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Re: [PATCH for-5.1 v2 2/2] file-posix: Allow byte-aligned O_DIRECT with
From: |
Max Reitz |
Subject: |
Re: [PATCH for-5.1 v2 2/2] file-posix: Allow byte-aligned O_DIRECT with NFS |
Date: |
Fri, 17 Jul 2020 13:15:56 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 |
On 16.07.20 16:26, Kevin Wolf wrote:
> Since commit a6b257a08e3 ('file-posix: Handle undetectable alignment'),
> we assume that if we open a file with O_DIRECT and alignment probing
> returns 1, we just couldn't find out the real alignment requirement
> because some filesystems make the requirement only for allocated blocks.
> In this case, a safe default of 4k is used.
>
> This is too strict for NFS, which does actually allow byte-aligned
> requests even with O_DIRECT. Because we can't distinguish both cases
> with generic code, let's just look at the file system magic and disable
> s->needs_alignment for NFS. This way, O_DIRECT can still be used on NFS
> for images that are not aligned to 4k.
>
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> Reviewed-by: Eric Blake <eblake@redhat.com>
> ---
> block/file-posix.c | 26 +++++++++++++++++++++++++-
> 1 file changed, 25 insertions(+), 1 deletion(-)
Reviewed-by: Max Reitz <mreitz@redhat.com>
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