On Mon, Apr 19, 2021 at 07:47:34PM +0100, Dr. David Alan Gilbert wrote: > * Daniel P. Berrangé ([email protected]) wrote: > > On Mon, Apr 19, 2021 at 06:15:56PM +0100, Daniel P. Berrangé wrote: > > > On Mon, Apr 19, 2021 at 06:11:47PM +0100, Dr. David Alan Gilbert wrote: > > > > * Eduardo Habkost ([email protected]) wrote: > > > > > I would make live migration policy an enum, just to make sure > > > > > we are explicit about the requirements: > > > > > > > > > > - UNKNOWN: this is the current state in QEMU 6.0, where we don't > > > > > really know what the user expects. > > > > > This can be the default on existing versioned machine types, > > > > > just for compatibility. > > > > > I suggest making this print warnings for every migration > > > > > blocker (like this patch does). > > > > > I suggest deprecating this behavior as soon as we can. > > > > > > > > > > - PREFERRED: try to make the VM migratable when possible, but > > > > > don't print a warning or error out if migration is blocked. > > > > > This seems to be the behavior expected by libvirt today. > > > > > > > > > > - NOT_NEEDED: live migration is not needed, and QEMU is free to > > > > > enable features that block live migration or change guest ABI. > > > > > We can probably make this the default on machine types that > > > > > never supported live migration. > > > > > > > > I suggest you could do this by adding: > > > > -warn-none-migratable > > > > -no-warn-none-migratable > > > > > > > > and then argue about defaults another time. > > > > > > If we're going to add new args, lets at least future proof our > > > approach with an extensible option that we can wire into QMP > > > too later > > > > > > -migratable none|preferred|required > > > > > > and letting us add extra key/value pairs to tune it if desired. > > > > Having said that, we potentially don't need a dedicated arg if we > > just make 'migratable=none|preferred|required' be a property of > > the machine type and hook everything off that > > I think my only difficulty with that is that I don't find any of those > 3 words 'obvious'.
Any suggestions of replacements for those 3 words? Would the descriptions below be enough to clarify their meaning in documentation? - NONE: live migration is not needed, and device or machine code is allowed to enable features that block live migration or change guest ABI. (Not implemented yet) - PREFERRED: machine and device code should try to make the VM migratable when possible, but won't emit a warning or error out if migration is blocked. (Current default behavior) - REQUIRED: live migration support is required, and adding a migration blocker will be an error. (Implemented today by --only-migratable) -- Eduardo
