l4-hackers October 2018

l4-hackers@os.inf.tu-dresden.de

4 participants
4 discussions

Filesystem Architectures with L4Re and L4-Based Systems
by Paul Boddie 02 Dec '19

02 Dec '19

Hello, As this list can attest, I previously spent a bit of time diving into the way dynamic linking is supported by L4Re to get shared mode programs working. This turned out to have a relatively simple fix related to symbols employed by GCC- generated code. But during this exercise, I gained some familiarity with the way libraries are loaded, and this appears to involve the virtual filesystem support, with the loader perusing the filesystem to access libraries, and with these being provided as modules by the "rom" filesystem. Since then, I've spent some time looking at how files are provided by filesystems and accessed by code that uses the conventional C or POSIX library interfaces. It raises a few questions about why things are done in a particular way in L4Re, and which approaches are in use for other L4-based systems, especially those that seek to provide general-purpose, multi-user solutions. What I think I now understand about the virtual filesystem support in L4Re is as follows. The virtual filesystem itself is a "client-side" construct, meaning that it resides within any given program. That programs have their own view of a filesystem is not too different from what the documentation about systems like the Hurd describes and advocates, and I suppose it is a tempting approach because it gives each program the flexibility to be customised in this regard. However, it seems that beyond the internal "mount tree" representation, configuration of the namespace hierarchy is largely done using the L4Re namespace concept, with namespaces acting as directories, and non-namespace objects within the hierarchy interpreted as particular file types. Apart from the interpretation of namespaces as directories, it seems that for the most part, dataspaces are employed to be interpreted as file objects. I will admit that I didn't really look very hard at how different systems provide file access before now, but what surprised me slightly was the apparent lack of delegation in L4Re. As far as I can tell, on systems based on kernels like Linux, the open library function will employ a system call to delegate the matter of finding the file and obtaining a way of accessing it to the familiar monolithic-kernel-plus-filesystems arrangement. On more "exotic" systems (than Linux) like Minix 3 or the Hurd, it appears that delegation to a virtual filesystem server [1] or servers [2] occurs to mediate access to specific files. Some systems like Inferno and Plan 9 employ protocols [3] to formalise the client-server relationship. I had almost expected to find similar things in L4Re, but I could only confirm their absence after reviewing the various VFS abstractions. One thing I wonder about is whether the current L4Re approach is able to satisfactorily deal with filesystem content that needs to serve different user entities, with content having different permission and ownership rights. It seems that the filesystem logic has to be available as a library within a program, which is not necessarily a problem. But to avoid filesystem content being completely exposed to the discretion of user programs (reminiscent of the problems with early Network File System implementations), the library would need to call out to other entities, which doesn't appear to be done with the current L4Re abstractions. One could implement support for, say, the ext3 filesystem in a library, operating on a dataspace provided at some kind of mountpoint in a directory (with the directory being provided by a namespace, of course) but it would be like giving a user program access to a block device in a traditional Unix-like system. Are there any articles about the design of L4Re that might explain the motivations here? And are there any accessible-but-detailed articles about other microkernel-based systems and the way in which they structure their filesystem architectures? I looked around on the TU-Dresden site for materials, but I didn't immediately find anything obviously relevant. Paul [1] https://wiki.minix3.org/doku.php?id=developersguide:vfsinternals [2] https://www.gnu.org/software/hurd/hurd-talk.html#pat [3] http://doc.cat-v.org/inferno/4th_edition/styx

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FOSDEM 2019 - Microkernels developer room - CfP
by Sebastian Sumpf 12 Oct '18

