Re: [XenAccess-devel] Difference between libvirt and XenAccess

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

> I like the idea of XenAccess and will take a look at the source  
> code, but
> there are some things not clear to me. Can somebody give me an  
> exmplanation?
>
> 1) What does XenAccess add to the libvirt functionality? As I saw  
> homepages
> of both they seemed quite similar.

XenAccess uses libvirt to obtain some basic information about the  
domain (e.g., version of the running kernel).  However, there are  
many differences between the two  libraries.  Libvirt provides access  
to specific high-level information about the domains.  Typically,  
this is the type of information that you can extract from the  
existing xen APIs.  The benefit of libvirt is that it will be capable  
of getting this same information from other virtualization systems as  
well.  On the other hand, XenAccess provides access to information  
about the OSes running inside each domain, and this information is  
not directly available through libvirt or any of the Xen libraries.

For example, right now XenAccess provides raw kernel memory access  
whereas libvirt provides a string that indicates the kernel version.   
Both are useful, they just have different uses...


> 2) The libvirt says: 'some very specific capabilities which are not  
> generic
> enough may not be provided as libvirt APIs'. Do you plan to use  
> some direct
> access to Xen via its API? (although it is pretty unstable now).

XenAccess does, in fact, make use of libxc.  This is the primary  
means for accessing memory in the other domains.  Libxc seems to be  
stable from my experience.


> 3) I use xen3.0.2 and the libvirt does not find dom 1 even there is  
> one
> according to xm list:
>
> root@elf:/home/koubat/source/xen/xenaccess/trunk/libxa/examples
> $ LD_PRELOAD=../libxenaccess.so ./module-list
> (0) (null)
> ERROR: Failed to find Domain 1
> ERROR: failed to get domain info for domain id 1
> ERROR: could not get kernel name for domain id 1
> ERROR: failed to lookup 'swapper_pg_dir' address
> failed to init XenAccess library: Bad address
>
> root@elf:/home/koubat/source/xen/xenaccess/trunk/libxa/examples
> $ xm list
> Name                              ID Mem(MiB) VCPUs State  Time(s)
> Domain-0                           0      744     2 r----- 16098.9
> ce                                 1      256     1 -b----   342.5

Ahhh, yes.  I believe that you're running into the same problem that  
someone else mentioned on this list a while back.  The next release  
(coming soon!) will have an updated README file that addresses this  
problem.  For now, I'll cut and paste the solution below.

----------
This looks like libvirt cannot connect to the Xend deamon.  I believe  
that
libvirt requires the xend-http-server to be enabled (which is no longer
the default setting for Xen).  Try adding or uncommenting the following
line from /etc/xen/xend-config.sxp:

(xend-http-server yes)

After the edit you will need to restart xend:

service xend restart
----------

I hope that helps...

Cheers,
bryan


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