Subject: Re: [PATCH v3] libfdt: Add support for using aliases in fdt_path_offset()

From: Mitch Bradley <[email-masked]>
Date: Thu, 14 Aug 2008 15:51:05 -1000

David Gibson wrote:
> On Thu, Aug 14, 2008 at 12:43:48PM -0500, Scott Wood wrote:
>   
>> On Thu, Aug 14, 2008 at 08:28:19AM -0500, Kumar Gala wrote:
>>     
>>> -	if (*path != '/')
>>> -		return -FDT_ERR_BADPATH;
>>> +	/* see if we have an alias */
>>> +	if (*path != '/') {
>>> +		const char *q;
>>> +		int aliasoffset = fdt_path_offset(fdt, "/aliases");
>>> +
>>> +		if (aliasoffset < 0)
>>> +			return -FDT_ERR_BADPATH;
>>> +
>>> +		q = strchr(path, '/');
>>> +		if (!q)
>>> +			q = end;
>>> +
>>> +		p = fdt_getprop_namelen(fdt, aliasoffset, path, q - p, NULL);
>>> +		if (!p)
>>> +			return -FDT_ERR_BADPATH;
>>> +		offset = fdt_path_offset(fdt, p);
>>> +
>>> +		p = q;
>>> +	}
>>>       
>> Can we limit the recursion depth to avoid falling off the stack if an
>> alias points to itself?  Or if aliases pointing to aliases are
>> disallowed, check for a leading '/' before recursively calling
>> fdt_path_offset.
>>     
>
> Hmm.. my reading of 1275 says that an alias pointing to another alias
> is not permitted, but I'm not terribly confident I'm not misreading
> it.  Segher, do you know whether this is allowed?
>   

The 1275 spec doesn't require multiple levels of aliasing, but my 
current implementation allows it and uses it for things like components 
of the network stack.

> If that's the case then, yes, we should not recurse if the alias value
> doesn't start with a /.  In fact, if I factor out a fdt_get_alias()
> function, it should probably check the alias and return an error if
> it's not an absolute path.
>
>