[Sheepdog] [PATCH v3] sheep: change snapshot/clone flow

[MORITA Kazutaka]

At Fri, 20 Apr 2012 14:40:26 +0800,
yaohaiting.wujue at gmail.com wrote:
> 
> From: HaiTing Yao <wujue.yht at taobao.com>
> 
> When create snapshot for source VDI, the new created VDI used as source
> VDI, and the old source VDI used as snapshot. This flow make users
> confused about VDI and snapshot relation. The snapshot metadata maybe is
> stored on multi-VDI, so need read multi VDIs inode to get snapshot list.
> 
> When create snapshot, we does not need change new created VDI to source
> VDI. The source VDI just need use snapshot VDI ID as its object data ID.
> 
> Show one example.
> 
> Before modification:
> 
>   Name        Id    Size    Used  Shared    Creation time   VDI id   Tag
> s v1           1   64 MB   20 MB  0.0 MB 2012-03-26 16:55   709128
> s v1           2   64 MB  0.0 MB   20 MB 2012-03-26 16:56   709129   sn3
>   v1           3   64 MB  0.0 MB   20 MB 2012-03-26 16:56   70912a
> 
> After modification:
> 
>   Name        Id    Size    Used  Shared    Creation time   VDI id   Tag
>   v1           0   64 MB   20 MB  0.0 MB 2012-03-27 11:06   709128
> s v1           1   64 MB  0.0 MB   20 MB 2012-03-27 11:06   709129
> s v1           2   64 MB  0.0 MB   20 MB 2012-03-27 11:07   70912a   sn3
> 
> Signed-off-by: HaiTing Yao <wujue.yht at taobao.com>
> ---
>  collie/common.c          |    2 +-
>  collie/vdi.c             |   33 ++++++++++++++++++++++-----------
>  include/sheepdog_proto.h |    6 ++++--
>  sheep/vdi.c              |   18 ++++++++++--------
>  4 files changed, 37 insertions(+), 22 deletions(-)

Your patch breaks the relationship between VDI snapshots.
For example:
==
 $ collie cluster format -c 1

 $ qemu-img create sheepdog:test 4G
 $ qemu-img snapshot -c tag1 sheepdog:test
 $ qemu-img snapshot -c tag2 sheepdog:test
 $ qemu-img snapshot -c tag3 sheepdog:test

 $ qemu-img create sheepdog:test2 4G
 $ qemu-img snapshot -c tag1 sheepdog:test2
 $ qemu-img snapshot -c tag2 sheepdog:test2
 $ qemu-io -c "write 0 512" sheepdog:test2:1
 $ qemu-img snapshot -c tag3 sheepdog:test2

 $ collie vdi tree
==

and the expected output is:
==
  test---[2012-04-21 05:51]---[2012-04-21 05:51]---[2012-04-21 05:51]---(you are here)
  test2---[2012-04-21 05:51]-+-[2012-04-21 05:51]---[2012-04-21 05:51]
                             `-[2012-04-21 05:51]---(you are here)
==

BTW, How about displaying the current Id as zero and removing VDI id
from the output of 'collie vdi list'?  VDI IDs are used for internal
purpose only, so I think we don't need to display them here.  I'd like
to avoid changing the VDI structure if possible.

Thanks,

Kazutaka