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authorMarkus Armbruster <armbru@redhat.com>2019-04-01 11:08:24 +0200
committerMarkus Armbruster <armbru@redhat.com>2019-04-02 13:38:05 +0200
commit811f8652712a4ec2ff73c2c5dca35581a25112a4 (patch)
tree4ec88472a9e1980ecfce118533cbfc700c5c0b0a /migration/tls.h
parent2fa23277d58ce7ec527541b3baf52894ded530cc (diff)
Revert "migration: move only_migratable to MigrationState"
This reverts commit 3df663e575f1876d7f3bc684f80e72fca0703d39. This reverts commit b605c47b57b58e61a901a50a0762dccf43d94783. Command line option --only-migratable is for disallowing any configuration that can block migration. Initially, --only-migratable set global variable @only_migratable. Commit 3df663e575 "migration: move only_migratable to MigrationState" replaced it by MigrationState member @only_migratable. That was a mistake. First, it doesn't make sense on the design level. MigrationState captures the state of an individual migration, but --only-migratable isn't a property of an individual migration, it's a restriction on QEMU configuration. With fault tolerance, we could have several migrations at once. --only-migratable would certainly protect all of them. Storing it in MigrationState feels inappropriate. Second, it contributes to a dependency cycle that manifests itself as a bug now. Putting @only_migratable into MigrationState means its available only after migration_object_init(). We can't set it before migration_object_init(), so we delay setting it with a global property (this is fixup commit b605c47b57 "migration: fix handling for --only-migratable"). We can't get it before migration_object_init(), so anything that uses it can only run afterwards. Since migrate_add_blocker() needs to obey --only-migratable, any code adding migration blockers can run only afterwards. This contributes to the following dependency cycle: * configure_blockdev() must run before machine_set_property() so machine properties can refer to block backends * machine_set_property() before configure_accelerator() so machine properties like kvm-irqchip get applied * configure_accelerator() before migration_object_init() so that Xen's accelerator compat properties get applied. * migration_object_init() before configure_blockdev() so configure_blockdev() can add migration blockers The cycle was closed when recent commit cda4aa9a5a0 "Create block backends before setting machine properties" added the first dependency, and satisfied it by violating the last one. Broke block backends that add migration blockers. Moving @only_migratable into MigrationState was a mistake. Revert it. This doesn't quite break the "migration_object_init() before configure_blockdev() dependency, since migrate_add_blocker() still has another dependency on migration_object_init(). To be addressed the next commit. Note that the reverted commit made -only-migratable sugar for -global migration.only-migratable=on below the hood. Documentation has only ever mentioned -only-migratable. This commit removes the arcane & undocumented alternative to -only-migratable again. Nobody should be using it. Conflicts: include/migration/misc.h migration/migration.c migration/migration.h vl.c Signed-off-by: Markus Armbruster <armbru@redhat.com> Message-Id: <20190401090827.20793-3-armbru@redhat.com> Reviewed-by: Igor Mammedov <imammedo@redhat.com>
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