Make busybox an optional applet

If it's disabled, code shrinks by about 900 bytes:

function                                             old     new   delta
usr_bin                                               10       -     -10
usr_sbin                                              11       -     -11
install_dir                                           20       -     -20
applet_install_loc                                   184       -    -184
run_applet_and_exit                                  686      21    -665
------------------------------------------------------------------------------
(add/remove: 0/4 grow/shrink: 0/1 up/down: 0/-890)           Total: -890 bytes
   text    data     bss     dec     hex filename
 911327     493    7336  919156   e0674 busybox_old
 909848     493    7336  917677   e00ad busybox_unstripped

but busybox executable by itself does not say anything useful:

$ busybox
busybox: applet not found

Based on the patch by Ron Yorston <rmy@pobox.com>

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

2 files changed, 19 insertions, 3 deletions

diff --git a/Config.in b/Config.in
index 0a0b5d7cb..3d1870966 100644
--- a/Config.in
+++ b/Config.in
@@ -116,9 +116,21 @@ config FEATURE_COMPRESS_USAGE
           and have very little memory, this might not be a win. Otherwise,
           you probably want this.
 
+config BUSYBOX
+        bool "Include busybox applet"
+        default y
+        help
+          The busybox applet provides general help regarding busybox and
+          allows the included applets to be listed.  It's also required
+          if applet links are to be installed at runtime.
+
+          If you can live without these features disabling this will save
+          some space.
+
 config FEATURE_INSTALLER
         bool "Support --install [-s] to install applet links at runtime"
         default y
+        depends on BUSYBOX
         help
           Enable 'busybox --install [-s]' support. This will allow you to use
           busybox at runtime to create hard links or symlinks for all the
diff --git a/libbb/appletlib.c b/libbb/appletlib.c
index b682e6b85..281123c37 100644
--- a/libbb/appletlib.c
+++ b/libbb/appletlib.c
@@ -701,7 +701,7 @@ static void install_links(const char *busybox, int use_symbolic_links,
                         continue;
         }
 }
-# else
+# elif ENABLE_BUSYBOX
 static void install_links(const char *busybox UNUSED_PARAM,
                 int use_symbolic_links UNUSED_PARAM,
                 char *custom_install_dir UNUSED_PARAM)
@@ -709,6 +709,7 @@ static void install_links(const char *busybox UNUSED_PARAM,
 }
 # endif
 
+# if ENABLE_BUSYBOX
 /* If we were called as "busybox..." */
 static int busybox_main(char **argv)
 {
@@ -784,10 +785,10 @@ static int busybox_main(char **argv)
                 const char *a = applet_names;
                 dup2(1, 2);
                 while (*a) {
-# if ENABLE_FEATURE_INSTALLER
+#  if ENABLE_FEATURE_INSTALLER
                         if (argv[1][6]) /* --list-full? */
                                 full_write2_str(install_dir[APPLET_INSTALL_LOC(i)] + 1);
-# endif
+#  endif
                         full_write2_str(a);
                         full_write2_str("\n");
                         i++;
@@ -843,6 +844,7 @@ static int busybox_main(char **argv)
         /* POSIX: "If a command is not found, the exit status shall be 127" */
         exit(127);
 }
+# endif
 
 void FAST_FUNC run_applet_no_and_exit(int applet_no, char **argv)
 {
@@ -886,8 +888,10 @@ void FAST_FUNC run_applet_and_exit(const char *name, char **argv)
 {
         int applet;
 
+# if ENABLE_BUSYBOX
         if (is_prefixed_with(name, "busybox"))
                 exit(busybox_main(argv));
+# endif
         /* find_applet_by_name() search is more expensive, so goes second */
         applet = find_applet_by_name(name);
         if (applet >= 0)