From 0da9856851dcca09222a1467e16ddd05dc66e460 Mon Sep 17 00:00:00 2001 From: Nir Soffer Date: Fri, 19 Feb 2021 18:07:52 +0200 Subject: nbd: server: Report holes for raw images When querying image extents for raw image, qemu-nbd reports holes as zero: $ qemu-nbd -t -r -f raw empty-6g.raw $ qemu-img map --output json nbd://localhost [{ "start": 0, "length": 6442450944, "depth": 0, "zero": true, "data": true, "offset": 0}] $ qemu-img map --output json empty-6g.raw [{ "start": 0, "length": 6442450944, "depth": 0, "zero": true, "data": false, "offset": 0}] Turns out that qemu-img map reports a hole based on BDRV_BLOCK_DATA, but nbd server reports a hole based on BDRV_BLOCK_ALLOCATED. The NBD protocol says: NBD_STATE_HOLE (bit 0): if set, the block represents a hole (and future writes to that area may cause fragmentation or encounter an NBD_ENOSPC error); if clear, the block is allocated or the server could not otherwise determine its status. qemu-img manual says: whether the sectors contain actual data or not (boolean field data; if false, the sectors are either unallocated or stored as optimized all-zero clusters); To me, data=false looks compatible with NBD_STATE_HOLE. From user point of view, getting same results from qemu-nbd and qemu-img is more important than being more correct about allocation status. Changing nbd server to report holes using BDRV_BLOCK_DATA makes qemu-nbd results compatible with qemu-img map: $ qemu-img map --output json nbd://localhost [{ "start": 0, "length": 6442450944, "depth": 0, "zero": true, "data": false, "offset": 0}] Signed-off-by: Nir Soffer Message-Id: <20210219160752.1826830-1-nsoffer@redhat.com> Reviewed-by: Eric Blake Reviewed-by: Vladimir Sementsov-Ogievskiy Signed-off-by: Eric Blake --- tests/qemu-iotests/241.out | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'tests/qemu-iotests') diff --git a/tests/qemu-iotests/241.out b/tests/qemu-iotests/241.out index 75f9f465e5..3f8c173cc8 100644 --- a/tests/qemu-iotests/241.out +++ b/tests/qemu-iotests/241.out @@ -5,7 +5,7 @@ QA output created by 241 size: 1024 min block: 1 [{ "start": 0, "length": 1000, "depth": 0, "zero": false, "data": true, "offset": OFFSET}, -{ "start": 1000, "length": 24, "depth": 0, "zero": true, "data": true, "offset": OFFSET}] +{ "start": 1000, "length": 24, "depth": 0, "zero": true, "data": false, "offset": OFFSET}] 1 KiB (0x400) bytes allocated at offset 0 bytes (0x0) === Exporting unaligned raw image, forced server sector alignment === @@ -23,6 +23,6 @@ WARNING: Image format was not specified for 'TEST_DIR/t.raw' and probing guessed size: 1024 min block: 1 [{ "start": 0, "length": 1000, "depth": 0, "zero": false, "data": true, "offset": OFFSET}, -{ "start": 1000, "length": 24, "depth": 0, "zero": true, "data": true, "offset": OFFSET}] +{ "start": 1000, "length": 24, "depth": 0, "zero": true, "data": false, "offset": OFFSET}] 1 KiB (0x400) bytes allocated at offset 0 bytes (0x0) *** done -- cgit v1.2.3-55-g7522