Re: [PATCH v4 6/9] qemu-img: Add bitmap sub-command

[Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>]

14.05.2020 17:20, Eric Blake wrote:
> On 5/14/20 1:45 AM, Vladimir Sementsov-Ogievskiy wrote:
>> 13.05.2020 04:16, Eric Blake wrote:
>>> Include actions for --add, --remove, --clear, --enable, --disable, and
>>> --merge (note that --clear is a bit of fluff, because the same can be
>>> accomplished by removing a bitmap and then adding a new one in its
>>> place, but it matches what QMP commands exist).  Listing is omitted,
>>> because it does not require a bitmap name and because it was already
>>> possible with 'qemu-img info'.  A single command line can play one or
>>> more bitmap commands in sequence on the same bitmap name (although all
>>> added bitmaps share the same granularity, and and all merged bitmaps
>>> come from the same source file).  Merge defaults to other bitmaps in
>>> the primary image, but can also be told to merge bitmaps from a
>>> distinct image.
>>>
> 
>>
>> I'm sorry for asking it only now on v4.. But still. Why do we need it? 
> 
> Ease of use.
> 
>> We can instead run qemu binary (or even new qemu-storage-daemon) and just use existing qmp commands. Is there a real benefit in developing qemu-img, maintaining two interfaces for the same thing?
> 
> If it makes someone's life easier, and is not hard to maintain, then yes.  A command line interface that calls into QMP is not hard to maintain.  And _I_ certainly found it easier to write iotests with this patch in place, so it already has at least one client.
> 
>> Of-course, just run qmp commands from terminal is a lot less comfortable than just a qemu img command.. But may be we need some wrapper, which make it simple to run one qmp command on an image?
>>
>> It's simple to make a python wrapper working like
>>
>> qemu-qmp block-dirty-bitmap-add '{node: self, name: bitmap0, persistent: true}' /path/to/x.qcow2
> 
> This _IS_ such a wrapper.  The whole point of this patch is that it is now simpler to run one (or more) QMP command on an offline image from the command line.  Just because I wrote it in C instead of python, and attached it to an existing tool instead of writing a new tool, doesn't change the fact that it is just a wrapper around the existing QMP commands.
> 

OK, that's right.

The thing that I didn't like is that we have to make cli-to-qapi interface mapping by hand. But I see now that interface you implementing is prepared to make several actions with same bitmap-name, which can't be achieved with some kind of automatic interface matching anyway, so my proposal don't match your needs, sorry for my haste)


-- 
Best regards,
Vladimir