Re: [Xen-devel] [PATCH v3 15/24] xen/dts: Provide an helper to get a DT node from a path provided by a guest

[Julien Grall <julien.grall@xxxxxxxxxx>]

On 11/03/15 12:34, Ian Campbell wrote:
> On Tue, 2015-03-10 at 13:58 +0000, Julien Grall wrote:
>> On 23/02/15 16:27, Ian Campbell wrote:
>>> On Mon, 2015-02-23 at 16:01 +0000, Julien Grall wrote:
>>>> Hi Ian,
>>>>
>>>> On 23/02/15 15:30, Ian Campbell wrote:
>>>>> On Tue, 2015-01-13 at 14:25 +0000, Julien Grall wrote:
>>>>>
>>>>>> +/* This limit is used by the hypercalls to restrict the size of the 
>>>>>> path */
>>>>>> +#define DEVICE_TREE_MAX_PATHLEN 1024
>>>>>
>>>>> Is this something you've made up or derived from the DT spec/ePAPR etc?
>>>>
>>>> I didn't find a such requirements on the spec.
>>>
>>> I vaguely recall a limit on the length of a single node name, and a
>>> limit on the depth which they may nest, which can be multiplied. It's
>>> probably an unhelpfully large number though, so...
>>>
>>>> I chose this number based on the linux pathlen because the path is also
>>>> used in the sysfs (/sys/firmware/devicetree).
>>>
>>> ...that's a good as anything I suppose!
>>
>> Hmmm... I'm not so sure about the 1024 limit anymore. Linux is defining
>> PATH_MAX to 4096 but I don't see many usage in the sysfs code.
>>
>> And this value may change from one OS to another. Although, 1024 sounds
>> a very long path to write in the configuration file...
> 
> I imagine in practice it will be cut-and-pasted, but yes.
> 
>>  Maybe we should
>> support alias too?
> 
> Perhaps 2048 + (optionally, perhaps later) add alias support?
> 
> 2048 because I assume 4096 being PAGE_SIZE would have some interesting
> corner cases, especially for a target buffer on the stack. If not then
> why not go straight for 4096?

XSM seems to use 4096 to copy string for an hypercall buffer. I will use
the same here.

Regards,

-- 
Julien Grall

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