Re: [Qemu-devel] [PATCH v5 2/2] vmdk: Optimize cluster allocation

[Stefan Hajnoczi]

On Tue, May 27, 2014 at 04:49:22PM +0800, Fam Zheng wrote:
> +    if (!bs->backing_hd) {
> +        memset(whole_grain, 0,  skip_start_sector << BDRV_SECTOR_BITS);
> +        memset(whole_grain + (skip_end_sector << BDRV_SECTOR_BITS), 0,
> +               cluster_bytes - (skip_end_sector << BDRV_SECTOR_BITS));
> +    }
> +
> +    assert(skip_end_sector <= sector_num + extent->cluster_sectors);

Does this assertion make sense?  skip_end_sector is a small number of
sectors (relative to start of cluster), while sector_num +
extent->cluster_sectors is a large absolute sector offset.

> +/**
> + * get_cluster_offset
> + *
> + * Look up cluster offset in extent file by sector number, and store in
> + * @cluster_offset.
> + *
> + * For flat extent, the start offset as parsed from the description file is

s/extent/extents/

> + * returned.
> + *
> + * For sparse extent, look up in L1, L2 table. If allocate is true, return an

s/extent/extents/

> + * offset for a new cluster and update L2 cache. If there is a backing file,
> + * COW is done before returning; otherwise, zeroes are written to the 
> allocated
> + * cluster. Both COW and zero writting skips the sector range

s/writting/writing/

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