Re: [Qemu-devel] [PATCH v2 0/6] Mirrored writes using blockdev-transaction

[Kevin Wolf]

Am 01.03.2012 22:10, schrieb Anthony Liguori:
> On 03/01/2012 05:21 AM, Paolo Bonzini wrote:
>> This implements all ingredients to establish mirrored writes.
>> The drive-reopen command that is used to terminate mirrored writes
>> is not included in this series.
>>
>> Tested with the following scenarios:
>>
>> a) mirror only
>>
>> 1) create base.qcow2 and start QEMU with it
>>
>> 2) Execute the following QMP command
>>
>> { "execute": "qmp_capabilities" }
>> { "execute": "blockdev-transaction", "arguments":
>>    {'actions': [
>>      { 'type': 'mirror', 'data' :
>>        { 'device': 'ide0-hd0', 'target': '/home/pbonzini/mirror.qcow2' } } ] 
>> } }
>> { "execute": "cont" }
>>
>> 3) hibernate the guest (this requires an IDE disk and -cpu kvm64,-kvmclock)
>>
>> 4) restart the guest with mirror.qcow2
>>
>>
>> b) atomic snapshot+mirror
>>
>> 1) start QEMU with an existing image test.img
>>
>> 2) Execute the following QMP command
>>
>> { "execute": "qmp_capabilities" }
>> { "execute": "blockdev-transaction", "arguments":
>>    {'actions': [
>>      { 'type': 'snapshot', 'data' :
>>        { 'device': 'ide0-hd0', 'snapshot-file': '/home/pbonzini/base.qcow2' 
>> } },
>>      { 'type': 'mirror', 'data' :
>>        { 'device': 'ide0-hd0', 'target': '/home/pbonzini/mirror.qcow2' } } ] 
>> } }
>> { "execute": "cont" }
> 
> We don't have schema introspection today.  How would one determine when new 
> transaction types are available?
> 
> I think we need some sort of introspection method too in order for clients to 
> figure out when the command is extended.

How about coupling the types with independently available commands for
now? We would rename 'snapshot' to 'blockdev-snapshot-sync', which does
the same thing outside of transactions. The mirror patches would then
introduce a 'drive-mirror' top-level command at the same time as they
introduce a 'drive-mirror' transaction type.

Kevin