On Wed, Dec 26, 2001 at 12:19:32PM -0500, Javier Guerra wrote: > >Nonsense. If you're doing without a filesystem, you can't do userland > >_at all_. > > it might be nonsense (in most cases) to do everything in kernelspace, > but that wasn't what i'd like. it's not hard to imagine a kernel > that creates proceses out of ROM, or the network, or a serial port; It actually is quite hard to imagine. How would you like to load those processes from the network? Tftp is policy, so it belongs to userland. Same goes for serial port: zmodem is policy. BTW, the easiest way to create processes out of a ROM is to have a filesystem on that ROM (cramfs, JFFS2): no special tricks needed, runs out of the box. I know that a lot of kernel initialisation policy is currently still done in the kernel (bootp, NFS root, ACPI, etc.), but one of the most interesting new things happening right now in linux-2.5 is that a lot of the initialisation stuff is moved to userland. The kernel image will contain a cpio image of the rootfs that contains a couple of binaries that will do things like ACPI table parsing, bootp protocol, NFS root, ask the user for the ramdisk floppy, etc. Why all this? Because we want to get rid of the policy in the kernel, and we can get rid of a lot of special casing and other crap in the kernel code. > and these processes could ran in userland, and talk to each other via > IPC Guess what... IPC needs a filesystem as well (see Documentation/filesystems/tmpfs.txt). > but in UNIX, the mantra "everything is a file" presupones a > filesystem. I wouldn't call it a mantra, it's more like one of the UNIX design philosophies. But yes, a UNIX kernel needs a filesystem to do something useful at all. > in QNX, "everything is a message" doesn't. You're comparing apples with polar bears. As a micro kernel, QNX uses message passing to let the separate subsystems within the kernel communicate with each other (Linux uses direct function calls). What we were discussing is how a UNIX-like operating system (and a micro kernel can behave like that, see Minix and GNU HURD) could work at all without a filesystem for userland processes. > you can see a working example, the PalmPilot doesn't have a filesystem! PalmOS somehow has to index the contents of the RAM (programs and user records). It might be hidden to the user, but that index actually is a filesystem. Erik -- J.A.K. (Erik) Mouw, Information and Communication Theory Group, Faculty of Information Technology and Systems, Delft University of Technology, PO BOX 5031, 2600 GA Delft, The Netherlands Phone: +31-15-2783635 Fax: +31-15-2781843 Email: J.A.K.Mouw@its.tudelft.nl WWW: http://www-ict.its.tudelft.nl/~erik/ -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ IRC Channel: irc.openprojects.net / #kernelnewbies Web Page: http://www.kernelnewbies.org/
