When netbooting a vm using the `-B net' option, set the hostname DHCP

option in the lease to the name of the vm. Makes it easier to use
dedicated autoinstall response files for different vms.

ok ccardenas@

usr.sbin/vmd/dhcp.c

@@ -1,4 +1,4 @@
-/*	$OpenBSD: dhcp.c,v 1.7 2018/12/06 09:20:06 claudio Exp $	*/
+/*	$OpenBSD: dhcp.c,v 1.8 2018/12/27 19:51:30 anton Exp $	*/
 
 /*
  * Copyright (c) 2017 Reyk Floeter <reyk@openbsd.org>
@@ -24,6 +24,7 @@
 #include <netinet/if_ether.h>
 #include <arpa/inet.h>
 
+#include <resolv.h>
 #include <stdlib.h>
 #include <string.h>
 #include <stddef.h>
@@ -44,8 +45,10 @@ dhcp_request(struct vionet_dev *dev, char *buf, size_t buflen, char **obuf)
 	struct packet_ctx	 pc;
 	struct dhcp_packet	 req, resp;
 	struct in_addr		 server_addr, mask, client_addr, requested_addr;
-	size_t			 resplen, o;
+	size_t			 len, resplen, o;
 	uint32_t		 ltime;
+	struct vmd_vm		*vm;
+	const char		*hostname = NULL;
 
 	if (buflen < (ssize_t)(BOOTP_MIN_LEN + sizeof(struct ether_header)))
 		return (-1);
@@ -108,8 +111,12 @@ dhcp_request(struct vionet_dev *dev, char *buf, size_t buflen, char **obuf)
 	resp.hlen = req.hlen;
 	resp.xid = req.xid;
 
-	if (dev->pxeboot)
+	if (dev->pxeboot) {
 		strlcpy(resp.file, "auto_install", sizeof resp.file);
+		vm = vm_getbyvmid(dev->vm_vmid);
+		if (vm && res_hnok(vm->vm_params.vmc_params.vcp_name))
+			hostname = vm->vm_params.vmc_params.vcp_name;
+	}
 
 	if ((client_addr.s_addr =
 	    vm_priv_addr(&env->vmd_cfg,
@@ -206,6 +213,14 @@ dhcp_request(struct vionet_dev *dev, char *buf, size_t buflen, char **obuf)
 	memcpy(&resp.options[o], &server_addr, sizeof(server_addr));
 	o += sizeof(server_addr);
 
+	if (hostname != NULL) {
+		len = strlen(hostname);
+		resp.options[o++] = DHO_HOST_NAME;
+		resp.options[o++] = len;
+		memcpy(&resp.options[o], hostname, len);
+		o += len;
+	}
+
 	resp.options[o++] = DHO_END;
 
 	resplen = offsetof(struct dhcp_packet, options) + o;