filter-rewriter: rewrite tcp packet to keep secondary connection

We will rewrite tcp packet secondary received and sent.
When colo guest is a tcp server.

Firstly, client start a tcp handshake. the packet's seq=client_seq,
ack=0,flag=SYN. COLO primary guest get this pkt and mirror(filter-mirror)
to secondary guest, secondary get it use filter-redirector.
Then,primary guest response pkt
(seq=primary_seq,ack=client_seq+1,flag=ACK|SYN).
secondary guest response pkt
(seq=secondary_seq,ack=client_seq+1,flag=ACK|SYN).
In here,we use filter-rewriter save the secondary_seq to it's tcp connection.
Finally handshake,client send pkt
(seq=client_seq+1,ack=primary_seq+1,flag=ACK).
Here,filter-rewriter can get primary_seq, and rewrite ack from primary_seq+1
to secondary_seq+1, recalculate checksum. So the secondary tcp connection
kept good.

When we send/recv packet.
client send pkt(seq=client_seq+1+data_len,ack=primary_seq+1,flag=ACK|PSH).
filter-rewriter rewrite ack and send to secondary guest.

primary guest response pkt
(seq=primary_seq+1,ack=client_seq+1+data_len,flag=ACK)
secondary guest response pkt
(seq=secondary_seq+1,ack=client_seq+1+data_len,flag=ACK)
we rewrite secondary guest seq from secondary_seq+1 to primary_seq+1.
So tcp connection kept good.

In code We use offset( = secondary_seq - primary_seq )
to rewrite seq or ack.
handle_primary_tcp_pkt: tcp_pkt->th_ack += offset;
handle_secondary_tcp_pkt: tcp_pkt->th_seq -= offset;

Signed-off-by: Zhang Chen <zhangchen.fnst@cn.fujitsu.com>
Signed-off-by: Li Zhijian <lizhijian@cn.fujitsu.com>
Signed-off-by: Wen Congyang <wency@cn.fujitsu.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>

net/colo.c

@@ -134,6 +134,8 @@ Connection *connection_new(ConnectionKey *key)
 
     conn->ip_proto = key->ip_proto;
     conn->processing = false;
+    conn->offset = 0;
+    conn->syn_flag = 0;
     g_queue_init(&conn->primary_list);
     g_queue_init(&conn->secondary_list);
 

net/colo.h

@@ -62,6 +62,13 @@ typedef struct Connection {
     /* flag to enqueue unprocessed_connections */
     bool processing;
     uint8_t ip_proto;
+    /* offset = secondary_seq - primary_seq */
+    tcp_seq  offset;
+    /*
+     * we use this flag update offset func
+     * run once in independent tcp connection
+     */
+    int syn_flag;
 } Connection;
 
 uint32_t connection_key_hash(const void *opaque);

net/filter-rewriter.c

@@ -10,6 +10,7 @@
  */
 
 #include "qemu/osdep.h"
+#include "trace.h"
 #include "net/colo.h"
 #include "net/filter.h"
 #include "net/net.h"
@@ -58,6 +59,93 @@ static int is_tcp_packet(Packet *pkt)
     }
 }
 
