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[Qemu-devel] [PATCH 1/2] [SLIRP] Simple ARP table


From: Fabien Chouteau
Subject: [Qemu-devel] [PATCH 1/2] [SLIRP] Simple ARP table
Date: Tue, 26 Jul 2011 18:21:31 +0200

This patch adds a simple ARP table in Slirp and also adds handling of
gratuitous ARP requests.

Signed-off-by: Fabien Chouteau <address@hidden>
---
 Makefile.objs     |    2 +-
 slirp/arp_table.c |   61 +++++++++++++++++++++++++++++++++++++++++++++++
 slirp/bootp.c     |   15 ++++++-----
 slirp/slirp.c     |   68 ++++++++++++++++------------------------------------
 slirp/slirp.h     |   51 +++++++++++++++++++++++++++++++++++++--
 5 files changed, 139 insertions(+), 58 deletions(-)
 create mode 100644 slirp/arp_table.c

diff --git a/Makefile.objs b/Makefile.objs
index 6991a9f..0c10557 100644
--- a/Makefile.objs
+++ b/Makefile.objs
@@ -151,7 +151,7 @@ common-obj-y += qemu-timer.o qemu-timer-common.o
 
 slirp-obj-y = cksum.o if.o ip_icmp.o ip_input.o ip_output.o
 slirp-obj-y += slirp.o mbuf.o misc.o sbuf.o socket.o tcp_input.o tcp_output.o
-slirp-obj-y += tcp_subr.o tcp_timer.o udp.o bootp.o tftp.o
+slirp-obj-y += tcp_subr.o tcp_timer.o udp.o bootp.o tftp.o arp_table.o
 common-obj-$(CONFIG_SLIRP) += $(addprefix slirp/, $(slirp-obj-y))
 
 # xen backend driver support
diff --git a/slirp/arp_table.c b/slirp/arp_table.c
new file mode 100644
index 0000000..e3251ed
--- /dev/null
+++ b/slirp/arp_table.c
@@ -0,0 +1,61 @@
+#include "slirp.h"
+
+void arp_table_flush(ArpTable *arptbl)
+{
+    int i;
+
+    assert(arptbl != NULL);
+
+    for (i = 0; i < ARP_TABLE_SIZE; i++) {
+        arptbl->table[i].ar_sip = 0;
+    }
+    arptbl->next_victim = 0;
+}
+
+void arp_table_add(ArpTable      *arptbl,
+                   struct arphdr *ahdr)
+{
+    int i;
+
+    DEBUG_CALL("arp_table_add");
+    DEBUG_ARG("ip = 0x%x", ahdr->ar_sip);
+    DEBUG_ARGS((dfd, " hw addr = %02x:%02x:%02x:%02x:%02x:%02x\n",
+                ahdr->ar_sha[0], ahdr->ar_sha[1], ahdr->ar_sha[2],
+                ahdr->ar_sha[3], ahdr->ar_sha[4], ahdr->ar_sha[5]));
+
+    /* Search for an entry */
+    for (i = 0; i < ARP_TABLE_SIZE && arptbl->table[i].ar_sip != 0; i++) {
+        if (arptbl->table[i].ar_sip == ahdr->ar_sip) {
+            /* Update the entry */
+            memcpy(arptbl->table[i].ar_sha,  ahdr->ar_sha, ETH_ALEN);
+            return;
+        }
+    }
+
+    /* No entry found, create a new one */
+    arptbl->table[arptbl->next_victim].ar_sip = ahdr->ar_sip;
+    memcpy(arptbl->table[arptbl->next_victim].ar_sha,  ahdr->ar_sha, ETH_ALEN);
+    arptbl->next_victim = (arptbl->next_victim + 1) % ARP_TABLE_SIZE;
+}
+
+bool arp_table_search(ArpTable *arptbl,
+                      int       in_ip_addr,
+                      uint8_t   out_ethaddr[ETH_ALEN])
+{
+    int i;
+
+    DEBUG_CALL("arp_table_search");
+    DEBUG_ARG("ip = 0x%x", in_ip_addr);
+
+    for (i = 0; i < ARP_TABLE_SIZE; i++) {
+        if (arptbl->table[i].ar_sip == in_ip_addr) {
+            memcpy(out_ethaddr, arptbl->table[i].ar_sha,  ETH_ALEN);
+            DEBUG_ARGS((dfd, " found hw addr = 
%02x:%02x:%02x:%02x:%02x:%02x\n",
+                        out_ethaddr[0], out_ethaddr[1], out_ethaddr[2],
+                        out_ethaddr[3], out_ethaddr[4], out_ethaddr[5]));
+            return 1;
+        }
+    }
+
+    return 0;
+}
diff --git a/slirp/bootp.c b/slirp/bootp.c
index 1eb2ed1..ccca93b 100644
--- a/slirp/bootp.c
+++ b/slirp/bootp.c
@@ -149,6 +149,7 @@ static void bootp_reply(Slirp *slirp, const struct bootp_t 
*bp)
     struct in_addr preq_addr;
     int dhcp_msg_type, val;
     uint8_t *q;
+    uint8_t client_ethaddr[ETH_ALEN];
 
