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Subject: Re: [PATCH] bug in setpgid()? process groups and thread groups
From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: Florian Weimer <fw@deneb.enyo.de>
Cc: Roland McGrath <roland@redhat.com>, Jeremy Fitzhardinge <jeremy@goop.org>,
       Ulrich Drepper <drepper@redhat.com>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       Andrew Morton <akpm@osdl.org>
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On Sul, 2003-08-03 at 08:22, Florian Weimer wrote:
> Alan Cox <alan@lxorguk.ukuu.org.uk> writes:
> 
> > #1 Lots of non posix afflicted intelligent programmers use the per
> > thread uid stuff in daemons. Its really really useful
> 
> It doesn't work reliably because the threading implementation might
> have to send signals which the current combination of credentials does
> not allow.

It works beautifully.  Its very effective for clone() using applications


> IMHO, POSIX is wrong to favor process attributes so strongly.  It
> wouldn't be a problem if there were other ways to pass these implicit
> parameters (such as thread-specific attributes, or, even better,
> syscall arguments).  But often there isn't.

The restriction in this case comes from a more fundamental thing - posix pthreads
is full of compromises so it can be done in user space. Clearly you can't split
uid's in user space very sanely.