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Date:   Fri, 9 Feb 2018 13:46:07 +0100
From:   Ulf Magnusson <ulfalizer@gmail.com>
To:     Masahiro Yamada <yamada.masahiro@socionext.com>
Cc:     Linux Kbuild mailing list <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 <linux-s390@vger.kernel.org>,
        Jiri Kosina <jkosina@suse.cz>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [RFC PATCH 4/7] kconfig: support new special property shell=
Message-ID: <20180209124607.akjhncb5sempjqcn@huvuddator>
References: <1518106752-29228-1-git-send-email-yamada.masahiro@socionext.com>
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On Fri, Feb 09, 2018 at 06:19:19PM +0900, Masahiro Yamada wrote:
> 2018-02-09 14:30 GMT+09:00 Ulf Magnusson <ulfalizer@gmail.com>:
> > 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:
> 
> 
> Your comments are really helpful, as always!
> 
> 
> 
> >> ---
> >>
> >>  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
> 
> Right.  This is confusing.  Will rename.
> 
> 
> >> +     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().
> 
> Oops.  I added xrealloc() for this, but missed to use it here, somehow.
> 
> >> +             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.
> 
> Good catch!
> 
> >> +             if (!p)
> >
> > Could warn.
> >
> > Maybe it'd be helpful to warn if pclose() != 0 as well (non-zero exit
> > status or obscure error).
> 
> Yes.
> 
> 
> >> +                     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...
> 
> Oh, I was misunderstanding the fgets() behavior.
> 
> You are right.  Will remove this unneeded termination.
> 
> 
> >> +                     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.
> >
> 
> Observant comments.
> 
> Both "option env=" and "option shell="
> are turned into 'default' property after all.

Yep, took me a while before I discovered that for 'option env'. The
internal UNAME_RELEASE variable is implemented the same way.

> 
> config FOO
>         string
>         option env="foo"
> 
> could be written
> 
> 
> config FOO
>         string
>         default env="foo"
> 
> (syntax is not so important)
> 
> 
> Having multiple defaults with visibility control could be useful.
> 
> config FOO
>         string "foo"
>         default env="foo1" if CASE1
>         default env="foo2" if CASE2
> 
> 
> shell= seems the same logic.

A simpler (and naturally unambiguous) syntax would be possible with a
few more keywords too:

	config FOO
		string "foo"
		default_env "FOO" if CASE1
		default_env "BAR" if CASE2
		default_shell "foo --bar" if CASE3
		default "otherwise"

Speaking of syntax nits, the whole 'option' construct feels pointless.
'option allnoconfig_y' could just be 'allnoconfig_y', etc., the way the
'optional' keyword works for choices.


There's a subtlety re. 'option env' btw: Those symbols never get written
out to .config files or headers, because SYMBOL_AUTO is set on them.

I don't think it would actually hurt to write them out:

	- If the symbol is not user-assignable, then the user value in
	  the .config file will be ignored when the .config file is read
	  back in, and the symbol will always get its value from the
	  environment.
	
	- If the symbol is user-assignable, then it makes sense to
	  remember and respect the user value, if any, since that was
	  the point of making the symbol user-assignable.

For the kernel, writing out 'option env' symbols would mean that ARCH,
SRCARCH, and KERNELVERSION would show up in .config files and autoconf.h
files. I'm not familiar enough with the make parts of Kbuild to know
what the effects of that might be. If it breaks things, then that might
explain why SYMBOL_AUTO is set on them.

They would always be fetched from the environment in any case, since
they are not user-assignable (lack prompts).


Some philosophical rambling re. .config files below:

One thing that makes Kconfig confusing (though it works well enough in
practice) is that .config files both record user selections (the saved
configuration) and serve as a configuration output format for make.

It becomes easier to think about .config files once you realize that
assignments to promptless symbols never have an effect on Kconfig
itself: They're just configuration output, intermixed with the saved
user selections.

Assume 'option env' symbols got written out for example:

	- For a non-user-assignable symbol, the entry in the .config
	  file is just configuration output and ignored by Kconfig,
	  which will fetch the value from the environment instead.

	- For an assignable 'option env' symbol, the entry in the
	  .config file is a saved user selection (as well as
	  configuration output), and will be respected by Kconfig.

defconfig files are closer to a "pure" output-independent saved
configuration format in a way, since they only include user selections
and don't mix it with configuration output.

Hopefully some of that made sense. Don't feel forced to reply to the
rambly parts. It's just a way of thinking of it that helps me. ;)

> 
> 
> 
> 
> -- 
> Best Regards
> Masahiro Yamada

Cheers,
Ulf