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

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Message-Id: <20140523211326.62E83C41623@trevor.secretlab.ca>
Date:	Fri, 23 May 2014 22:13:26 +0100
From:	Grant Likely <grant.likely@...aro.org>
To:	frowand.list@...il.com
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 Thu, 22 May 2014 18:14:38 -0700, Frank Rowand <frowand.list@...il.com> wrote:
> 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.
> 

I've gone ahead and merged in the trailing '/' fix. It can be relaxed
later if deemed important.

g.

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