kvm tools: Add ARP support for uip

- Introduce struct uip_arp to present ARP package
- uip_tx_do_arp()
  Clone incoming ARP ethernet frame, if ARP is requesting
  host IP address, tell guest host MAC address.

Signed-off-by: Asias He <asias.hejun@gmail.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>

Makefile

@@ -45,6 +45,7 @@ OBJS	+= disk/qcow.o
 OBJS	+= disk/raw.o
 OBJS	+= ioeventfd.o
 OBJS	+= irq.o
+OBJS	+= uip/arp.o
 OBJS	+= uip/buf.o
 OBJS	+= kvm-cmd.o
 OBJS	+= kvm-debug.o

include/kvm/uip.h

@@ -21,6 +21,19 @@ struct uip_eth {
 	u16 type;
 } __attribute__((packed));
 
+struct uip_arp {
+	struct uip_eth eth;
+	u16 hwtype;
+	u16 proto;
+	u8 hwlen;
+	u8 protolen;
+	u16 op;
+	struct uip_eth_addr smac;
+	u32 sip;
+	struct uip_eth_addr dmac;
+	u32 dip;
+} __attribute__((packed));
+
 struct uip_info {
 	struct list_head udp_socket_head;
 	struct list_head tcp_socket_head;
@@ -60,6 +73,8 @@ struct uip_tx_arg {
 	int eth_len;
 };
 
+int uip_tx_do_arp(struct uip_tx_arg *arg);
+
 struct uip_buf *uip_buf_set_used(struct uip_info *info, struct uip_buf *buf);
 struct uip_buf *uip_buf_set_free(struct uip_info *info, struct uip_buf *buf);
 struct uip_buf *uip_buf_get_used(struct uip_info *info);

uip/arp.c

@@ -0,0 +1,30 @@
+#include "kvm/uip.h"
+
+int uip_tx_do_arp(struct uip_tx_arg *arg)
+{
+	struct uip_arp *arp, *arp2;
+	struct uip_info *info;
+	struct uip_buf *buf;
+
+	info = arg->info;
+	buf = uip_buf_clone(arg);
+
+	arp	 = (struct uip_arp *)(arg->eth);
+	arp2	 = (struct uip_arp *)(buf->eth);
+
+	/*
+	 * ARP replay code: 2
+	 */
+	arp2->op   = htons(0x2);
+	arp2->dmac = arp->smac;
+	arp2->dip  = arp->sip;
+
+	if (arp->dip == htonl(info->host_ip)) {
+		arp2->smac = info->host_mac;
+		arp2->sip = htonl(info->host_ip);
+
+		uip_buf_set_used(info, buf);
+	}
+
+	return 0;
+}