
> + * This syscall gets a copy of a file descriptor from another process
> + * based on the pidfd, and file descriptor number. It requires that
> + * the calling process has the ability to ptrace the process represented
> + * by the pidfd. The process which is having its file descriptor copied
> + * is otherwise unaffected.
> + *
> + * Return: On success, a cloexec file descriptor is returned.
> + *         On error, a negative errno number will be returned.
> + */
> +SYSCALL_DEFINE3(pidfd_getfd, int, pidfd, int, fd,
> +               unsigned int, flags)

This is the most sensible definition I can see. I can not tell
whether we should or want to have it, but if everyone thinks
this is a good idea, then this ABI makes sense.

Reviewed-by: Arnd Bergmann <arnd@...db.de>