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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