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Date: Thu, 04 Nov 2010 13:54:03 +0100
From: Kevin Wolf <kwolf@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] block: fix the use of protocols in backing
	files
References: <1288203550-23698-1-git-send-email-aliguori@us.ibm.com>
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To: Anthony Liguori <aliguori@us.ibm.com>
Cc: Adam Litke <agl@us.ibm.com>, qemu-devel@nongnu.org, Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>

Am 27.10.2010 20:19, schrieb Anthony Liguori:
> Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
> 
> diff --git a/block.c b/block.c
> index 1a965b2..00b6f21 100644
> --- a/block.c
> +++ b/block.c
> @@ -603,10 +603,16 @@ int bdrv_open(BlockDriverState *bs, const char *filename, int flags,
>          BlockDriver *back_drv = NULL;
>  
>          bs->backing_hd = bdrv_new("");
> -        path_combine(backing_filename, sizeof(backing_filename),
> -                     filename, bs->backing_file);
> -        if (bs->backing_format[0] != '\0')
> -            back_drv = bdrv_find_format(bs->backing_format);
> +        back_drv = bdrv_find_protocol(bs->backing_file);
> +        if (!back_drv) {

If no protocol is specified, bdrv_find_protocol doesn't return NULL but
the file: driver.

This breaks all backing file related qemu-iotests cases because qcow2
backing files are opened as raw files now.

Kevin