static bool is_zero(BlockDriverState *bs, int64_t offset, int64_t bytes) { int nr; int64_t res; int64_t start; /* TODO: Widening to sector boundaries should only be needed as * long as we can't query finer granularity. */ start = QEMU_ALIGN_DOWN(offset, BDRV_SECTOR_SIZE); bytes = QEMU_ALIGN_UP(offset + bytes, BDRV_SECTOR_SIZE) - start; /* Clamp to image length, before checking status of underlying sectors */ if (start + bytes > bs->total_sectors * BDRV_SECTOR_SIZE) { bytes = bs->total_sectors * BDRV_SECTOR_SIZE - start; } if (!bytes) { return true; } res = bdrv_get_block_status_above(bs, NULL, start >> BDRV_SECTOR_BITS, bytes >> BDRV_SECTOR_BITS, &nr, NULL); return res >= 0 && (res & BDRV_BLOCK_ZERO) && nr * BDRV_SECTOR_SIZE == bytes; }