From: Max Reitz <mreitz@redhat.com>
To: Kevin Wolf <kwolf@redhat.com>, qemu-block@nongnu.org
Cc: qemu-devel@nongnu.org
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 [thread overview]
Message-ID: <47600125-fb5d-24a7-a6df-e7103b99e845@redhat.com> (raw)
In-Reply-To: <20200716142601.111237-3-kwolf@redhat.com>
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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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prev parent reply other threads:[~2020-07-17 11:16 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-16 14:25 [PATCH for-5.1 v2 0/2] qemu-img convert: Fix abort with unaligned image size Kevin Wolf
2020-07-16 14:26 ` [PATCH for-5.1 v2 1/2] block: Require aligned image size to avoid assertion failure Kevin Wolf
2020-07-17 11:02 ` Max Reitz
2020-07-17 11:32 ` Kevin Wolf
2020-07-17 11:36 ` Max Reitz
2020-07-16 14:26 ` [PATCH for-5.1 v2 2/2] file-posix: Allow byte-aligned O_DIRECT with NFS Kevin Wolf
2020-07-17 11:15 ` Max Reitz [this message]
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