Re: [Qemu-devel] [PATCH] block:Fix FIXED base vpc be probed to raw format

[Stefan Hajnoczi <stefanha@gmail.com>]

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On Sun, Feb 08, 2015 at 08:39:52PM +0800, Xiaodong Gong wrote:
> When open the vpc snapshot based FIXED format, its backing file,
> this FIXED vpc image, could be probed as a raw image, because that
> the find_image_format just checkout the first sector.
> 
> Add a re-probe for the last sector to FIXED base vpc image,when get
> a NULL or raw driver in first sector probe.
> 
> Signed-off-by: Xiaodong Gong <gongxiaodong1@huawei.com>
> ---
>  block.c | 55 ++++++++++++++++++++++++++++++++++++++++++++++++-------
>  1 file changed, 48 insertions(+), 7 deletions(-)

This approach is likely to cause issues because it makes no distiction
between headers and footers.  Most image formats only have a header and
would now be misdetected if a raw image had a header in its last sector.

When a vpc image has a backing file, does it make sense to set the
bs->backing_format to "vpc"?  That way we'll try to open the backing
file as a vpc image without probing.

Stefan

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