[PATCH] lib/string: update match_string() doc-strings with correct behavior

[PATCH] lib/string: update match_string() doc-strings with correct behavior

[Alexandru Ardelean]

There were a few attempts at changing behavior of the match_string()
helpers (i.e. 'match_string()' & 'sysfs_match_string()'), to change &
extend the behavior according to the doc-string.

But the simplest approach is to just fix the doc-strings. The current
behavior is fine as-is, and some bugs were introduced trying to fix it.

As for extending the behavior, new helpers can always be introduced if
needed.

The match_string() helpers behave more like 'strncmp()' in the sense that
they go up to n elements or until the first NULL element in the array of
strings.

This change updates the doc-strings with this info.

Some references to the previous attempts (in no particular order):
  https://lore.kernel.org/lkml/20190508111913.7276-1-alexandru.ardelean@analog.com/
  https://lore.kernel.org/lkml/20190625130104.29904-1-alexandru.ardelean@analog.com/
  https://lore.kernel.org/lkml/20190422083257.21805-1-alexandru.ardelean@analog.com/
  

Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
---
 lib/string.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/lib/string.c b/lib/string.c
index f607b967d978..061a17b062b1 100644
--- a/lib/string.c
+++ b/lib/string.c
@@ -696,9 +696,12 @@ EXPORT_SYMBOL(sysfs_streq);
 /**
  * match_string - matches given string in an array
  * @array:	array of strings
- * @n:		number of strings in the array or -1 for NULL terminated arrays
+ * @n:		number of strings in the array to compare
  * @string:	string to match with
  *
+ * This routine will look for a string in an array of strings up to the
+ * n-th element in the array or until the first NULL element.
+ *
  * Return:
  * index of a @string in the @array if matches, or %-EINVAL otherwise.
  */
@@ -722,11 +725,14 @@ EXPORT_SYMBOL(match_string);
 /**
  * __sysfs_match_string - matches given string in an array
  * @array: array of strings
- * @n: number of strings in the array or -1 for NULL terminated arrays
+ * @n: number of strings in the array to compare
  * @str: string to match with
  *
  * Returns index of @str in the @array or -EINVAL, just like match_string().
  * Uses sysfs_streq instead of strcmp for matching.
+ *
+ * This routine will look for a string in an array of strings up to the
+ * n-th element in the array or until the first NULL element.
  */
 int __sysfs_match_string(const char * const *array, size_t n, const char *str)
 {
-- 
2.20.1

Re: [PATCH] lib/string: update match_string() doc-strings with correct behavior

[Andy Shevchenko]

On Wed, Feb 12, 2020 at 04:47:23PM +0200, Alexandru Ardelean wrote:
> There were a few attempts at changing behavior of the match_string()
> helpers (i.e. 'match_string()' & 'sysfs_match_string()'), to change &
> extend the behavior according to the doc-string.
> 
> But the simplest approach is to just fix the doc-strings. The current
> behavior is fine as-is, and some bugs were introduced trying to fix it.
> 
> As for extending the behavior, new helpers can always be introduced if
> needed.
> 
> The match_string() helpers behave more like 'strncmp()' in the sense that
> they go up to n elements or until the first NULL element in the array of
> strings.
> 
> This change updates the doc-strings with this info.
> 
> Some references to the previous attempts (in no particular order):
>   https://lore.kernel.org/lkml/20190508111913.7276-1-alexandru.ardelean@analog.com/
>   https://lore.kernel.org/lkml/20190625130104.29904-1-alexandru.ardelean@analog.com/
>   https://lore.kernel.org/lkml/20190422083257.21805-1-alexandru.ardelean@analog.com/

...

>  /**
>   * match_string - matches given string in an array
>   * @array:	array of strings
> - * @n:		number of strings in the array or -1 for NULL terminated arrays
> + * @n:		number of strings in the array to compare

But this change won't be helpful, it actually hides the part of behaviour that
is being used.

>   * @string:	string to match with
>   *
> + * This routine will look for a string in an array of strings up to the
> + * n-th element in the array or until the first NULL element.
> + *

Perhaps this needs to be rephrased. Because now it has completely hidden the -1 case.

>   * Return:
>   * index of a @string in the @array if matches, or %-EINVAL otherwise.
>   */

Ditto for the second part.

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH] lib/string: update match_string() doc-strings with correct behavior

[Ardelean, Alexandru]

On Wed, 2020-02-12 at 18:46 +0200, Andy Shevchenko wrote:
> [External]
> 
> On Wed, Feb 12, 2020 at 04:47:23PM +0200, Alexandru Ardelean wrote:
> > There were a few attempts at changing behavior of the match_string()
> > helpers (i.e. 'match_string()' & 'sysfs_match_string()'), to change &
> > extend the behavior according to the doc-string.
> > 
> > But the simplest approach is to just fix the doc-strings. The current
> > behavior is fine as-is, and some bugs were introduced trying to fix it.
> > 
> > As for extending the behavior, new helpers can always be introduced if
> > needed.
> > 
> > The match_string() helpers behave more like 'strncmp()' in the sense that
> > they go up to n elements or until the first NULL element in the array of
> > strings.
> > 
> > This change updates the doc-strings with this info.
> > 
> > Some references to the previous attempts (in no particular order):
> >   
> > https://lore.kernel.org/lkml/20190508111913.7276-1-alexandru.ardelean@analog.com/
> >   
> > https://lore.kernel.org/lkml/20190625130104.29904-1-alexandru.ardelean@analog.com/
> >   
> > https://lore.kernel.org/lkml/20190422083257.21805-1-alexandru.ardelean@analog.com/
> 
> ...
> 
> >  /**
> >   * match_string - matches given string in an array
> >   * @array:	array of strings
> > - * @n:		number of strings in the array or -1 for NULL terminated
> > arrays
> > + * @n:		number of strings in the array to compare
> 
> But this change won't be helpful, it actually hides the part of behaviour that
> is being used.
> 
> >   * @string:	string to match with
> >   *
> > + * This routine will look for a string in an array of strings up to the
> > + * n-th element in the array or until the first NULL element.
> > + *
> 
> Perhaps this needs to be rephrased. Because now it has completely hidden the
> -1 case.

