Linux-kernel mailing list archive 1999-36,: Re: clone() and CLONE_PID

# Re: clone() and CLONE_PID

David Wragg (dpw@doc.ic.ac.uk)
09 Sep 1999 00:11:47 +0000

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Matthew Kirkwood <weejock@ferret.lmh.ox.ac.uk> writes:
> On Tue, 7 Sep 1999, Lorenzo Allegrucci wrote:
>
> > This is from the LinuxThreads README file:
>
> > One thing that they do not share
> > is their pid's and parent pid's. According to the standard, they
> > should have the same, but that's one thing we cannot achieve
> > in this implementation (until the CLONE_PID flag to clone() becomes
> > usable).
> >
> > When does the CLONE_PID flag to clone() becomes usable? 2.4.x? 2.5.x?
>
> 2.3 has the facility to share parent process ids.

Unfortunately that addition was half-baked, and introduced security
holes. Linus has been sent patches to fix this; it's probably time to
pester him again.

> [snip]
>
> Does the pthread standard really require the pid sharing semantics?
> That will break quite a bit of the kernel, and an awful lot of userspace.

POSIX is just an API; it doesn't tell you how to design a
kernel. Generally Linux directly implements POSIX features because
that is simpler, but for POSIX threads it's worth stepping back and
asking what it really needs from the kernel. My opinion is that doesn't
include pid sharing and tids.

David Wragg

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