linux-kernel - Re: [RFC][PATCH] fcntl: F_[SG]ETOWN

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Date:	Fri, 31 Jul 2009 14:11:22 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	oleg@...hat.com, eranian@...il.com, mingo@...e.hu,
	linux-kernel@...r.kernel.org, tglx@...utronix.de,
	robert.richter@....com, paulus@...ba.org, andi@...stfloor.org,
	mpjohn@...ibm.com, cel@...ibm.com, cjashfor@...ibm.com,
	mucci@...s.utk.edu, terpstra@...s.utk.edu,
	perfmon2-devel@...ts.sourceforge.net, mtk.manpages@...glemail.com,
	roland@...hat.com
Subject: Re: [RFC][PATCH] fcntl: F_[SG]ETOWN_TID

On Fri, 31 Jul 2009 10:35:20 +0200
Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:

> In order to direct the SIGIO signal to a particular thread of a
> multi-threaded application we cannot, like suggested by the manpage, put
> a TID into the regular fcntl(F_SETOWN) call. It will still be send to
> the whole process of which that thread is part.
> 
> Since people do want to properly direct SIGIO we introduce F_SETOWN_TID,
> which functions similarly to F_SETOWN, except positive arguments are
> interpreted as TIDs and negative arguments are interpreted as PIDs.
> 
> This extension is fully bug compatible with the old F_GETOWN
> implementation in that F_GETOWN_TID will be troubled by the negative
> return value for PIDs similarly to F_GETOWN's trouble with process
> groups.

I'd be interested in seeing a bit more explanation about the "people do
want to properly direct SIGIO" thing - use cases, how the current code
causes them problems, etc.  As it stands, it's a bit of a mystery-patch.

> [ compile tested only so far ]

I will continue to lurk :)

> arch/parisc/include/asm/fcntl.h |    2 +
> fs/fcntl.c                      |   64 +++++++++++++++++++++++++++++++++-----
> include/asm-generic/fcntl.h     |    4 ++
> include/linux/fs.h              |   11 +++++-
> net/socket.c                    |    2 +-

OK.



Alpha has private definitions of F_SETSIG and F_GETSIG which are
identical to the generic ones.  That's somewhat logical, given that
alpha's F_SETOWN/F_GETOWN _differ_ from the asm-generic ones.

Alpha appears to have made the decision to spell out _all_ the F_*
flags, given that some of them are different.  That has some merit, I
guess.

But your patch broke that.
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