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Date: Tue, 09 Sep 2008 10:42:50 -0600
From: "Chris Friesen" <cfriesen@nortel.com>
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To: Michael Kerrisk <mtk.manpages@gmail.com>
CC: Denys Vlasenko <dvlasenk@redhat.com>, linux-kernel@vger.kernel.org,
       Andrew Morton <akpm@linux-foundation.org>,
       Ulrich Drepper <drepper@redhat.com>,
       Peter Zijlstra <a.p.zijlstra@chello.nl>
Subject: Re: [PATCH] make setpriority POSIX compliant; introduce PRIO_THREAD
 extension
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Michael Kerrisk wrote:

> On 9/1/08, Denys Vlasenko <dvlasenk@redhat.com> wrote:
>> Since there may be programs which use the fact that
>>
>> setpriority(PRIO_PROCESS, tid, value)
>>
>> prior to this patch was setting priority for selected thread,
>> this behavior is retained in case when tid != pid.
>>
>> IOW: with PRIO_PROCESS, if pid specifies a thread group leader,
>> all threads' prios are set. Otherwise, only selected thread's priority
>> is set. (Alternative can be to just fail with ESRCH).


> I would expect
> setpriority(PRIO_PROCESS, getpid())
> and
> setpriority(PRIO_PROCESS, 0)
> to have the same affect (because: which == PRIO_PRCESS, who == 0
> conventionally means "the calling process").
> 
> But they do not: the latter call only changes the priority of the
> calling thread.  Is this intended?

The patch interprets 0 as the current pid rather than the current tgid.

It's up for discussion whether we should preserve old behaviour when 
specifying 0, or use a new and arguably more logical behaviour but 
possibly break old apps.

Chris