Re: [Qemu-devel] [RFC PATCH 1/3] block: add target-id option to drive-backup QMP command

[Paolo Bonzini]

Il 27/06/2013 13:37, Fam Zheng ha scritto:
>>> > > 
>>> > > Yes, this makes me realize that ref count it not a solution to retire
>>> > > bs->in_use, because we can't tell if drive-del or block-resize is safe
>>> > > with only reference number. But I can't think of two situations to deny
>>> > > different subsets of commands, shouldn't a general blocker, like in_use
>>> > > does, be good enough?
>> > 
>> > For example, right now nbd-server-add does not check bdrv_in_use.  But
>> > shrinking a device that is exposed via NBD could be surprising to the
>> > NBD clients.
>> > 
> So it seems to me that both block job and nbd server have the same
> restriction on device: don't resize, and notify on close. So my question
> is if we implement bdrv_add_command_blocker(), do the callers still need to 
> distinguish what actions to block, or it's generally to block all the actions 
> those change the device parameter?

It would be a good start to have a list of things that are setting and
checking bdrv_in_use.  Then we can make a matrix.

Paolo