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

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.