Re: [libvirt] [PATCH v2 1/4] config: Introduce <migration> for SPICE graphics

On Wed, Sep 19, 2012 at 03:26:49PM +0200, Michal Privoznik wrote: > On 15.09.2012 17:10, Daniel P. Berrange wrote: >> On Fri, Sep 14, 2012 at 05:23:16PM -0600, Eric Blake wrote: >>> [adding qemu] >>> >>> On 09/14/2012 11:47 AM, Daniel P. Berrange wrote: >>>> On Fri, Sep 14, 2012 at 07:34:50PM +0200, Michal Privoznik wrote: >>>>> With this element users will control how SPICE >>>>> server behaves upon migration. For now, there's >>>>> just one attribute 'seamless' turning seamless >>>>> migration on/off/default. >>>> >>>> Ewww, no. This information is a related to a API operation, >>>> not the VM configuration. It should be either auto-detected >>>> by libvirt to the best compatible setting, or passed as a >>>> flag to the virDomainMigrate API call if auto-detection is >>>> not possible. >>> >>> But with the current qemu implementation, there's no way to know if the >>> destination supports this until after you've started the source, and the >>> current implementation in qemu is that you must declare the semantics at >>> the time you start qemu, not at the time you send the 'migrate' monitor >>> command. For libvirt autodetection to work without polluting the domain >>> XML, we'd need to be able to auto-detect at the time we start migration. >>> >>> This sounds like we need to enhance the 'migrate-set-capabilities' >>> command to enable or disable this feature on the fly, according to what >>> libvirt detects from the remote end, rather than hard-coding it to the >>> startup state of qemu on the source side. >> >> Hmm, my understanding of the QEMU flag was different. Based on >> the commit message: >> >> spice: adding seamless-migration option to the command line >> >> The seamless-migration flag is required in order to identify >> whether libvirt supports the new QEVENT_SPICE_MIGRATE_COMPLETED or not >> (by default the flag is off). >> New libvirt versions that wait for QEVENT_SPICE_MIGRATE_COMPLETED should turn on this flag. >> When this flag is off, spice fallbacks to its old migration method, which >> can result in data loss. >> >> >> This says to me that any libvirt which knows about the new >> SPICE_MIGRATE_COMPLETED event, should set the seamless-migration >> flag unconditionally, to indicate that it can handle the event >> and thus the new migration method. It says nothing about only >> setting this flag if the destination QEMU also supports it. >> As such, IMHO, we can & should set this flag unconditonally >> on all QEMUs we run which support it. >> >> If it turns out that this flag does indeed require that the >> destination QEMU also has the same setting, then IMHO this >> flag is a fatally flawed design. At time of starting any QEMU >> instance, we can't know whether the destination QEMU we want >> to migrate to will have the support or not. Compatibility >> checks of this kind can only be decided at time the migrate >> command is actually issued. >> >> >> Daniel >> > > From my investigation I was able to migrate between qemu where one had > seamless_migration=on and the other one didn't support such argument at > all. Literally, on source I've checked out 27af778828db9 (the last > commit in Yonit's patchset) on destination f5bb039c6d97e (the last > before the patchset). Then I've migrated and receive both event and flag > set in query-spice response. So I guess the design is okay. Oh, BTW, when you tested did you have an actual SPICE client connected and did it migrate ok ?

Daniel