linux-kernel - Re: [PATCH 2/3] of: Make of_find_node_by

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Date:	Thu, 22 May 2014 18:14:38 -0700
From:	Frank Rowand <frowand.list@...il.com>
To:	Grant Likely <grant.likely@...aro.org>
CC:	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
	David Daney <david.daney@...ium.com>,
	Pantelis Antoniou <pantelis.antoniou@...sulko.com>
Subject: Re: [PATCH 2/3] of: Make of_find_node_by_path() handle /aliases

On 5/21/2014 6:16 PM, Grant Likely wrote:
> On Tue, 20 May 2014 19:41:22 -0700, Frank Rowand <frowand.list@...il.com> wrote:
>> On 5/18/2014 2:27 AM, Grant Likely wrote:
>>> On Fri, 16 May 2014 11:54:44 +0100, Grant Likely <grant.likely@...aro.org> wrote:
>>>> On Thu, 15 May 2014 19:51:17 -0700, Frank Rowand <frowand.list@...il.com> wrote:
>>>>> On 5/13/2014 7:58 AM, Grant Likely wrote:
>>>>>> Make of_find_node_by_path() handle aliases as prefixes. To make this
>>>>>> work the name search is refactored to search by path component instead
>>>>>> of by full string. This should be a more efficient search, and it makes
>>>>>> it possible to start a search at a subnode of a tree.
>>>>>>
>>>>>> Signed-off-by: David Daney <david.daney@...ium.com>
>>>>>> Signed-off-by: Pantelis Antoniou <pantelis.antoniou@...sulko.com>
>>>>>> [grant.likely: Rework to not require allocating at runtime]
>>>>>> Acked-by: Rob Herring <robh@...nel.org>
>>>>>> Signed-off-by: Grant Likely <grant.likely@...aro.org>
>>>>>> ---
>>>>>>  drivers/of/base.c | 60 +++++++++++++++++++++++++++++++++++++++++++++++++++----
>>>>>>  1 file changed, 56 insertions(+), 4 deletions(-)
>>>>>>
>>>>>> diff --git a/drivers/of/base.c b/drivers/of/base.c
>>>>>> index 6e240698353b..60089b9a3014 100644
>>>>>> --- a/drivers/of/base.c
>>>>>> +++ b/drivers/of/base.c
>>>>>> @@ -771,9 +771,38 @@ struct device_node *of_get_child_by_name(const struct device_node *node,
>>>>>>  }
>>>>>>  EXPORT_SYMBOL(of_get_child_by_name);
>>>>>>  
>>>>>> +static struct device_node *__of_find_node_by_path(struct device_node *parent,
>>>>>> +						const char *path)
>>>>>> +{
>>>>>> +	struct device_node *child;
>>>>>> +	int len = strchrnul(path, '/') - path;
>>>>>> +
>>>>>> +	if (!len)
>>>>>> +		return parent;
>>>>>
>>>>> (!len) is true if the the final character of the path passed into of_find_node_by_path()
>>>>> was "/".  Strictly speaking, ->full_name will never end with "/", so the return value
>>>>> should be NULL, indicating that the match fails.
>>>>
>>>> Ah, good catch. I should add a test case for that.
>>>
>>> In my testing this looks okay. The while loop that calls into
>>> __of_find_node_by_path() looks like this:
>>>
>>> 	while (np && *path == '/') {
>>> 		path++; /* Increment past '/' delimiter */
>>> 		np = __of_find_node_by_path(np, path);
>>> 		path = strchrnul(path, '/');
>>> 	}
>>>
>>> If the path ends with a '/', then the loop will go around one more time.
>>> The pointer will be incremented to point at the null character and len
>>> will be null because strchrnul() will point at the last item.
>>
>> Yes, that was my point.  The old version of of_find_node_by_path() would not
>> find a match if the path ended with a "/" (unless the full path was "/").
>> This patch series changes the behavior to be a match.
>>
>> I will reply to this email with an additional patch that restores the
>> original behavior.
>>
>> If you move the additional test cases you provide below and the test cases
>> in patch 3 to the beginning of the series, you can see the before and after
>> behavior of adding patch 1 and patch 2.
> 
> Ah, I see. That raises the question about what the behaviour /should/
> be. Off the top of my head, matching against a trailing '/' seems to be
> okay. Are there situations that you see or can think of where matching
> would be the wrong thing to do?

I have not thought of a case where matching against a trailing '/' would
hurt anything.  It just seemed better to be consistent in naming.

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