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[Qemu-devel] [PATCH V2 2/2] [SLIRP] Delayed IP packets


From: Fabien Chouteau
Subject: [Qemu-devel] [PATCH V2 2/2] [SLIRP] Delayed IP packets
Date: Fri, 29 Jul 2011 18:25:03 +0200

In the current implementation, if Slirp tries to send an IP packet to a client
with an unknown hardware address, the packet is simply dropped and an ARP
request is sent (if_encap in slirp/slirp.c).

With this patch, Slirp will send the ARP request, re-queue the packet and try
to send it later. The packet is dropped after one second if the ARP reply is
not received.

Signed-off-by: Fabien Chouteau <address@hidden>
---
 slirp/if.c    |   28 ++++++++++++++++++++---
 slirp/main.h  |    2 +-
 slirp/mbuf.c  |    2 +
 slirp/mbuf.h  |    2 +
 slirp/slirp.c |   67 ++++++++++++++++++++++++++++++--------------------------
 slirp/slirp.h |   15 ++++++++++++
 6 files changed, 80 insertions(+), 36 deletions(-)

diff --git a/slirp/if.c b/slirp/if.c
index 0f04e13..80a5c4e 100644
--- a/slirp/if.c
+++ b/slirp/if.c
@@ -6,6 +6,7 @@
  */
 
 #include <slirp.h>
+#include "qemu-timer.h"
 
 #define ifs_init(ifm) ((ifm)->ifs_next = (ifm)->ifs_prev = (ifm))
 
@@ -105,6 +106,9 @@ if_output(struct socket *so, struct mbuf *ifm)
        ifs_init(ifm);
        insque(ifm, ifq);
 
+        /* Expiration date = Now + 1 second */
+        ifm->expiration_date = qemu_get_clock_ns(vm_clock) + 1000000000ULL;
+
 diddit:
        slirp->if_queued++;
 
@@ -153,6 +157,9 @@ diddit:
 void
 if_start(Slirp *slirp)
 {
+    int requeued = 0;
+    uint64_t now;
+
        struct mbuf *ifm, *ifqt;
 
        DEBUG_CALL("if_start");
@@ -165,6 +172,8 @@ if_start(Slirp *slirp)
         if (!slirp_can_output(slirp->opaque))
             return;
 
+        now = qemu_get_clock_ns(vm_clock);
+
        /*
         * See which queue to get next packet from
         * If there's something in the fastq, select it immediately
@@ -199,11 +208,22 @@ if_start(Slirp *slirp)
                   ifm->ifq_so->so_nqueued = 0;
        }
 
-       /* Encapsulate the packet for sending */
-        if_encap(slirp, (uint8_t *)ifm->m_data, ifm->m_len);
-
-        m_free(ifm);
+        if (ifm->expiration_date < now) {
+            /* Expired */
+            m_free(ifm);
+        } else {
+            /* Encapsulate the packet for sending */
+            if (if_encap(slirp, ifm)) {
+                m_free(ifm);
+            } else {
+                /* re-queue */
+                insque(ifm, ifqt);
+                requeued++;
+            }
+        }
 
        if (slirp->if_queued)
           goto again;
+
+        slirp->if_queued = requeued;
 }
diff --git a/slirp/main.h b/slirp/main.h
index 0dd8d81..028df4b 100644
--- a/slirp/main.h
+++ b/slirp/main.h
@@ -42,5 +42,5 @@ extern int tcp_keepintvl;
 #define PROTO_PPP 0x2
 #endif
 
-void if_encap(Slirp *slirp, const uint8_t *ip_data, int ip_data_len);
+int if_encap(Slirp *slirp, struct mbuf *ifm);
 ssize_t slirp_send(struct socket *so, const void *buf, size_t len, int flags);
diff --git a/slirp/mbuf.c b/slirp/mbuf.c
index ce2eb84..c699c75 100644
--- a/slirp/mbuf.c
+++ b/slirp/mbuf.c
@@ -70,6 +70,8 @@ m_get(Slirp *slirp)
        m->m_len = 0;
         m->m_nextpkt = NULL;
         m->m_prevpkt = NULL;
+        m->arp_requested = false;
+        m->expiration_date = (uint64_t)-1;
 end_error:
        DEBUG_ARG("m = %lx", (long )m);
        return m;
diff --git a/slirp/mbuf.h b/slirp/mbuf.h
index b74544b..55170e5 100644
--- a/slirp/mbuf.h
+++ b/slirp/mbuf.h
@@ -86,6 +86,8 @@ struct mbuf {
                char    m_dat_[1]; /* ANSI don't like 0 sized arrays */
                char    *m_ext_;
        } M_dat;
+    bool     arp_requested;
+    uint64_t expiration_date;
 };
 
 #define m_next         m_hdr.mh_next
diff --git a/slirp/slirp.c b/slirp/slirp.c
index ba76757..b006620 100644
--- a/slirp/slirp.c
+++ b/slirp/slirp.c
@@ -237,6 +237,8 @@ Slirp *slirp_init(int restricted, struct in_addr vnetwork,
 
     QTAILQ_INSERT_TAIL(&slirp_instances, slirp, entry);
 
