From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([2001:4830:134:3::10]:55236)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <kwolf@redhat.com>) id 1ZeOfn-0001eW-5O
	for qemu-devel@nongnu.org; Tue, 22 Sep 2015 10:36:05 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <kwolf@redhat.com>) id 1ZeOfm-0001aB-9j
	for qemu-devel@nongnu.org; Tue, 22 Sep 2015 10:35:59 -0400
Date: Tue, 22 Sep 2015 16:35:51 +0200
From: Kevin Wolf <kwolf@redhat.com>
Message-ID: <20150922143551.GF3999@noname.str.redhat.com>
References: <1442589793-7105-1-git-send-email-mreitz@redhat.com>
	<1442589793-7105-21-git-send-email-mreitz@redhat.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <1442589793-7105-21-git-send-email-mreitz@redhat.com>
Subject: Re: [Qemu-devel] [PATCH v5 20/38] block: Prepare remaining BB
 functions for NULL BDS
List-Id: <qemu-devel.nongnu.org>
List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Max Reitz <mreitz@redhat.com>
Cc: Alberto Garcia <berto@igalia.com>, qemu-block@nongnu.org, John Snow <jsnow@redhat.com>, qemu-devel@nongnu.org, Markus Armbruster <armbru@redhat.com>, Stefan Hajnoczi <stefanha@redhat.com>

Am 18.09.2015 um 17:22 hat Max Reitz geschrieben:
> There are several BlockBackend functions which, in theory, cannot fail.
> This patch makes them cope with the BlockDriverState pointer being NULL
> by making them fall back to some default action like ignoring the value
> in setters and returning the default in getters.
> 
> Signed-off-by: Max Reitz <mreitz@redhat.com>
> Reviewed-by: Eric Blake <eblake@redhat.com>

Hm, okay, maybe bdrv_drain() belongs here. I just reviewed the end
result for completeness and didn't check which patch did what.

>  int blk_enable_write_cache(BlockBackend *blk)
>  {
> +    if (!blk->bs) {
> +        return 0;
> +    }
> +
>      return bdrv_enable_write_cache(blk->bs);
>  }
>  
>  void blk_set_enable_write_cache(BlockBackend *blk, bool wce)
>  {
> -    bdrv_set_enable_write_cache(blk->bs, wce);
> +    if (blk->bs) {
> +        bdrv_set_enable_write_cache(blk->bs, wce);
> +    }
>  }

WCE is part of the open_flags in BlockBackendRootState. The root state
doesn't seem to be used yet, and I wrote about my concerns about it in
reply to an earlier patch, but as long as we have it, should this
query/modify the root state if no BDS is attached?

Kevin