Re: [PATCH] libxl: do not call default block script

["Roger Pau Monné" <roger.pau@citrix.com>]

On 10/05/13 16:21, Ian Campbell wrote:
> On Fri, 2013-05-10 at 15:19 +0100, Roger Pau Monne wrote:
>> On 08/05/13 07:07, Marek Marczykowski wrote:
>>> When user didn't specified disk->script, libxl writes physical-device
>>> node itself, making script call redundant - especially the default one.
>>
>> This change will break NetBSD support, please also attach the necessary
>> NetBSD change or at least mention it in the commit message, so it can be
>> fixed.
> 
> I hadn't thought about NetBSD. This strongly suggests that if it is
> appropriate at all it is most definitely 4.4 material since it has
> non-obvious affects.
> 
>> If I'm right, the block script does other things apart from writing the
>> physical device major/minor, it also checks that no other domain is
>> using this device.
> 
> I nearly said that too but at least in the Linux scripts the presence of
> the physical-device node cause the script to exit before that check.
> Oops.

Ooops, I should have looked at the actual script before speaking so
quickly. It looks like this might cause trouble, specially because we no
longer check that the block device is not opened by two guests at the
same time, IMHO the right solution would be to prevent libxl from
writing the physical-device entry at all, and I'm not sure if this
shouldn't be considered as a bug fix for 4.3.

NetBSD for example prevents a block device from being opened more than
once at the same time, but I don't think Linux does this.

> 
>> If you want to make the hotplug script call non
>> redundant I would recommend to prevent libxl from witting physical
>> device major/minor instead of removing the execution of the hotplug script.
> 
> I think this is something we can resolve one way or the other with your
> hotplug script rework in 4.4, since it presumably adds new requirements
> here.
> 
> Ian.
> 
>