From mboxrd@z Thu Jan  1 00:00:00 1970
From: Florian Weimer <fweimer@redhat.com>
Subject: Re: extending wait4(2) or waitid(2) linux syscall
Date: Mon, 26 Nov 2018 16:18:40 +0100
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References: <20170420152051.568f2050.albert.aribaud@3adev.fr>
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	(Arnd Bergmann's message of "Fri, 16 Nov 2018 17:50:14 -0800")
To: Arnd Bergmann <arnd@arndb.de>
Cc: "Dmitry V. Levin" <ldv@altlinux.org>, Albert ARIBAUD <albert.aribaud@3adev.fr>, "H. Peter Anvin" <hpa@zytor.com>, GNU C Library <libc-alpha@sourceware.org>, Linux API <linux-api@vger.kernel.org>
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* 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