Re: [Libvir] Request and proposition about hardware capabilities in virNodeInfo
On Wed, Nov 15, 2006 at 05:38:54PM +0100, Philippe Berthault wrote:
Hello,
To administrate virtual machines by using livbvirt, we need to known if
the underlying hardware platform supports hvm (Intel-VT or AMD-V) or
not. Currently, this information is returned by the "xm info" command of
Xen in the "xen_caps" line but there is no equivalent in libvirt. So we
propose to add this information in libvirt API.
That's reasonnable, yes.
There is three possibilities for doing that:
1) Add one or several fields in the virNodeInfo structure returned by
the virNodeGetInfo() function. These fields would be either strings such
as strings returned by "xm info" or either bit fields with one bit per
hardware capability.
<grin/>
on one hand it makes sense to have a larger _virNodeInfo
on the other hand doing so breaks the ABI (for virNodeGetInfo) in an
horrible way.
2) Add one or several specific functions returning a boolean value
for
each hardware capability we want to test.
One specific function using a string input for the name of the capability
int virNodeGetCapability(const char *name, int flags)
would allow simple queries in an ABI compatible way
3) Add a specific function which returns either a bit fields of all
the
hardware capabilities or a structure such as virNodeInfo but far more
complete.
Good point over 2) is that we can query a lot of parameter in one go.
but we are at risk of hitting 1), so I would use padding in the structure
(and maybe versioning informations within) to allow smooth evolution.
The problem with the proposition #1 is that the size of the
virNodeInfo
structure is changed. This implies for all libvirt users to recompile
their programs linked with libvirt to avoid a 'core dump' at the
execution. This is the reason why propositions 2 and 3 exist.
yup
NB: On an IA32 system, we can check flags in /proc/cpuinfo but on an
IA64 platform with Montecito processors, there is no information about
hardware capabilities in /proc/cpuinfo and the only way to known if the
hardware supports hvm is by using the 'xm info' command.
What is your opinion about these propositions ?
2 is okay for small things like checking VMX support. 3 potentially allows
to query far more.
I guess it depends on how much more informations we may want to extract
in the future, and how structured they may be.
2) looks a safe option, one may be interested in checking a given capability
quickly without having to create a structure etc ...
I guess others may have an opinion on this,
Daniel
--
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Daniel Veillard | virtualization library http://libvirt.org/
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