rfork(2): Discourage rfork_thread-like approaches.

Calling rfork_thread(3) does not interoperate with pthreads and global state
is not properly protected.

Remove the BUGS section suggesting LinuxThreads entirely. With the current
pthread library libthr, all threads are kernel-level entities so there seems
little reason to use LinuxThreads.

lib/libc/sys/rfork.2

@@ -5,7 +5,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd May 14, 2007
+.Dd March 15, 2011
 .Dt RFORK 2
 .Os
 .Sh NAME
@@ -80,6 +80,7 @@ the new process to run on the provided stack.
 See
 .Xr rfork_thread 3
 for information.
+Note that a lot of code will not run correctly in such an environment.
 .It Dv RFSIGSHARE
 If set, the kernel will force sharing the sigacts structure between the
 child and the parent.
@@ -171,24 +172,9 @@ There is insufficient swap space for the new process.
 .Xr intro 2 ,
 .Xr minherit 2 ,
 .Xr vfork 2 ,
+.Xr pthread_create 3 ,
 .Xr rfork_thread 3
 .Sh HISTORY
 The
 .Fn rfork
 function first appeared in Plan9.
-.Sh BUGS
-.Fx
-does not yet implement a native
-.Fn clone
-library call, and the current pthreads implementation does not use
-.Fn rfork
-with RFMEM.
-A native port of the linux threads library,
-.Pa /usr/ports/devel/linuxthreads ,
-contains a working
-.Fn clone
-call that utilizes RFMEM.
-The
-.Xr rfork_thread 3
-function can often be used instead of
-.Fn clone .