From: Greg Kurz <groug@kaod.org>

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>
---
 docs/devel/migration.rst |  4 ++--
 hmp-commands.hx          |  3 ++-
 qapi/migration.json      | 10 ++++++----
 3 files changed, 10 insertions(+), 7 deletions(-)

diff --git a/docs/devel/migration.rst b/docs/devel/migration.rst
index bf97080dac..9d1b7657f0 100644
--- a/docs/devel/migration.rst
+++ b/docs/devel/migration.rst
@@ -387,8 +387,8 @@ doesn't finish in a given time the switch is made to postcopy.
 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 15620c94d3..d26eb4119b 100644
--- a/hmp-commands.hx
+++ b/hmp-commands.hx
@@ -1041,7 +1041,8 @@ ETEXI
         .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 4cd3d13158..7f465a1902 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
 #
-- 
2.14.3