See patch 1 for the detailed description why this is needed. The short
version is that libvirt needs to enable detect-zeroes on a mirror
target.
Peter, can you please check if this provides what you need? I checked
whether I could do the mirroring operation manually; and if I did it
right, it looks good to me. (Shortened) protocol of my test:
$ ./qemu-img create -f qcow2 /tmp/test.qcow2 64M
Formatting '/tmp/test.qcow2', fmt=qcow2 size=67108864 encryption=off
cluster_size=65536 lazy_refcounts=off refcount_bits=16
$ ./qemu-io -c 'write -P 0 0 64M' /tmp/test.qcow2
wrote 67108864/67108864 bytes at offset 0
64 MiB, 1 ops; 0.3141 sec (203.694 MiB/sec and 3.1827 ops/sec)
$ ls -lh /tmp/test.qcow2
-rw-r--r--. 1 kwolf kwolf 65M 23. Feb 17:57 /tmp/test.qcow2
$ ./qemu-img create -f qcow2 /tmp/copy.qcow2 64M
Formatting '/tmp/copy.qcow2', fmt=qcow2 size=67108864 encryption=off
cluster_size=65536 lazy_refcounts=off refcount_bits=16
$ x86_64-softmmu/qemu-system-x86_64 -qmp stdio -hda /tmp/test.qcow2
{"QMP": {"version": {"qemu": {"micro": 50, "minor": 5, "major": 2}, "package":
""}, "capabilities": []}}
{"execute":"qmp_capabilities"}
{"return": {}}
{"execute":"human-monitor-command","arguments":{"command-line":"drive_add -n 0
file.filename=/tmp/copy.qcow2,node-name=copy,detect-zeroes=on"}}
{"return": ""}
{"execute":"blockdev-mirror","arguments":{"device":"ide0-hd0","target":"copy","sync":"full"}}
{"return": {}}
{"timestamp": {"seconds": 1456247099, "microseconds": 895774}, "event":
"BLOCK_JOB_READY", "data": {"device": "ide0-hd0", "len": 67108864, "offset":
67108864, "speed": 0, "type": "mirror"}}
{"execute":"block-job-complete","arguments":{"device":"ide0-hd0"}}
{"return": {}}
{"timestamp": {"seconds": 1456247127, "microseconds": 552227}, "event":
"BLOCK_JOB_COMPLETED", "data": {"device": "ide0-hd0", "len": 67108864,
"offset": 67108864, "speed": 0, "type": "mirror"}}
$ ls -lh /tmp/copy.qcow2
-rw-r--r--. 1 kwolf kwolf 320K 23. Feb 18:04 /tmp/copy.qcow2
Kevin Wolf (2):
hmp: 'drive_add -n' for creating a node without BB
hmp: Extend drive_del to delete nodes without BB
blockdev.c | 39 +++++++++++++++++++++++++++++++++++++++
device-hotplug.c | 7 +++++++
hmp-commands.hx | 4 ++--
include/block/block_int.h | 2 ++
4 files changed, 50 insertions(+), 2 deletions(-)
--
1.8.3.1
