[libvirt] [PATCH 3/4] Cache result of QEMU capabilities extraction

[Guido Günther]

Hi Daniel,
On Wed, Mar 05, 2014 at 05:53:53PM +0000, Daniel P. Berrange wrote:
[..snip..] 
> +    /* Discard if cache is older that QEMU binary */
> +    /* XXX must also compare to libvirtd timestamp  */
> +    if (sb.st_mtime < qemuCaps->mtime) {
I think looking at the mtime isn't sufficent here. Tools like dpkg set
the mtime to the time the package was built at not the installation time
so we might end up updating qemu but still having an mtime older than
the time the xml was created (same holds for downgrades to older qemu
versions) or are we simply requiring distributors to clean the cache
upon package upgrades (which would mandate using a trigger)?

Maybe we need to actually calculate the binaries checksum not only the
pathname? We could then simply just wipe alle checksums upon libvirt
upgrades to get rid of old entries.
Cheers,
 -- Guido