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Date: Tue, 10 Mar 2015 17:24:25 +0300
From: Roman Kagan <rkagan@parallels.com>
Message-ID: <20150310142425.GC6024@rkaganb.sw.ru>
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Subject: Re: [Qemu-devel] [PATCH 18/27] block/parallels: implement
 parallels_check method of block driver
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To: "Denis V. Lunev" <den@openvz.org>
Cc: Kevin Wolf <kwolf@redhat.com>, qemu-devel@nongnu.org, Stefan Hajnoczi <stefanha@redhat.com>

On Tue, Mar 10, 2015 at 11:51:12AM +0300, Denis V. Lunev wrote:
> The check is very simple at the moment. It calculates necessary stats
> and fix only the following errors:
> - space leak at the end of the image. This would happens due to
>   preallocation
> - clusters outside the image are zeroed. Nothing else could be done here
> 
> Signed-off-by: Denis V. Lunev <den@openvz.org>
> CC: Roman Kagan <rkagan@parallels.com>
> CC: Kevin Wolf <kwolf@redhat.com>
> CC: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  block/parallels.c | 82 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 82 insertions(+)
> 
> diff --git a/block/parallels.c b/block/parallels.c
> index 65f6418..e5b475e 100644
> --- a/block/parallels.c
> +++ b/block/parallels.c
> @@ -228,6 +228,87 @@ fail:
>      return ret;
>  }
>  
> +
> +static int parallels_check(BlockDriverState *bs, BdrvCheckResult *res,
> +                           BdrvCheckMode fix)
> +{
> +    BDRVParallelsState *s = bs->opaque;
> +    int64_t size, prev_off, high_off;
> +    int ret;
> +    uint32_t i;
> +    bool flush_bat = false;
> +    int cluster_size = s->tracks << BDRV_SECTOR_BITS;
> +
> +    size = bdrv_getlength(bs->file);
> +    if (size < 0) {
> +        res->check_errors++;
> +        return size;
> +    }
> +
> +    res->bfi.total_clusters = s->bat_size;
> +    res->bfi.compressed_clusters = 0; /* compression is not supported */
> +
> +    high_off = 0;
> +    prev_off = 0;
> +    for (i = 0; i < s->bat_size; i++) {
> +        int64_t off = bat2sect(s, i) << BDRV_SECTOR_BITS;
> +        if (off == 0)
> +            continue;

If you don't update prev_off here you can get fragmentation stats wrong
(dunno how important it is)

> +
> +        /* cluster outside the image */
> +        if (off > size) {
> +            fprintf(stderr, "%s cluster %u is outside image\n",
> +                    fix & BDRV_FIX_ERRORS ? "Repairing" : "ERROR", i);
> +            res->corruptions++;
> +            if (fix & BDRV_FIX_ERRORS) {
> +                s->bat_bitmap[i] = 0;
> +                res->corruptions_fixed++;
> +                flush_bat = true;
> +                continue;
> +            }

Ditto

Roman.