On Wed, Sep 17, 2008 at 08:44:09AM -0400, Konrad Rzeszutek wrote: > 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. I don't want us to rely on obscure tricks like that in public facing APIs. We have a very simple rule - everything in include/libvirt is append only. No existing APIs or structs can be changed. New APIs & structs can be added. Clear, easy to understand and risk free. > This is how it is done in the RHEL kernels to work-around the kABI. This is true, but the usage in RHEL kernels is internal API and isolated to RHEL-5's branch of the kernel. Regards, Daniel -- |: Red Hat, Engineering, London -o- http://people.redhat.com/berrange/ :| |: http://libvirt.org -o- http://virt-manager.org -o- http://ovirt.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: GnuPG: 7D3B9505 -o- F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 9505 :| -- Libvir-list mailing list Libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list