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[[meta title="Porting the Hurd to L4: Hurd/L4"]]

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, 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]].


Development was done in the `hurd-l4` module of the Hurd CVS repository.  The
`doc` directory contains a design document that is worth reading for anyone who
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.