Re: [Qemu-devel] [PATCH 1/2] Introducing qcow2 extensions + keep backing file format (v4)

[Anthony Liguori]

Uri Lublin wrote:
> Qcow2 extensions are build of magic (id) len (in bytes) and data.
> They reside between the end of the header and the filename.
>
> We can keep the backing file format in a such a qcow2 extension, to
> 1. Provide a way to know the backing file format without probing
>    it (setting the format at creation time).
> 2. Enable using qcow2 format over host block devices.
>    (only if the user specifically asks for it, by providing the format
>    at creation time).
>
> I've added bdrv_create2 and drv->bdrv_create2 (implemented only
> by block-qcow2 currently) to pass the backing-format to create.
>
> Based on a work done by Shahar Frank.
>
> Also fixes a security flaw found by Daniel P. Berrange on [1]
> which summarizes: "Autoprobing: just say no."
>
> [1] http://lists.gnu.org/archive/html/qemu-devel/2008-12/msg01083.html
>
> Signed-off-by: Uri Lublin <address@hidden>
>   

This made it through my regression testing but...

>  int bdrv_create(BlockDriver *drv,
>                  const char *filename, int64_t size_in_sectors,
>                  const char *backing_file, int flags)
> @@ -348,6 +362,9 @@ int bdrv_open2(BlockDriverState *bs, const char *filename, 
> int flags,
>  
>          /* if there is a backing file, use it */
>          bs1 = bdrv_new("");
> +/*         if (drv) */
> +/*             pstrcpy(bs1->backing_format, sizeof(bs->backing_format), */
> +/*                     drv->format_name); */
>   

I don't know if I missed this before or it was added since v3 but I'm 
curious why this is here and why it's commented out.

Regards,

Anthony Liguori