linux-kernel - Re: [PATCH] AFS: Implement file locking

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Message-ID: <18750.1180255870@redhat.com>
Date:	Sun, 27 May 2007 09:51:10 +0100
From:	David Howells <dhowells@...hat.com>
To:	"J. Bruce Fields" <bfields@...ldses.org>
Cc:	akpm@...l.org, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] AFS: Implement file locking

J. Bruce Fields <bfields@...ldses.org> wrote:

> > > Do you allow upgrades and downgrades?  (Just curious.)
> > 
> > AFS does not, as far as I know.
> 
> So if I request a write lock while holding a read lock, my request will
> be denied?

At the moment, yes.  Don't the POSIX and flock lock-handling routines in the
kernel normally do that anyway?

> This is a little strange, though--if there's somebody waiting for a
> write lock on an inode (because somebody else already holds a read lock
> on it), that shouldn't block requests for read locks.

That depends on whether you want fairness or not.  Allowing read locks to jump
the queue like this can lead to starvation for your writers.

David
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