From: Andrew Morton <akpm@osdl.org>
To: Andy Isaacson <adi@hexapodia.org>
Cc: bug-coreutils@gnu.org, linux-kernel@vger.kernel.org
Subject: Re: dd PATCH: add conv=direct
Date: Wed, 7 Apr 2004 11:18:41 -0700 [thread overview]
Message-ID: <20040407111841.78ae0021.akpm@osdl.org> (raw)
In-Reply-To: <20040407173116.GB2814@hexapodia.org>
Andy Isaacson <adi@hexapodia.org> wrote:
>
> On Tue, Apr 06, 2004 at 05:33:26PM -0700, Andrew Morton wrote:
> > Andy Isaacson <adi@hexapodia.org> wrote:
> > > dd(1) is convenient for this purpose, but is lacking a method
> > > to force O_DIRECT. The enclosed patch adds a "conv=direct" flag to
> > > enable this usage.
> >
> > This would be rather nice to have. You'll need to ensure that the data
> > is page-aligned in memory.
>
> So, some confusion on my part about O_DIRECT: I can't get O_DIRECT to
> work on ext3, at all, on 2.4.25
ext3 doesn't support O_DIRECT in 2.4 kernels. I did a patch once and I
think it's in 2.4-aa kernels.
ext3 supports O_DIRECT in 2.6 kernels. Quite a number of filesystems do.
> -- open(O_DIRECT) succeeds, but the write
> returns EINVAL.
Yup that's a bit silly. In 2.6 we do the check at open() and fcntl() time.
In 2.4 we don't fail until the actual I/O attempt.
> Same code works fine when writing to a block device.
> If the problem is that ext3 can't support O_DIRECT, why does the open
> succeed?
We have been insufficiently assiduous in merging externally-supported
patches into the mainline 2.4 tree.
> > While you're there, please add an fsync-before-closing option.
>
> Easy enough. How does this look? Note that C_TWOBUFS ensures the
> output buffer is getpagesize()-aligned.
Looks nice and simple. You'll need an ext2 filesystem to test it under 2.4.
Be aware that it's rather a challenge to actually get the O_DIRECT #define
in scope under some glibc versions. I think you need to define _GNU_SOURCE
or something like that.
next prev parent reply other threads:[~2004-04-07 18:21 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-04-06 22:03 dd PATCH: add conv=direct Andy Isaacson
2004-04-07 0:33 ` Andrew Morton
2004-04-07 16:21 ` Bruce Allen
2004-04-07 16:42 ` Andrew Morton
2004-04-07 17:31 ` Andy Isaacson
2004-04-07 18:18 ` Andrew Morton [this message]
2004-04-07 19:24 ` Andy Isaacson
2004-04-07 19:34 ` Andrew Morton
2004-04-07 19:47 ` Andy Isaacson
2004-04-07 20:03 ` Andrew Morton
2004-04-07 20:43 ` Andy Isaacson
2004-04-07 21:00 ` Valdis.Kletnieks
2004-04-07 21:35 ` Bruce Allen
2004-04-08 6:56 ` Paul Eggert
2004-04-08 11:07 ` Jim Meyering
2004-04-08 19:32 ` Paul Eggert
2004-04-08 19:51 ` Paul Jarc
2004-04-08 21:34 ` Jim Meyering
2004-04-08 16:23 ` Philippe Troin
2004-04-08 20:20 ` dd patch to remove noctty Paul Eggert
2004-04-08 21:40 ` Jim Meyering
2004-04-09 0:37 ` dd PATCH: add conv=direct Anton Blanchard
2004-04-09 1:42 ` Wim Coekaerts
2004-04-10 21:28 ` Jim Meyering
2004-04-07 20:46 ` Paul Eggert
2004-04-07 21:06 ` Andrew Morton
2004-04-07 21:09 ` Andy Isaacson
2004-04-07 19:12 ` Miquel van Smoorenburg
2004-04-07 20:14 ` Andy Isaacson
2004-04-07 22:02 ` Nathan Straz
2004-04-07 22:09 ` Andy Isaacson
2004-04-08 11:44 ` Miquel van Smoorenburg
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