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@socionext.com>

1 files changed, 41 insertions, 0 deletions

diff --git a/scripts/kconfig/preprocess.c b/scripts/kconfig/preprocess.c
index f32a496626da..528be594e1d0 100644
--- a/scripts/kconfig/preprocess.c
+++ b/scripts/kconfig/preprocess.c
@@ -106,8 +106,49 @@ struct function {
         char *(*func)(int argc, char *argv[]);
 };
 
+static char *do_shell(int argc, char *argv[])
+{
+        FILE *p;
+        char buf[256];
+        char *cmd;
+        size_t nread;
+        int i;
+
+        cmd = argv[0];
+
+        p = popen(cmd, "r");
+        if (!p) {
+                perror(cmd);
+                exit(1);
+        }
+
+        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);
+                exit(1);
+        }
+
+        return xstrdup(buf);
+}
+
 static const struct function function_table[] = {
         /* Name         MIN     MAX     Function */
+        { "shell",      1,      1,      do_shell },
 };
 
 #define FUNCTION_MAX_ARGS               16