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Re: extending wait4(2) or waitid(2) linux syscall
- From: Florian Weimer <fweimer at redhat dot com>
- To: Arnd Bergmann <arnd at arndb dot de>
- Cc: "Dmitry V. Levin" <ldv at altlinux dot org>, Albert ARIBAUD <albert dot aribaud at 3adev dot fr>, "H. Peter Anvin" <hpa at zytor dot com>, GNU C Library <libc-alpha at sourceware dot org>, Linux API <linux-api at vger dot kernel dot org>
- Date: Mon, 26 Nov 2018 16:18:40 +0100
- Subject: Re: extending wait4(2) or waitid(2) linux syscall
- References: <20170420152051.568f2050.albert.aribaud@3adev.fr> <20181115140441.GA2171@altlinux.org> <CAK8P3a0Gsqa8WTbALOUchRyEA7E2f3P1f=XQ8nD2xQaemfPpcQ@mail.gmail.com> <20181115153008.GC2171@altlinux.org> <CAK8P3a38zcMikOiaHXrKbc3URL6-6kETk=1F-Bx7LywPyRh=yg@mail.gmail.com>
* Arnd Bergmann:
> 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?
A descriptor-based solution would not be useful to glibc because
applications assume that glibc does not (persistently) open any file
descriptors behind t heir back.
Thanks,
Florian