[Qemu-devel] [Patch] Add -net dump option

[Tristan Gingold]

Hi,

this patch add a new network pseudo nic that dump traffic to a tcpdump
compatible file.  I have found this feature useful to debug network protocols
with the user stack.

Signed-off-by: Tristan Gingold <address@hidden>
Tristan.


diff --git a/qemu-doc.texi b/qemu-doc.texi
index b2fa19e..73c133a 100644
--- a/qemu-doc.texi
+++ b/qemu-doc.texi
@@ -739,6 +739,15 @@ vde_switch -F -sock /tmp/myswitch
 qemu linux.img -net nic -net vde,sock=/tmp/myswitch
 @end example
 
address@hidden -net dump[,address@hidden,address@hidden,address@hidden
+Dump network traffic on VLAN @var{n} to file @var{file} (@file{qemu.tcpdump} by
+default).  At most @var{len} bytes (64 by default) by packet are stored.  The
+dump can be analyzed with tools such as tcpdump.
+
+For better results you'd better to use this option before the @samp{-net user}
+one as the user stack may send replies before the initial packet was propagated
+to all receivers.
+
 @item -net none
 Indicate that no network devices should be configured. It is used to
 override the default configuration (@option{-net nic -net user}) which

diff --git a/net.c b/net.c
index 8d9b3de..872a17e 100644
--- a/net.c
+++ b/net.c
@@ -1064,6 +1064,75 @@ static int net_vde_init(VLANState *vlan, const char 
*model,
 }
 #endif
 
+static VLANClientState *tcpdump_vc;
+static FILE *tcpdump_file;
+static int tcpdump_caplen;
+
+#define TCPDUMP_MAGIC          0xa1b2c3d4
+
+struct pcap_file_hdr {
+    uint32_t magic;
+    uint16_t version_major;
+    uint16_t version_minor;
+    int32_t thiszone;
+    uint32_t sigfigs;
+    uint32_t snaplen;
+    uint32_t linktype;
+};
+
+struct pcap_sf_pkthdr {
+    struct {
+       int32_t tv_sec;
+       int32_t tv_usec;
+    } ts;
+    uint32_t caplen;
+    uint32_t len;
+};
+    
+static void tcpdump_receive(void *opaque, const uint8_t *buf, int size)
+{
+    struct pcap_sf_pkthdr hdr;
+    int64_t ts = muldiv64 (qemu_get_clock(vm_clock),1000000, ticks_per_sec);
+    int caplen = size > tcpdump_caplen ? tcpdump_caplen : size;
+
+    hdr.ts.tv_sec = ts / 1000000000LL;
+    hdr.ts.tv_usec = ts % 1000000;
+    hdr.caplen = caplen;
+    hdr.len = size;
+    fwrite(&hdr, sizeof(hdr), 1, tcpdump_file);
+    fwrite(buf, caplen, 1, tcpdump_file);
+}
+
+static int net_tcpdump_init(VLANState *vlan, const char *device,
+                           const char *name, const char *filename, int len)
+{
+    struct pcap_file_hdr hdr;
+
+    tcpdump_file = fopen(filename, "wb");
+    if (!tcpdump_file) {
+       fprintf(stderr, "-net dump: can't open %s\n", filename);
+       exit(1);
+    }
+
+    tcpdump_caplen = len;
+
+    hdr.magic = TCPDUMP_MAGIC;
+    hdr.version_major = 2;
+    hdr.version_minor = 4;
+    hdr.thiszone = 0;
+    hdr.sigfigs = 0;
+    hdr.snaplen = tcpdump_caplen;
+    hdr.linktype = 1;
+
+    fwrite(&hdr, sizeof(hdr), 1, tcpdump_file);
+
+    tcpdump_vc = qemu_new_vlan_client(vlan, device, name,
+                                     tcpdump_receive, NULL, NULL);
+    snprintf(tcpdump_vc->info_str, sizeof(tcpdump_vc->info_str),
+            "tcpdump to %s (len=%d)", filename, len);
+    return 0;
+}
+
 /* network connection */
 typedef struct NetSocketState {
     VLANClientState *vc;
@@ -1701,6 +1770,18 @@ int net_client_init(const char *device, const char *p)
        ret = net_vde_init(vlan, device, name, vde_sock, vde_port, vde_group, 
vde_mode);
     } else
 #endif
+    if (!strcmp(device, "dump")) {
+       int len = 64;
+        if (get_param_value(buf, sizeof(buf), "len", p) > 0) {
+            len = strtol(buf, NULL, 0);
+       }
+
+        if (!get_param_value(buf, sizeof(buf), "file", p)) {
+           strcpy(buf, "qemu.tcpdump");
+        }
+        vlan->nb_host_devs++;
+        ret = net_tcpdump_init(vlan, device, name, buf, len);
+    } else
     {
         fprintf(stderr, "Unknown network device: %s\n", device);
         if (name)

diff --git a/vl.c b/vl.c
index 3676537..69dbe63 100644
--- a/vl.c
+++ b/vl.c
@@ -3943,6 +3943,8 @@ static void help(int exitcode)
            "                Use group 'groupname' and mode 'octalmode' to 
change default\n"
            "                ownership and permissions for communication 
port.\n"
 #endif
+           "-net dump[,vlan=n][,file=f][,len=n]\n"
+           "                dump traffic on vlan 'n' to file 'f' (max n bytes 
per packet)\n"
            "-net none       use it alone to have zero network devices; if no 
-net option\n"
            "                is provided, the default is '-net nic -net user'\n"
 #ifdef CONFIG_SLIRP