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>