12 Oct '18

FOSDEM 2019 - Microkernels and Component-based OSes devroom CALL FOR PARTICIPATION The developers of several free and open-source microkernel-based operating systems will meet at FOSDEM 2019 [1] in Brussels, Belgium and will share a developer room on Sunday February 03, 2019 [2]. The devroom is currently looking for content in the form of talks and activities related to the area of microkernel-, unikernel-, and componenent-based operating systems. Possible topics include, but are not limited to: * introduction of a specific OS or framework * design of subsystems and the general architecture of an OS * enabling support for hardware (architectures, device drivers) * used languages and tools * maintenance and testing * security and robustness * trends and challenges * use cases, experiences, lessons learned and demos Please use the Pentabarf [3] system to submit your proposals. You do not need to create a new account if you already have one. When in doubt, please use the devroom mailing list [4]. If you do not want to give a talk yourself, you may still send suggestions for what else you would like to see, or do in the devroom. Please send your suggestions to the mailing list. The deadline for your proposal is on December the 1st 2018. Make sure to include the following in your proposal: * title of your talk (will be printed in the FOSDEM booklet) * your full name (will be printed in the FOSDEM booklet) * a short abstract (one or two paragraphs) * duration of your talk (please, at least 25 and no longer than 55 min) The official devroom schedule (along with the accepted talks) will be announced on December the 15th on the devroom's mailing list and the speakers will be notified via e-mail. The schedule will also be published on the FOSDEM website. About FOSDEM FOSDEM is a two-day event organised by volunteers to promote the widespread use of free and open source software. Taking place in the beautiful city of Brussels (Belgium), FOSDEM is widely recognised as the best such conference in Europe. FOSDEM covers a wide spectrum of free and open source software projects, and offers a platform for people to collaborate. To this end, FOSDEM has set up developer rooms (devrooms) with network/internet connectivity and projectors where teams can meet and showcase their projects. Devrooms are a place for teams to discuss, hack and publicly present latest directions, lightning talks, news and discussions. Besides developer rooms, FOSDEM also offers main tracks, lightning talks, certification exams and project stands. Every year, FOSDEM hosts more than 5000 developers at the ULB Solbosch campus. Participation and attendance is totally free, though the organisers gratefully accept donations and sponsorship. No registration necessary. About the devroom Since the first Microkernel devroom in 2012 this devroom has been part of each following FOSDEM. By now it has become a somewhat institutionalized tradition for the micro kernel community to meet there; to this date over a dozen projects have participated in one way or another. Each of the projects face similar challenges but come up with partially different solutions. Therefore, the goal of the Microkernel devroom is to bring the various projects together, let them exchange ideas, cross-pollinate and socialize. Social events It also has become a habit that the microkernel projects dine together somewhere in Brussels. The year 2019 will not be any different, so there is going to be a microkernel family dinner on Saturday night. We try place a reservation, so we will inform you about the exact location and time later. Consult the FOSDEM web and other projects for additional social events such as the famous FOSDEM-organized Friday Beer Event and the FOSDEM-arranged free sightseeing tours for spouses. Important dates recap * 01.12.2018: Deadline for submissions * 15.12.2018: Schedule published and speakers notified of acceptance * 03.02.2019: The devroom takes places Links [1] http://fosdem.org [2] https://fosdem.org/2019/practical/transportation [3] https://penta.fosdem.org/submission/FOSDEM19 [4] https://lists.fosdem.org/listinfo/microkernel-devroom See you all at FOSDEM!

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Information on implementing L4
by John 05 Oct '18

05 Oct '18

Hi all. I've been looking at Google and Wikipedia for information about L4, and it's fairly thin. I've come up with that L4 has read and write registers and performs IPC by fixed-length registers, with all actions synchronous (I guess that means you send a message and block until the target thread reads the message). Is there a more concrete document anywhere about implementing an L4 microkernel and what makes it L4? I'm surveying the field at the moment and looking at all the advances made in computer software—security, managed language runtimes, hypervisors, real-time OS—and trying to project the possibilities for a next-generation operating system. There's enough divergence that a rewrite from scratch might make sense; and besides, I've drawn up a method for getting a self-hosting CLR running with only anonymous memory allocation and VFS file page mapping, along with a method of getting the CLR to self-host and getting it up and running before an actual OS kernel. In other words: it's readily-achievable to write a CLR in C#, get it running on itself before the kernel comes up, then load a kernel, VMM, VFS, ABI, scheduler, and so forth—all written in C#, compiled to CIL, and totally independent of the hardware architecture underneath—and then throw away the loader and bring up init. The kernel would need to use an abstract factory model to do common tasks which require hardware-specific code, and the CLR would need to load an assembly with a concrete factory for the particular hardware and a few built-in native assembly calls; but it's doable. This is all theoretical at the moment, and I want to explore the particular edges a little to see what I find out.

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OS/Microkernel Engineers Wanted!
by Osman Ismael 02 Oct '18

02 Oct '18

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l4-hackers October 2018