linux-kernel - Re: [PATCH] kconfig: redo fake deps at include/config/*.h

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Date:   Thu, 15 Apr 2021 13:58:35 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Alexey Dobriyan <adobriyan@...il.com>
Cc:     Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] kconfig: redo fake deps at include/config/*.h

On Thu, Apr 15, 2021 at 7:01 AM Alexey Dobriyan <adobriyan@...il.com> wrote:
>
> Make include/config/foo/bar.h fake deps files generation simpler.
>
> * delete .h suffix
>         those aren't header files, shorten filenames,
>
> * delete tolower()
>         Linux filesystems can deal with both upper and lowercase
>         filenames very well,
>
> * put everything in 1 directory
>         Presumably 'mkdir -p' split is from dark times when filesystems
>         handled huge directories badly, disks were round adding to
>         seek times.


I am not sure about the impact of this change
given various file systems in the wild,
but this simplification is attractive.

With a quick search, I found a comment
'performance issues past 10,000' on ext2  [1]
but that may not be what we care about much...

[1]: https://webmasters.stackexchange.com/questions/99539/what-is-a-recommended-maximum-number-of-files-in-a-directory-on-your-webserver





> @@ -124,36 +124,12 @@ static void xprintf(const char *format, ...)
>         va_end(ap);
>  }
>
> -static void xputchar(int c)
> -{
> -       int ret;
> -
> -       ret = putchar(c);
> -       if (ret == EOF) {
> -               perror("fixdep");
> -               exit(1);
> -       }
> -}
> -
>  /*
>   * Print out a dependency path from a symbol name
>   */
>  static void print_dep(const char *m, int slen, const char *dir)
>  {
> -       int c, prev_c = '/', i;
> -
> -       xprintf("    $(wildcard %s/", dir);
> -       for (i = 0; i < slen; i++) {
> -               c = m[i];
> -               if (c == '_')
> -                       c = '/';
> -               else
> -                       c = tolower(c);
> -               if (c != '/' || prev_c != '/')
> -                       xputchar(c);
> -               prev_c = c;
> -       }
> -       xprintf(".h) \\\n");
> +       xprintf("    $(wildcard %s/%.*s) \\\n", dir, slen, m);



Since this function now contains just one line,
can you hard-code

    xprintf("    $(wildcard include/config/%.*s) \\\n", slen, m);

in use_config() ?



>  }
>
>  struct item {
> --- a/scripts/kconfig/confdata.c
> +++ b/scripts/kconfig/confdata.c
> @@ -130,19 +130,14 @@ static size_t depfile_prefix_len;
>  static int conf_touch_dep(const char *name)
>  {
>         int fd, ret;
> -       const char *s;
> -       char *d, c;
> +       char *d;
>
>         /* check overflow: prefix + name + ".h" + '\0' must fit in buffer. */
>         if (depfile_prefix_len + strlen(name) + 3 > sizeof(depfile_path))

Since you dropped the ".h" suffix,
please fix up this line.





Also, you can fix

  # changed, Kconfig touches the corresponding timestamp file
include/config/*.h.

in kernel/gen_kheaders.sh





>                 return -1;
>
>         d = depfile_path + depfile_prefix_len;
> -       s = name;
> -
> -       while ((c = *s++))
> -               *d++ = (c == '_') ? '/' : tolower(c);
> -       strcpy(d, ".h");
> +       strcpy(d, name);
>
>         /* Assume directory path already exists. */
>         fd = open(depfile_path, O_WRONLY | O_CREAT | O_TRUNC, 0644);
> @@ -465,7 +460,7 @@ int conf_read_simple(const char *name, int def)
>                                          * Reading from include/config/auto.conf
>                                          * If CONFIG_FOO previously existed in
>                                          * auto.conf but it is missing now,
> -                                        * include/config/foo.h must be touched.
> +                                        * include/config/FOO must be touched.
>                                          */
>                                         conf_touch_dep(line + strlen(CONFIG_));
>                                 else



--
Best Regards
Masahiro Yamada