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authorNir Soffer <nirsof@gmail.com>2021-02-19 18:07:52 +0200
committerEric Blake <eblake@redhat.com>2021-03-08 13:08:45 -0600
commit0da9856851dcca09222a1467e16ddd05dc66e460 (patch)
tree5f67be723ef2e26ce4d56dcd4b1a55b056027933 /nbd
parent3d9330ece5c5cb7b5e8fec1bef4da8fe78134fc2 (diff)
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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 <nsoffer@redhat.com> Message-Id: <20210219160752.1826830-1-nsoffer@redhat.com> Reviewed-by: Eric Blake <eblake@redhat.com> Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Signed-off-by: Eric Blake <eblake@redhat.com>
Diffstat (limited to 'nbd')
-rw-r--r--nbd/server.c4
1 files changed, 2 insertions, 2 deletions
diff --git a/nbd/server.c b/nbd/server.c
index 7229f48..86a44a9 100644
--- a/nbd/server.c
+++ b/nbd/server.c
@@ -2087,8 +2087,8 @@ static int blockstatus_to_extents(BlockDriverState *bs, uint64_t offset,
return ret;
}
- flags = (ret & BDRV_BLOCK_ALLOCATED ? 0 : NBD_STATE_HOLE) |
- (ret & BDRV_BLOCK_ZERO ? NBD_STATE_ZERO : 0);
+ flags = (ret & BDRV_BLOCK_DATA ? 0 : NBD_STATE_HOLE) |
+ (ret & BDRV_BLOCK_ZERO ? NBD_STATE_ZERO : 0);
if (nbd_extent_array_add(ea, num, flags) < 0) {
return 0;