Re: [Qemu-devel] [PATCH v2 6/9] block: Read only one sector for format probing

[Max Reitz <mreitz@redhat.com>]

On 2014-11-07 at 20:39, Kevin Wolf wrote:
> The only image format driver that even potentially accesses anything
> after 512 bytes in its bdrv_probe() implementation is VMDK, which reads
> a plain-text descriptor file. In practice, the field it's looking for
> seems to come first and will be well within the first 512 bytes, too.
>
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>   block.c                   | 2 +-
>   include/block/block_int.h | 2 ++
>   2 files changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/block.c b/block.c
> index 2fdc33f..1fd4b8e 100644
> --- a/block.c
> +++ b/block.c
> @@ -682,7 +682,7 @@ static int find_image_format(BlockDriverState *bs, const char *filename,
>                                BlockDriver **pdrv, Error **errp)
>   {
>       BlockDriver *drv;
> -    uint8_t buf[2048];
> +    uint8_t buf[BLOCK_PROBE_BUF_SIZE];
>       int ret = 0;
>   
>       /* Return the raw BlockDriver * to scsi-generic devices or empty drives */
> diff --git a/include/block/block_int.h b/include/block/block_int.h
> index a1c17b9..cd94559 100644
> --- a/include/block/block_int.h
> +++ b/include/block/block_int.h
> @@ -57,6 +57,8 @@
>   #define BLOCK_OPT_REDUNDANCY        "redundancy"
>   #define BLOCK_OPT_NOCOW             "nocow"
>   
> +#define BLOCK_PROBE_BUF_SIZE        512
> +
>   typedef struct BdrvTrackedRequest {
>       BlockDriverState *bs;
>       int64_t offset;

You should change the description of the buf_size parameter for 
bdrv_probe_all, as I wrote in my review for patch 5.

With that description fixed (either here or in patch 5):

Reviewed-by: Max Reitz <mreitz@redhat.com>