migration: improve documentation of postcopy-ram
This capability must have the same value on both source and destination,
otherwise migration fails (commit 875fcd013ab6 "migration: incoming
postcopy advise sanity checks").
Let's write it down in various places where postcopy-ram is documented.
Signed-off-by: Greg Kurz <groug@kaod.org>
Message-Id: <151801810352.29167.4832480228518630626.stgit@bahia.lan>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
diff --git a/docs/devel/migration.rst b/docs/devel/migration.rst
index bf97080..9d1b765 100644
--- a/docs/devel/migration.rst
+++ b/docs/devel/migration.rst
@@ -387,8 +387,8 @@
Enabling postcopy
-----------------
-To enable postcopy, issue this command on the monitor prior to the
-start of migration:
+To enable postcopy, issue this command on the monitor (both source and
+destination) prior to the start of migration:
``migrate_set_capability postcopy-ram on``
diff --git a/hmp-commands.hx b/hmp-commands.hx
index 15620c9..d26eb41 100644
--- a/hmp-commands.hx
+++ b/hmp-commands.hx
@@ -1041,7 +1041,8 @@
.params = "",
.help = "Followup to a migration command to switch the migration"
" to postcopy mode. The postcopy-ram capability must "
- "be set before the original migration command.",
+ "be set on both source and destination before the "
+ "original migration command .",
.cmd = hmp_migrate_start_postcopy,
},
diff --git a/qapi/migration.json b/qapi/migration.json
index 4cd3d13..7f465a1 100644
--- a/qapi/migration.json
+++ b/qapi/migration.json
@@ -327,8 +327,10 @@
# to speed up convergence of RAM migration. (since 1.6)
#
# @postcopy-ram: Start executing on the migration target before all of RAM has
-# been migrated, pulling the remaining pages along as needed. NOTE: If
-# the migration fails during postcopy the VM will fail. (since 2.6)
+# been migrated, pulling the remaining pages along as needed. The
+# capacity must have the same setting on both source and target
+# or migration will not even start. NOTE: If the migration fails during
+# postcopy the VM will fail. (since 2.6)
#
# @x-colo: If enabled, migration will never end, and the state of the VM on the
# primary side will be migrated continuously to the VM on secondary
@@ -742,8 +744,8 @@
# @migrate-start-postcopy:
#
# Followup to a migration command to switch the migration to postcopy mode.
-# The postcopy-ram capability must be set before the original migration
-# command.
+# The postcopy-ram capability must be set on both source and destination
+# before the original migration command.
#
# Since: 2.5
#
