hurd/history/port_to_l4: Extend.

1 files changed, 29 insertions, 2 deletions

diff --git a/hurd/history/port_to_l4.mdwn b/hurd/history/port_to_l4.mdwn
index 6504f1b5..6a17d1ff 100644
--- a/hurd/history/port_to_l4.mdwn
+++ b/hurd/history/port_to_l4.mdwn
@@ -15,8 +15,11 @@ There was an effort to port the Hurd from [[microkernel/Mach]] to the
 [[L4_microkernel_family|microkernel/L4]], mostly lead by Marcus Brinkmann and
 Neal Walfield.  Even though there was progress, this port never reached a
 releasable state.  Eventually, a straight-forward port of the original Hurd's
-design wasn't deemed feasible anymore by the developers.  Read the [[critique]]
-and a [[ng/position_paper]].
+design wasn't deemed feasible anymore by the developers, partly due to them not
+cosidering L4 suitable for implementing a general-purpose operating system on
+top of it, and because of deficiencies in the original Hurd's design, which
+they discovered along their way.  Read the [[critique]] and a
+[[ng/position_paper]].
 
 By now, the development of Hurd/L4 has stopped.  However, Neal Walfield moved
 on to working on a newly designed kernel called [[microkernel/viengoos]].
@@ -27,3 +30,27 @@ Development was done in the `hurd-l4` module of the Hurd CVS repository.  The
 wishes to learn more about Hurd/L4.  Discussion have been held on the
 [[mailing_lists/l4-hurd]] mailing list, which is still the right place for
 [[next-generation_Hurd|ng]] discussions.
+
+
+One goal of porting the Hurd to L4 was to make the Hurd independend of Mach
+interfaces, to make it somewhat microkernel-agnostic.
+
+Mach wasn't maintained by its original authors anymore, so switching to a
+well-maintained current [[microkernel]] was expected to yield a more solid
+foundation for a Hurd system than the decaying Mach design and implementation
+was able to.
+
+L4 being a second-generation [[microkernel]] was deemed to provide for a faster
+system kernel implementation, especially in the time-critical [[IPC]] paths.
+Also, as L4 was already implemented for a bunch of different architectures
+(IA32, Alpha, MIPS; SMP), and the Hurd itself being rather archtecture-unaware,
+it was expected to be able to easily support more platforms than with the
+existing system.
+
+A design upon the lean L4 kernel would finally have moved devices drivers out
+of the kernel's [[TCB]].
+
+
+One idea was to first introduce a Mach-on-L4 emulation layer, to easily get a
+usable (though slow) Hurd-using-Mach-interfaces-on-L4 system, and then
+gradually move the Hurd servers to use L4 intefaces rather than Mach ones.