qemu-img: Allow target be aligned to sector size

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 9c60a5d197,
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>
Message-Id: <20210819101200.64235-1-hreitz@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>

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);