[Qemu-devel] [PATCH v4 0/2] qcow2: Patch for shrinking qcow2 disk image

[Jun Li <junmuzi@gmail.com>]

v4:
  Add deal with COW clusters in l2 table. When using COW, some of (l2_entry >>
s->cluster_bits) will larger than s->refcount_table_size, so need to discard
this l2_entry.

v3:
  Fixed host cluster leak.

A simple testing:

Step 1,
# /opt/qemu-git-arm/bin/qemu-img info /home/lijun/Work/tmp/shrink.qcow2
image: /home/lijun/Work/tmp/shrink.qcow2
file format: qcow2
virtual size: 2.0G (2147483648 bytes)
disk size: 2.0G
cluster_size: 65536
Format specific information:
    compat: 1.1
    lazy refcounts: false
    corrupt: false

Step 2,
# /opt/qemu-git-arm/bin/qemu-img resize /home/lijun/Work/tmp/shrink.qcow2 -100M
Image resized.

Step 3,
# /opt/qemu-git-arm/bin/qemu-img info /home/lijun/Work/tmp/shrink.qcow2
image: /home/lijun/Work/tmp/shrink.qcow2
file format: qcow2
virtual size: 1.9G (2042626048 bytes)
disk size: 1.9G
cluster_size: 65536
Format specific information:
    compat: 1.1
    lazy refcounts: false
    corrupt: false

Step 4,
# /opt/qemu-git-arm/bin/qemu-img check /home/lijun/Work/tmp/shrink.qcow2
No errors were found on the image.
24576/31168 = 78.85% allocated, 0.80% fragmented, 0.00% compressed clusters
Image end offset: 1631911936

As above show, in step 1, "disk size" and "virtual size" are all 2.0G.
After Step 3, "disk size" and "virtual size" are all 1.9G.

BTW, above is also a simple testing. I will submit a test case for
qemu-iotests later. But I am not so familar with howto write qemu-iotests now.

In file block/qcow2.c, just using ftruncate to fix host cluster leak.

In file block/qcow2-cluster.c, just re-copy qcow2_grow_l1_table to
realize qcow2_shrink_l1_and_l2_table.

In file block/qcow2-refcount.c, also update the realization to handle self-describing
refcount blocks in function update_refcount.

Thanks.


Jun Li (2):
  qcow2: Add qcow2_shrink_l1_and_l2_table for qcow2 shrinking
  qcow2: add update refcount table realization for update_refcount

 block/qcow2-cluster.c  | 186 +++++++++++++++++++++++++++++++++++++++++++++++++
 block/qcow2-refcount.c |  46 +++++++++++-
 block/qcow2.c          |  40 +++++++++--
 block/qcow2.h          |   2 +
 4 files changed, 269 insertions(+), 5 deletions(-)

-- 
1.9.3