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diff --git a/history/port_to_l4.mdwn b/history/port_to_l4.mdwn new file mode 100644 index 00000000..b58c0d91 --- /dev/null +++ b/history/port_to_l4.mdwn @@ -0,0 +1,108 @@ +[[!meta copyright="Copyright © 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, +2009, 2010 Free Software Foundation, Inc."]] + +[[!meta license="""[[!toggle id="license" text="GFDL 1.2+"]][[!toggleable +id="license" text="Permission is granted to copy, distribute and/or modify this +document under the terms of the GNU Free Documentation License, Version 1.2 or +any later version published by the Free Software Foundation; with no Invariant +Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license +is included in the section entitled +[[GNU Free Documentation License|/fdl]]."]]"""]] + +[[!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]]. + +The idea of using L4 as a [[microkernel]] for a [[Hurd_system|hurd]] was +initially voiced in the [[Hurd_community|community]] by Okuji Yoshinori, who, +for discussing this purpose, created the [[mailing lists/l4-hurd]] mailing list +in November 2000. + +The project itself then was mostly lead by Marcus Brinkmann and Neal Walfield. +Even though there was progress -- see, for example, the +[[QEMU image for L4|hurd/running/qemu/image for l4]] -- 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 [[hurd/critique]] and a +[[hurd/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]]. + +Over the years, a lot of discussion have been held on the +[[mailing lists/l4-hurd]] mailing list, which today is still the right place +for [[next-generation Hurd|hurd/ng]] discussions. + +Development of Hurd/L4 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. + + +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. + + +Neal Walfield started the original Hurd/L4 port while at Karlsruhe in 2002. He +explains: + +> My intention was to adapt the Hurd to exploit L4's concepts and intended +> [[design_pattern]]s; it was not to simply provide a Mach +> [[compatibility_layer]] on top of L4. When I left Karlsruhe, I no longer had +> access to [[microkernel/l4/Pistachio]] as I was unwilling to sign an NDA. +> Although the specification was available, the Karlsruhe group only [released +> their code in May +> 2003](https://lists.ira.uni-karlsruhe.de/pipermail/l4ka/2003-May/000345.html). +> Around this time, Marcus began hacking on Pistachio. He created a relatively +> complete run-time. I didn't really become involved again until the second +> half of 2004, after I complete by Bachelors degree. + +> Before Marcus and I considered [[microkernel/Coyotos]], we had already +> rejected some parts of the Hurd's design. The +> [[open issues/resource management problems]] were +> what prompted me to look at L4. Also, some of the problems with +> [[hurd/translator]]s were already well-known to us. (For a more detailed +> description of the problems we have identified, see our [[hurd/critique]] in the +> 2007 July's SIGOPS OSR. We have also written a forward-looking +> [[hurd/ng/position paper]].) + +> We visited Jonathan Shapiro at Hopkins in January 2006. This resulted in a +> number of discussions, some quite influential, and not always in a way which +> aligned our position with that of Jonathan's. This was particularly true of +> a number of security issues. + +A lange number of discussion threads can be found in the archives of the +[[mailing lists/l4-hurd]] mailing list. + +> Hurd-NG, as we originally called it, was an attempt to articulate the system +> that we had come to envision in terms of interfaces and description of the +> system's structure. The new name was selected, if I recall correctly, as it +> clearly wasn't the Hurd nor the Hurd based on L4. + + +The source code is still available in [CVS module +`hurd-l4`](http://savannah.gnu.org/cgi-bin/viewcvs/hurd/hurd-l4/) (note that +this repository has in the beginning also been used for Neal's +[[microkernel/Viengoos]]). |