Re: [Xen-devel] [PATCH RFC 04/12] libxl: create a local xenstore libxl and device-model dir for guests

[Roger Pau Monnà <roger.pau@xxxxxxxxxx>]

On 26/09/13 11:39, Ian Campbell wrote:
> On Thu, 2013-09-26 at 11:27 +0200, Roger Pau Monnà wrote:
>> On 25/09/13 15:48, Ian Campbell wrote:
>>> On Mon, 2013-09-23 at 12:30 +0200, Roger Pau Monne wrote:
>>>> If libxl is executed inside a guest domain it needs write access to
>>>> the local libxl xenstore dir (/local/<domid>/libxl) to store internal
>>>> data.
>>>
>>> These sorts of changes need a patch against docs/misc/xenstore-paths.txt
>>> too.
>>
>> Ack.
>>
>>>
>>>>  This also applies to Qemu which needs a
>>>> /local/<domid>/device-model xenstore directory.
>>>
>>> Is this a new requirement or a separate preexisting issue? How have we
>>> lived without it?
>>
>> This entry is so far only created on Dom0 (because it's the only domain
>> that launches Qemu, and is created by Qemu if needed), but when running
>> on a guest, the guest doesn't have permissions to write on
>> /local/<domid>/, so we have to create the directory in the toolstack
>> domain and assign write permissions for the guest.
>>
>> This path is hardcoded in Qemu, so it's quite difficult to change it,
>> that's why I've opted for creating it on domain creation.
> 
> OK :-/
> 
>>>> This patch creates the mentioned directories for each guest launched
>>>> from libxl.
>>>
>>> I don't really like leaking toolstack "internals" into the normal guest
>>> namespace. Can we add an option to specify "this is a toolstack domain"
>>> and key off that?
>>
>> OK, something like driver_domain=1|0
> 
> Something like that, yes.
> 
>>> I also wonder if this shouldn't be /libxl/<domid> at the top level.
>>
>> I don't have a strong opinion on this, but I generally prefer to keep
>> all the xenstore related keys for a domain inside /libxl/<domid>.
> 
> Are you agreeing with me or did you mean /local/(domain/)<domid> ?

I would prefer to place it in /local/domain/<domid>/libxl/ because I get
the feeling it's more contained, but frankly I don't have a strong
opinion on this, if you prefer to use /libxl/<domid> I can go for it.

However keep in mind that we will have to create the
/local/domain/<domid>/libxl dir anyway, because we have to write the
hotplug disable key there (/local/domain/<domid>/libxl/disable_udev).


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