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Subject: Re: [PATCH v2] signal: add procfd_signal() syscall
To:     Arnd Bergmann <arnd@arndb.de>
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>
From:   Christian Brauner <christian@brauner.io>
Message-ID: <7D934AED-82E4-4DC3-8CCB-973680316B60@brauner.io>
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On November 30, 2018 10:40:49 AM GMT+13:00, Arnd Bergmann <arnd@arndb=2Ede>=
 wrote:
>On Thu, Nov 29, 2018 at 10:35 PM Christian Brauner
><christian@brauner=2Eio> 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=2Enet> 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=2E 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=2E
>> The thread will be uniquely identified by the tid descriptor and no
>> combination of /proc/<pid> and /proc/<pid>/task/<tid> is needed=2E Does
>> that sound reasonable?
>
>Yes=2E 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?

Yes=2E :)

>
>I suppose we can always add more flags if needed, and you
>already ensure that flags is zero for the moment=2E

Yep=2E

>
>> > 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=2E
>> > 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=2E 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=2E
>>
>> 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=2E
>
>waitid() probably remains on my plate anyway, and I hope understand
>where we're at with it=2E
>
>     Arnd