Re: [Qemu-devel] [PATCH v2 5/7] QAPI: add command for live block commit, 'block-commit'

[Jeff Cody <jcody@redhat.com>]

On 09/26/2012 10:13 AM, Kevin Wolf wrote:
> Am 25.09.2012 18:29, schrieb Jeff Cody:
>> The command for live block commit is added, which has the following
>> arguments:
>>
>> device: the block device to perform the commit on (mandatory)
>> base:   the base image to commit into; optional (if not specified,
>>         it is the underlying original image)
>> top:    the top image of the commit - all data from inside top down
>>         to base will be committed into base. optional (if not specified,
>>         it is one below the active image) - see note below
>> speed:  maximum speed, in bytes/sec
>>
>> note: eventually this will support merging down the active layer,
>>       but that code is not yet complete.  If the active layer is passed
>>       in currently as top, or top is left to the default, then an error
>>       will be returned.
>>
>> The is done as a block job, so upon completion a BLOCK_JOB_COMPLETED will
>> be emitted.
>>
>> Signed-off-by: Jeff Cody <jcody@redhat.com>
> 
>> diff --git a/qapi-schema.json b/qapi-schema.json
>> index 14e4419..e614453 100644
>> --- a/qapi-schema.json
>> +++ b/qapi-schema.json
>> @@ -1468,6 +1468,41 @@
>>    'returns': 'str' }
>>  
>>  ##
>> +# @block-commit
>> +#
>> +# Live commit of data from overlay image nodes into backing nodes - i.e.,
>> +# writes data between 'top' and 'base' into 'base'.
>> +#
>> +# @device:  the name of the device
>> +#
>> +# @base:   #optional The file name of the backing image to write data into.
>> +#                    If not specified, this is the deepest backing image
>> +#
>> +# @top:    #optional The file name of the backing image within the image chain,
>> +#                    which contains the topmost data to be committed down.
>> +#                    If not specified, this is one layer below the active
>> +#                    layer (i.e. active->backing_hd).
> 
> Why isn't active the default any more? I know, we don't support it yet,
> but long term this is what makes most sense as a default.
> 

Eric had a similar question, and asked if anyone had any preference -
this was my response:

---

I guess I don't have a strong preference either - I originally had it
the other way, but then that meant the default in the current
implementation was actually an error.

Also, I assumed (danger!) that the most common use of commit would be a
snapshot, followed by a commit of active->backing_hd. With that
assumption, it seemed like a sane default.

---

I can certainly revert back to having the active layer be the top, if
that is the preference.

>> +#
>> +#                    If top == base, that is an error.
>> +#
>> +#
>> +# @speed:  #optional the maximum speed, in bytes per second
>> +#
>> +# Returns: Nothing on success
>> +#          If commit or stream is already active on this device, DeviceInUse
>> +#          If @device does not exist, DeviceNotFound
>> +#          If image commit is not supported by this device, NotSupported
>> +#          If @base does not exist, a generic error is returned
>> +#          If @top does not exist, a generic error is returned
>> +#          If @speed is invalid, InvalidParameter
>> +#
>> +# Since: 1.3
>> +#
>> +##
>> +{ 'command': 'block-commit',
>> +  'data': { 'device': 'str', '*base': 'str', '*top': 'str',
>> +            '*speed': 'int' } }
> 
> Kevin
>