UML and VMI ... how does UML work?

UML and VMI ... how does UML work?

[John R Moser]

I've been googling around but can't find a good resource for technically how UML
works.  I'm thinking about specifically the task of implementing a
virtualization platform without kernel hooks... this lead me to dancing around
checking out existing technology and noticing claims that UML can run on an
unmodified kernel without special needs.

In short, I'm curious about how UML works because I'm interested in knowing if
it's theoretically possible to remove the UML code (i.e. compile it out) and
then boot a kernel within an application that gives it a VMI structure to ...
act exactly as UML.

I know, it's probably really hard to have an application with no kernel
assistance actually load a kernel and expose a VMI API to it in the first place;
I'm not interested in X can't happen because Y can't happen, I'm just interested
in understanding the field.

Re: UML and VMI ... how does UML work?

[Jeff Dike]

On Mon, May 19, 2008 at 11:58:40PM +0000, John R Moser wrote:
> I've been googling around but can't find a good resource for
> technically how UML works.  I'm thinking about specifically the task
> of implementing a virtualization platform without kernel
> hooks... this lead me to dancing around checking out existing
> technology and noticing claims that UML can run on an unmodified
> kernel without special needs.

There's nothing magic.  It turns out that the system call interface is
sufficient to virtualize an entire system, and UML is an existence
proof of that.  The major mappings are:
      system calls -> ptrace
      memory -> mmap, munmap, mprotect
      interrupts -> signals
      timer -> interval timer

> In short, I'm curious about how UML works because I'm interested in knowing if
> it's theoretically possible to remove the UML code (i.e. compile it out) and
> then boot a kernel within an application that gives it a VMI structure to ...
> act exactly as UML.

This paragraph is very unclear to me...

     	       	       Jeff

-- 
Work email - jdike at linux dot intel dot com