Re: [libvirt] [PATCH] Introduce a -libvirt-caps flag as a stop-gap
On Tue, Jul 27, 2010 at 10:55:03AM -0500, Anthony Liguori wrote:
Today libvirt parses -help output to attempt to enumerate
capabilities. This
is very broken and has led to multiple failures. Since libvirt is an important
management interface to QEMU, we need to do a better job giving them the ability
to detect what a QEMU executable supports. Right now, we keep fixing up help
output to appease it's parsing code but this is undesirable.
The Right Solution is to introduce a robust capabilities advertisement that
enumerates every feature we have. As with most Right Solutions, we don't have
mergable code today and it's unclear that we'll get there by the next release.
This patch introduces an incremental solution of just spitting out the handful
of capabilities libvirt is probing for today. This interface will need to
remain forever but can stop being updated once we have a Right Solution.
This isn't really workable because it only encodes the subset of things
that libvirt currently looks for. If someone comes along with a libvirt
patch for a new features that is already supported by QEMU, but isn't
in this simple output, we're stuck. Adding a one-off special case for
the 0.13 release that we know will be obsolete in 0.14, and obviously
can't be used in qemu < 0.12 is not really a worthwhile use of time.
libvirt has to keep supporting help parsing indefinitely for <= 0.12
releases & expects to support a new extensible & flexible approach for
qemu >= 0.14. Adding a special case that both libvirt & qemu have to
support indefinitely for 0.13 is not really very nice.
Daniel
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