     /* extract exact DHCP msg type */
     dhcp_decode(bp, &dhcp_msg_type, &preq_addr);
@@ -165,7 +166,7 @@ static void bootp_reply(Slirp *slirp, const struct bootp_t 
*bp)
         dhcp_msg_type != DHCPREQUEST)
         return;
     /* XXX: this is a hack to get the client mac address */
-    memcpy(slirp->client_ethaddr, bp->bp_hwaddr, 6);
+    memcpy(client_ethaddr, bp->bp_hwaddr, ETH_ALEN);
 
     m = m_get(slirp);
     if (!m) {
@@ -178,25 +179,25 @@ static void bootp_reply(Slirp *slirp, const struct 
bootp_t *bp)
 
     if (dhcp_msg_type == DHCPDISCOVER) {
         if (preq_addr.s_addr != htonl(0L)) {
-            bc = request_addr(slirp, &preq_addr, slirp->client_ethaddr);
+            bc = request_addr(slirp, &preq_addr, client_ethaddr);
             if (bc) {
                 daddr.sin_addr = preq_addr;
             }
         }
         if (!bc) {
          new_addr:
-            bc = get_new_addr(slirp, &daddr.sin_addr, slirp->client_ethaddr);
+            bc = get_new_addr(slirp, &daddr.sin_addr, client_ethaddr);
             if (!bc) {
                 DPRINTF("no address left\n");
                 return;
             }
         }
-        memcpy(bc->macaddr, slirp->client_ethaddr, 6);
+        memcpy(bc->macaddr, client_ethaddr, ETH_ALEN);
     } else if (preq_addr.s_addr != htonl(0L)) {
-        bc = request_addr(slirp, &preq_addr, slirp->client_ethaddr);
+        bc = request_addr(slirp, &preq_addr, client_ethaddr);
         if (bc) {
             daddr.sin_addr = preq_addr;
-            memcpy(bc->macaddr, slirp->client_ethaddr, 6);
+            memcpy(bc->macaddr, client_ethaddr, ETH_ALEN);
         } else {
             daddr.sin_addr.s_addr = 0;
         }
@@ -218,7 +219,7 @@ static void bootp_reply(Slirp *slirp, const struct bootp_t 
*bp)
     rbp->bp_xid = bp->bp_xid;
     rbp->bp_htype = 1;
     rbp->bp_hlen = 6;
-    memcpy(rbp->bp_hwaddr, bp->bp_hwaddr, 6);
+    memcpy(rbp->bp_hwaddr, bp->bp_hwaddr, ETH_ALEN);
 
     rbp->bp_yiaddr = daddr.sin_addr; /* Client IP address */
     rbp->bp_siaddr = saddr.sin_addr; /* Server IP address */
diff --git a/slirp/slirp.c b/slirp/slirp.c
index df787ea..29966e6 100644
--- a/slirp/slirp.c
+++ b/slirp/slirp.c
@@ -31,11 +31,11 @@
 struct in_addr loopback_addr;
 
 /* emulated hosts use the MAC addr 52:55:IP:IP:IP:IP */
-static const uint8_t special_ethaddr[6] = {
+static const uint8_t special_ethaddr[ETH_ALEN] = {
     0x52, 0x55, 0x00, 0x00, 0x00, 0x00
 };
 
-static const uint8_t zero_ethaddr[6] = { 0, 0, 0, 0, 0, 0 };
+static const uint8_t zero_ethaddr[ETH_ALEN] = { 0, 0, 0, 0, 0, 0 };
 
 /* XXX: suppress those select globals */
 fd_set *global_readfds, *global_writefds, *global_xfds;
@@ -237,6 +237,8 @@ Slirp *slirp_init(int restricted, struct in_addr vnetwork,
 
     QTAILQ_INSERT_TAIL(&slirp_instances, slirp, entry);
 
