Re: execute a user process in the kernel

From: Robert Watson (rwatson_at_freebsd.org)
Date: 09/24/04

  • Next message: Dag-Erling Smørgrav: "Re: execute a user process in the kernel" 
    Date: Fri, 24 Sep 2004 14:11:19 -0400 (EDT)
To: Dag-Erling Smørgrav <des@des.no>

    On Fri, 24 Sep 2004, Dag-Erling Smørgrav wrote:

    > execve(2) assumes you already have a process. You get a process by
    > forking another process. The only process we ever create from scratch
    > is init(8), and that takes a s**tload of work (see kern/init_main.c).
    > This is why we have stuff like nfsiod(8) which does nothing but provide
    > the kernel with a process context it can use for other stuff.
    >
    > You could, of course, write a kernel API for creating processes from
    > scratch. They'd still need a parent, but you can use init(8) (pid 1)
    > for that.

    Well, we have kproc/kthread APIs, but none of that is semantically
    compatible with the notion of execve(), which is a very user-centric
    concept ("replace the address space with a mapping of binary <x>"). You
    could fudge together a related notion, though, involving loadable kernel
    modules that have a main() routine run from a thread. That said, the
    notion of simply running user code in kernel (as has been pointed out) is
    fraught with peril, primarily because the kernel is basically one big
    program with many special requirements, and user applications are written
    with the assumption that they are the only program, not running in the
    context of another program.

    Robert N M Watson FreeBSD Core Team, TrustedBSD Projects
    robert@fledge.watson.org Principal Research Scientist, McAfee Research

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  • Next message: Dag-Erling Smørgrav: "Re: execute a user process in the kernel"

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