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Date: Fri, 17 Jan 2014 15:23:00 +0800
From: Stefan Hajnoczi <stefanha@gmail.com>
Message-ID: <20140117072300.GC19441@stefanha-thinkpad.redhat.com>
References: <cover.1389644007.git.jcody@redhat.com>
	<677e470b5c2823a06afd63ba72f17f083d944fa3.1389644007.git.jcody@redhat.com>
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In-Reply-To: <677e470b5c2823a06afd63ba72f17f083d944fa3.1389644007.git.jcody@redhat.com>
Subject: Re: [Qemu-devel] [PATCH 1/2] block: resize backing file image
 during offline commit, if necessary
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To: Jeff Cody <jcody@redhat.com>
Cc: kwolf@redhat.com, famz@redhat.com, qemu-devel@nongnu.org, stefanha@redhat.com

On Mon, Jan 13, 2014 at 03:18:45PM -0500, Jeff Cody wrote:
> @@ -1904,7 +1904,19 @@ int bdrv_commit(BlockDriverState *bs)
>          }
>      }
>  
> -    total_sectors = bdrv_getlength(bs) >> BDRV_SECTOR_BITS;
> +    length = bdrv_getlength(bs);
> +
> +    /* If our top snapshot is larger than the backing file image,
> +     * grow the backing file image if possible.  If not possible,
> +     * we must return an error */
> +    if (length > bdrv_getlength(bs->backing_hd)) {
> +        ret = bdrv_truncate(bs->backing_hd, length);

bdrv_getlength() is allowed to return -errno.  It's unlikely here but we
should at least check bdrv_getlength(bs), probably also
bdrv_getlength(bs->backing_hd).