Re: [PATCH] Device duplicate check fix

[Michal Novotny <minovotn@redhat.com>]

Hi,
you don't see the need to add this check to xend since the same check is 
already present in the hotplug scripts? So, is this useless and should I 
do nothing about that and let it be reverted like Keir wrote he did and 
do nothing about that?

Michal

Stefano Stabellini wrote:
> Sorry for the late reply, but I only now I realized that this patch
> breaks stubdoms: an exception is needed to allow a disk to be shared
> between the guest and its own stubdom.
>
> Beside I do not see the need to add this check to xend since the same
> check is already present in the hotplug scripts.
>
> Michal Novotny wrote:
>
>   
>> *Hello,
>> I've checked the duplicate-check code here and I found that's checked 
>> only in the context of one domain but not cross-domain. The thing is 
>> that we should check tap/vbd device cross-domain not to allow another 
>> guest to use the same disk image in some circumstances to prevent VM's 
>> disk corruption.
>>
>> The patch included denies disk image addition under those circumstances:
>>  1. **We're adding read-only disk that's already used as write-exclusive
>>  2. **We're adding write-shared disk that's already used as write-exclusive
>>  3. **We're adding write-exclusive disk that's already used
>>  4. **We're adding read-only disk that's already used as write-shared* 
>> (because of I/O caching issues etc.)
>> *
>> The vif device duplicate check remains the same it was and it's checked 
>> in the context of current domain only so that behaviour has been preserved.
>>
>> Michal
>>
>> Signed-off-by: Michal Novotny <minovotn@redhat.com>
>> *
>>
>>     
>
>
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