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Date: Thu, 29 Aug 2013 11:18:20 +0200
From: Kevin Wolf <kwolf@redhat.com>
Message-ID: <20130829091820.GF2961@dhcp-200-207.str.redhat.com>
References: <1377701706-965-1-git-send-email-mreitz@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH v2 3/5] qcow2: Employ metadata overlap
	checks
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To: Max Reitz <mreitz@redhat.com>
Cc: qemu-devel@nongnu.org, Stefan Hajnoczi <stefanha@redhat.com>

Am 28.08.2013 um 16:55 hat Max Reitz geschrieben:
> The pre-write overlap check function is now called before most of the
> qcow2 writes (aborting it on collision or other error).
> 
> Signed-off-by: Max Reitz <mreitz@redhat.com>
> ---
>  block/qcow2-cache.c    | 17 +++++++++++++++++
>  block/qcow2-cluster.c  | 21 +++++++++++++++++++++
>  block/qcow2-snapshot.c | 22 ++++++++++++++++++++++
>  block/qcow2.c          | 36 +++++++++++++++++++++++++++++++++++-
>  4 files changed, 95 insertions(+), 1 deletion(-)

> @@ -1753,10 +1779,18 @@ static int qcow2_save_vmstate(BlockDriverState *bs, QEMUIOVector *qiov,
>      BDRVQcowState *s = bs->opaque;
>      int growable = bs->growable;
>      int ret;
> +    int64_t offset = qcow2_vm_state_offset(s) + pos;
>  
>      BLKDBG_EVENT(bs->file, BLKDBG_VMSTATE_SAVE);
>      bs->growable = 1;
> -    ret = bdrv_pwritev(bs, qcow2_vm_state_offset(s) + pos, qiov);
> +
> +    ret = qcow2_pre_write_overlap_check(bs, QCOW2_OL_DEFAULT, offset,
> +                                        qiov->size);
> +    if (ret < 0) {
> +        return ret;
> +    }
> +
> +    ret = bdrv_pwritev(bs, offset, qiov);
>      bs->growable = growable;
>  
>      return ret;

Sorry for not catching it in v1, this one is actually wrong. The
bdrv_pwritev() is against bs, not bs->file, so you would be comparing
virtual/guest offsets with physical/host offsets.

I think you can simply leave the check out here, the one in
qcow2_co_writev() should already do the right thing inside
bdrv_pwritev().

Kevin