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Date: Sat, 1 Oct 2016 07:47:46 -0400
From: Felix Janda <felix.janda@posteo.de>
Message-ID: <20161001114746.GA274@nyan>
References: <20160930233959.GB5887@nyan>
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Subject: Re: [Qemu-devel] [PATCH] linux-user: include <linux/fcntl.h> for
 F_EXLCK and F_SHLCK
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To: Peter Maydell <peter.maydell@linaro.org>
Cc: QEMU Developers <qemu-devel@nongnu.org>, Riku Voipio <riku.voipio@iki.fi>

Peter Maydell wrote:
> On 30 September 2016 at 16:39, Felix Janda <felix.janda@posteo.de> wrote:
> > The F_EXLCK and F_SHLCK fcntl lock constants are obsolete synonyms for
> > F_WRLCK and F_RDLCK.
> 
> This seems unlikely, since on for instance Alpha F_EXLCK is
> 16, F_SHLCK is 32, F_RDLCK is 1 and F_WRLCK is 2, so they're
> all distinct:
> http://lxr.free-electrons.com/source/arch/alpha/include/uapi/asm/fcntl.h#L52

I've now looked at linux-1.0, linux-2.0 and linux-2.4. In all of them,
the constants are used in fs/locks.c. In linux-1.0, F_SHLCK has almost
the same effect as F_RDLCK, except that F_SHLCK accepts also files with
write but without read permission. Similarly for F_EXLCK. In linux-2.0
when F_EXLCK or F_SHLCK are used, the flag F_BROKEN gets set. Finally,
in linux-2.4 they just lead to EINVAL.

So I guess that the commit message should more accurately say that the
constants were used in the past for a broken flock implementation.

With this closer look at the history of these constants, it is also not
clear to me whether qemu should care at all about translating them.

Felix