loader.efi: Apply command-line DHCP overrides earlier

Ability to override DHCP options with command-line arguments
was affected by intoduction of initmd support. Initmd discovery
configures the network before loader arguments
were parsed, so a dhcp.root-path override was unavailable
during the first network configuration. Move parsing
arguments earlier and apply dhcp.root-path even if DHCP response
does not contain option 17. This allows providing a dynamic NFS
root e.g. by chain loading loader.efi from iPXE.

Signed-off-by: Krzysztof Galazka <[email protected]>

Reviewed by:	imp
Assisted by:    Github Copilot (GPT-5.6 Sol)
Sponsored by:   Intel Corporation
Differential Revision:	https://reviews.freebsd.org/D59998

stand/common/dev_net.c

@@ -248,6 +248,7 @@ static int
 net_getparams(int sock)
 {
 	char buf[MAXHOSTNAMELEN];
+	const char *val;
 	n_long rootaddr, smask;
 
 #ifdef	SUPPORT_BOOTP
@@ -306,6 +307,8 @@ net_getparams(int sock)
 		return (EIO);
 	}
 exit:
+	if ((val = getenv("dhcp.root-path")) != NULL)
+		strlcpy(rootpath, val, sizeof(rootpath));
 	if ((rootaddr = net_parse_rootpath()) != htonl(INADDR_NONE))
 		rootip.s_addr = rootaddr;
 

stand/efi/loader/main.c

@@ -1382,6 +1382,12 @@ main(int argc, CHAR16 *argv[])
 
 	devinit();
 
+	/*
+	 * Parse command line arguments before any operation that may configure
+	 * the network so DHCP overrides are available on the first attempt.
+	 */
+	howto = parse_args(argc, argv);
+
 	/*
 	 * If we didn't find a ipxe image, and we're netbooting, try to
 	 * download an initmd that the dhcp server tells us about.
@@ -1394,7 +1400,6 @@ main(int argc, CHAR16 *argv[])
 	 * args (eg -h) or via the UEFI ConOut variable.
 	 */
 	has_kbd = has_keyboard();
-	howto = parse_args(argc, argv);
 	if (!has_kbd && (howto & RB_PROBE))
 		howto |= RB_SERIAL | RB_MULTIPLE;
 	howto &= ~RB_PROBE;

stand/libsa/bootp.c

@@ -474,9 +474,7 @@ vend_rfc1048(u_char *cp, u_int len)
 			bcopy(cp, &rootip.s_addr, sizeof(rootip.s_addr));
 		}
 		if (tag == TAG_ROOTPATH) {
-			if ((val = getenv("dhcp.root-path")) == NULL)
-				val = (const char *)cp;
-			strlcpy(rootpath, val, sizeof(rootpath));
+			strlcpy(rootpath, (const char *)cp, sizeof(rootpath));
 		}
 		if (tag == TAG_HOSTNAME) {
 			if ((val = getenv("dhcp.host-name")) == NULL)