+/* handle tcp packet from primary guest */
+static int handle_primary_tcp_pkt(NetFilterState *nf,
+                                  Connection *conn,
+                                  Packet *pkt)
+{
+    struct tcphdr *tcp_pkt;
+
+    tcp_pkt = (struct tcphdr *)pkt->transport_header;
+    if (trace_event_get_state(TRACE_COLO_FILTER_REWRITER_DEBUG)) {
+        char *sdebug, *ddebug;
+        sdebug = strdup(inet_ntoa(pkt->ip->ip_src));
+        ddebug = strdup(inet_ntoa(pkt->ip->ip_dst));
+        trace_colo_filter_rewriter_pkt_info(__func__, sdebug, ddebug,
+                    ntohl(tcp_pkt->th_seq), ntohl(tcp_pkt->th_ack),
+                    tcp_pkt->th_flags);
+        trace_colo_filter_rewriter_conn_offset(conn->offset);
+        g_free(sdebug);
+        g_free(ddebug);
+    }
+
+    if (((tcp_pkt->th_flags & (TH_ACK | TH_SYN)) == TH_SYN)) {
+        /*
+         * we use this flag update offset func
+         * run once in independent tcp connection
+         */
+        conn->syn_flag = 1;
+    }
+
+    if (((tcp_pkt->th_flags & (TH_ACK | TH_SYN)) == TH_ACK)) {
+        if (conn->syn_flag) {
+            /*
+             * offset = secondary_seq - primary seq
+             * ack packet sent by guest from primary node,
+             * so we use th_ack - 1 get primary_seq
+             */
+            conn->offset -= (ntohl(tcp_pkt->th_ack) - 1);
+            conn->syn_flag = 0;
+        }
+        /* handle packets to the secondary from the primary */
+        tcp_pkt->th_ack = htonl(ntohl(tcp_pkt->th_ack) + conn->offset);
+
+        net_checksum_calculate((uint8_t *)pkt->data, pkt->size);
+    }
+
+    return 0;
+}
+
+/* handle tcp packet from secondary guest */
+static int handle_secondary_tcp_pkt(NetFilterState *nf,
+                                    Connection *conn,
+                                    Packet *pkt)
+{
+    struct tcphdr *tcp_pkt;
+
+    tcp_pkt = (struct tcphdr *)pkt->transport_header;
+
+    if (trace_event_get_state(TRACE_COLO_FILTER_REWRITER_DEBUG)) {
+        char *sdebug, *ddebug;
+        sdebug = strdup(inet_ntoa(pkt->ip->ip_src));
+        ddebug = strdup(inet_ntoa(pkt->ip->ip_dst));
+        trace_colo_filter_rewriter_pkt_info(__func__, sdebug, ddebug,
+                    ntohl(tcp_pkt->th_seq), ntohl(tcp_pkt->th_ack),
+                    tcp_pkt->th_flags);
+        trace_colo_filter_rewriter_conn_offset(conn->offset);
+        g_free(sdebug);
+        g_free(ddebug);
+    }
+
+    if (((tcp_pkt->th_flags & (TH_ACK | TH_SYN)) == (TH_ACK | TH_SYN))) {
+        /*
+         * save offset = secondary_seq and then
+         * in handle_primary_tcp_pkt make offset
+         * = secondary_seq - primary_seq
+         */
+        conn->offset = ntohl(tcp_pkt->th_seq);
+    }
+
+    if ((tcp_pkt->th_flags & (TH_ACK | TH_SYN)) == TH_ACK) {
+        /* handle packets to the primary from the secondary*/
+        tcp_pkt->th_seq = htonl(ntohl(tcp_pkt->th_seq) - conn->offset);
+
+        net_checksum_calculate((uint8_t *)pkt->data, pkt->size);
+    }
+
+    return 0;
+}
+
 static ssize_t colo_rewriter_receive_iov(NetFilterState *nf,
                                          NetClientState *sender,
                                          unsigned flags,
@@ -97,10 +185,30 @@ static ssize_t colo_rewriter_receive_iov(NetFilterState *nf,
 
         if (sender == nf->netdev) {
             /* NET_FILTER_DIRECTION_TX */
-            /* handle_primary_tcp_pkt */
+            if (!handle_primary_tcp_pkt(nf, conn, pkt)) {
+                qemu_net_queue_send(s->incoming_queue, sender, 0,
+                (const uint8_t *)pkt->data, pkt->size, NULL);
+                packet_destroy(pkt, NULL);
+                pkt = NULL;
+                /*
+                 * We block the packet here,after rewrite pkt
+                 * and will send it
+                 */
+                return 1;
+            }
         } else {
             /* NET_FILTER_DIRECTION_RX */
-            /* handle_secondary_tcp_pkt */
+            if (!handle_secondary_tcp_pkt(nf, conn, pkt)) {
+                qemu_net_queue_send(s->incoming_queue, sender, 0,
+                (const uint8_t *)pkt->data, pkt->size, NULL);
+                packet_destroy(pkt, NULL);
+                pkt = NULL;
+                /*
+                 * We block the packet here,after rewrite pkt
+                 * and will send it
+                 */
+                return 1;
+            }
         }
     }
 

trace-events

@@ -150,6 +150,11 @@ colo_compare_ip_info(int psize, const char *sta, const char *stb, int ssize, con
 colo_old_packet_check_found(int64_t old_time) "%" PRId64
 colo_compare_miscompare(void) ""
 
+# net/filter-rewriter.c
+colo_filter_rewriter_debug(void) ""
+colo_filter_rewriter_pkt_info(const char *func, const char *src, const char *dst, uint32_t seq, uint32_t ack, uint32_t flag) "%s: src/dst: %s/%s p: seq/ack=%u/%u  flags=%x\n"
+colo_filter_rewriter_conn_offset(uint32_t offset) ": offset=%u\n"
+
 ### Guest events, keep at bottom
 
 # @vaddr: Access' virtual address.