[Skiboot] [PATCH 1/3] core/device: Add function to return child node using name and length

[Dan Horák]

Hi Athira,

On Thu, 5 Jan 2023 12:41:33 +0530
Athira Rajeev <atrajeev at linux.vnet.ibm.com> wrote:

> 
> 
> > On 05-Jan-2023, at 12:35 PM, Madhavan Srinivasan <maddy at linux.ibm.com> wrote:
> > 
> > 
> > On Mon,  2 Jan 2023 08:45:22 +0530
> > Athira Rajeev <atrajeev at linux.vnet.ibm.com> wrote:
> > 
> >> Add a function dt_find_by_name_len() that returns the child node if
> >> it matches the first "n" characters of a given name, otherwise NULL.
> >> This is helpful for cases with node name like: "name at addr". In
> >> scenarios where nodes are added with "name at addr" format and if the
> >> value of "addr" is not known, that node can't be matched with node
> >> name or addr. Hence matching with substring as node name will return
> >> the expected result. Patch adds dt_find_by_name_len() function
> >> and testcase for the same in core/test/run-device.c
> > 
> > wouldn't it be better to automatically compare the name up to the "@"
> > character in the node name when searching for the match instead of
> > having to hard-code the lengths? I think it should be good enough for
> > the use case described above.
> > 
> > something like
> > ...
> > pos = strchr(child->name, '@')
> > if (!strncmp(child->name, name, pos - child->name))
> >  ...
> > 
> > 
> > 		Dan
> 
> Hi Dan,
> 
> Thanks for checking the patch.
> 
> Comparing upto "@" while searching for the match will restrict the string search only for patterns with "@".
> By having dt_find_by_name_len which uses length, will be useful for generic substring search for different patterns.
> So prefered to use length instead of hardcoding character.
> 
> Please let us know your thoughts.

I understand the presented solution is a pretty generic one, but I think
the question is whether the added complexity brings the benefits
compared to the simpler "separator char" solution.

And thinking even more about the generic "length" approach, it might
bring some false positive hits. Imagine nodes abc at 1, abcd at 2 and you are
looking for "abc". A search for (abc,3) will match also the "abcd"
one. And if the search string will always contain the "@" character,
then specifying the length is not required. And I believe the length
parameter might be totally redundant, because it can be derived from
the search string and the new function would be like
"dt_find_by_name_substr()".


	With regards,

		Dan

> Thanks
> Athira
> 
> > 
> >> Signed-off-by: Athira Rajeev <atrajeev at linux.vnet.ibm.com>
> >> ---
> >> core/device.c          | 20 ++++++++++++++++++++
> >> core/test/run-device.c | 11 +++++++++++
> >> include/device.h       |  4 ++++
> >> 3 files changed, 35 insertions(+)
> >> diff --git a/core/device.c b/core/device.c
> >> index 2de37c74..72c54e85 100644
> >> --- a/core/device.c
> >> +++ b/core/device.c
> >> @@ -395,6 +395,26 @@ struct dt_node *dt_find_by_name(struct dt_node *root, const char *name)
> >> }
> >>  +struct dt_node *dt_find_by_name_len(struct dt_node *root,
> >> +					const char *name, int len)
> >> +{
> >> +	struct dt_node *child, *match;
> >> +
> >> +	if (len <= 0)
> >> +		return NULL;
> >> +
> >> +	list_for_each(&root->children, child, list) {
> >> +		if (!strncmp(child->name, name, len))
> >> +			return child;
> >> +
> >> +		match = dt_find_by_name_len(child, name, len);
> >> +		if (match)
> >> +			return match;
> >> +	}
> >> +
> >> +	return NULL;
> >> +}
> >> +
> >> struct dt_node *dt_new_check(struct dt_node *parent, const char *name)
> >> {
> >> 	struct dt_node *node = dt_find_by_name(parent, name);
> >> diff --git a/core/test/run-device.c b/core/test/run-device.c
> >> index 4a12382b..8c552103 100644
> >> --- a/core/test/run-device.c
> >> +++ b/core/test/run-device.c
> >> @@ -466,6 +466,17 @@ int main(void)
> >> 	new_prop_ph = dt_prop_get_u32(ut2, "something");
> >> 	assert(!(new_prop_ph == ev1_ph));
> >> 	dt_free(subtree);
> >> +
> >> +	/* Test dt_find_by_name_len */
> >> +	root = dt_new_root("");
> >> +	addr1 = dt_new_addr(root, "node", 0x1);
> >> +	addr2 = dt_new_addr(root, "node0_1", 0x2);
> >> +	assert(dt_find_by_name(root, "node at 1") == addr1);
> >> +	assert(dt_find_by_name(root, "node0_1 at 2") == addr2);
> >> +	assert(dt_find_by_name_len(root, "node@", 5) == addr1);
> >> +	assert(dt_find_by_name_len(root, "node0_1@", 8) == addr2);
> >> +	dt_free(root);
> >> +
> >> 	return 0;
> >> }
> >> diff --git a/include/device.h b/include/device.h
> >> index 93fb90ff..f5e0fb79 100644
> >> --- a/include/device.h
> >> +++ b/include/device.h
> >> @@ -184,6 +184,10 @@ struct dt_node *dt_find_by_path(struct dt_node *root, const char *path);
> >> /* Find a child node by name */
> >> struct dt_node *dt_find_by_name(struct dt_node *root, const char *name);
> >> +/* Find a child node by name and len */
> >> +struct dt_node *dt_find_by_name_len(struct dt_node *root,
> >> +                                        const char *name, int len);
> >> +
> >> /* Find a node by phandle */
> >> struct dt_node *dt_find_by_phandle(struct dt_node *root, u32 phandle);
> >> -- 
> >> 2.27.0
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