+    arp_table_flush(&slirp->arp_table);
+
     return slirp;
 }
 
@@ -599,42 +601,8 @@ void slirp_select_poll(fd_set *readfds, fd_set *writefds, 
fd_set *xfds,
         global_xfds = NULL;
 }
 
-#define ETH_ALEN 6
-#define ETH_HLEN 14
-
-#define ETH_P_IP       0x0800          /* Internet Protocol packet     */
-#define ETH_P_ARP      0x0806          /* Address Resolution packet    */
-
-#define        ARPOP_REQUEST   1               /* ARP request                  
*/
-#define        ARPOP_REPLY     2               /* ARP reply                    
*/
-
-struct ethhdr
-{
-       unsigned char   h_dest[ETH_ALEN];       /* destination eth addr */
-       unsigned char   h_source[ETH_ALEN];     /* source ether addr    */
-       unsigned short  h_proto;                /* packet type ID field */
-};
-
-struct arphdr
-{
-       unsigned short  ar_hrd;         /* format of hardware address   */
-       unsigned short  ar_pro;         /* format of protocol address   */
-       unsigned char   ar_hln;         /* length of hardware address   */
-       unsigned char   ar_pln;         /* length of protocol address   */
-       unsigned short  ar_op;          /* ARP opcode (command)         */
-
-        /*
-         *      Ethernet looks like this : This bit is variable sized 
however...
-         */
-       unsigned char           ar_sha[ETH_ALEN];       /* sender hardware 
address      */
-       uint32_t                ar_sip;                 /* sender IP address    
        */
-       unsigned char           ar_tha[ETH_ALEN];       /* target hardware 
address      */
-       uint32_t                ar_tip  ;               /* target IP address    
        */
-} __attribute__((packed));
-
 static void arp_input(Slirp *slirp, const uint8_t *pkt, int pkt_len)
 {
-    struct ethhdr *eh = (struct ethhdr *)pkt;
     struct arphdr *ah = (struct arphdr *)(pkt + ETH_HLEN);
     uint8_t arp_reply[max(ETH_HLEN + sizeof(struct arphdr), 64)];
     struct ethhdr *reh = (struct ethhdr *)arp_reply;
@@ -645,6 +613,13 @@ static void arp_input(Slirp *slirp, const uint8_t *pkt, 
int pkt_len)
     ar_op = ntohs(ah->ar_op);
     switch(ar_op) {
     case ARPOP_REQUEST:
+
+        if (ah->ar_tip == ah->ar_sip) {
+            /* Gratuitous ARP */
+            arp_table_add(&slirp->arp_table, ah);
+            return;
+        }
+
         if ((ah->ar_tip & slirp->vnetwork_mask.s_addr) ==
             slirp->vnetwork_addr.s_addr) {
             if (ah->ar_tip == slirp->vnameserver_addr.s_addr ||
@@ -657,8 +632,7 @@ static void arp_input(Slirp *slirp, const uint8_t *pkt, int 
pkt_len)
             return;
         arp_ok:
             memset(arp_reply, 0, sizeof(arp_reply));
-            /* XXX: make an ARP request to have the client address */
-            memcpy(slirp->client_ethaddr, eh->h_source, ETH_ALEN);
+            arp_table_add(&slirp->arp_table, ah);
 
             /* ARP request for alias/dns mac address */
             memcpy(reh->h_dest, pkt + ETH_ALEN, ETH_ALEN);
@@ -677,13 +651,11 @@ static void arp_input(Slirp *slirp, const uint8_t *pkt, 
int pkt_len)
             rah->ar_tip = ah->ar_sip;
             slirp_output(slirp->opaque, arp_reply, sizeof(arp_reply));
         }
+
+
         break;
     case ARPOP_REPLY:
-        /* reply to request of client mac address ? */
-        if (!memcmp(slirp->client_ethaddr, zero_ethaddr, ETH_ALEN) &&
-            ah->ar_sip == slirp->client_ipaddr.s_addr) {
-            memcpy(slirp->client_ethaddr, ah->ar_sha, ETH_ALEN);
-        }
+        arp_table_add(&slirp->arp_table, ah);
         break;
     default:
         break;
@@ -729,15 +701,16 @@ void if_encap(Slirp *slirp, const uint8_t *ip_data, int 
ip_data_len)
 {
     uint8_t buf[1600];
     struct ethhdr *eh = (struct ethhdr *)buf;
+    uint8_t ethaddr[ETH_ALEN];
+    const struct ip *iph = (const struct ip *)ip_data;
 
