Re: [PATCH] qemu: migration: don't open storage driver too early

On 10/12/20 5:05 AM, Daniel P. Berrangé wrote: > On Mon, Oct 12, 2020 at 10:55:52AM +0200, Michal Privoznik wrote: >> On 10/12/20 10:50 AM, Daniel P. Berrangé wrote: >>> On Sun, Oct 11, 2020 at 07:44:36PM -0400, Cole Robinson wrote: >>>> If storage migration is requested, and the destination storage does >>>> not exist on the remote host, qemu's migration support will call >>>> into the libvirt storage driver to precreate the destination storage. >>>> >>>> The storage driver virConnectPtr is opened too early though, adding >>>> an unnecessary dependency on the storage driver for several cases >>>> that don't require it. This currently requires kubevirt to install >>>> the storage driver even though they aren't actually using it. >>>> >>>> Push the virGetConnectStorage calls to right before the cases they are >>>> actually needed. >>> >>> This pushes the connection open attempts inside a loop body. So if the >>> VM has multiple disks, then we're going to be repeatedly opening and >>> closing the connection which is not desirable. >>> >>> I think we need a global connection across all disks, which is lazy >>> opened on first access. >> >> Doesn't virGetConnectStorage() cache the connection? > > Yes & no. > > You can call virSetConnectStorage(conn) to populate the cache with a > pre-opened connection. If you haven't done that, then a new connection > will be opened every time. The ltter is what this code will be doing. > What is the use case for not caching the connection by default?

virSetConnect* has very few users, but virGetConnect* is sprinkled in many places, including multiple uses in generic code in domain_conf.c. Can this be done as part of virGetConnect*?