Refactor the migration control logic by eliminating the
`RAM_SAVE_CONTROL_NOT_SUPP` return value within the migration codebase.

This involves moving the checks for RDMA migration status and postcopy
state from rdma_control_save_page() to control_save_page()

With this change, control_save_page() now takes responsibility for
determining whether RDMA operations can proceed, based on the state of
migration.

Signed-off-by: Li Zhijian <lizhijian@fujitsu.com>
---
 migration/ram.c  | 19 ++++++++++---------
 migration/rdma.c |  4 +---
 migration/rdma.h |  3 +--
 3 files changed, 12 insertions(+), 14 deletions(-)

diff --git a/migration/ram.c b/migration/ram.c
index 424df6d9f13..b7157b9b175 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -1155,18 +1155,19 @@ static bool control_save_page(PageSearchStatus *pss,
 {
     int ret;
 
-    ret = rdma_control_save_page(pss->pss_channel, pss->block->offset, offset,
-                                 TARGET_PAGE_SIZE);
-    if (ret == RAM_SAVE_CONTROL_NOT_SUPP) {
-        return false;
-    }
+    if (migrate_rdma() && !migration_in_postcopy()) {
+        ret = rdma_control_save_page(pss->pss_channel, pss->block->offset,
+                                     offset, TARGET_PAGE_SIZE);
 
-    if (ret == RAM_SAVE_CONTROL_DELAYED) {
-        *pages = 1;
+        if (ret == RAM_SAVE_CONTROL_DELAYED) {
+            *pages = 1;
+        } else {
+            *pages = ret;
+        }
         return true;
     }
-    *pages = ret;
-    return true;
+
+    return false;
 }
 
 /*
diff --git a/migration/rdma.c b/migration/rdma.c
index af8e6234a9f..c6876347e1e 100644
--- a/migration/rdma.c
+++ b/migration/rdma.c
@@ -3284,9 +3284,7 @@ err:
 int rdma_control_save_page(QEMUFile *f, ram_addr_t block_offset,
                            ram_addr_t offset, size_t size)
 {
-    if (!migrate_rdma() || migration_in_postcopy()) {
-        return RAM_SAVE_CONTROL_NOT_SUPP;
-    }
+    assert(migrate_rdma());
 
     int ret = qemu_rdma_save_page(f, block_offset, offset, size);
 
diff --git a/migration/rdma.h b/migration/rdma.h
index f55f28bbed1..8eeb0117b91 100644
--- a/migration/rdma.h
+++ b/migration/rdma.h
@@ -33,7 +33,6 @@ void rdma_start_incoming_migration(InetSocketAddress *host_port, Error **errp);
 #define RAM_CONTROL_ROUND     1
 #define RAM_CONTROL_FINISH    3
 
-#define RAM_SAVE_CONTROL_NOT_SUPP -1000
 #define RAM_SAVE_CONTROL_DELAYED  -2000
 
 #ifdef CONFIG_RDMA
@@ -56,7 +55,7 @@ static inline
 int rdma_control_save_page(QEMUFile *f, ram_addr_t block_offset,
                            ram_addr_t offset, size_t size)
 {
-    return RAM_SAVE_CONTROL_NOT_SUPP;
+    g_assert_not_reached();
 }
 #endif
 #endif
-- 
2.44.0