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Re: dd PATCH: add conv=direct
From: |
Andrew Morton |
Subject: |
Re: dd PATCH: add conv=direct |
Date: |
Wed, 7 Apr 2004 11:18:41 -0700 |
Andy Isaacson <address@hidden> wrote:
>
> On Tue, Apr 06, 2004 at 05:33:26PM -0700, Andrew Morton wrote:
> > Andy Isaacson <address@hidden> 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.
- dd PATCH: add conv=direct, Andy Isaacson, 2004/04/07
- Re: dd PATCH: add conv=direct, Andrew Morton, 2004/04/07
- Re: dd PATCH: add conv=direct, Bruce Allen, 2004/04/07
- Re: dd PATCH: add conv=direct, Andy Isaacson, 2004/04/07
- Re: dd PATCH: add conv=direct,
Andrew Morton <=
- Re: dd PATCH: add conv=direct, Andy Isaacson, 2004/04/07
- Re: dd PATCH: add conv=direct, Andrew Morton, 2004/04/07
- Re: dd PATCH: add conv=direct, Andy Isaacson, 2004/04/07
- Re: dd PATCH: add conv=direct, Andrew Morton, 2004/04/07
- Re: dd PATCH: add conv=direct, Andy Isaacson, 2004/04/07
- Re: dd PATCH: add conv=direct, Valdis . Kletnieks, 2004/04/08
- Re: dd PATCH: add conv=direct, Bruce Allen, 2004/04/08
- Re: dd PATCH: add conv=direct, Paul Eggert, 2004/04/08
- Re: dd PATCH: add conv=direct, Jim Meyering, 2004/04/08
- Re: dd PATCH: add conv=direct, Paul Eggert, 2004/04/08