Marcus Brinkmann <Marcus.Brinkmann@ruhr-uni-bochum.de> writes: > On Sun, Aug 17, 2003 at 05:27:32PM +0100, Mark Wilkinson wrote: > > If the decision has been made to go to L4, IMHO work should have > > halted on Mach. > > People have halted on Mach long before L4 even entered the picture. > > > Forgive my ignorance, but why is L4 3-5 years away? > > L4 was released a month ago or so. But it is not a drop in > replacement for Mach. > > > If the decision has been made to move to a kernel structure that > > doesn't exist yet, that strikes me as an *interesting* decision. > > The L4 kernel is truly minimal. The Hurd depends on a couple of > features in Mach that simply don't exist in L4. The three core > issues: > > * Device drivers > * Virtual memory management > * A capability based IPC system > > L4 does not have any device drivers. Some people are working on a > new device driver infrastructure for GNU Hurd/L4, and drivers for > that infrastructure. It's a huge task, but it is also an interesting > challenge. Device drivers will be in user space and thus can be > multi-threaded. This allows to keep state about a device active in > the thread, and can greatly simplify a driver. > > L4 does not have any Virtual memory management, just some primitives > to recursively map pages into other address spaces. The physical > memory is provided directly to the user space. So we have to > implement a VM system. Neal has some great and ambitious ideas about > doing VM management locally in every task, instead of a global > server. This is a dramatic departure from traditional OS design > (even from Mach and the Hurd as it is now), and thus needs to be > fleshed out from scratch (there are some academic papers on it, but I > don't know of a production system doing it this way). > > L4 provides a minimal IPC system, that allows direct thread-to-thread > message sending. But it only gives a single protection primitive. > So it is not usable for a user space multi server system as the Hurd, > where untrusted communication is happen on a frequent basis. This is > why a more featureful capability system is needed. Instead doing it > in a central global server (like the port system in Mach is > centralized), we want, again, do it locally in each task. This seems > to be a new design to me, and I have worked on the protocols and data > srtuctures for that in the last weeks. I am currently working on an > implementation, which is needed very early in any porting effort to > L4. > > So you see, it is not about L4, but about glueing Hurd to L4. Mach > did a lot of things for us that L4 is not doing, and we take the > chance to try to more consequently implement the Hurd's fundamental > design ideas. Freedom to the users! Freedom to map your physical > memory as you want it, freedom to use the IPC policy you want, and > the freedom to have functional device drivers without getting them > approved by a kernel master geek ;) Amen ! zeDek -- "Ich habe kein Interesse an einem "Fan"-Forum, hatte aber erklaert, dass ich ein eigenes Forum z.B. mit dem Namen de.alt.wal begruessen wuerde." Norbert Harry Marzahn <71Vk5$7LbXB@nm01.vision.IN-BRB.DE>
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