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Date: Wed, 21 Aug 2013 17:44:08 +0200
From: Stefan Hajnoczi <stefanha@gmail.com>
Message-ID: <20130821154408.GC18303@stefanha-thinkpad.redhat.com>
References: <1377073564-25502-1-git-send-email-asias@redhat.com>
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In-Reply-To: <1377073564-25502-1-git-send-email-asias@redhat.com>
Subject: Re: [Qemu-devel] [PATCH] block: Introduce bs->zero_beyond_eof
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To: Asias He <asias@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Stefan Hajnoczi <stefanha@redhat.com>, qemu-devel@nongnu.org, MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>, Bharata B Rao <bharata@linux.vnet.ibm.com>

On Wed, Aug 21, 2013 at 04:26:04PM +0800, Asias He wrote:
> @@ -868,6 +868,7 @@ int bdrv_file_open(BlockDriverState **pbs, const char *filename,
>      QDECREF(options);
>  
>      bs->growable = 1;
> +    bs->zero_beyond_eof = true;
>      *pbs = bs;
>      return 0;
>  
> @@ -978,6 +979,7 @@ int bdrv_open(BlockDriverState *bs, const char *filename, QDict *options,
>      }
>  
>      bs->options = options;
> +    bs->zero_beyond_eof = true;
>      options = qdict_clone_shallow(options);
>  
>      /* For snapshot=on, create a temporary qcow2 overlay */

We chatted about whether to duplicate bs->zero_beyond_eof = true on IRC.
Now I think you could put it in bdrv_open_common() to avoid duplication.
Every BDS should have ->zero_beyond_eof = true by default.

Stefan