libbb: introduce and use is_prefixed_with()

function                                             old     new   delta
is_prefixed_with                                       -      18     +18
complete_username                                     78      77      -1
man_main                                             737     735      -2
fsck_device                                          429     427      -2
unpack_ar_archive                                     80      76      -4
strip_unsafe_prefix                                  105     101      -4
singlemount                                         1054    1050      -4
rtc_adjtime_is_utc                                    90      86      -4
resolve_mount_spec                                    88      84      -4
parse_one_line                                      1029    1025      -4
parse_conf                                          1460    1456      -4
may_wakeup                                            83      79      -4
loadkmap_main                                        219     215      -4
get_irqs_from_stat                                   103      99      -4
get_header_cpio                                      913     909      -4
findfs_main                                           79      75      -4
fbsplash_main                                       1230    1226      -4
load_crontab                                         776     771      -5
expand_vars_to_list                                 1151    1146      -5
date_main                                            881     876      -5
skip_dev_pfx                                          30      24      -6
make_device                                         2199    2193      -6
complete_cmd_dir_file                                773     767      -6
run_applet_and_exit                                  715     708      -7
uudecode_main                                        321     313      -8
pwdx_main                                            197     189      -8
execute                                              568     560      -8
i2cdetect_main                                      1186    1176     -10
procps_scan                                         1242    1230     -12
procps_read_smaps                                   1017    1005     -12
process_module                                       746     734     -12
patch_main                                          1903    1891     -12
nfsmount                                            3572    3560     -12
stack_machine                                        126     112     -14
process_timer_stats                                  449     435     -14
match_fstype                                         111      97     -14
do_ipaddr                                           1344    1330     -14
open_list_and_close                                  359     343     -16
get_header_tar                                      1795    1779     -16
prepend_new_eth_table                                340     323     -17
fsck_main                                           1811    1794     -17
find_iface_state                                      56      38     -18
dnsd_main                                           1321    1303     -18
base_device                                          179     158     -21
find_keyword                                         104      82     -22
handle_incoming_and_exit                            2785    2762     -23
parse_and_put_prompt                                 774     746     -28
modinfo                                              347     317     -30
find_action                                          204     171     -33
update_passwd                                       1470    1436     -34
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 0/49 up/down: 18/-540)         Total: -522 bytes

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

libbb/appletlib.c

@@ -193,7 +193,7 @@ void lbb_prepare(const char *applet
 	if (argv[1]
 	 && !argv[2]
 	 && strcmp(argv[1], "--help") == 0
-	 && strncmp(applet, "busybox", 7) != 0
+	 && !is_prefixed_with(applet, "busybox")
 	) {
 		/* Special case. POSIX says "test --help"
 		 * should be no different from e.g. "test --foo".  */
@@ -673,7 +673,7 @@ static int busybox_main(char **argv)
 		return 0;
 	}
 
-	if (strncmp(argv[1], "--list", 6) == 0) {
+	if (is_prefixed_with(argv[1], "--list")) {
 		unsigned i = 0;
 		const char *a = applet_names;
 		dup2(1, 2);
@@ -778,7 +778,7 @@ void FAST_FUNC run_applet_and_exit(const char *name, char **argv)
 	int applet = find_applet_by_name(name);
 	if (applet >= 0)
 		run_applet_no_and_exit(applet, argv);
-	if (strncmp(name, "busybox", 7) == 0)
+	if (is_prefixed_with(name, "busybox"))
 		exit(busybox_main(argv));
 }
 
@@ -817,7 +817,7 @@ int main(int argc UNUSED_PARAM, char **argv)
 
 #if defined(SINGLE_APPLET_MAIN)
 	/* Only one applet is selected in .config */
-	if (argv[1] && strncmp(argv[0], "busybox", 7) == 0) {
+	if (argv[1] && is_prefixed_with(argv[0], "busybox")) {
 		/* "busybox <applet> <params>" should still work as expected */
 		argv++;
 	}