     if (ip_data_len + ETH_HLEN > sizeof(buf))
         return;
-    
-    if (!memcmp(slirp->client_ethaddr, zero_ethaddr, ETH_ALEN)) {
+
+    if (!arp_table_search(&slirp->arp_table, iph->ip_dst.s_addr, ethaddr)) {
         uint8_t arp_req[ETH_HLEN + sizeof(struct arphdr)];
         struct ethhdr *reh = (struct ethhdr *)arp_req;
         struct arphdr *rah = (struct arphdr *)(arp_req + ETH_HLEN);
-        const struct ip *iph = (const struct ip *)ip_data;
 
         /* If the client addr is not known, there is no point in
            sending the packet to it. Normally the sender should have
@@ -764,8 +737,9 @@ void if_encap(Slirp *slirp, const uint8_t *ip_data, int 
ip_data_len)
         rah->ar_tip = iph->ip_dst.s_addr;
         slirp->client_ipaddr = iph->ip_dst;
         slirp_output(slirp->opaque, arp_req, sizeof(arp_req));
+
     } else {
-        memcpy(eh->h_dest, slirp->client_ethaddr, ETH_ALEN);
+        memcpy(eh->h_dest, ethaddr, ETH_ALEN);
         memcpy(eh->h_source, special_ethaddr, ETH_ALEN - 4);
         /* XXX: not correct */
         memcpy(&eh->h_source[2], &slirp->vhost_addr, 4);
diff --git a/slirp/slirp.h b/slirp/slirp.h
index 16bb6ba..13d7471 100644
--- a/slirp/slirp.h
+++ b/slirp/slirp.h
@@ -170,6 +170,52 @@ int inet_aton(const char *cp, struct in_addr *ia);
 /* osdep.c */
 int qemu_socket(int domain, int type, int protocol);
 
+#define ETH_ALEN 6
+#define ETH_HLEN 14
+
+#define ETH_P_IP  0x0800        /* Internet Protocol packet  */
+#define ETH_P_ARP 0x0806        /* Address Resolution packet */
+
+#define ARPOP_REQUEST 1         /* ARP request */
+#define ARPOP_REPLY   2         /* ARP reply   */
+
+struct ethhdr {
+    unsigned char  h_dest[ETH_ALEN];   /* destination eth addr */
+    unsigned char  h_source[ETH_ALEN]; /* source ether addr    */
+    unsigned short h_proto;            /* packet type ID field */
+};
+
+struct arphdr {
+    unsigned short ar_hrd;      /* format of hardware address */
+    unsigned short ar_pro;      /* format of protocol address */
+    unsigned char  ar_hln;      /* length of hardware address */
+    unsigned char  ar_pln;      /* length of protocol address */
+    unsigned short ar_op;       /* ARP opcode (command)       */
+
+    /*
+     *  Ethernet looks like this : This bit is variable sized however...
+     */
+    unsigned char ar_sha[ETH_ALEN]; /* sender hardware address */
+    uint32_t      ar_sip;           /* sender IP address       */
+    unsigned char ar_tha[ETH_ALEN]; /* target hardware address */
+    uint32_t      ar_tip;           /* target IP address       */
+} __attribute__((packed));
+
+#define ARP_TABLE_SIZE 16
+
+typedef struct ArpTable {
+    struct arphdr table[ARP_TABLE_SIZE];
+    int next_victim;
+} ArpTable;
+
+void arp_table_flush(ArpTable *arptbl);
+
+void arp_table_add(ArpTable      *arptbl,
+                   struct arphdr *ahdr);
+
+bool arp_table_search(ArpTable *arptbl,
+                      int       in_ip_addr,
+                      uint8_t out_ethaddr[ETH_ALEN]);
 
 struct Slirp {
     QTAILQ_ENTRY(Slirp) entry;
@@ -181,9 +227,6 @@ struct Slirp {
     struct in_addr vdhcp_startaddr;
     struct in_addr vnameserver_addr;
 
-    /* ARP cache for the guest IP addresses (XXX: allow many entries) */
-    uint8_t client_ethaddr[6];
-
     struct in_addr client_ipaddr;
     char client_hostname[33];
 
@@ -227,6 +270,8 @@ struct Slirp {
     char *tftp_prefix;
     struct tftp_session tftp_sessions[TFTP_SESSIONS_MAX];
 
+    ArpTable arp_table;
+
     void *opaque;
 };
 
-- 
1.7.4.1




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