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Re: extending wait4(2) or waitid(2) linux syscall


On Thu, Nov 15, 2018 at 7:30 AM Dmitry V. Levin <ldv@altlinux.org> wrote:
> On Thu, Nov 15, 2018 at 06:39:03AM -0800, Arnd Bergmann wrote:
> > On Thu, Nov 15, 2018 at 6:05 AM Dmitry V. Levin wrote:
> > > On Thu, Apr 20, 2017 at 03:20:51PM +0200, Albert ARIBAUD wrote:
>
> 1. strace needs a race-free invocation of wait4(2) or waitid(2)
> with a different signal mask, this cannot be achieved without
> an extended version of syscall, similar to pselect6(2) extension
> over select(2) and ppoll(2) extension over poll(2).
>
> Signal mask specification in linux requires two parameters:
> "const sigset_t *sigmask" and "size_t sigsetsize".
> Creating pwait6(2) as an extension of wait4(2) with two arguments
> is straightforward.
> Creating pwaitid(2) as an extension of waitid(2) that already has 5
> arguments would require an indirection similar to pselect6(2).

Getting back to this point: you could also do the same thing with
the CLONE_FD approach from Josh Triplett[1] or Casey Dahlin's
older waitfd() syscall, correct?

Neither of them got merged, bu t we could revisit the ideas if they
make it easier to solve your problem by calling ppoll().

        Arnd

[1] https://lwn.net/Articles/638613/
[2] https://lore.kernel.org/lkml/49639EB8.40204@redhat.com/


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