net: Add support for capturing VLANs (Jan Kiszka)

This patch is derived from Tristan Gingold's patch. It adds a new VLAN
client type that writes all traffic on the VLAN it is attached to into a
pcap file. Such a file can then be analyzed offline with Wireshark or
tcpdump.

Besides rebasing and some minor cleanups, the major differences to the
original version are:
 - support for enabling/disabling via the monitor (host_net_add/remove)
 - no special ordering of VLAN client list, qemu_send_packet now takes
   care of properly ordered packets
 - 64k default capturing limit (I hate tcpdump's default)

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>


git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@7200 c046a42c-6fe2-441c-8c8c-71466251a162

qemu-options.hx

@@ -745,6 +745,8 @@ DEF("net", HAS_ARG, QEMU_OPTION_net, \
     "                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")
 STEXI
@@ -865,6 +867,11 @@ vde_switch -F -sock /tmp/myswitch
 qemu linux.img -net nic -net vde,sock=/tmp/myswitch
 @end example
 
+@item -net dump[,vlan=@var{n}][,file=@var{file}][,len=@var{len}]
+Dump network traffic on VLAN @var{n} to file @var{file} (@file{qemu-vlan0.pcap} by default).
+At most @var{len} bytes (64k by default) per packet are stored. The file format is
+libpcap, so it can be analyzed with tools such as tcpdump or Wireshark.
+
 @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