Better document gif interface cloning intrastructure.

MFC After:	2 days

share/man/man4/gif.4

@@ -50,13 +50,17 @@ On
 .Nm
 can also tunnel ISO traffic over IPv[46] using EON encapsulation.
 .Pp
+Each
 .Nm
-interfaces are allocated at runtime using interface cloning.
+interface is created at runtime using interface cloning.
 This is
 most easily done with the
 .Xr ifconfig 8
 .Cm create
-command.
+command or using the
+.No gifconfig_ Ns Em interface
+variable in
+.Xr rc.conf 5 .
 .Pp
 To use
 .Nm ,

share/man/man5/rc.conf.5

@@ -604,6 +604,26 @@ Entries in
 are automatically appended to
 .Va network_interfaces
 for configuration.
+.It Va gif_interfaces
+.Pq Vt str
+Set to the list of
+.Xr gif 4
+tunnel interfaces to configure on this host.
+A
+.No gifconfig_ Ns Em interface
+variable is assumed to exist for each value of
+.Em interface .
+The value of this variable is used to configure the link layer of the
+tunnel according to the syntax of the
+.Cm tunnel
+option to
+.Xr ifconfig 8 .
+Additionaly, this option insures that each listed interface is created
+via the
+.Cm create
+option to
+.Xr ifconfig 8
+before attempting to configure it.
 .It Va ppp_enable
 .Pq Vt bool
 If set to

usr.sbin/gifconfig/gifconfig.8

@@ -91,12 +91,18 @@ Please note that it is very easy to create infinite routing loop,
 when you configure tunnel over same address family
 (e.g. IPv4-over-IPv4).
 .Pp
+Each
 .Xr gif 4
-interfaces are allocated at runtime using interface cloning.
-This is most easily done with the
+interface is created at runtime using interface cloning.
+This is
+most easily done with the
 .Xr ifconfig 8
 .Cm create
-command.
+command or using the
+.No gifconfig_ Ns Em interface
+variable in
+.Xr rc.conf 5 .
+.Xr
 .Sh EXAMPLES
 If you would like to configure IPv6 over IPv4
 (aka IPv6 in IPv4)