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qemu: migration: Reactivate block nodes after migration if VM is left paused

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On incoming migration qemu doesn't activate the block graph nodes right
away. This is to properly facilitate locking of the images.

The block nodes are normally re-activated when starting the CPUs after
migration, but in cases (e.g. when a paused VM was migrated) when the VM
is left paused the block nodes are not re-activated by qemu.

This means that blockjobs which would want to write to an existing
backing chain member would fail. Generally read-only jobs would succeed
with older qemu's but this was not intended.

Instead with new qemu you'll always get an error if attempting to access
a inactive node:

 error: internal error: unable to execute QEMU command 'blockdev-mirror': Inactive 'libvirt-1-storage' can't be a backing child of active '#block052'

This is the case for explicit blockjobs (virsh blockcopy) but also for
non shared-storage migration (virsh migrate --copy-storage-all).

Since qemu now provides 'blockdev-set-active' QMP command which can
on-demand re-activate the nodes we can re-activate them in similar cases
as when we'd be starting vCPUs if the VM weren't left paused.

The only exception is on the source in case of a failed post-copy
migration as the VM already ran on destination so it won't ever run on
the source even when recovered.

Resolves: https://issues.redhat.com/browse/RHEL-78398
Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Jiri Denemark <jdenemar@redhat.com>
This commit is contained in:
Peter Krempa 2025-02-10 19:49:10 +01:00
parent d8f9cfb5e4
commit 2626fa0569
1 changed files with 52 additions and 3 deletions
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55
src/qemu/qemu_migration.c
View File

@ -220,6 +220,43 @@ qemuMigrationSrcStoreDomainState(virDomainObj *vm)
}
/**
* qemuMigrationBlockNodesReactivate:
*
* In case when we're keeping the VM paused qemu will not re-activate the block
* device backend tree so blockjobs would fail. In case when qemu supports the
* 'blockdev-set-active' command this function will re-activate the block nodes.
*/
static void
qemuMigrationBlockNodesReactivate(virDomainObj *vm,
virDomainAsyncJob asyncJob)
{
virErrorPtr orig_err;
qemuDomainObjPrivate *priv = vm->privateData;
int rc;
if (!virQEMUCapsGet(priv->qemuCaps, QEMU_CAPS_BLOCKDEV_SET_ACTIVE))
return;
VIR_DEBUG("re-activating block nodes");
virErrorPreserveLast(&orig_err);
if (qemuDomainObjEnterMonitorAsync(vm, asyncJob) < 0)
goto cleanup;
rc = qemuMonitorBlockdevSetActive(priv->mon, NULL, true);
qemuDomainObjExitMonitor(vm);
if (rc < 0)
VIR_WARN("failed to re-activate block nodes after migration of VM '%s'", vm->def->name);
cleanup:
virErrorRestore(&orig_err);
}
static void
qemuMigrationSrcRestoreDomainState(virQEMUDriver *driver, virDomainObj *vm)
{
@ -236,14 +273,17 @@ qemuMigrationSrcRestoreDomainState(virQEMUDriver *driver, virDomainObj *vm)
virDomainStateTypeToString(state),
virDomainStateReasonToString(state, reason));
if (preMigrationState != VIR_DOMAIN_RUNNING ||
state != VIR_DOMAIN_PAUSED ||
if (state == VIR_DOMAIN_PAUSED &&
reason == VIR_DOMAIN_PAUSED_POSTCOPY_FAILED)
return;
if (preMigrationState != VIR_DOMAIN_RUNNING ||
state != VIR_DOMAIN_PAUSED)
goto reactivate;
if (reason == VIR_DOMAIN_PAUSED_IOERROR) {
VIR_DEBUG("Domain is paused due to I/O error, skipping resume");
return;
goto reactivate;
}
VIR_DEBUG("Restoring pre-migration state due to migration error");
@ -266,7 +306,14 @@ qemuMigrationSrcRestoreDomainState(virQEMUDriver *driver, virDomainObj *vm)
VIR_DOMAIN_EVENT_SUSPENDED_API_ERROR);
virObjectEventStateQueue(driver->domainEventState, event);
}
goto reactivate;
}
return;
reactivate:
qemuMigrationBlockNodesReactivate(vm, VIR_ASYNC_JOB_MIGRATION_OUT);
}
@ -6795,6 +6842,8 @@ qemuMigrationDstFinishFresh(virQEMUDriver *driver,
if (*inPostCopy)
*doKill = false;
} else {
qemuMigrationBlockNodesReactivate(vm, VIR_ASYNC_JOB_MIGRATION_IN);
}
if (mig->jobData) {