Hmm, it does make sense to specify the -1 behavior purely for historical
purposes.
Otheriwse, I don't feel it's that important to mention it, since you could
technically specify UINT_MAX [or similar] and get the same behavior.

> 
> >   * Return:
> >   * index of a @string in the @array if matches, or %-EINVAL otherwise.
> >   */
> 
> Ditto for the second part.
> 

[PATCH v2] lib/string: update match_string() doc-strings with correct behavior

[Alexandru Ardelean]

There were a few attempts at changing behavior of the match_string()
helpers (i.e. 'match_string()' & 'sysfs_match_string()'), to change &
extend the behavior according to the doc-string.

But the simplest approach is to just fix the doc-strings. The current
behavior is fine as-is, and some bugs were introduced trying to fix it.

As for extending the behavior, new helpers can always be introduced if
needed.

The match_string() helpers behave more like 'strncmp()' in the sense that
they go up to n elements or until the first NULL element in the array of
strings.

This change updates the doc-strings with this info.

Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
---
 lib/string.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/lib/string.c b/lib/string.c
index f607b967d978..6012c385fb31 100644
--- a/lib/string.c
+++ b/lib/string.c
@@ -699,6 +699,14 @@ EXPORT_SYMBOL(sysfs_streq);
  * @n:		number of strings in the array or -1 for NULL terminated arrays
  * @string:	string to match with
  *
+ * This routine will look for a string in an array of strings up to the
+ * n-th element in the array or until the first NULL element.
+ *
+ * Historically the value of -1 for @n, was used to search in arrays that
+ * are NULL terminated. However, the function does not make a distinction
+ * when finishing the search: either @n elements have been compared OR
+ * the first NULL element was found.
+ *
  * Return:
  * index of a @string in the @array if matches, or %-EINVAL otherwise.
  */
@@ -727,6 +735,14 @@ EXPORT_SYMBOL(match_string);
  *
  * Returns index of @str in the @array or -EINVAL, just like match_string().
  * Uses sysfs_streq instead of strcmp for matching.
+ *
+ * This routine will look for a string in an array of strings up to the
+ * n-th element in the array or until the first NULL element.
+ *
+ * Historically the value of -1 for @n, was used to search in arrays that
+ * are NULL terminated. However, the function does not make a distinction
+ * when finishing the search: either @n elements have been compared OR
+ * the first NULL element was found.
  */
 int __sysfs_match_string(const char * const *array, size_t n, const char *str)
 {
-- 
2.20.1

Re: [PATCH v2] lib/string: update match_string() doc-strings with correct behavior

[Andy Shevchenko]

On Thu, Feb 13, 2020 at 09:27:22AM +0200, Alexandru Ardelean wrote:
> There were a few attempts at changing behavior of the match_string()
> helpers (i.e. 'match_string()' & 'sysfs_match_string()'), to change &
> extend the behavior according to the doc-string.
> 
> But the simplest approach is to just fix the doc-strings. The current
> behavior is fine as-is, and some bugs were introduced trying to fix it.
> 
> As for extending the behavior, new helpers can always be introduced if
> needed.
> 
> The match_string() helpers behave more like 'strncmp()' in the sense that
> they go up to n elements or until the first NULL element in the array of
> strings.
> 
> This change updates the doc-strings with this info.

Thanks, looks good to me now.
Acked-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

> 
> Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
> ---
>  lib/string.c | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
> 
> diff --git a/lib/string.c b/lib/string.c
> index f607b967d978..6012c385fb31 100644
> --- a/lib/string.c
> +++ b/lib/string.c
> @@ -699,6 +699,14 @@ EXPORT_SYMBOL(sysfs_streq);
>   * @n:		number of strings in the array or -1 for NULL terminated arrays
>   * @string:	string to match with
>   *
> + * This routine will look for a string in an array of strings up to the
> + * n-th element in the array or until the first NULL element.
> + *
> + * Historically the value of -1 for @n, was used to search in arrays that
> + * are NULL terminated. However, the function does not make a distinction
> + * when finishing the search: either @n elements have been compared OR
> + * the first NULL element was found.
> + *
>   * Return:
>   * index of a @string in the @array if matches, or %-EINVAL otherwise.
>   */
> @@ -727,6 +735,14 @@ EXPORT_SYMBOL(match_string);
>   *
>   * Returns index of @str in the @array or -EINVAL, just like match_string().
>   * Uses sysfs_streq instead of strcmp for matching.
> + *
> + * This routine will look for a string in an array of strings up to the
> + * n-th element in the array or until the first NULL element.
> + *
> + * Historically the value of -1 for @n, was used to search in arrays that
> + * are NULL terminated. However, the function does not make a distinction
> + * when finishing the search: either @n elements have been compared OR
> + * the first NULL element was found.
>   */
>  int __sysfs_match_string(const char * const *array, size_t n, const char *str)
>  {
> -- 
> 2.20.1
> 

-- 
With Best Regards,
Andy Shevchenko