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Date:   Fri, 9 Feb 2018 06:30:38 +0100
From:   Ulf Magnusson <ulfalizer@gmail.com>
To:     Masahiro Yamada <yamada.masahiro@socionext.com>
Cc:     linux-kbuild@vger.kernel.org,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Kees Cook <keescook@chromium.org>,
        Nicolas Pitre <nicolas.pitre@linaro.org>,
        "Luis R . Rodriguez" <mcgrof@suse.com>,
        Randy Dunlap <rdunlap@infradead.org>,
        Sam Ravnborg <sam@ravnborg.org>,
        Michal Marek <michal.lkml@markovi.net>,
        Martin Schwidefsky <schwidefsky@de.ibm.com>,
        Pavel Machek <pavel@ucw.cz>, linux-s390@vger.kernel.org,
        Jiri Kosina <jkosina@suse.cz>, linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH 4/7] kconfig: support new special property shell=
Message-ID: <20180209053038.pscoijvowmyudyzf@huvuddator>
References: <1518106752-29228-1-git-send-email-yamada.masahiro@socionext.com>
 <1518106752-29228-5-git-send-email-yamada.masahiro@socionext.com>
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On Fri, Feb 09, 2018 at 01:19:09AM +0900, Masahiro Yamada wrote:
> This works with bool, int, hex, string types.
> 
> For bool, the symbol is set to 'y' or 'n' depending on the exit value
> of the command.
> 
> For int, hex, string, the symbol is set to the value to the stdout
> of the command. (only the first line of the stdout)
> 
> The following shows how to write this and how it works.
> 
> --------------------(example Kconfig)------------------
> config srctree
>         string
>         option env="srctree"
> 
> config CC
>         string
>         option env="CC"
> 
> config CC_HAS_STACKPROTECTOR
>         bool
>         option shell="$CC -Werror -fstack-protector -c -x c /dev/null"
> 
> config CC_HAS_STACKPROTECTOR_STRONG
>         bool
>         option shell="$CC -Werror -fstack-protector-strong -c -x c /dev/null"
> 
> config CC_VERSION
>         int
>         option shell="$srctree/scripts/gcc-version.sh $CC | sed 's/^0*//'"
>         help
>           gcc-version.sh returns 4 digits number. Unfortunately, the preceding
>           zero would cause 'number is invalid'.  Cut it off.
> 
> config CC_IS_CLANG
>         bool
>         option shell="$CC --version | grep -q clang"
> 
> config CC_IS_GCC
>         bool
>         option shell="$CC --version | grep -q gcc"
> -----------------------------------------------------
> 
>   $ make alldefconfig
>   scripts/kconfig/conf  --alldefconfig Kconfig
>   #
>   # configuration written to .config
>   #
>   $ cat .config
>   #
>   # Automatically generated file; DO NOT EDIT.
>   # Linux Kernel Configuration
>   #
>   CONFIG_CC_HAS_STACKPROTECTOR=y
>   CONFIG_CC_HAS_STACKPROTECTOR_STRONG=y
>   CONFIG_CC_VERSION=504
>   # CONFIG_CC_IS_CLANG is not set
>   CONFIG_CC_IS_GCC=y
> 
> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
> Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

I know this is just an RFC/incomplete, but in case it's helpful:

> ---
> 
>  scripts/kconfig/expr.h     |  1 +
>  scripts/kconfig/kconf_id.c |  1 +
>  scripts/kconfig/lkc.h      |  1 +
>  scripts/kconfig/menu.c     |  3 ++
>  scripts/kconfig/symbol.c   | 74 ++++++++++++++++++++++++++++++++++++++++++++++
>  5 files changed, 80 insertions(+)
> 
> diff --git a/scripts/kconfig/expr.h b/scripts/kconfig/expr.h
> index c16e82e..83029f92 100644
> --- a/scripts/kconfig/expr.h
> +++ b/scripts/kconfig/expr.h
> @@ -183,6 +183,7 @@ enum prop_type {
>  	P_IMPLY,    /* imply BAR */
>  	P_RANGE,    /* range 7..100 (for a symbol) */
>  	P_ENV,      /* value from environment variable */
> +	P_SHELL,    /* shell command */
>  	P_SYMBOL,   /* where a symbol is defined */
>  };
>  
> diff --git a/scripts/kconfig/kconf_id.c b/scripts/kconfig/kconf_id.c
> index 3ea9c5f..0db9d1c 100644
> --- a/scripts/kconfig/kconf_id.c
> +++ b/scripts/kconfig/kconf_id.c
> @@ -34,6 +34,7 @@ static struct kconf_id kconf_id_array[] = {
>  	{ "defconfig_list",	T_OPT_DEFCONFIG_LIST,	TF_OPTION },
>  	{ "env",		T_OPT_ENV,		TF_OPTION },
>  	{ "allnoconfig_y",	T_OPT_ALLNOCONFIG_Y,	TF_OPTION },
> +	{ "shell",		T_OPT_SHELL,		TF_OPTION },
>  };
>  
>  #define KCONF_ID_ARRAY_SIZE (sizeof(kconf_id_array)/sizeof(struct kconf_id))
> diff --git a/scripts/kconfig/lkc.h b/scripts/kconfig/lkc.h
> index 4e23feb..8d05042 100644
> --- a/scripts/kconfig/lkc.h
> +++ b/scripts/kconfig/lkc.h
> @@ -60,6 +60,7 @@ enum conf_def_mode {
>  #define T_OPT_DEFCONFIG_LIST	2
>  #define T_OPT_ENV		3
>  #define T_OPT_ALLNOCONFIG_Y	4
> +#define T_OPT_SHELL		5
>  
>  struct kconf_id {
>  	const char *name;
> diff --git a/scripts/kconfig/menu.c b/scripts/kconfig/menu.c
> index 9922285..6254dfb 100644
> --- a/scripts/kconfig/menu.c
> +++ b/scripts/kconfig/menu.c
> @@ -216,6 +216,9 @@ void menu_add_option(int token, char *arg)
>  	case T_OPT_ENV:
>  		prop_add_env(arg);
>  		break;
> +	case T_OPT_SHELL:
> +		prop_add_shell(arg);
> +		break;
>  	case T_OPT_ALLNOCONFIG_Y:
>  		current_entry->sym->flags |= SYMBOL_ALLNOCONFIG_Y;
>  		break;
> diff --git a/scripts/kconfig/symbol.c b/scripts/kconfig/symbol.c
> index 893eae6..02ac4f4 100644
> --- a/scripts/kconfig/symbol.c
> +++ b/scripts/kconfig/symbol.c
> @@ -4,6 +4,7 @@
>   */
>  
>  #include <ctype.h>
> +#include <stdio.h>
>  #include <stdlib.h>
>  #include <string.h>
>  #include <regex.h>
> @@ -1370,6 +1371,8 @@ const char *prop_get_type_name(enum prop_type type)
>  		return "prompt";
>  	case P_ENV:
>  		return "env";
> +	case P_SHELL:
> +		return "shell";
>  	case P_COMMENT:
>  		return "comment";
>  	case P_MENU:
> @@ -1420,3 +1423,74 @@ static void prop_add_env(const char *env)
>  	else
>  		menu_warn(current_entry, "environment variable %s undefined", env);
>  }
> +
> +static void prop_add_shell(const char *cmd)
> +{
> +	struct symbol *sym, *sym2;
> +	struct property *prop;
> +	char *expanded_cmd;
> +	FILE *p;
> +	char stdout[256];

