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Re: [Qemu-block] [PATCH v6 0/4] Add shrink image for qcow2


From: John Snow
Subject: Re: [Qemu-block] [PATCH v6 0/4] Add shrink image for qcow2
Date: Wed, 16 Aug 2017 17:07:40 -0400
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1

Over a month with no replies and we're nearing the next QEMU release. If
this patchset is still applicable, can you rebase and resend for 2.11?

--js

On 07/14/2017 11:37 AM, Pavel Butsykin wrote:
> This patch add shrinking of the image file for qcow2. As a result, this allows
> us to reduce the virtual image size and free up space on the disk without
> copying the image. Image can be fragmented and shrink is done by punching 
> holes
> in the image file.
> 
> # ./qemu-img create -f qcow2 image.qcow2 4G
> Formatting 'image.qcow2', fmt=qcow2 size=4294967296 encryption=off 
> cluster_size=65536 lazy_refcounts=off refcount_bits=16
> 
> # ./qemu-io -c "write -P 0x22 0 1G" image.qcow2
> wrote 1073741824/1073741824 bytes at offset 0
> 1 GiB, 1 ops; 0:00:04.59 (222.886 MiB/sec and 0.2177 ops/sec)
> 
> # ./qemu-img resize image.qcow2 512M
> warning: qemu-img: Shrinking an image will delete all data beyond the 
> shrunken image's end. Before performing such an operation, make sure there is 
> no important data there.
> error: qemu-img: Use the --shrink option to perform a shrink operation.
> 
> # ./qemu-img resize --shrink image.qcow2 128M
> Image resized.
> 
> # ./qemu-img info image.qcow2
> image: image.qcow2
> file format: qcow2
> virtual size: 128M (134217728 bytes)
> disk size: 128M
> cluster_size: 65536
> Format specific information:
>     compat: 1.1
>     lazy refcounts: false
>     refcount bits: 16
>     corrupt: false
> 
> # du -h image.qcow2
> 129M    image.qcow2
> 
> Changes from v1:
> - add --shrink flag for qemu-img resize
> - add qcow2_cache_discard
> - simplify qcow2_shrink_l1_table() to reduce the likelihood of image 
> corruption
> - add new qemu-iotests for shrinking images
> 
> Changes from v2:
> - replace qprintf() on error_report() (1)
> - rewrite warning messages (1)
> - enforce --shrink flag for all formats except raw (1)
> - split qcow2_cache_discard() (2)
> - minor fixes according to comments (3)
> - rewrite the last part of qcow2_shrink_reftable() to avoid
>   qcow2_free_clusters() calls inside (3)
> - improve test for shrinking image (4)
> 
> Changes from v3:
> - rebase on "Implement a warning_report function" Alistair's patch-set (1)
> - spelling fixes (1)
> - the man page fix according to the discussion (1)
> - add call qcow2_signal_corruption() in case of image corruption (3)
> 
> Changes from v4:
> - rebase on https://github.com/XanClic/qemu/commits/block Max's block branch
> 
> Changes from v5:
> - the condition refcount == 0 should be enough to evict the l2/refcount 
> cluster
>   from the cache (2)
> - overwrite the l1/refcount table in memory with zeros, even if overwriting 
> the
>   l1/refcount table on disk has failed (3)
> - replace g_try_malloc() on g_malloc() for allocation reftable_tmp (3)
> 
> Pavel Butsykin (4):
>   qemu-img: add --shrink flag for resize
>   qcow2: add qcow2_cache_discard
>   qcow2: add shrink image support
>   qemu-iotests: add shrinking image test
> 
>  block/qcow2-cache.c        |  26 +++++++
>  block/qcow2-cluster.c      |  50 +++++++++++++
>  block/qcow2-refcount.c     | 140 ++++++++++++++++++++++++++++++++++++-
>  block/qcow2.c              |  43 +++++++++---
>  block/qcow2.h              |  17 +++++
>  qapi/block-core.json       |   3 +-
>  qemu-img-cmds.hx           |   4 +-
>  qemu-img.c                 |  23 ++++++
>  qemu-img.texi              |   6 +-
>  tests/qemu-iotests/102     |   4 +-
>  tests/qemu-iotests/163     | 170 
> +++++++++++++++++++++++++++++++++++++++++++++
>  tests/qemu-iotests/163.out |   5 ++
>  tests/qemu-iotests/group   |   1 +
>  13 files changed, 475 insertions(+), 17 deletions(-)
>  create mode 100644 tests/qemu-iotests/163
>  create mode 100644 tests/qemu-iotests/163.out
> 



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