Implement NetGDB(4)

NetGDB(4) is a component of a system using a panic-time network stack to
remotely debug crashed FreeBSD kernels over the network, instead of
traditional serial interfaces.

There are three pieces in the complete NetGDB system.

First, a dedicated proxy server must be running to accept connections from
both NetGDB and gdb(1), and pass bidirectional traffic between the two
protocols.

Second, the NetGDB client is activated much like ordinary 'gdb' and
similarly to 'netdump' in ddb(4) after a panic.  Like other debugnet(4)
clients (netdump(4)), the network interface on the route to the proxy server
must be online and support debugnet(4).

Finally, the remote (k)gdb(1) uses 'target remote <proxy>:<port>' (like any
other TCP remote) to connect to the proxy server.

The NetGDB v1 protocol speaks the literal GDB remote serial protocol, and
uses a 1:1 relationship between GDB packets and sequences of debugnet
packets (fragmented by MTU).  There is no encryption utilized to keep
debugging sessions private, so this is only appropriate for local
segments or trusted networks.

Submitted by:	John Reimer <john.reimer AT emc.com> (earlier version)
Discussed some with:	emaste, markj
Relnotes:	sure
Differential Revision:	https://reviews.freebsd.org/D21568

3 files changed, 12 insertions, 5 deletions

diff --git a/sys/conf/NOTES b/sys/conf/NOTES
index 7892a2391bc8..002d809eae5d 100644
--- a/sys/conf/NOTES
+++ b/sys/conf/NOTES
@@ -1038,13 +1038,17 @@ options 	TCP_SIGNATURE		#include support for RFC 2385
 # a smooth scheduling of the traffic.
 options 	DUMMYNET
 
+# The DEBUGNET option enables a basic debug/panic-time networking API.  It
+# is used by NETDUMP and NETGDB.
+options 	DEBUGNET
+
 # The NETDUMP option enables netdump(4) client support in the kernel.
 # This allows a panicking kernel to transmit a kernel dump to a remote host.
 options 	NETDUMP
 
-# The DEBUGNET option enables a basic debug/panic-time networking API.  It
-# is used by NETDUMP.
-options 	DEBUGNET
+# The NETGDB option enables netgdb(4) support in the kernel.  This allows a
+# panicking kernel to be debugged as a GDB remote over the network.
+options 	NETGDB
 
 #####################################################################
 # FILESYSTEM OPTIONS
diff --git a/sys/conf/files b/sys/conf/files
index d910a1f0ce17..e47fe27466cf 100644
--- a/sys/conf/files
+++ b/sys/conf/files
@@ -3546,6 +3546,7 @@ fs/tmpfs/tmpfs_subr.c 		optional tmpfs
 gdb/gdb_cons.c			optional gdb
 gdb/gdb_main.c			optional gdb
 gdb/gdb_packet.c		optional gdb
+gdb/netgdb.c			optional ddb debugnet gdb netgdb inet
 geom/bde/g_bde.c		optional geom_bde
 geom/bde/g_bde_crypt.c		optional geom_bde
 geom/bde/g_bde_lock.c		optional geom_bde
diff --git a/sys/conf/options b/sys/conf/options
index d9ea0a821cb3..0600bf52203b 100644
--- a/sys/conf/options
+++ b/sys/conf/options
@@ -319,10 +319,12 @@ NFS_ROOT	opt_nfsroot.h
 # SMB/CIFS requester
 NETSMB		opt_netsmb.h
 
-# Enable netdump(4) client support.
-NETDUMP 	opt_global.h
 # Enable debugnet(4) networking support.
 DEBUGNET 	opt_global.h
+# Enable netdump(4) client support.
+NETDUMP 	opt_global.h
+# Enable netgdb(4) support.
+NETGDB 		opt_global.h
 
 # Options used only in subr_param.c.
 HZ		opt_param.h