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From:   Masahiro Yamada <yamada.masahiro@socionext.com>
Date:   Thu, 24 May 2018 13:45:15 +0900
Message-ID: <CAK7LNARMMWj+z_E7urs4kOFMC4+1NiCYt4ueB6gVFr86vgiVKg@mail.gmail.com>
Subject: Re: [PATCH v4 03/31] kconfig: reference environment variables
 directly and remove 'option env='
To:     Ulf Magnusson <ulfalizer@gmail.com>
Cc:     Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Sam Ravnborg <sam@ravnborg.org>,
        "Luis R . Rodriguez" <mcgrof@kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Nicholas Piggin <npiggin@gmail.com>,
        Kees Cook <keescook@chromium.org>,
        Emese Revfy <re.emese@gmail.com>, X86 ML <x86@kernel.org>
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2018-05-21 20:06 GMT+09:00 Ulf Magnusson <ulfalizer@gmail.com>:

>>
>> static char *__expand_string(const char **str, bool (*is_end)(const char *))
>> {
>>         const char *in, *prev_in, *p;
>>         char *new, *out;
>>         size_t outlen;
>>
>>         out = xmalloc(1);
>>         *out = 0;
>>
>>         p = in = *str;
>>
>>         while (1) {
>>                 if (*p == '$') {
>>                         prev_in = in;
>>                         in = p + 1;
>>                         new = expand_dollar(&in);
>>                         outlen = strlen(out) + (p - prev_in) + strlen(new) + 1;
>>                         out = xrealloc(out, outlen);
>>                         strncat(out, prev_in, p - prev_in);
>>                         strcat(out, new);
>>                         free(new);
>>                         p = in;
>>                         continue;
>>                 }
>>
>>                 if (is_end(p))
>>                         break;
>>
>>                 p++;
>>         }
>>
>>         outlen = strlen(out) + (p - in) + 1;
>>         out = xrealloc(out, outlen);
>>         strncat(out, in, p - in);
>>
>>         *str = p;
>>
>>         return out;
>> }
>>
>> static bool is_end_of_str(const char *s)
>> {
>>         return !*s;
>> }
>>
>> char *expand_string(const char *in)
>> {
>>         return __expand_string(&in, is_end_of_str);
>> }
>>
>> static bool is_end_of_token(const char *s)
>> {
>>         return !(isalnum(*s) || *s == '_' || *s == '-' || *s == '.' ||
>> *s == '/');
>> }
>>
>> char *expand_one_token(const char **str)
>> {
>>         return __expand_string(str, is_end_of_token);
>> }
>
> Yep, something like that would be nicer I think.
>
> This variant might work too (untested):
>
>   dollar_i = p;
>   p++;
>   expansion = expand_dollar(&p);
>
>   out = xrealloc(out, strlen(out) + (dollar_i - in)
>                       + strlen(expansion) + 1);
>   strncat(out, in, dollar_i - in);
>   strcat(out, expansion);
>   free(expansion);
>
>   in = p;
>
>   continue;
>
> The p++ would disappear if expand_dollar() took a pointer to the '$'.
>


I took the variable name "expansion" because
it is more descriptive than "new".


I rewrote like follows:


static char *__expand_string(const char **str, bool (*is_end)(const char *))
{
        const char *in, *p;
        char *expansion, *out;
        size_t in_len, out_len;

        out = xmalloc(1);
        *out = 0;
        out_len = 1;

        p = in = *str;

        while (1) {
                if (*p == '$') {
                        in_len = p - in;
                        p++;
                        expansion = expand_dollar(&p);
                        out_len += in_len + strlen(expansion);
                        out = xrealloc(out, out_len);
                        strncat(out, in, in_len);
                        strcat(out, expansion);
                        free(expansion);
                        in = p;
                        continue;
                }

                if (is_end(p))
                        break;

                p++;
        }

        in_len = p - in;
        out_len += in_len;
        out = xrealloc(out, out_len);
        strncat(out, in, in_len);

        /* Advance 'str' to the end character */
        *str = p;

        return out;
}


I used "out_len" to remember the length of "out"
instead of calculating strlen(out) every time.

I do not need dollar_p.


-- 
Best Regards
Masahiro Yamada