Re: [libvirt] [PATCH 2/6] Added public API to enable post-copy migration

On 2014-09-24 14:32, Jiri Denemark wrote: > On Tue, Sep 23, 2014 at 16:09:57 +0200, Cristian Klein wrote: >> Added a new `libvirt` migration flag `VIR_MIGRATE_POSTCOPY` and the >> necessary code to pass this flag to qemu as migration capability. >> >> Signed-off-by: Cristian Klein <cristian.klein(a)cs.umu.se&gt; >> --- >> include/libvirt/libvirt.h.in | 1 + >> src/libvirt.c | 7 +++++++ >> src/qemu/qemu_migration.c | 43 +++++++++++++++++++++++++++++++++++++++++++ >> src/qemu/qemu_migration.h | 3 ++- >> 4 files changed, 53 insertions(+), 1 deletion(-) >> >> diff --git a/include/libvirt/libvirt.h.in b/include/libvirt/libvirt.h.in >> index 6371b7b..bdc33c6 100644 >> --- a/include/libvirt/libvirt.h.in >> +++ b/include/libvirt/libvirt.h.in >> @@ -1225,6 +1225,7 @@ typedef enum { >> VIR_MIGRATE_ABORT_ON_ERROR = (1 << 12), /* abort migration on I/O errors happened during migration */ >> VIR_MIGRATE_AUTO_CONVERGE = (1 << 13), /* force convergence */ >> VIR_MIGRATE_RDMA_PIN_ALL = (1 << 14), /* RDMA memory pinning */ >> + VIR_MIGRATE_POSTCOPY = (1 << 15), /* enable (but don't start) post-copy */ >> } virDomainMigrateFlags;

>> @@ -3580,6 +3619,10 @@ qemuMigrationRun(virQEMUDriverPtr driver, >> if (flags & VIR_MIGRATE_RDMA_PIN_ALL && >> qemuMigrationSetPinAll(driver, vm, >> QEMU_ASYNC_JOB_MIGRATION_OUT) < 0) >> + >> + if (flags & VIR_MIGRATE_POSTCOPY && >> + qemuMigrationSetPostCopy(driver, vm, >> + QEMU_ASYNC_JOB_MIGRATION_OUT) < 0) >> goto cleanup; >> >> if (qemuDomainObjEnterMonitorAsync(driver, vm, > > I'd expect similar thing would need to be done in the Prepare phase on > destination... However, if destination does not need to set the > capability, we at least need to check if destination QEMU supports it > and report failure from Prepare if it doesn't. And the > QEMU_ASYNC_JOB_MIGRATION_IN branch in qemuMigrationSetPostCopy would be > unreachable in that case. It's up to the source qemu (through the migration protocol) to activate post-copy on the destination qemu. So there are no other steps to be done on the source. I have mixed feelings about having libvirt check the necessary capability on the destination. Personally, I would prefer qemu to return an error like "post-copy unavailable" when the "migrate" command is issued, as there might be more factors that influence the availability of post-copy. For example, it's not sufficient for the destination qemu to support post-copy, but the destination kernel also needs userfault support.