Six - User mode Linux 2.1 for Solaris sparc/x86

• Briefly, what is Six?

Six is Linux 2.1 "tweaked" to run as a user process on top of solaris 2.x. in other words, "a" linux which compiles and runs on solaris like any other user level application.


• And in some detail?

once compiled, Six is just another solaris executable - but the code it executes is that of a linux 2.1 kernel. the whole of the application lies in virtual memory like any other solaris executable; it mmaps a configurable amount of memory (default - 32M) which is its "ram". its "hard disk" is a solaris file that contains an ext2 file system. the "hardware clock" of Six is an unending stream of SIGALRMS, requested via a setitimer() call. any keyboard activity results comes in via a SIGPOLL. user programs are read in from the disk file, mapped and executed. each time the scheduler picks up a process to run, its mappings are restored. user programs request kernel services by issuing a SIGUSR1, which effectively is the "software interrupt'" of Six. the core of process switching is implemented via the solaris context() routines - setcontext, getcontext, swapcontext, and makecontext. As it might be obvious, Six is heavily inspired by "SMX" - Solaris user-mode-Minix. the debugging limitations of smx and the "complexities" of the popular, more real, original user mode linux were the prime reasons behind such an attempt.


• Ok so what is the idea?

idea is to have a "cute", or "toy", kernel that works, but yet can be "tossed" or "pushed" or "fiddled" around. In other words, to take an "industrial strength" kernel and make a toy out of it. obviously, such an application will find its uses/purposes to be entirely along educational lines.


• And so where can it be downloaded?

Here.

download it, gunzip it, untar it.

then do a "gmake symlinks".

and then a "gmake".


• Ok so what works?

there is around 140,000 lines of source code till now. the whole thing compiles and runs on both sparc and x86 versions of solarix 2.x. the whole of the kernel, mm, fs with ext2, terminal and keyboard drivers, hard disk driver, etc are done. a basic set of user level applications have been completed. compiling a new application and loading it into the "disk file" - say to debug a particular system call etc - is very easy. the entire range of system calls (almost), and a decent C library, is available to an application. a text screenshot of six booting up looks like this.


• And what does not?


• there is no support for any sort of "networking" yet. which means that, if one wants to debug say how the bind() or listen() system call works, or how the network driver runs - there is no way right now.
• some sort (hint: heavy) of a "code cleanup" needs to be done.
• x86 support is lagging quite a bit. Six compiles on x86, but runs with numerous bugs.
• more user applications, more function support in libc. right now the libc is a very thin layer over the system call wrapper library, which itself is ultra thin in the first place. a functional curses library would be another idea.
• various run time bugs and race conditions need to be fixed.

roughly - 80% done, 20% todo.


• suggestions/criticisms/bugs/abuses etc to?

motorbreathing@gmail.com