[uml-devel] Host kernel requirements for UML

[uml-devel] Host kernel requirements for UML

[Srivatsa Vaddagiri]

Hi,
	I am trying to get a quick answer for a question I had on UML.
As I understand, UML kernel makes use of host kernel's 
system call interface for its functionality. The questions is, does the
host kernel need to support *all* system calls or only a subset?
Does UML rely on /proc or any other such filesystems on host?
This is assuming that we want all possible features inside UML.


-- 


Thanks and Regards,
Srivatsa Vaddagiri,
Linux Technology Center,
IBM Software Labs,
Bangalore, INDIA - 560017


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Re: [uml-devel] Host kernel requirements for UML

[Jeff Dike]

On Wed, Aug 03, 2005 at 03:18:05PM +0530, Srivatsa Vaddagiri wrote:
> Hi,
> 	I am trying to get a quick answer for a question I had on UML.
> As I understand, UML kernel makes use of host kernel's 
> system call interface for its functionality. The questions is, does the
> host kernel need to support *all* system calls or only a subset?

Only a small subset.

> Does UML rely on /proc or any other such filesystems on host?

It looks at /proc/cpuinfo for some information about cmov and xmm support
on the processor.

				Jeff


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Re: [uml-devel] Host kernel requirements for UML

[Srivatsa Vaddagiri]

On Wed, Aug 03, 2005 at 10:39:57AM -0400, Jeff Dike wrote:
> On Wed, Aug 03, 2005 at 03:18:05PM +0530, Srivatsa Vaddagiri wrote:
> > Hi,
> > 	I am trying to get a quick answer for a question I had on UML.
> > As I understand, UML kernel makes use of host kernel's 
> > system call interface for its functionality. The questions is, does the
> > host kernel need to support *all* system calls or only a subset?
> 
> Only a small subset.

Thanks for the info. Is there any place where this subset is documented?
I was hoping to avoid looking at the unresoled symbols in UML binary to 
get this info!

-- 


Thanks and Regards,
Srivatsa Vaddagiri,
Linux Technology Center,
IBM Software Labs,
Bangalore, INDIA - 560017


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Re: [uml-devel] Host kernel requirements for UML

[Blaisorblade]

On Wednesday 03 August 2005 19:15, Srivatsa Vaddagiri wrote:
> On Wed, Aug 03, 2005 at 10:39:57AM -0400, Jeff Dike wrote:
> > On Wed, Aug 03, 2005 at 03:18:05PM +0530, Srivatsa Vaddagiri wrote:
> > > Hi,
> > > 	I am trying to get a quick answer for a question I had on UML.
> > > As I understand, UML kernel makes use of host kernel's
> > > system call interface for its functionality. The questions is, does the
> > > host kernel need to support *all* system calls or only a subset?

> > Only a small subset.

> Thanks for the info. Is there any place where this subset is documented?
Surely not. However, that *does not* yet include any fancy 2.6 features. Why 
are you looking for it? What are you going to port/run UML to?

> I was hoping to avoid looking at the unresoled symbols in UML binary to
> get this info!

That wouldn't work... how would you discover that recent UMLs require the host 
to support PTRACE_O_SYSGOOD (a ptrace option set through PTRACE_SETOPTIONS)?

That's only in recent ones and that support has been added in 2.4, so it's 
safe.

Hey, if you look at the man page, you won't find out what they're about, 
either!

For the core, it just requires (*heavily*) mmap and friends, standard 
filesystem support (possibly including largefile-aware versions) and signals. 
But it extends a lot for terminal support, for instance it will make the 
stdin/stdout terminal "raw" with cfmakeraw(3), probably through some IOCTLs, 
bundled inside libraries...
-- 
Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
Paolo Giarrusso, aka Blaisorblade (Skype ID "PaoloGiarrusso", ICQ 215621894)
http://www.user-mode-linux.org/~blaisorblade

	

	
		
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