Re: [libvirt PATCH 7/7] qemu_migration: Implement VIR_MIGRATE_ZEROCOPY flag

On Thu, Jun 23, 2022 at 15:08:30 +0100, Daniel P. Berrangé wrote: > On Thu, Jun 23, 2022 at 03:58:12PM +0200, Jiri Denemark wrote: > > Resolves: https://gitlab.com/libvirt/libvirt/-/issues/306 > > > > Signed-off-by: Jiri Denemark <jdenemar(a)redhat.com&gt; > > --- > > src/qemu/qemu_migration.c | 21 +++++++++++++++++++++ > > src/qemu/qemu_migration.h | 1 + > > src/qemu/qemu_migration_params.c | 6 ++++++ > > src/qemu/qemu_migration_params.h | 1 + > > 4 files changed, 29 insertions(+) > > > > diff --git a/src/qemu/qemu_migration.c b/src/qemu/qemu_migration.c > > index 272f1b1b59..02a465f6cb 100644 > > --- a/src/qemu/qemu_migration.c > > +++ b/src/qemu/qemu_migration.c > > @@ -2634,6 +2634,12 @@ qemuMigrationSrcBeginPhase(virQEMUDriver *driver, > > } > > } > > > > + if (flags & VIR_MIGRATE_ZEROCOPY && !(flags & VIR_MIGRATE_PARALLEL)) { > > + virReportError(VIR_ERR_OPERATION_INVALID, "%s", > > + _("zero-copy is only available for parallel migration")); > > + return NULL; > > + } > > It is also not compatible with compression, or TLS. Yeah, no zero-copy when you need to transform the data in any way. I think QEMU provides a reasonable error message already. But since it mentions "multifd" while our flag is called "parallel", I decided to explicitly handle this case: internal error: unable to execute QEMU command 'migrate-set-capabilities': Zero copy only available for non-compressed non-TLS multifd migration Do you think I should explicitly check all flags instead?

> > diff --git a/src/qemu/qemu_migration_params.c b/src/qemu/qemu_migration_params.c > > index 4e83d8d8bd..cc66ed8229 100644 > > --- a/src/qemu/qemu_migration_params.c > > +++ b/src/qemu/qemu_migration_params.c > > @@ -94,6 +94,7 @@ VIR_ENUM_IMPL(qemuMigrationCapability, > > "multifd", > > "dirty-bitmaps", > > "return-path", > > + "zero-copy-send", > > ); > > Note the QEMU name was picked in case we later get zero copy > receive, as a separately enabled feature. The question is whether we need to do the same or if we can have a single zero copy which would enable the right one depending on the side of migration...