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DragonFly users List (threaded) for 2006-10
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Re: Xen vs VMware

From: Matthew Dillon <dillon@xxxxxxxxxxxxxxxxxxxx>
Date: Wed, 18 Oct 2006 13:37:26 -0700 (PDT)

:Possibly offtopic for this thread, but:
:Will the approach your taking with DragonFly allow for quickly and
:easily migrating the virtualized kernels between machines?
:Also, what about the possibility of running your userland kernels
:under other operating systems?  One of the advantages that Xen and
:VMWare has is that you CAN run multiple operating systems when you are
:forced to.

    I think its possible, but those other operating systems would still
    have to implement the virtualization system calls and mmap support.
    It isn't possible to run a kernel as a userland process without them
    because the kernel would not be able to manage the VM spaces for
    its own 'user' processes (from the point of view of the virtual kernel).

    It would be possible to make this into a defacto standard.  The actual
    work involved isn't all that great... the hard part is switching
    between VM spaces and managing the execution contexts... which is the
    part I'm working on now.

	* Implement specialized mmap() operations that allow manipulation 
	  of managed VM spaces instead of the calling process's VM space.

	* Implement switching to the calling process's VM space (in order
	  to run a managed VM space), then switching back if a signal
	  ocurs or the managed VM space takes a page-fault, trap, or
	  makes a system call.  NOT DONE.

	* Implement a build for the virtualized kernel itself that
	  links into a standard user program binary, plus drivers
	  that emulate network, disk, and other resources.  NOT DONE.


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