Depending on the order of starting RDMA and setting capability,
they can be categorized into the following scenarios:
Source:
 S1: [set capabilities] -> [Start RDMA outgoing]
Destination:
 D1: [set capabilities] -> [Start RDMA incoming]
 D2: [Start RDMA incoming] -> [set capabilities]

Previously, compatibility between RDMA and capabilities was verified only
in scenario D1, potentially causing migration failures in other situations.

For scenarios S1 and D1, we can seamlessly incorporate
migration_transport_compatible() to address compatibility between
channels and capabilities vs transport.

For scenario D2, ensure compatibility within migrate_caps_check().

Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Li Zhijian <lizhijian@fujitsu.com>
---

V4:
  - Remove Reviewed-tag and cover above D2 scenario

V3:
  - collect Reviewed tag
  - reorder: 5th -> 2nd
---
 migration/migration.c | 30 ++++++++++++++++++++----------
 migration/options.c   | 21 +++++++++++++++++++++
 migration/options.h   |  1 +
 3 files changed, 42 insertions(+), 10 deletions(-)

diff --git a/migration/migration.c b/migration/migration.c
index c597aa707e5..0736d3a6728 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -238,6 +238,24 @@ migration_channels_and_transport_compatible(MigrationAddress *addr,
     return true;
 }
 
+static bool
+migration_capabilities_and_transport_compatible(MigrationAddress *addr,
+                                                Error **errp)
+{
+    if (addr->transport == MIGRATION_ADDRESS_TYPE_RDMA) {
+        return migrate_rdma_caps_check(migrate_get_current()->capabilities,
+                                       errp);
+    }
+
+    return true;
+}
+
+static bool migration_transport_compatible(MigrationAddress *addr, Error **errp)
+{
+    return migration_channels_and_transport_compatible(addr, errp) &&
+           migration_capabilities_and_transport_compatible(addr, errp);
+}
+
 static gint page_request_addr_cmp(gconstpointer ap, gconstpointer bp)
 {
     uintptr_t a = (uintptr_t) ap, b = (uintptr_t) bp;
@@ -716,7 +734,7 @@ static void qemu_start_incoming_migration(const char *uri, bool has_channels,
     }
 
     /* transport mechanism not suitable for migration? */
-    if (!migration_channels_and_transport_compatible(addr, errp)) {
+    if (!migration_transport_compatible(addr, errp)) {
         return;
     }
 
@@ -735,14 +753,6 @@ static void qemu_start_incoming_migration(const char *uri, bool has_channels,
         }
 #ifdef CONFIG_RDMA
     } else if (addr->transport == MIGRATION_ADDRESS_TYPE_RDMA) {
-        if (migrate_xbzrle()) {
-            error_setg(errp, "RDMA and XBZRLE can't be used together");
-            return;
-        }
-        if (migrate_multifd()) {
-            error_setg(errp, "RDMA and multifd can't be used together");
-            return;
-        }
         rdma_start_incoming_migration(&addr->u.rdma, errp);
 #endif
     } else if (addr->transport == MIGRATION_ADDRESS_TYPE_EXEC) {
@@ -2159,7 +2169,7 @@ void qmp_migrate(const char *uri, bool has_channels,
     }
 
     /* transport mechanism not suitable for migration? */
-    if (!migration_channels_and_transport_compatible(addr, errp)) {
+    if (!migration_transport_compatible(addr, errp)) {
         return;
     }
 
diff --git a/migration/options.c b/migration/options.c
index bb259d192a9..c6f18df5864 100644
--- a/migration/options.c
+++ b/migration/options.c
@@ -439,6 +439,20 @@ static bool migrate_incoming_started(void)
     return !!migration_incoming_get_current()->transport_data;
 }
 
+bool migrate_rdma_caps_check(bool *caps, Error **errp)
+{
+    if (caps[MIGRATION_CAPABILITY_XBZRLE]) {
+        error_setg(errp, "RDMA and XBZRLE can't be used together");
+        return false;
+    }
+    if (caps[MIGRATION_CAPABILITY_MULTIFD]) {
+        error_setg(errp, "RDMA and multifd can't be used together");
+        return false;
+    }
+
+    return true;
+}
+
 /**
  * @migration_caps_check - check capability compatibility
  *
@@ -602,6 +616,13 @@ bool migrate_caps_check(bool *old_caps, bool *new_caps, Error **errp)
         }
     }
 
+    /*
+     * On destination side, check the cases that capability is being set
+     * after incoming thread has started.
+    */
+    if (migrate_rdma() && !migrate_rdma_caps_check(new_caps, errp)) {
+        return false;
+    }
     return true;
 }
 
diff --git a/migration/options.h b/migration/options.h
index 762be4e641a..82d839709e7 100644
--- a/migration/options.h
+++ b/migration/options.h
@@ -57,6 +57,7 @@ bool migrate_tls(void);
 
 /* capabilities helpers */
 
+bool migrate_rdma_caps_check(bool *caps, Error **errp);
 bool migrate_caps_check(bool *old_caps, bool *new_caps, Error **errp);
 
 /* parameters */
-- 
2.44.0