On 07/09/2012 06:10 AM, Peter Maydell wrote: > On 9 July 2012 13:07, Eric Blake <ebl...@redhat.com> wrote: >> That is, we are filtering based on the explicit presence of a literal >> '?' in the help output to determine whether we can further filter based >> on '-device device,?' queries without confusing qemu or libvirt; >> changing the 'help' output means that old libvirt with new qemu won't >> run the extra queries (as if it had been targeting qemu 0.12.x), even >> though the older spelling of the query would still work. >> >> If that is not a concern (that is, if you are willing to state that use >> of newer qemu is intended to be coupled with newer libvirt that has been >> taught to use 'help' instead of '?'), then this patch is probably fine. > > My personal position would be that people who parse -help > output deserve to get bitten, but I don't get to make that > call :-)
Obviously, newer libvirt can just proceed to try '-device device,help' rather than attempting to parse -h output in the first place (that is, making this change will not cause undue grief to libvirt 0.10.0, because it's a very short patch to teach libvirt.git to parse this new scheme, even without relying on -h output). That is, my concern is not about what future libvirt will be fixed to do, but about the existing interaction of old libvirt with qemu (libvirt 0.9.13 + qemu 1.2 would fail to take full advantage of the qemu 1.2 features because of the change in the -h output that libvirt 0.9.13 was hard-coded to expect). And yes, I agree that libvirt has been bitten more than once because it tries to parse unstable -h output, but that is only because qemu has never provided anything more stable and more machine-parseable than -h output, even though the topic has come up several times in the past. For example, we still don't have a way to run 'query-commands' to see what the QMP monitor will support without first creating a dummy guest. -- Eric Blake ebl...@redhat.com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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