Maybe this could be called stdout_buf to avoid confusing it with the
stdio streams. Those are macros too, though glibc just does

	#define stdout stdout

> +	int ret, len;
> +
> +	sym = current_entry->sym;
> +	for_all_properties(sym, prop, P_SHELL) {
> +		sym2 = prop_get_symbol(prop);
> +		if (strcmp(sym2->name, cmd))
> +			menu_warn(current_entry, "redefining shell command symbol from %s",
> +				  sym2->name);
> +		return;
> +	}
> +
> +	prop = prop_alloc(P_SHELL, sym);
> +	prop->expr = expr_alloc_symbol(sym_lookup(cmd, SYMBOL_CONST));
> +
> +	expanded_cmd = sym_expand_string_value(cmd);
> +
> +	/* surround the command with ( ) in case it is piped commands */
> +	len = strlen(expanded_cmd);
> +	expanded_cmd = xrealloc(expanded_cmd, len + 3);
> +	memmove(expanded_cmd + 1, expanded_cmd, len);
> +	expanded_cmd[0] = '(';
> +	expanded_cmd[len + 1] = ')';
> +	expanded_cmd[len + 2] = 0;
> +
> +	switch (sym->type) {
> +	case S_BOOLEAN:
> +		/* suppress both stdout and stderr. */
> +		len = strlen(expanded_cmd) + strlen(" >/dev/null 2>&1") + 1;
> +		expanded_cmd = realloc(expanded_cmd, len);

Could use the new xrealloc().

> +		strcat(expanded_cmd, " >/dev/null 2>&1");
> +
> +		ret = system(expanded_cmd);
> +		sym_add_default(sym, ret == 0 ? "y" : "n");
> +		break;
> +	case S_INT:
> +	case S_HEX:
> +	case S_STRING:
> +		/* suppress only stderr. we want to get stdout. */
> +		len = strlen(expanded_cmd) + strlen(" 2>/dev/null") + 1;
> +		expanded_cmd = realloc(expanded_cmd, len);

Could use the new xrealloc().

> +		strcat(expanded_cmd, " 2>/dev/null");
> +
> +		p = popen(expanded_cmd, "r");

Should be pclose()d.

> +		if (!p)

Could warn.

Maybe it'd be helpful to warn if pclose() != 0 as well (non-zero exit
status or obscure error).

> +			goto free;
> +		if (fgets(stdout, sizeof(stdout), p)) {
> +			stdout[sizeof(stdout) - 1] = 0;

fgets() already guarantees null termination if any characters are read.

strncpy() is that evil one...

> +			len = strlen(stdout);
> +			if (stdout[len - 1] == '\n')
> +				stdout[len - 1] = 0;
> +		} else {
> +			stdout[0] = 0;
> +		}
> +		sym_add_default(sym, stdout);
> +		break;
> +	default:
> +		menu_warn(current_entry, "unsupported type for shell command\n");
> +		break;
> +	}
> +
> +free:
> +	free(expanded_cmd);
> +}
> -- 
> 2.7.4
> 

I think the general behavior makes sense for user-assignable
'option shell' symbols too (though I don't know if they'd ever get used in
practice):

	- The output of the shell command turns into a regular default on
	  user-assignable symbols. User values can override that default.

	- For savedefconfig, user-assignable symbols get written out only if
	  they have been changed from the default given by the shell
	  command. They will be recalculated when the defconfig is used if
	  they weren't changed.

	  Maybe there's some too-obscure-to-worry about cases there, but it
	  seems to work out pretty well.

Cheers,
Ulf