linux-kernel - Re: [PATCH 17/18] [GFS2] Remove support for unused and pointless flag

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Date:	Fri, 11 Jul 2008 12:52:19 +0100
From:	Steven Whitehouse <swhiteho@...hat.com>
To:	"linux-os (Dick Johnson)" <linux-os@...logic.com>
Cc:	linux-kernel@...r.kernel.org, cluster-devel@...hat.com
Subject: Re: [PATCH 17/18] [GFS2] Remove support for unused and pointless
	flag

Hi,

On Fri, 2008-07-11 at 07:19 -0400, linux-os (Dick Johnson) wrote:
> On Fri, 11 Jul 2008 swhiteho@...hat.com wrote:
> 
> > From: Steven Whitehouse <swhiteho@...hat.com>
> >
> > The ability to mark files for direct i/o access when opened
> > normally is both unused and pointless, so this patch removes
> > support for that feature.
> [Snipped...]
> 
> So linux is no longer going to support commercial databases?
> Oracle and others need the O_DIRECT attribute. Linux can
> probably igonore it, but such an open cannot fail or else
> Linux gets thrown out of the commercial enterprise when
> an upgrade disables an entire financial institution.
> 
> Cheers,
> Dick Johnson
> Penguin : Linux version 2.6.22.1 on an i686 machine (5588.28 BogoMips).
> My book : http://www.AbominableFirebug.com/
> _
> 
No, thats not what it means...., but perhaps I could have explained it
better. You can still use O_DIRECT flags in open syscalls in exactly the
same way as before. What this patch removes is the (never used, and IMHO
pointless) feature of being able to set a flag on the inode (via
chattr/setattr) to force open's to set O_DIRECT in every case, even when
the application didn't ask for it. The reason that its pointless is that
applications which don't otherwise support O_DIRECT are very unlikely to
supply suitably aligned buffers and I/O requests, so that overriding the
O_DIRECT flag for such applications will most likely result in an I/O
error.

GFS2 will still support O_DIRECT just the same as it has always done,
and this doesn't affect any other filesystem's support for that feature
either,

Steve.


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