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>
diff --git a/e2fsprogs/fsck.c b/e2fsprogs/fsck.c
index d32f396..d2d312e 100644
--- a/e2fsprogs/fsck.c
+++ b/e2fsprogs/fsck.c
@@ -199,7 +199,7 @@
 	}
 
 	/* Handle DAC 960 devices */
-	if (strncmp(cp, "rd/", 3) == 0) {
+	if (is_prefixed_with(cp, "rd/")) {
 		cp += 3;
 		if (cp[0] != 'c' || !isdigit(cp[1])
 		 || cp[2] != 'd' || !isdigit(cp[3]))
@@ -224,9 +224,9 @@
 #if ENABLE_FEATURE_DEVFS
 	/* Now let's handle devfs (ugh) names */
 	len = 0;
-	if (strncmp(cp, "ide/", 4) == 0)
+	if (is_prefixed_with(cp, "ide/"))
 		len = 4;
-	if (strncmp(cp, "scsi/", 5) == 0)
+	if (is_prefixed_with(cp, "scsi/"))
 		len = 5;
 	if (len) {
 		cp += len;
@@ -237,38 +237,38 @@
 		 * some number of digits at each level, abort.
 		 */
 		for (hier = devfs_hier; *hier; hier++) {
-			len = strlen(*hier);
-			if (strncmp(cp, *hier, len) != 0)
+			cp = is_prefixed_with(cp, *hier);
+			if (!cp)
 				goto errout;
-			cp += len;
-			while (*cp != '/' && *cp != 0) {
+			while (*cp != '/' && *cp != '\0') {
 				if (!isdigit(*cp))
 					goto errout;
 				cp++;
 			}
+//FIXME: what if *cp = '\0' now? cp++ moves past it!!!
 			cp++;
 		}
-		cp[-1] = 0;
+		cp[-1] = '\0';
 		return str;
 	}
 
 	/* Now handle devfs /dev/disc or /dev/disk names */
-	disk = 0;
-	if (strncmp(cp, "discs/", 6) == 0)
+	disk = NULL;
+	if (is_prefixed_with(cp, "discs/"))
 		disk = "disc";
-	else if (strncmp(cp, "disks/", 6) == 0)
+	else if (is_prefixed_with(cp, "disks/"))
 		disk = "disk";
 	if (disk) {
 		cp += 6;
-		if (strncmp(cp, disk, 4) != 0)
+		cp = is_prefixed_with(cp, disk);
+		if (!cp)
 			goto errout;
-		cp += 4;
-		while (*cp != '/' && *cp != 0) {
+		while (*cp != '/' && *cp != '\0') {
 			if (!isdigit(*cp))
 				goto errout;
 			cp++;
 		}
-		*cp = 0;
+		*cp = '\0';
 		return str;
 	}
 #endif
@@ -593,8 +593,8 @@
 					type, "from fstab");
 	} else if (fstype
 	 && (fstype[0] != 'n' || fstype[1] != 'o') /* != "no" */
-	 && strncmp(fstype, "opts=", 5) != 0
-	 && strncmp(fstype, "loop", 4) != 0
+	 && !is_prefixed_with(fstype, "opts=")
+	 && !is_prefixed_with(fstype, "loop")
 	 && !strchr(fstype, ',')
 	) {
 		type = fstype;
@@ -627,8 +627,8 @@
 #ifdef BASE_MD
 	/* Don't check a soft raid disk with any other disk */
 	if (instance_list
-	 && (!strncmp(instance_list->device, BASE_MD, sizeof(BASE_MD)-1)
-	     || !strncmp(device, BASE_MD, sizeof(BASE_MD)-1))
+	 && (is_prefixed_with(instance_list->device, BASE_MD)
+	     || is_prefixed_with(device, BASE_MD))
 	) {
 		return 1;
 	}
@@ -895,7 +895,7 @@
 		if (strcmp(s, "loop") == 0)
 			/* loop is really short-hand for opts=loop */
 			goto loop_special_case;
-		if (strncmp(s, "opts=", 5) == 0) {
+		if (is_prefixed_with(s, "opts=")) {
 			s += 5;
  loop_special_case:
 			fs_type_flag[num] = negate ? FS_TYPE_FLAG_NEGOPT : FS_TYPE_FLAG_OPT;