Re: [PATCH 1/4] block-common: Fix same_vm for no targets

[Jan Beulich <jbeulich@xxxxxxxx>]

On 08.02.2024 03:25, Jason Andryuk wrote:
> On Wed, Feb 7, 2024 at 7:50 AM Jan Beulich <jbeulich@xxxxxxxx> wrote:
>>
>> On 06.02.2024 12:45, Anthony PERARD wrote:
>>> On Thu, Feb 01, 2024 at 01:30:21PM -0500, Jason Andryuk wrote:
>>>> same_vm is broken when the two main domains do not have targets.  otvm
>>>> and targetvm are both missing, which means they get set to -1 and then
>>>> converted to empty strings:
>>>>
>>>> ++10697+ local targetvm=-1
>>>> ++10697+ local otvm=-1
>>>> ++10697+ otvm=
>>>> ++10697+ othervm=/vm/cc97bc2f-3a91-43f7-8fbc-4cb92f90b4e4
>>>> ++10697+ targetvm=
>>>> ++10697+ local frontend_uuid=/vm/844dea4e-44f8-4e3e-8145-325132a31ca5
>>>>
>>>> The final comparison returns true since the two empty strings match:
>>>>
>>>> ++10697+ '[' /vm/844dea4e-44f8-4e3e-8145-325132a31ca5 = 
>>>> /vm/cc97bc2f-3a91-43f7-8fbc-4cb92f90b4e4 -o '' = 
>>>> /vm/cc97bc2f-3a91-43f7-8fbc-4cb92f90b4e4 -o 
>>>> /vm/844dea4e-44f8-4e3e-8145-325132a31ca5 = '' -o '' = '' ']'
>>>>
>>>> Replace -1 with distinct strings indicating the lack of a value and
>>>> remove the collescing to empty stings.  The strings themselves will no
>>>> longer match, and that is correct.
>>>>
>>>> ++12364+ '[' /vm/844dea4e-44f8-4e3e-8145-325132a31ca5 = 
>>>> /vm/cc97bc2f-3a91-43f7-8fbc-4cb92f90b4e4 -o 'No target' = 
>>>> /vm/cc97bc2f-3a91-43f7-8fbc-4cb92f90b4e4 -o 
>>>> /vm/844dea4e-44f8-4e3e-8145-325132a31ca5 = 'No other target' -o 'No 
>>>> target' = 'No other target' ']'
>>>>
>>>> Signed-off-by: Jason Andryuk <jandryuk@xxxxxxxxx>
>>>
>>> Reviewed-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>
>>
>> I've committed this, but I take the absence of a Fixes: tag as indication
>> that this doesn't want/need backporting.
> 
> Hmmm, maybe this should have a Fixes.  Sorry I didn't investigate that
> better before submission.
> 
> Looks like this would be the commit:
> https://xenbits.xen.org/gitweb/?p=xen.git;a=commitdiff;h=f3a7ca02400d1c416e97451b4aebfaf608fc8192
> 
> f3a7ca02400d1 ("hotplug/Linux: fix same_vm check in block script")
> 
> I need to circle back on this.  IIRC, when I set up a conflicting
> assignment of a writable disk to two VMs with block-tap, it was
> allowed and not denied.  That is what prompted this change.
> 
> I'll have to double check there isn't something in the regular block
> that might prevent that.

Okay, I'll wait for a result here before deciding whether to queue.

Jan