On Wed, Sep 17, 2008 at 10:42:00AM +0100, Daniel P. Berrange wrote:
On Tue, Sep 16, 2008 at 04:45:09PM -0400, Ben Guthro wrote:
Hi,
We're finding that we are going to be needing the cpu flags (as reported in /proc/cpuinfo) ..specifically to find out if we are a vmx enabled machine.
So - off I went looking into this for a patch to submit upstream. Unfortunately, I ran into some questions which need answering before I really proceed with this
It seems to me that this info would best be parsed in src/nodeinfo.c This is where other cpuinfo things are parsed...and stored in the nodeinfo struct Perhaps we store this as a bitmask encoded int, as defined in /usr/include/asm/cpufeature.h and tack this onto the end of sad struct.
My concern is that adding to the nodeinfo struct breaks the API - such that the structs will be different sizes between versions.
Would it be possible to hack around this? For example you could use a unused bit of the old structure to set a flag for 'new-type-of-struct'. The old libvirt would ignore it, the new one would look for it. For example if it was an int enty and it was used as a flag entry wherein only 4 bits would be used, you could use the 5th bit that would tell it: "this is version 2 of the struct" and then the libvirt would cast it to the new struct which would contain the extra data-bits. This is how it is done in the RHEL kernels to work-around the kABI.