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From: Hanna Reitz <hreitz@redhat.com>
To: qemu-block@nongnu.org
Cc: Kevin Wolf <kwolf@redhat.com>, qemu-devel@nongnu.org
Subject: Re: [PATCH] qemu-img: Allow target be aligned to sector size
Date: Tue, 7 Sep 2021 11:58:35 +0200	[thread overview]
Message-ID: <089b83f0-6511-f4b1-5d1e-ccaa70ac236c@redhat.com> (raw)
In-Reply-To: <20210819101200.64235-1-hreitz@redhat.com>

Ping – any thoughts on this?

Hanna

On 19.08.21 12:12, Hanna Reitz wrote:
> We cannot write to images opened with O_DIRECT unless we allow them to
> be resized so they are aligned to the sector size: Since 9c60a5d1978,
> bdrv_node_refresh_perm() ensures that for nodes whose length is not
> aligned to the request alignment and where someone has taken a WRITE
> permission, the RESIZE permission is taken, too).
>
> Let qemu-img convert pass the BDRV_O_RESIZE flag (which causes
> blk_new_open() to take the RESIZE permission) when using cache=none for
> the target, so that when writing to it, it can be aligned to the target
> sector size.
>
> Without this patch, an error is returned:
>
> $ qemu-img convert -f raw -O raw -t none foo.img /mnt/tmp/foo.img
> qemu-img: Could not open '/mnt/tmp/foo.img': Cannot get 'write'
> permission without 'resize': Image size is not a multiple of request
> alignment
>
> Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=1994266
> Signed-off-by: Hanna Reitz <hreitz@redhat.com>
> ---
> As I have written in the BZ linked above, I am not sure what behavior we
> want.  It can be argued that the current behavior is perfectly OK
> because we want the target to have the same size as the source, so if
> this cannot be done, we should just print the above error (which I think
> explains the problem well enough that users can figure out they need to
> resize the source image).
>
> OTOH, it is difficult for me to imagine a case where the user would
> prefer the above error to just having qemu-img align the target image's
> length.
> ---
>   qemu-img.c | 8 ++++++++
>   1 file changed, 8 insertions(+)
>
> diff --git a/qemu-img.c b/qemu-img.c
> index 908fd0cce5..d4b29bf73e 100644
> --- a/qemu-img.c
> +++ b/qemu-img.c
> @@ -2628,6 +2628,14 @@ static int img_convert(int argc, char **argv)
>           goto out;
>       }
>   
> +    if (flags & BDRV_O_NOCACHE) {
> +        /*
> +         * If we open the target with O_DIRECT, it may be necessary to
> +         * extend its size to align to the physical sector size.
> +         */
> +        flags |= BDRV_O_RESIZE;
> +    }
> +
>       if (skip_create) {
>           s.target = img_open(tgt_image_opts, out_filename, out_fmt,
>                               flags, writethrough, s.quiet, false);



  parent reply	other threads:[~2021-09-07  9:59 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-19 10:12 [PATCH] qemu-img: Allow target be aligned to sector size Hanna Reitz
2021-08-19 14:31 ` Jose R. Ziviani
2021-08-19 15:14   ` Hanna Reitz
2021-08-19 18:58     ` Jose R. Ziviani
2021-09-07  9:58 ` Hanna Reitz [this message]
2021-09-07 11:29 ` Vladimir Sementsov-Ogievskiy
2021-09-07 12:48   ` Hanna Reitz
2021-09-07 13:44     ` Vladimir Sementsov-Ogievskiy
2021-09-07 14:00       ` Hanna Reitz
2021-09-07 14:18         ` Vladimir Sementsov-Ogievskiy
2021-09-14  9:24 ` Hanna Reitz

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