setup_environment: code shrink

run_shell: mark as NORETURN
setup_environment, run_shell: add usage comments
login: add FIXME :(

function                                             old     new   delta
UNSPEC_print                                          64      66      +2
sulogin_main                                         509     506      -3
mkfs_minix_main                                     3070    3067      -3
login_main                                          1615    1612      -3
su_main                                              461     448     -13
setup_environment                                    261     206     -55
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 1/5 up/down: 2/-77)             Total: -75 bytes
   text    data     bss     dec     hex filename
 772578    1051   10724  784353   bf7e1 busybox_old
 772502    1051   10724  784277   bf795 busybox_unstripped

3 files changed, 13 insertions, 8 deletions

diff --git a/loginutils/login.c b/loginutils/login.c
index 5d5053840..7f8907543 100644
--- a/loginutils/login.c
+++ b/loginutils/login.c
@@ -432,7 +432,9 @@ int login_main(int argc, char **argv)
 	tmp = pw->pw_shell;
 	if (!tmp || !*tmp)
 		tmp = DEFAULT_SHELL;
+	/* setup_environment params: shell, loginshell, changeenv, pw */
 	setup_environment(tmp, 1, !(opt & LOGIN_OPT_p), pw);
+	/* FIXME: login shell = 1 -> 3rd parameter is ignored! */
 
 	motd();
 
@@ -463,7 +465,8 @@ int login_main(int argc, char **argv)
 	 * should it leave SIGINT etc enabled or disabled? */
 	signal(SIGINT, SIG_DFL);
 
-	run_shell(tmp, 1, 0, 0);	/* exec the shell finally */
+	/* Exec login shell with no additional parameters */
+	run_shell(tmp, 1, NULL, NULL);
 
-	return EXIT_FAILURE;
+	/* return EXIT_FAILURE; - not reached */
 }
diff --git a/loginutils/su.c b/loginutils/su.c
index b4681fb6a..123907e28 100644
--- a/loginutils/su.c
+++ b/loginutils/su.c
@@ -36,7 +36,7 @@ int su_main(int argc, char **argv)
 	/* get user if specified */
 	if (argc) {
 		opt_username = argv[0];
-//		argc--;
+		//argc--; - not used below anyway
 		argv++;
 	}
 
@@ -86,18 +86,19 @@ int su_main(int argc, char **argv)
 		   compromise the account by allowing access with a standard
 		   shell.  */
 		bb_error_msg("using restricted shell");
-		opt_shell = 0;
+		opt_shell = NULL;
 	}
 #endif
 	if (!opt_shell)
 		opt_shell = pw->pw_shell;
 
 	change_identity(pw);
+	/* setup_environment params: shell, loginshell, changeenv, pw */
 	setup_environment(opt_shell, flags & SU_OPT_l, !(flags & SU_OPT_mp), pw);
 	USE_SELINUX(set_current_security_context(NULL);)
 
 	/* Never returns */
 	run_shell(opt_shell, flags & SU_OPT_l, opt_command, (const char**)argv);
 
-	return EXIT_FAILURE;
+	/* return EXIT_FAILURE; - not reached */
 }
diff --git a/loginutils/sulogin.c b/loginutils/sulogin.c
index 5f0a4081d..5c73bda93 100644
--- a/loginutils/sulogin.c
+++ b/loginutils/sulogin.c
@@ -112,14 +112,15 @@ int sulogin_main(int argc, char **argv)
 	USE_SELINUX(renew_current_security_context());
 
 	shell = getenv("SUSHELL");
-	if (!shell) shell = getenv("sushell");
+	if (!shell)
+		shell = getenv("sushell");
 	if (!shell) {
 		shell = "/bin/sh";
 		if (pwd->pw_shell[0])
 			shell = pwd->pw_shell;
 	}
-	run_shell(shell, 1, 0, 0);
-	/* never returns */
+	/* Exec login shell with no additional parameters. Never returns. */
+	run_shell(shell, 1, NULL, NULL);
 
 auth_error:
 	bb_error_msg_and_die("no password entry for 'root'");