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| author | Nir Soffer | 2021-02-19 17:07:52 +0100 |
|---|---|---|
| committer | Eric Blake | 2021-03-08 20:08:45 +0100 |
| commit | 0da9856851dcca09222a1467e16ddd05dc66e460 (patch) | |
| tree | 5f67be723ef2e26ce4d56dcd4b1a55b056027933 /nbd | |
| parent | MAINTAINERS: add Vladimir as co-maintainer of NBD (diff) | |
| download | qemu-0da9856851dcca09222a1467e16ddd05dc66e460.tar.gz qemu-0da9856851dcca09222a1467e16ddd05dc66e460.tar.xz qemu-0da9856851dcca09222a1467e16ddd05dc66e460.zip | |
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.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/nbd/server.c b/nbd/server.c index 7229f487d2..86a44a9b41 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; |