dhcpc: refactor xmalloc_optname_optval to shrink binary size

function                                             old     new   delta
len_of_option_as_string                               14      13      -1
dhcp_option_lengths                                   14      13      -1
udhcp_str2optset                                     641     637      -4
static.xmalloc_optname_optval                        777     718     -59
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 0/4 up/down: 0/-65)             Total: -65 bytes

Signed-off-by: Martin Lewis <martin.lewis.x84@gmail.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

networking/udhcp/common.h

@@ -78,7 +78,7 @@ struct BUG_bad_sizeof_struct_ip_udp_dhcp_packet {
 /*** Options ***/
 
 enum {
-	OPTION_IP = 1,
+	OPTION_IP = 0,
 	OPTION_IP_PAIR,
 	OPTION_STRING,
 	/* Opts of STRING_HOST type will be sanitized before they are passed

networking/udhcp/dhcpc.c

@@ -208,9 +208,8 @@ static NOINLINE char *xmalloc_optname_optval(uint8_t *option, const struct dhcp_
 		case OPTION_IP:
 		case OPTION_IP_PAIR:
 			dest += sprint_nip(dest, "", option);
-			if (type == OPTION_IP)
-				break;
-			dest += sprint_nip(dest, "/", option + 4);
+			if (type == OPTION_IP_PAIR)
+				dest += sprint_nip(dest, "/", option + 4);
 			break;
 //		case OPTION_BOOLEAN:
 //			dest += sprintf(dest, *option ? "yes" : "no");
@@ -312,7 +311,7 @@ static NOINLINE char *xmalloc_optname_optval(uint8_t *option, const struct dhcp_
 			 * IPv4MaskLen <= 32,
 			 * 6rdPrefixLen <= 128,
 			 * 6rdPrefixLen + (32 - IPv4MaskLen) <= 128
-			 * (2nd condition need no check - it follows from 1st and 3rd).
+			 * (2nd condition needs no check - it follows from 1st and 3rd).
 			 * Else, return envvar with empty value ("optname=")
 			 */
 			if (len >= (1 + 1 + 16 + 4)
@@ -326,17 +325,12 @@ static NOINLINE char *xmalloc_optname_optval(uint8_t *option, const struct dhcp_
 				/* 6rdPrefix */
 				dest += sprint_nip6(dest, /* "", */ option);
 				option += 16;
-				len -= 1 + 1 + 16 + 4;
-				/* "+ 4" above corresponds to the length of IPv4 addr
-				 * we consume in the loop below */
-				while (1) {
-					/* 6rdBRIPv4Address(es) */
-					dest += sprint_nip(dest, " ", option);
-					option += 4;
-					len -= 4; /* do we have yet another 4+ bytes? */
-					if (len < 0)
-						break; /* no */
-				}
+				len -= 1 + 1 + 16;
+				*dest++ = ' ';
+				/* 6rdBRIPv4Address(es), use common IPv4 logic to process them */
+				type = OPTION_IP;
+				optlen = 4;
+				continue;
 			}
 
 			return ret;
@@ -358,23 +352,18 @@ static NOINLINE char *xmalloc_optname_optval(uint8_t *option, const struct dhcp_
 			 */
 			option++;
 			len--;
+			if (option[-1] == 1) {
+				/* use common IPv4 logic to process IP addrs */
+				type = OPTION_IP;
+				optlen = 4;
+				continue;
+			}
 			if (option[-1] == 0) {
 				dest = dname_dec(option, len, ret);
 				if (dest) {
 					free(ret);
 					return dest;
 				}
-			} else
-			if (option[-1] == 1) {
-				const char *pfx = "";
-				while (1) {
-					len -= 4;
-					if (len < 0)
-						break;
-					dest += sprint_nip(dest, pfx, option);
-					pfx = " ";
-					option += 4;
-				}
 			}
 			return ret;
 #endif