Re: [Qemu-devel] [PATCH v2 0/3] HMP/snapshot changes - do not use ID anymore

[Max Reitz]

On 09.01.19 15:21, Kevin Wolf wrote:
> Am 09.01.2019 um 15:10 hat Max Reitz geschrieben:
>> On 06.09.18 13:11, Daniel Henrique Barboza wrote:
>>> changes in v2:
>>> - removed the "RFC" marker;
>>> - added a new patch (patch 2) that removes
>>> bdrv_snapshot_delete_by_id_or_name from the code;
>>> - made changes in patch 1 as suggested by Murilo;
>>> - previous patch set link:
>>> https://lists.gnu.org/archive/html/qemu-devel/2018-08/msg04658.html
>>>
>>>
>>> It is not uncommon to see bugs being opened by testers that attempt to
>>> create VM snapshots using HMP. It turns out that "0" and "1" are quite
>>> common snapshot names and they trigger a lot of bugs. I gave an example
>>> in the commit message of patch 1, but to sum up here: QEMU treats the
>>> input of savevm/loadvm/delvm sometimes as 'ID', sometimes as 'name'. It
>>> is documented as such, but this can lead to strange situations.
>>>
>>> Given that it is strange for an API to consider a parameter to be 2 fields
>>> at the same time, and inadvently treating them as one or the other, and
>>> that removing the ID field is too drastic, my idea here is to keep the
>>> ID field for internal control, but do not let the user set it.
>>>
>>> I guess there's room for discussion about considering this change an API
>>> change or not. It doesn't affect users of HMP and it doesn't affect Libvirt,
>>> but simplifying the meaning of the parameters of savevm/loadvm/delvm.
>>
>> (Yes, very late reply, I'm sorry...)
>>
>> I do think it affects users of HMP, because right now you can delete
>> snapshots with their ID, and after this series you cannot.
> 
> Can there be snapshots that can't be identified by a snapshot name, but
> only by their ID?

I don't know, but what I meant is that if you have scripts to do all
this, you might have to adjust them with this change.

>> I think we had a short discussion about just disallowing numeric
>> snapshot names.  How bad would that be?
> 
> It would be incompatible with existing images and result in a more
> complex snapshot identifier resolution. Why would it be any better?

It wouldn't be incompatible with existing images if we'd just disallow
creating such snapshots.  I don't see how the identifier resolution
would be more complex.

I don't know if it'd be better.  I'd just find it simpler (for us, that
is -- for users, I'm not sure).

Max

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