Re: [PATCH v3 22/24] tools/libxl: arm: Use an higher value for the GIC phandle

[Julien Grall <julien.grall@linaro.org>]

On 23/02/2015 14:36, Ian Campbell wrote:
> On Thu, 2015-01-29 at 13:48 +0000, Julien Grall wrote:
>> On 29/01/15 12:28, Stefano Stabellini wrote:
>>> On Thu, 29 Jan 2015, Julien Grall wrote:
>>>> On 29/01/15 11:07, Stefano Stabellini wrote:
>>>>> On Tue, 13 Jan 2015, Julien Grall wrote:
>>>>>> The partial device tree may contains phandle. The Device Tree Compiler
>>>>>> tends to allocate the phandle from 1.
>>>>>>
>>>>>> Reserve the ID 65000 for the GIC phandle. I think we can safely assume
>>>>>> that the partial device tree will never contain a such ID.
>>>>>>
>>>>>> Signed-off-by: Julien Grall <julien.grall@linaro.org>
>>>>>> Cc: Ian Jackson <ian.jackson@eu.citrix.com>
>>>>>> Cc: Wei Liu <wei.liu2@citrix.com>
>>>>>>
>>>>>
>>>>> Shouldn't we at least check that the partial device tree doesn't contain
>>>>> a conflicting phandle?
>>>>
>>>> I don't think so. This will unlikely happen, and if it happens the guest
>>>> will crash with an obvious error.
>>>
>>> It is good that the error is obvious.
>>>
>>> But how expensive is to check for it?
>>
>> I would have to check the validity of the properties (name + value
>> size). At least the properties "linux,phandle" and "phandle" should be
>> checked.
>>
>> Though I could do in copy_properties but I find it hackish.
>
> Can't you just track the largest phandle ever seen during
> copy_properties and then use N+1 for the GIC?

Now the we decided to trust the input device tree, it would be easier to 
write the code.

I will give a look.

>
>>> Think about the poor user that ends up in this situation: the fact that
>>> is unlikely only makes it harder for a user to figure out what to do to
>>> fix it.
>>
>> The poor use will have to write his device tree by hand to hit this
>> error ;).
>
> Or use a new version of dtc which does things differently for some
> reason.

And you would not be able to get a phandle for the GIC if largest 
phandle is too high.

So the guest won't work correctly.

Regards,

-- 
Julien Grall