+    slirp->delayed = NULL;
+
     return slirp;
 }
 
@@ -693,54 +695,57 @@ void slirp_input(Slirp *slirp, const uint8_t *pkt, int 
pkt_len)
 }
 
 /* output the IP packet to the ethernet device */
-void if_encap(Slirp *slirp, const uint8_t *ip_data, int ip_data_len)
+int if_encap(Slirp *slirp, struct mbuf *ifm)
 {
     uint8_t buf[1600];
     struct ethhdr *eh = (struct ethhdr *)buf;
     uint8_t ethaddr[ETH_ALEN];
-    const struct ip *iph = (const struct ip *)ip_data;
+    const struct ip *iph = (const struct ip *)ifm->m_data;
 
-    if (ip_data_len + ETH_HLEN > sizeof(buf))
-        return;
+    if (ifm->m_len + ETH_HLEN > sizeof(buf))
+        return 1;
 
     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);
 
-        /* If the client addr is not known, there is no point in
-           sending the packet to it. Normally the sender should have
-           done an ARP request to get its MAC address. Here we do it
-           in place of sending the packet and we hope that the sender
-           will retry sending its packet. */
-        memset(reh->h_dest, 0xff, ETH_ALEN);
-        memcpy(reh->h_source, special_ethaddr, ETH_ALEN - 4);
-        memcpy(&reh->h_source[2], &slirp->vhost_addr, 4);
-        reh->h_proto = htons(ETH_P_ARP);
-        rah->ar_hrd = htons(1);
-        rah->ar_pro = htons(ETH_P_IP);
-        rah->ar_hln = ETH_ALEN;
-        rah->ar_pln = 4;
-        rah->ar_op = htons(ARPOP_REQUEST);
-        /* source hw addr */
-        memcpy(rah->ar_sha, special_ethaddr, ETH_ALEN - 4);
-        memcpy(&rah->ar_sha[2], &slirp->vhost_addr, 4);
-        /* source IP */
-        rah->ar_sip = slirp->vhost_addr.s_addr;
-        /* target hw addr (none) */
-        memset(rah->ar_tha, 0, ETH_ALEN);
-        /* target IP */
-        rah->ar_tip = iph->ip_dst.s_addr;
-        slirp->client_ipaddr = iph->ip_dst;
-        slirp_output(slirp->opaque, arp_req, sizeof(arp_req));
+        if (!ifm->arp_requested) {
+
+            /* If the client addr is not known, send an ARP request */
+            memset(reh->h_dest, 0xff, ETH_ALEN);
+            memcpy(reh->h_source, special_ethaddr, ETH_ALEN - 4);
+            memcpy(&reh->h_source[2], &slirp->vhost_addr, 4);
+            reh->h_proto = htons(ETH_P_ARP);
+            rah->ar_hrd = htons(1);
+            rah->ar_pro = htons(ETH_P_IP);
+            rah->ar_hln = ETH_ALEN;
+            rah->ar_pln = 4;
+            rah->ar_op = htons(ARPOP_REQUEST);
+            /* source hw addr */
+            memcpy(rah->ar_sha, special_ethaddr, ETH_ALEN - 4);
+            memcpy(&rah->ar_sha[2], &slirp->vhost_addr, 4);
+            /* source IP */
+            rah->ar_sip = slirp->vhost_addr.s_addr;
+            /* target hw addr (none) */
+            memset(rah->ar_tha, 0, ETH_ALEN);
+            /* target IP */
+            rah->ar_tip = iph->ip_dst.s_addr;
+            slirp->client_ipaddr = iph->ip_dst;
+            slirp_output(slirp->opaque, arp_req, sizeof(arp_req));
+            ifm->arp_requested = true;
+        }
+        return 0;
     } else {
+        ifm->arp_requested = false;
         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);
         eh->h_proto = htons(ETH_P_IP);
-        memcpy(buf + sizeof(struct ethhdr), ip_data, ip_data_len);
-        slirp_output(slirp->opaque, buf, ip_data_len + ETH_HLEN);
+        memcpy(buf + sizeof(struct ethhdr), ifm->m_data, ifm->m_len);
+        slirp_output(slirp->opaque, buf, ifm->m_len + ETH_HLEN);
+        return 1;
     }
 }
 
diff --git a/slirp/slirp.h b/slirp/slirp.h
index 103b39d..07d7d29 100644
--- a/slirp/slirp.h
+++ b/slirp/slirp.h
@@ -216,6 +216,15 @@ bool arp_table_search(ArpTable *arptbl,
                       int       in_ip_addr,
                       uint8_t out_ethaddr[ETH_ALEN]);
 
+struct DelayedIpPacket;
+typedef struct DelayedIpPacket DelayedIpPacket;
+
+struct DelayedIpPacket {
+    uint8_t         *data;
+    int              len;
+    DelayedIpPacket *next;
+};
+
 struct Slirp {
     QTAILQ_ENTRY(Slirp) entry;
 
@@ -271,6 +280,12 @@ struct Slirp {
 
     ArpTable arp_table;
 
+    /* List of delayed IP packets.
+     * These packets are delayed because the target hw address is unknown. 
Slirp
+     * will try to send them each time the arp table is updated.
+     */
+    DelayedIpPacket *delayed;
+
     void *opaque;
 };
 
-- 
1.7.4.1




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