On Fri, Feb 22, 2008 at 08:23:43AM -0500, Daniel Veillard wrote:
On Thu, Feb 21, 2008 at 02:36:10PM +0000, Daniel P. Berrange wrote:
- Else probe each registered driver in order until one succeeds
For the latter I think we could add a 'probe' method to the internal driver API table. Then we can just call 'probe' on each driver in turn until we find one which is available on the system.
At the same time it could be worth having a public API to 'detect drivers' which will call probe for each driver and return a list of all drivers which are available. This allows an app to easily ask libvirt what it supports
I actually started to look at that and while it sounds good 'on paper' it's a bit messy in practice, for example: - test driver: if compiled in, you would think the probe should return true, but as a result if trying an operation whyle no hypervisor is available you would end up doing it on the test driver instead of returning a failure, annoying - qemu driver: well QEmu is actually a driver for a potentially large set, KVM, QEmu for the current architecture, QEmu for emulated architectures. Would the probe return true if it finds /usr/bin/qemu-mips ? Or the KVM package may be present but would not be usable because the current kernel doesn't have a kvm module
Trying to be a bit systematic purely based on the driver model proves harder than expected, still worth trying but I prefer early feedback :-)
Okay, first patch enclosed, it seems to work for me: - grow the internal driver adding a const char *probe(void) entry point, it returns the URI to use to access the driver I did a bit of reformating of driver.h to maintain alignment of fields - define the entry point for OpenVZ, test, Xen (probe is arch specific as suggested for Solaris), and QEmu. In the last case I just checked /usr/bin/qemu and /usr/bin/qemu-kvm presence, and if non root return the session URI instead of the system one. - in do_open check first for LIBVIRT_DEFAULT_URI, if still empty, then go though the probes, ignore the test driver to avoid surprises and if Xen is found give it priority compared to others to maintain compatibility with previous behaviour - added a virFileExists to util.[ch] keeping code clean Daniel -- Red Hat Virtualization group http://redhat.com/virtualization/ Daniel Veillard | virtualization library http://libvirt.org/ veillard@redhat.com | libxml GNOME XML XSLT toolkit http://xmlsoft.org/ http://veillard.com/ | Rpmfind RPM search engine http://rpmfind.net/