Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
MIME-Version: 1.0
References: <20181120105124.14733-1-christian@brauner.io> <87in0g5aqo.fsf@oldenburg.str.redhat.com>
 <36323361-90BD-41AF-AB5B-EE0D7BA02C21@amacapital.net> <993B98AC-51DF-4131-AF7F-7DA2A7F485F1@brauner.io>
 <CALCETrWnQNMQcCmFZrftVVYgAMW6DT3gyxvVb_v9_enUCUkHiw@mail.gmail.com>
 <20181129195551.woe2bl3z3yaysqb6@brauner.io> <6E21165F-2C76-4877-ABD9-0C86D55FD6AA@amacapital.net>
 <CAK8P3a2i9DFaS9-3A9V_pKwFfwVR0bDqgLosmivge3Cx2VyiuQ@mail.gmail.com> <20181129213458.4h44dpg6ltqow4k4@brauner.io>
In-Reply-To: <20181129213458.4h44dpg6ltqow4k4@brauner.io>
From:   Arnd Bergmann <arnd@arndb.de>
Date:   Thu, 29 Nov 2018 22:40:49 +0100
Message-ID: <CAK8P3a1_if7+Ak2eefU6JeZT9KW827gkLHaObX-QOsHrB5ZwfA@mail.gmail.com>
Subject: Re: [PATCH v2] signal: add procfd_signal() syscall
To:     christian@brauner.io
Cc:     Andy Lutomirski <luto@amacapital.net>,
        Andy Lutomirski <luto@kernel.org>,
        Florian Weimer <fweimer@redhat.com>,
        "Eric W . Biederman" <ebiederm@xmission.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "Serge E. Hallyn" <serge@hallyn.com>, Jann Horn <jannh@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Oleg Nesterov <oleg@redhat.com>, cyphar@cyphar.com,
        Al Viro <viro@zeniv.linux.org.uk>,
        Linux FS-devel Mailing List <linux-fsdevel@vger.kernel.org>,
        Linux API <linux-api@vger.kernel.org>,
        Daniel Colascione <dancol@google.com>,
        Tim Murray <timmurray@google.com>, linux-man@vger.kernel.org,
        Kees Cook <keescook@chromium.org>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Thu, Nov 29, 2018 at 10:35 PM Christian Brauner <christian@brauner.io> wrote:
> On Thu, Nov 29, 2018 at 10:02:13PM +0100, Arnd Bergmann wrote:
> > On Thu, Nov 29, 2018 at 9:14 PM Andy Lutomirski <luto@amacapital.net> wrote:
> >
> > Is the current procfd_signal() proposal (under whichever name) sufficient
> > to correctly implement both sys_rt_sigqueueinfo() and sys_rt_tgsigqueueinfo()?
>
> Yes, I see no reason why not. My idea is to extend it - after we have a
> basic version in - to also work with:
> /proc/<pid>/task/<tid>
> If I'm not mistaken this should be sufficient to get rt_tgsigqueueinfo.
> The thread will be uniquely identified by the tid descriptor and no
> combination of /proc/<pid> and /proc/<pid>/task/<tid> is needed. Does
> that sound reasonable?

Yes. So it would currently replace rt_gsigqueueinfo() but
not rt_tgsigqueueinfo(), and could be extended to do both
afterwards, without making the interface ugly in any form?

I suppose we can always add more flags if needed, and you
already ensure that flags is zero for the moment.

> > Can we implement sys_rt_sigtimedwait() based on signalfd()?
> >
> > If yes, that would leave waitid(), which already needs a replacement
> > for y2038, and that should then also return a signalfd_siginfo.
> > My current preference for waitid() would be to do a version that
> > closely resembles the current interface, but takes a signalfd_siginfo
> > and a __kernel_timespec based rusage replacement (possibly
> > two of them to let us map wait6), but does not operate on procfd or
> > take a signal mask. That would require yet another syscall, but I
> > don't think I can do that before we want to have the set of y2038
> > safe syscalls.
>
> All sounds reasonable to me but that's not a blocker for the current
> syscall though, is it?

I'd like to at least understand about sys_rt_sigtimedwait() before
we go on, so we all know what's coming, and document the
plans in the changelog.

waitid() probably remains on my plate anyway, and I hope understand
where we're at with it.

     Arnd