Re: [Qemu-devel] [PATCH V3 1/4] block: drop bs_snapshots global variable

[Wenchao Xia <xiawenc@linux.vnet.ibm.com>]

于 2013-5-27 23:18, Kevin Wolf 写道:
> Am 25.05.2013 um 05:09 hat Wenchao Xia geschrieben:
>> From: Stefan Hajnoczi <stefanha@redhat.com>
>>
>> The bs_snapshots global variable points to the BlockDriverState which
>> will be used to save vmstate.  This is really a savevm.c concept but was
>> moved into block.c:bdrv_snapshots() when it became clear that hotplug
>> could result in a dangling pointer.
>>
>> While auditing the block layer's global state I came upon bs_snapshots
>> and realized that a variable is not necessary here.  Simply find the
>> first BlockDriverState capable of internal snapshots each time this is
>> needed.
>>
>> The behavior of bdrv_snapshots() is preserved across hotplug because new
>> drives are always appended to the bdrv_states list.  This means that
>> calling the new find_vmstate_bs() function is idempotent - it returns
>> the same BlockDriverState unless it was hot-unplugged.
>>
>> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
>> Reviewed-by: Eric Blake <eblake@redhat.com>
>> Reviewed-by: Wenchao Xia <xiawenc@linux.vnet.ibm.com>
>> Signed-off-by: Wenchao Xia <xiawenc@linux.vnet.ibm.com>
>
> I am not totally convinced by this approach, especially when it's nowhere
> documented that the order of BDSes in the list is important. However, I
> think the current code is suboptimal as well, so I'll apply this for
> now.
>
> What we really want is this: savevm lets you choose which image to save
> the VM state to, and if you don't specify one, it automatically picks
> one like today. loadvm checks all images and loads the VM state from the
> image that has the VM state for this snapshot. If loadvm finds that it's
> not exactly one image that has a VM state, this is an error condition.
>
> Is anyone interested in implementing this?
>
> Kevin
>
   I think that can came up after Pavel's savevm transaction, which
add parameter telling which image to save vmstate. This patch simply
keep what it is now not touching that part.



-- 
Best Regards

Wenchao Xia