ggsn: add support for GTP kernel data encapsulationosmo-ggsn

This patch adds the -g, --gtpnl=device option that allows you to
enable the GTP kernel tunneling mode in openggsn. You have to specify
the real downlink device that will be used to tunnel traffic, eg.

	-g=eth0

This means that the gtp0 device will be created and it will use eth0
as the real device to encapsulate packet coming from the Internet that
are addressed to the MS (so the tunnel devuce encapsulates these IP
packets in GTP packets when traveling to the SGSN).

Alternatively, you can also add this to the ggsn.conf configuration file:

	gtpnl eth0

The device has to be the real device that can route packets to the SGSN,
if you select the wrong device, the kernel routing code may not find a
way to reach the SSGN, you've been warned.

Therefore, if this option is set, the operational becomes the following:

1) A gtp0 device is created via rtnetlink and configure the socket
   encapsulation infrastructure in the kernel.
2) Whenever a PDP context is created, this adds the necessary tunnel
   configuration via genetlink GTP interface.
3) Whenever a PDP context is destroyed, this deletes the tunnel via
   genetlink GTP interface.
4) Destroy the gtp0 device if ggsn is stopped, including all of the
   existing tunnels.

You require the osmo-ggsn.git tree, which contains the kernel module
gtp.ko and the libgtpnl library that you have to compile and install.
Make sure you have loaded the gtp.ko kernel module before launching
the ggsn daemon using the kernel driver mode, otherwise you will get
a nice "operation not supported" error message ;-).

This patch also adds supports for "ipup" configuration option to invoke
an external script after the gtp0 device has been brought up. Typical
command to add the route to reach the MS behind the GGSN is required,
eg. ip route add 10.0.0.0/8 dev gtp0.

The (horrible) ggsn parser has been manually extended to support the
new configuration option. That code doesn't look nice, but it just
mimics what we already have there for consistency, please don't blame
me for that.

If you want to run in debugging mode, I suggest you to use:

	sudo ggsn -c ggsn.conf -f -d

Note that you do have to run openggsn as root to bring up the gtp0
device. You have to see this message that announce that the GTP kernel
mode is enabled.

openggsn[1106]: ggsn.c: 656: Using the GTP kernel mode (genl ID is 25)

This patch also automagically sets up route to reach MS from Internet
just like tun mode does. This is fundamental to get this working,
better don't leave to the admin, he may forget to add this route.

In this patch, I tried to encapsulate this new feature as much as
possible as Harald initially suggested.

To compile this feature, you have to pass --enable-gtp-kernel, ie.

./configire --enable-gtp-kernel

Otherwise, the code to interact with the gtp kernel part is not compiled.

1 files changed, 5 insertions, 3 deletions

diff --git a/ggsn/cmdline.h b/ggsn/cmdline.h
index f3636e8..2cb4791 100644
--- a/ggsn/cmdline.h
+++ b/ggsn/cmdline.h
@@ -1,6 +1,6 @@
 /** @file cmdline.h
  *  @brief The header file for the command line option parser
- *  generated by GNU Gengetopt version 2.22.6
+ *  generated by GNU Gengetopt version 2.22.5
  *  http://www.gnu.org/software/gengetopt.
  *  DO NOT modify this file, since it can be overwritten
  *  @author GNU Gengetopt by Lorenzo Bettini */
@@ -92,6 +92,9 @@ struct gengetopt_args_info
   char * logfile_arg;	/**< @brief Logfile for errors.  */
   char * logfile_orig;	/**< @brief Logfile for errors original value given at command line.  */
   const char *logfile_help; /**< @brief Logfile for errors help description.  */
+  char * gtpnl_arg;	/**< @brief GTP kernel support (default='eth0').  */
+  char * gtpnl_orig;	/**< @brief GTP kernel support original value given at command line.  */
+  const char *gtpnl_help; /**< @brief GTP kernel support help description.  */
   
   unsigned int help_given ;	/**< @brief Whether help was given.  */
   unsigned int version_given ;	/**< @brief Whether version was given.  */
@@ -112,6 +115,7 @@ struct gengetopt_args_info
   unsigned int apn_given ;	/**< @brief Whether apn was given.  */
   unsigned int qos_given ;	/**< @brief Whether qos was given.  */
   unsigned int logfile_given ;	/**< @brief Whether logfile was given.  */
+  unsigned int gtpnl_given ;	/**< @brief Whether gtpnl was given.  */
 
 } ;
 
@@ -129,8 +133,6 @@ struct cmdline_parser_params
 extern const char *gengetopt_args_info_purpose;
 /** @brief the usage string of the program */
 extern const char *gengetopt_args_info_usage;
-/** @brief the description string of the program */
-extern const char *gengetopt_args_info_description;
 /** @brief all the lines making the help output */
 extern const char *gengetopt_args_info_help[];