Date: Tue, 5 Feb 2013 09:35:15 -0500
From: "J. Bruce Fields" <bfields@fieldses.org>
To: Pavel Shilovsky <piastry@etersoft.ru>
Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        linux-cifs@vger.kernel.org, linux-nfs@vger.kernel.org,
        wine-devel@winehq.org
Subject: Re: [PATCH v2 3/8] vfs: Add O_DENYREAD/WRITE flags support for open
 syscall
Message-ID: <20130205143514.GA9886@fieldses.org>
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 <20130130221602.GC15584@fieldses.org>
 <CAKywueRh++TBazK8_kRN7AUb=EFhGv=Sv2CV0BESkfLFy+g5wA@mail.gmail.com>
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On Tue, Feb 05, 2013 at 03:45:31PM +0400, Pavel Shilovsky wrote:
> 2013/1/31 J. Bruce Fields <bfields@fieldses.org>:
> > On Thu, Jan 17, 2013 at 08:52:59PM +0400, Pavel Shilovsky wrote:
> >> If O_DENYMAND flag is specified, O_DENYREAD/WRITE/MAND flags are
> >> translated to flock's flags:
> >>
> >> !O_DENYREAD  -> LOCK_READ
> >> !O_DENYWRITE -> LOCK_WRITE
> >> O_DENYMAND   -> LOCK_MAND
> >>
> >> and set through flock_lock_file on a file.
> >>
> >> This change only affects opens that use O_DENYMAND flag - all other
> >> native Linux opens don't care about these flags. It allow us to
> >> enable this feature for applications that need it (e.g. NFS and
> >> Samba servers that export the same directory for Windows clients,
> >> or Wine applications that access the same files simultaneously).
> >
> > The use of an is_conflict callback seems unnecessarily convoluted.
> >
> > If we need two different behaviors, let's just use another flag (or an
> > extra boolean argument if we need to, or something).
> 
> Ok, we can pass "bool is_mand" to flock_lock_file that will pass it
> further to flock_locks_conflict.
> 
> >
> > The only caller for this new deny_lock_file is in the nfs code--I'm a
> > little unclear why that is.
> 
> deny_lock_file is called not only in the nfs code but also in 2 places
> of fs/namei.c -- that enable this logic for VFS.

Oops, apologies, I overlooked those somehow.

What prevents somebody else from grabbing a lock on a newly-created file
before we grab our own lock?

I couldn't tell on a quick look whether we hold some lock that prevents
that.

--b.