From: Oleg Nesterov <oleg@redhat.com>
To: Christian Brauner <christian@brauner.io>
Cc: torvalds@linux-foundation.org, viro@zeniv.linux.org.uk,
jannh@google.com, dhowells@redhat.com, linux-api@vger.kernel.org,
linux-kernel@vger.kernel.org, serge@hallyn.com, luto@kernel.org,
arnd@arndb.de, ebiederm@xmission.com, keescook@chromium.org,
tglx@linutronix.de, mtk.manpages@gmail.com,
akpm@linux-foundation.org, cyphar@cyphar.com,
joel@joelfernandes.org, dancol@google.com
Subject: Re: [PATCH 2/4] clone: add CLONE_PIDFD
Date: Mon, 15 Apr 2019 15:24:16 +0200 [thread overview]
Message-ID: <20190415132416.GB22204@redhat.com> (raw)
In-Reply-To: <20190415114204.ydczeuwmi74wfsuv@brauner.io>
On 04/15, Christian Brauner wrote:
>
> > CLONE_PARENT_SETTID doesn't look very usefule, so what if we add
> >
> > if ((clone_flags & (CLONE_PIDFD|CLONE_PARENT_SETTID)) ==
> > (CLONE_PIDFD|CLONE_PARENT_SETTID))
> > return ERR_PTR(-EINVAL);
> >
> > at the start of copy_process() ?
> >
> > Then it can do
> >
> > if (clone_flags & CLONE_PIDFD) {
> > retval = pidfd_create(pid, &pidfdf);
> > if (retval < 0)
> > goto bad_fork_free_pid;
> > retval = put_user(retval, parent_tidptr)
> > if (retval < 0)
> > goto bad_fork_free_pid;
> > }
>
> Uhhh Oleg, that is nifty. I have to say I like that a lot. This would
> let us return the pid and the pidfd in one go and we can also start
> pidfd numbering at 0.
Christian, sorry if it was already discussed, but I can't force myself to
read all the previous discussions ;)
If we forget about CONFIG_PROC_FS, why do we really want to create a file?
Suppose we add a global u64 counter incremented by copy_process and reported
in /proc/$pid/status. Suppose that clone(CLONE_PIDFD) writes this counter to
*parent_tidptr. Let's denote this counter as UNIQ_PID.
Now, if you want to (say) safely kill a task and you have its UNIQ_PID, you
can do
kill_by_pid_uniq(int pid, u64 uniq_pid)
{
pidfd = open("/proc/$pid", O_DIRECTORY);
status = openat(pidfd, "status");
u64 this_uniq_pid = ... read UNIQ_PID from status ...;
if (uniq_pid != this_uniq_pid)
return;
pidfd_send_signal(pidfd);
}
Why else do we want pidfd?
Oleg.
next prev parent reply other threads:[~2019-04-15 13:24 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-14 20:14 [PATCH 0/4] clone: add CLONE_PIDFD Christian Brauner
2019-04-14 20:14 ` [PATCH 1/4] Make anon_inodes unconditional Christian Brauner
2019-04-14 20:14 ` [PATCH 2/4] clone: add CLONE_PIDFD Christian Brauner
2019-04-15 10:52 ` Oleg Nesterov
2019-04-15 11:42 ` Christian Brauner
2019-04-15 13:24 ` Oleg Nesterov [this message]
2019-04-15 13:52 ` Christian Brauner
2019-04-15 16:25 ` Joel Fernandes
2019-04-15 17:15 ` Jonathan Kowalski
2019-04-15 19:39 ` Daniel Colascione
2019-04-14 20:14 ` [PATCH 3/4] signal: support CLONE_PIDFD with pidfd_send_signal Christian Brauner
2019-04-14 20:14 ` [PATCH 4/4] samples: show race-free pidfd metadata access Christian Brauner
2019-04-15 10:08 ` RFC: on adding new CLONE_* flags [WAS Re: [PATCH 0/4] clone: add CLONE_PIDFD] Enrico Weigelt, metux IT consult
2019-04-15 15:50 ` Serge E. Hallyn
2019-04-16 18:32 ` Enrico Weigelt, metux IT consult
2019-04-29 15:49 ` Serge E. Hallyn
2019-04-29 17:31 ` Enrico Weigelt, metux IT consult
2019-05-05 2:32 ` Serge E. Hallyn
2019-04-15 19:59 ` Aleksa Sarai
2019-04-15 20:29 ` Andy Lutomirski
2019-04-15 21:27 ` Jonathan Kowalski
2019-04-15 23:58 ` Andy Lutomirski
2019-04-16 18:45 ` Enrico Weigelt, metux IT consult
2019-04-16 21:31 ` Andy Lutomirski
2019-04-17 12:03 ` Enrico Weigelt, metux IT consult
2019-04-17 12:54 ` Christian Brauner
2019-04-18 15:46 ` Enrico Weigelt, metux IT consult
2019-04-17 12:19 ` Florian Weimer
2019-04-17 16:46 ` Andy Lutomirski
2019-04-20 7:14 ` Kevin Easton
2019-04-20 11:15 ` Christian Brauner
2019-04-20 15:06 ` Daniel Colascione
2019-04-29 19:30 ` Jann Horn
2019-04-29 19:55 ` Jann Horn
2019-04-29 20:21 ` Linus Torvalds
2019-04-29 20:38 ` Florian Weimer
2019-04-29 20:51 ` Christian Brauner
2019-04-29 21:31 ` Linus Torvalds
2019-04-30 7:01 ` Florian Weimer
2019-04-30 0:38 ` Jann Horn
2019-04-30 2:16 ` Linus Torvalds
2019-04-30 8:21 ` Florian Weimer
2019-04-30 16:19 ` Linus Torvalds
2019-04-30 16:26 ` Linus Torvalds
2019-04-30 17:07 ` Florian Weimer
2019-04-30 12:39 ` Oleg Nesterov
2019-04-30 16:24 ` Linus Torvalds
2019-04-29 20:49 ` Florian Weimer
2019-04-29 20:52 ` Christian Brauner
2019-04-20 15:28 ` Al Viro
2019-04-16 18:37 ` Enrico Weigelt, metux IT consult
2019-04-15 10:16 ` [PATCH 0/4] clone: add CLONE_PIDFD Enrico Weigelt, metux IT consult
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20190415132416.GB22204@redhat.com \
--to=oleg@redhat.com \
--cc=akpm@linux-foundation.org \
--cc=arnd@arndb.de \
--cc=christian@brauner.io \
--cc=cyphar@cyphar.com \
--cc=dancol@google.com \
--cc=dhowells@redhat.com \
--cc=ebiederm@xmission.com \
--cc=jannh@google.com \
--cc=joel@joelfernandes.org \
--cc=keescook@chromium.org \
--cc=linux-api@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=luto@kernel.org \
--cc=mtk.manpages@gmail.com \
--cc=serge@hallyn.com \
--cc=tglx@linutronix.de \
--cc=torvalds@linux-foundation.org \
--cc=viro@zeniv.linux.org.uk \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).