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SubjectRe: [PATCH v1 1/8] lib/string: introduce match_string() helper
Date
On Thu, Jan 07 2016, Andy Shevchenko <andriy.shevchenko@linux.intel.com> wrote:

> From time to time we have to match a string in an array. Make a simple helper
> for that purpose.
>
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> ---
> include/linux/string.h | 2 ++
> lib/string.c | 26 ++++++++++++++++++++++++++
> 2 files changed, 28 insertions(+)
>
> diff --git a/include/linux/string.h b/include/linux/string.h
> index b0a732b..37062fb 100644
> --- a/include/linux/string.h
> +++ b/include/linux/string.h
> @@ -131,6 +131,8 @@ extern void argv_free(char **argv);
> extern bool sysfs_streq(const char *s1, const char *s2);
> extern int strtobool(const char *s, bool *res);
>
> +int match_string(const char * const *array, size_t len, const char *string);
> +
> #ifdef CONFIG_BINARY_PRINTF
> int vbin_printf(u32 *bin_buf, size_t size, const char *fmt, va_list args);
> int bstr_printf(char *buf, size_t size, const char *fmt, const u32 *bin_buf);
> diff --git a/lib/string.c b/lib/string.c
> index 0323c0d..dd02270 100644
> --- a/lib/string.c
> +++ b/lib/string.c
> @@ -631,6 +631,32 @@ bool sysfs_streq(const char *s1, const char *s2)
> EXPORT_SYMBOL(sysfs_streq);
>
> /**
> + * match_string - matches given string in an array
> + * @array: array of strings
> + * @len: number of strings in the array or 0 for NULL terminated arrays
> + * @string: string to match with
> + *
> + * Return:
> + * index of a @string in the @array if matches, or %-ENODATA otherwise.
> + */
> +int match_string(const char * const *array, size_t len, const char *string)
> +{
> + int index = 0;
> + const char *item;
> +
> + do {
> + item = array[index];
> + if (!item)
> + break;
> + if (!strcmp(item, string))
> + return index;
> + } while (++index < len || !len);
> +
> + return -ENODATA;
> +}
> +EXPORT_SYMBOL(match_string);
> +

I'd suggest making it -1 (which, since len is a size_t, is effectively
infinity) having the meaning "the array is terminated by a NULL
entry". match_string(..., ARRAY_SIZE(my_array), ...) will break if the
array happens to be empty, which could e.g. happen in a case like

const char *my_array[] = {
#ifdef CONFIG_THIS
"this",
#endif
#ifdef CONFIG_THAT
"that",
#endif
};

I also think the condition/loop above is unreadable.

for (index = 0; index < len; index++) {
...
}

is much clearer.

Why -ENODATA and not just -1? It is rather unlikely that anyone would
pass on that particular -Exxx value. Not a biggie, just curious.

Would there be more potential users if we had a flag argument allowing
case-insensitive matching? Would there be more potential users if a flag
allowed to ask whether the given string is a _prefix_ of one of the
strings in the array, or vice versa? Something like

#define MATCH_STRING_CASE 0x01
#define MATCH_STRING_PREFIX_OF_ARRAY_ELEM 0x02 /* yeah, that name sucks */
#define MATCH_ARRAY_ELEM_PREFIX_OF_STRING 0x04 /* this too */

int match_string(const char * const *array, size_t len, const char *string, unsigned flags)
{
#define MATCH_PREFIX (MATCH_... | MATCH_...)
int index;
const char *item;
int (*match_func)(const char *, const char *) =
flags & MATCH_STRING_CASE ? strcasecmp : strcmp;
int (*prefix_func)(const char *, const char *, size_t) =
flags & MATCH_STRING_CASE ? strncasecmp : strncmp;

for (index = 0; index < len; ++index) {
item = array[index];
if (!item)
break;
if (flags & MATCH_PREFIX) {
size_t len = strlen(flags & MATCH_STRING_PREFIX_OF_ARRAY_ELEM ?
string : item);
if (!prefix_func(item, string, len))
return index;
} else if (!match_func(item, string)) {
return index;
}
}
return -1;
}

(Ok, it's not that pretty; maybe it'd be better to use
switch(flags&MATCH_PREFIX) {}. Or maybe just the case-insensitive part
is worth keeping; in that case the above isn't that bad.)

Rasmus

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