If a BlockDriverState supports backing files but has none then any unallocated area reads back as zeroes.
bdrv_co_block_status() is only reporting this is if want_zero is true, but this is an inexpensive test and there is no reason not to do it in all cases. Suggested-by: Vladimir Sementsov-Ogievskiy <vsement...@virtuozzo.com> Signed-off-by: Alberto Garcia <be...@igalia.com> --- block/io.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/block/io.c b/block/io.c index ad3a51ed53..1b0ae29610 100644 --- a/block/io.c +++ b/block/io.c @@ -2408,16 +2408,16 @@ static int coroutine_fn bdrv_co_block_status(BlockDriverState *bs, if (ret & (BDRV_BLOCK_DATA | BDRV_BLOCK_ZERO)) { ret |= BDRV_BLOCK_ALLOCATED; - } else if (want_zero && bs->drv->supports_backing) { - if (bs->backing) { + } else if (bs->drv->supports_backing) { + if (!bs->backing) { + ret |= BDRV_BLOCK_ZERO; + } else if (want_zero) { BlockDriverState *bs2 = bs->backing->bs; int64_t size2 = bdrv_getlength(bs2); if (size2 >= 0 && offset >= size2) { ret |= BDRV_BLOCK_ZERO; } - } else { - ret |= BDRV_BLOCK_ZERO; } } -- 2.20.1