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

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Date:	Thu, 22 May 2014 10:16:00 +0900
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 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?

g.
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