[sheepdog] [PATCH v4] sheepdog: fix loadvm operation

[Liu Yuan]

On 04/25/2013 09:06 PM, MORITA Kazutaka wrote:
> At Thu, 25 Apr 2013 20:49:39 +0800,
> Liu Yuan wrote:
>>
>> From: Liu Yuan <tailai.ly at taobao.com>
>>
>> Currently the 'loadvm' opertaion works as following:
>> 1. switch to the snapshot
>> 2. mark current working VDI as a snapshot
>> 3. rely on sd_create_branch to create a new working VDI based on the snapshot
>>
>> This works not the same as other format as QCOW2. For e.g,
>>
>> qemu > savevm # get a live snapshot snap1
>> qemu > savevm # snap2
>> qemu > loadvm 1 # This will steally create snap3 of the working VDI
>>
>> Which will result in following snapshot chain:
>>
>> base <-- snap1 <-- snap2 <-- snap3
>>           ^
>>           |
>>       working VDI
>>
>> snap3 was unnecessarily created and might be annoying users.
>>
>> This patch discard the unnecessary 'snap3' creation. and implement
>> rollback(loadvm) operation to the specified snapshot by
>> 1. switch to the snapshot
>> 2. delete working VDI
>> 3. rely on sd_create_branch to create a new working VDI based on the snapshot
>>
>> The snapshot chain for above example will be:
>>
>> base <-- snap1 <-- snap2
>>           ^
>>           |
>>       working VDI
>>
>> Cc: qemu-devel at nongnu.org
>> Cc: MORITA Kazutaka <morita.kazutaka at lab.ntt.co.jp>
>> Cc: Kevin Wolf <kwolf at redhat.com>
>> Cc: Stefan Hajnoczi <stefanha at redhat.com>
>> Signed-off-by: Liu Yuan <tailai.ly at taobao.com>
>> ---
>> v4:
>>  - print an error message when NO_VDI found
>>
>> v3:
>>  - let boot from snapshot behave like 'loadvm'
>>
>> v2:
>>  - use do_req() because sd_delete isn't in coroutine
>>  - don't break old behavior if we boot up on the snapshot by using s->reverted
>>    to indicate if we delete working VDI successfully
>>  - fix a subtle case that sd_create_branch() isn't called yet while another
>>    'loadvm' is executed
>>
>>  block/sheepdog.c |   54 +++++++++++++++++++++++++++++++++++++++++++++++++++++-
>>  1 file changed, 53 insertions(+), 1 deletion(-)
> 
> Reviewed-by: MORITA Kazutaka <morita.kazutaka at lab.ntt.co.jp>

Missed this one, Stefan?

Thanks,
Yuan