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Date: Wed, 28 Jan 2015 13:31:48 -0500
From: John Snow <jsnow@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH RESEND 17/50] block: Respect empty BB in
 bdrv_lookup_bs()
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To: Max Reitz <mreitz@redhat.com>, qemu-devel@nongnu.org
Cc: Kevin Wolf <kwolf@redhat.com>, Jeff Cody <jcody@redhat.com>, Fam Zheng <famz@redhat.com>, Markus Armbruster <armbru@redhat.com>, Stefan Hajnoczi <stefanha@redhat.com>



On 01/27/2015 02:45 PM, Max Reitz wrote:
> blk_by_name() may return a BlockBackend for which blk_bs() returns NULL.
> In this case, an error should be returned (instead of just returning
> NULL without modifying *errp).
>
> Signed-off-by: Max Reitz <mreitz@redhat.com>
> ---
>   block.c | 5 +++++
>   1 file changed, 5 insertions(+)
>
> diff --git a/block.c b/block.c
> index 9a0a510..b7e631c 100644
> --- a/block.c
> +++ b/block.c
> @@ -3718,6 +3718,11 @@ BlockDriverState *bdrv_lookup_bs(const char *device,
>           blk = blk_by_name(device);
>
>           if (blk) {
> +            if (!blk_bs(blk)) {
> +                error_set(errp, QERR_DEVICE_HAS_NO_MEDIUM, device);
> +                return NULL;
> +            }
> +
>               return blk_bs(blk);
>           }
>       }
>

Do we have a consensus on The One True And Proper Way to report errors? 
I know Markus usually campaigns against error_set() in favor of 
error_setg().