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Date: Wed, 12 Sep 2018 17:34:08 +0800
From: Fam Zheng <famz@redhat.com>
Message-ID: <20180912093408.GG2526@lemon.usersys.redhat.com>
References: <20180828031751.29507-1-yuchenlin@synology.com>
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Subject: Re: [Qemu-devel] [PATCH] vmdk: align end of file to a sector
 boundary
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To: yuchenlin@synology.com
Cc: qemu-devel@nongnu.org, qemu-block@nongnu.org

On Tue, 08/28 11:17, yuchenlin@synology.com wrote:
> From: yuchenlin <yuchenlin@synology.com>
> 
> There is a rare case which the size of last compressed cluster
> is larger than the cluster size, which will cause the file is
> not aligned at the sector boundary.

I don't understand. Doesn't it mean that if you force the alignment by
truncating out the extra bytes, some data is lost?

> 
> Signed-off-by: yuchenlin <yuchenlin@synology.com>
> ---
>  block/vmdk.c | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
> 
> diff --git a/block/vmdk.c b/block/vmdk.c
> index a9d0084e36..a8ae7c65d2 100644
> --- a/block/vmdk.c
> +++ b/block/vmdk.c
> @@ -1698,6 +1698,24 @@ static int coroutine_fn
>  vmdk_co_pwritev_compressed(BlockDriverState *bs, uint64_t offset,
>                             uint64_t bytes, QEMUIOVector *qiov)
>  {
> +    if (bytes == 0) {

Where is this bytes == 0 condition from?

> +        /* align end of file to a sector boundary. */
> +        BDRVVmdkState *s = bs->opaque;
> +        int i, ret;
> +        int64_t length;
> +
> +        for (i = 0; i < s->num_extents; i++) {
> +            length = bdrv_getlength(s->extents[i].file->bs);
> +            if (length < 0) {
> +                return length;
> +            }
> +            ret = bdrv_truncate(s->extents[i].file, length, PREALLOC_MODE_OFF, NULL);
> +            if (ret < 0) {
> +                return ret;
> +            }
> +        }
> +        return 0;
> +    }
>      return vmdk_co_pwritev(bs, offset, bytes, qiov, 0);
>  }
>  
> -- 
> 2.17.0
> 

Fam