linux-kernel - [PATCH 09/30] kconfig: add 'shell' built-in function

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Message-Id: <1523595999-27433-10-git-send-email-yamada.masahiro@socionext.com>
Date:   Fri, 13 Apr 2018 14:06:18 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     linux-kbuild@...r.kernel.org
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Sam Ravnborg <sam@...nborg.org>,
        Ulf Magnusson <ulfalizer@...il.com>,
        Nicholas Piggin <npiggin@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Emese Revfy <re.emese@...il.com>, x86@...nel.org,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH 09/30] kconfig: add 'shell' built-in function

This accepts a single command to execute.  It returns the standard
output from it.

[Example code]

  config HELLO
          string
          default "$(shell echo hello world)"

  config Y
          def_bool $(shell echo y)

[Result]

  $ make -s alldefconfig && tail -n 2 .config
  CONFIG_HELLO="hello world"
  CONFIG_Y=y

Caveat:
Like environments, functions are expanded in the lexer.  You cannot
pass symbols to function arguments.  This is a limitation to simplify
the implementation.  I want to avoid the dynamic function evaluation,
which would introduce much more complexity.

Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
---

Changes in v3: None
Changes in v2: None

 scripts/kconfig/preprocess.c | 66 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 66 insertions(+)

diff --git a/scripts/kconfig/preprocess.c b/scripts/kconfig/preprocess.c
index e77cf7c..f4c606f 100644
--- a/scripts/kconfig/preprocess.c
+++ b/scripts/kconfig/preprocess.c
@@ -86,7 +86,73 @@ struct function {
 	char *(*func)(int argc, char *argv[]);
 };
 
+/*
+ * Some commands treats commas verbatim.  Concatenate arguments to get
+ * back the original input.  The returned string must be freed when done.
+ */
+static char *join_args(int argc, char *argv[])
+{
+	size_t len = 0;
+	char *out;
+	int i;
+
+	for (i = 0; i < argc; i++)
+		len += strlen(argv[i]) + 1;
+
+	out = xmalloc(len);
+	out[0] = 0;
+	for (i = 0; i < argc; i++) {
+		strcat(out, argv[i]);
+		if (i != argc - 1)
+			strcat(out, ",");
+	}
+
+	return out;
+}
+
+static char *do_shell(int argc, char *argv[])
+{
+	FILE *p;
+	char buf[256];
+	char *cmd;
+	size_t nread;
+	int i;
+
+	cmd = join_args(argc, argv);
+
+	p = popen(cmd, "r");
+	if (!p) {
+		perror(cmd);
+		goto free;
+	}
+
+	nread = fread(buf, 1, sizeof(buf), p);
+	if (nread == sizeof(buf))
+		nread--;
+
+	/* remove trailing new lines */
+	while (buf[nread - 1] == '\n')
+		nread--;
+
+	buf[nread] = 0;
+
+	/* replace a new line with a space */
+	for (i = 0; i < nread; i++) {
+		if (buf[i] == '\n')
+			buf[i] = ' ';
+	}
+
+	if (pclose(p) == -1)
+		perror(cmd);
+
+free:
+	free(cmd);
+
+	return xstrdup(buf);
+}
+
 static const struct function function_table[] = {
+	{ .name = "shell", .func = do_shell },
 };
 
 static char *function_call(const char *name, int argc, char *argv[])
-- 
2.7.4