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Date: Thu, 16 Sep 2010 10:08:59 +0200
From: Kevin Wolf <kwolf@redhat.com>
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Subject: [Qemu-devel] Re: [PATCH 2/3] block-nbd: fix use of protocols in
 backing files and nbd probing
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To: Anthony Liguori <aliguori@us.ibm.com>
Cc: Juan Quintela <quintela@redhat.com>, qemu-devel@nongnu.org, Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>

Am 11.09.2010 16:04, schrieb Anthony Liguori:
> The use of protocols in backing_files is currently broken because of some
> checks for adjusting relative pathnames.
> 
> Additionally, there's a spurious read when using an nbd protocol that can be
> quite destructive when using copy-on-read.  Potentially, this can lead to
> probing an image file over top of NBD but this is completely wrong as NBD
> devices are not growable.
> 
> Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
> ---
> NB: this is absolutely not ideal.  A more elegant suggestion would be
> appreciated.  I don't think NBD cleanly fits the model of a protocol as it
> stands today.
> 
> diff --git a/block.c b/block.c
> index cd2ee31..a32d5dd 100644
> --- a/block.c
> +++ b/block.c
> @@ -344,6 +344,12 @@ static int find_image_format(const char *filename, BlockDriver **pdrv)
>          return ret;
>      }
>  
> +    if (strcmp(bs->drv->protocol_name, "nbd") == 0) {
> +        drv = bs->drv;
> +        bdrv_delete(bs);
> +        goto out;
> +    }

Is nbd really the only protocol that behaves like this? I don't like
hardcoding driver names in generic block layer code.

Kevin