Re: [XenAccess-devel] Towards HVM support

[Bryan D. P. <br...@th...>]

> I previously reported on this list that xenaccess-0.1 with  
> libvirt-0.1.1 did
> not work with Xen HVM guests.  Here is the error it generated at  
> the time:

Thanks for continuing to look into this :-)

> # ./run ./module-list 8
> ERROR: failed to lookup 'swapper_pg_dir' address
> failed to init XenAccess library: Bad address
>
>
> Now we're getting into stuff I can't easily understand.  I have no  
> idea if
> an how we're getting a hold of the guest's System.map-2.6.17 file.   
> And if
> we are, I don't know if or how we're getting the address for  
> swapper_pg_dir.

The error that you are getting is (most likely) because XenAccess  
cannot find the System map file.  Looking at the xml output that you  
provided, it looks as if libvirt doesn't have guest kernel  
information for an HVM domain.  Normally, XenAccess would use this  
information to guess the location of the System map file.  However,  
without this information, it won't find the System map file.

Note: here's the precise list of potential causes for that error  
message in what I believe is the order of likelihood for each error  
-- most likely first (Note to self, I should probably enable more  
descriptive error messages!):

* cannot find system map file
* cannot find 'swapper_pg_dir' symbol in the System map file
* cannot allocate enough memory to look for the symbol in the System  
map file

One question, for HVM domains do you still boot off a kernel stored  
in dom0?  If so, I wonder why the kernel info isn't included in  
libvirt's output.  If not, then we may have to manually install the  
System map file into dom0 and find some way to point XenAccess to the  
appropriate file.


> I'm not looking for a general solution just yet.  I simply want to
> proof-of-concept the ability to get module lists from an HVM.   
> Bryan, can
> you give me any ideas on how to proceed?  I'm attaching an .rtf  
> that, if
> opened in MS Word, compares the xml formats for paravirtualized and  
> hvms,
> for what it's worth.  Oh, and thanks for version 0.2!

I think that the first step is to think about the question that I  
asked above.  We need to get access to the correct System map file  
for the HVM domain.  It appears that my normal way of getting that  
information may not work for HVM domains.

Once we have the System map file, we can see where we are at :-)   
But, I'm hopeful that the critical functions that I use from Xen will  
behave the same in HVM domains.  If that turns out to be the case,  
then we are very close to getting this working.

Cheers,
bryan


-
Bryan D. Payne
Graduate Student, Computer Science
Georgia Tech Information Security Center
http://www.bryanpayne.org