linux-kernel - Re: [PATCH] lib/string: Introduce sysfs

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Message-ID: <CAKwvOdnaLT8sn4e3PQoASjKaNP4gUKQikhxtJM5G94-7CMUKTw@mail.gmail.com>
Date:   Wed, 7 Apr 2021 13:06:58 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Gioh Kim <gi-oh.kim@...os.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        laniel_francis@...vacyrequired.com,
        Kees Cook <keescook@...omium.org>,
        Daniel Axtens <dja@...ens.net>
Subject: Re: [PATCH] lib/string: Introduce sysfs_streqcase

On Tue, Apr 6, 2021 at 11:15 PM Gioh Kim <gi-oh.kim@...os.com> wrote:
>
> As the name shows, it checks if strings are equal in case insensitive
> manner.
>
> For example, drivers/infiniband/ulp/rtrs/rtrs-clt-sysfs.c uses
> strncasecmp to check that the input via sysfs is "mi". But it would
> work even-if the input is "min-wrongcommand".
>
> I found some more cases using strncasecmp to check the entire string
> such as rtrs-clt-sysfs.c does. drivers/pnp/interface.c checks
> "disable" command with strncasecmp but it would also work if the
> command is "disable-wrong".

Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>

I do wonder if these (sysfs_streqcase and sysfs_streq) could or should
be conditionally available on CONFIG_SYSFS=y; don't pay for what you
don't use (without needing CONFIG_LD_DEAD_CODE_DATA_ELIMINATION=y)?

Also, it might be nice to share the second half of the function with
sysfs_streq via a new static function.  Though it will just get
inlined in both for CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE=y, it might
help the compiler if CONFIG_CC_OPTIMIZE_FOR_SIZE=y was instead chosen
if the compiler cannot outline/deduplicate the shared code.  At the
least, there's less duplication between two very similar functions; if
one changes then authors may need to be careful to update both.

Are either of those concerns worth a v3? ¯\_(ツ)_/¯

>
> Signed-off-by: Gioh Kim <gi-oh.kim@...os.com>
> ---
>  include/linux/string.h |  1 +
>  lib/string.c           | 23 +++++++++++++++++++++++
>  2 files changed, 24 insertions(+)
>
> diff --git a/include/linux/string.h b/include/linux/string.h
> index 4fcfb56abcf5..36d00ff8013e 100644
> --- a/include/linux/string.h
> +++ b/include/linux/string.h
> @@ -184,6 +184,7 @@ extern char **argv_split(gfp_t gfp, const char *str, int *argcp);
>  extern void argv_free(char **argv);
>
>  extern bool sysfs_streq(const char *s1, const char *s2);
> +extern bool sysfs_streqcase(const char *s1, const char *s2);
>  extern int kstrtobool(const char *s, bool *res);
>  static inline int strtobool(const char *s, bool *res)
>  {
> diff --git a/lib/string.c b/lib/string.c
> index 7548eb715ddb..5e6bc0d3d5c6 100644
> --- a/lib/string.c
> +++ b/lib/string.c
> @@ -714,6 +714,29 @@ bool sysfs_streq(const char *s1, const char *s2)
>  }
>  EXPORT_SYMBOL(sysfs_streq);
>
> +/**
> + * sysfs_streqcase - same to sysfs_streq and case insensitive
> + * @s1: one string
> + * @s2: another string
> + *
> + */
> +bool sysfs_streqcase(const char *s1, const char *s2)
> +{
> +       while (*s1 && tolower(*s1) == tolower(*s2)) {
> +               s1++;
> +               s2++;
> +       }
> +
> +       if (*s1 == *s2)
> +               return true;
> +       if (!*s1 && *s2 == '\n' && !s2[1])
> +               return true;
> +       if (*s1 == '\n' && !s1[1] && !*s2)
> +               return true;
> +       return false;
> +}
> +EXPORT_SYMBOL(sysfs_streqcase);
> +
>  /**
>   * match_string - matches given string in an array
>   * @array:     array of strings
> --
> 2.25.1
>


-- 
Thanks,
~Nick Desaulniers