Re: [PATCH v2] signal: add procfd_signal() syscall

On November 30, 2018 10:40:49 AM GMT+13:00, Arnd Bergmann [off-list ref] wrote:

On Thu, Nov 29, 2018 at 10:35 PM Christian Brauner
[off-list ref] wrote:

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On Thu, Nov 29, 2018 at 10:02:13PM +0100, Arnd Bergmann wrote:

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On Thu, Nov 29, 2018 at 9:14 PM Andy Lutomirski

[off-list ref] wrote:

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Is the current procfd_signal() proposal (under whichever name)

sufficient

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to correctly implement both sys_rt_sigqueueinfo() and

sys_rt_tgsigqueueinfo()?

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Yes, I see no reason why not. My idea is to extend it - after we have

a

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basic version in - to also work with:
/proc/<pid>/task/<tid>
If I'm not mistaken this should be sufficient to get

rt_tgsigqueueinfo.

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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?

Yes. :)

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

Yep.

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Can we implement sys_rt_sigtimedwait() based on signalfd()?

If yes, that would leave waitid(), which already needs a

replacement

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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

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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