linux-kernel - Re: [PATCH v2 1/2] modpost: rework and consolidate logging interface

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Date:   Tue, 3 Mar 2020 23:42:07 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Jessica Yu <jeyu@...nel.org>
Cc:     Matthias Maennich <maennich@...gle.com>,
        Joe Perches <joe@...ches.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/2] modpost: rework and consolidate logging interface

On Wed, Feb 26, 2020 at 11:26 PM Jessica Yu <jeyu@...nel.org> wrote:
>
> Rework modpost's logging interface by consolidating merror(), warn(),
> and fatal() to use a single function, modpost_log(). Introduce different
> logging levels (WARN, ERROR, FATAL) as well as a conditional warn
> (warn_unless()). The conditional warn is useful in determining whether
> to use merror() or warn() based on a condition. This reduces code
> duplication overall.
>
> Signed-off-by: Jessica Yu <jeyu@...nel.org>
> ---
> v2:
>   - modpost_log: initialize level to ""
>   - remove parens () from case labels
>
>  scripts/mod/modpost.c | 69 +++++++++++++++++++++++----------------------------
>  scripts/mod/modpost.h | 22 +++++++++++++---
>  2 files changed, 50 insertions(+), 41 deletions(-)
>
> diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
> index 7edfdb2f4497..3201a2ac5cc4 100644
> --- a/scripts/mod/modpost.c
> +++ b/scripts/mod/modpost.c
> @@ -51,41 +51,37 @@ enum export {
>
>  #define MODULE_NAME_LEN (64 - sizeof(Elf_Addr))
>
> -#define PRINTF __attribute__ ((format (printf, 1, 2)))
> +#define PRINTF __attribute__ ((format (printf, 2, 3)))
>
> -PRINTF void fatal(const char *fmt, ...)
> +PRINTF void modpost_log(enum loglevel loglevel, const char *fmt, ...)
>  {
> +       char *level = "";


You can add 'const'.


          const char *level = "";



>         va_list arglist;
>
> -       fprintf(stderr, "FATAL: ");
> -
> -       va_start(arglist, fmt);
> -       vfprintf(stderr, fmt, arglist);
> -       va_end(arglist);
> -
> -       exit(1);
> -}
> -
> -PRINTF void warn(const char *fmt, ...)
> -{
> -       va_list arglist;
> +       switch(loglevel) {
> +       case LOG_WARN:
> +               level = "WARNING: ";
> +               break;
> +       case LOG_ERROR:
> +               level = "ERROR: ";
> +               break;
> +       case LOG_FATAL:
> +               level = "FATAL: ";
> +               break;
> +       default: /* invalid loglevel, ignore */
> +               break;
> +       }
>
> -       fprintf(stderr, "WARNING: ");
> +       fprintf(stderr, level);



If I apply this patch, I see this warning:

scripts/mod/modpost.c: In function ‘modpost_log’:
scripts/mod/modpost.c:77:2: warning: format not a string literal and
no format arguments [-Wformat-security]
  fprintf(stderr, level);
  ^~~~~~~


Please write like this:


     fprintf(stderr, "%s", level);




Or, you can delete 'level', then write
string literals directly in fprintf().


switch(loglevel) {
case LOG_WARN:
        fprintf(stderr, "WARNING: ");
        break;
case LOG_ERROR:
        fprintf(stderr, "ERROR: ");
        break;
case LOG_FATAL:
        fprintf(stderr, "FATAL: ");
        break;
}




> +       fprintf(stderr, "modpost: ");
>
>         va_start(arglist, fmt);
>         vfprintf(stderr, fmt, arglist);
>         va_end(arglist);
> -}
>

<snip>

> diff --git a/scripts/mod/modpost.h b/scripts/mod/modpost.h
> index 64a82d2d85f6..631d07714f7a 100644
> --- a/scripts/mod/modpost.h
> +++ b/scripts/mod/modpost.h
> @@ -198,6 +198,22 @@ void *grab_file(const char *filename, unsigned long *size);
>  char* get_next_line(unsigned long *pos, void *file, unsigned long size);
>  void release_file(void *file, unsigned long size);
>
> -void fatal(const char *fmt, ...);
> -void warn(const char *fmt, ...);
> -void merror(const char *fmt, ...);
> +enum loglevel {
> +       LOG_WARN,
> +       LOG_ERROR,
> +       LOG_FATAL
> +};
> +
> +void modpost_log(enum loglevel loglevel, const char *fmt, ...);
> +
> +#define warn(fmt, args...)     modpost_log(LOG_WARN, fmt, ##args)
> +#define merror(fmt, args...)   modpost_log(LOG_ERROR, fmt, ##args)
> +#define fatal(fmt, args...)    modpost_log(LOG_FATAL, fmt, ##args)
> +/* Warn unless condition is true, then use merror() */
> +#define warn_unless(condition, fmt, args...)   \
> +do {                                           \
> +       if (condition)                          \
> +               merror(fmt, ##args);            \
> +       else                                    \
> +               warn(fmt, ##args);              \
> +} while (0)


Hmm, warn_unless() is not intuitive naming...

You could use modpost_log() directly in C code,
what do you think?


            modpost_log(allow_missing_ns_imports ? LOG_WARN : LOG_ERROR,
                        "module %s uses symbol %s from namespace %s,
but does not import it.\n",
                        basename, exp->name, exp->namespace);







--
Best Regards
Masahiro Yamada