migration: Rework migrate_send_rp_req_pages() function

We duplicated the logic of maintaining the last_rb variable at both callers of
this function.  Pass *rb pointer into the function so that we can avoid
duplicating the logic.  Also, when we have the rb pointer, it's also easier to
remove the original 2nd & 4th parameters, because both of them (name of the
ramblock when needed, or the page size) can be fetched from the ramblock
pointer too.

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20200908203022.341615-3-peterx@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

migration/migration.c

@@ -314,25 +314,35 @@ error:
     return ret;
 }
 
-/* Request a range of pages from the source VM at the given
- * start address.
- *   rbname: Name of the RAMBlock to request the page in, if NULL it's the same
- *           as the last request (a name must have been given previously)
+/* Request one page from the source VM at the given start address.
+ *   rb: the RAMBlock to request the page in
  *   Start: Address offset within the RB
  *   Len: Length in bytes required - must be a multiple of pagesize
  */
-int migrate_send_rp_req_pages(MigrationIncomingState *mis, const char *rbname,
-                              ram_addr_t start, size_t len)
+int migrate_send_rp_req_pages(MigrationIncomingState *mis, RAMBlock *rb,
+                              ram_addr_t start)
 {
     uint8_t bufc[12 + 1 + 255]; /* start (8), len (4), rbname up to 256 */
     size_t msglen = 12; /* start + len */
+    size_t len = qemu_ram_pagesize(rb);
     enum mig_rp_message_type msg_type;
+    const char *rbname;
+    int rbname_len;
 
     *(uint64_t *)bufc = cpu_to_be64((uint64_t)start);
     *(uint32_t *)(bufc + 8) = cpu_to_be32((uint32_t)len);
 
-    if (rbname) {
-        int rbname_len = strlen(rbname);
+    /*
+     * We maintain the last ramblock that we requested for page.  Note that we
+     * don't need locking because this function will only be called within the
+     * postcopy ram fault thread.
+     */
+    if (rb != mis->last_rb) {
+        mis->last_rb = rb;
+
+        rbname = qemu_ram_get_idstr(rb);
+        rbname_len = strlen(rbname);
+
         assert(rbname_len < 256);
 
         bufc[msglen++] = rbname_len;

migration/migration.h

@@ -326,8 +326,8 @@ void migrate_send_rp_shut(MigrationIncomingState *mis,
                           uint32_t value);
 void migrate_send_rp_pong(MigrationIncomingState *mis,
                           uint32_t value);
-int migrate_send_rp_req_pages(MigrationIncomingState *mis, const char* rbname,
-                              ram_addr_t start, size_t len);
+int migrate_send_rp_req_pages(MigrationIncomingState *mis, RAMBlock *rb,
+                              ram_addr_t start);
 void migrate_send_rp_recv_bitmap(MigrationIncomingState *mis,
                                  char *block_name);
 void migrate_send_rp_resume_ack(MigrationIncomingState *mis, uint32_t value);

migration/postcopy-ram.c

@@ -684,14 +684,7 @@ int postcopy_request_shared_page(struct PostCopyFD *pcfd, RAMBlock *rb,
                                         qemu_ram_get_idstr(rb), rb_offset);
         return postcopy_wake_shared(pcfd, client_addr, rb);
     }
-    if (rb != mis->last_rb) {
-        mis->last_rb = rb;
-        migrate_send_rp_req_pages(mis, qemu_ram_get_idstr(rb),
-                                  aligned_rbo, pagesize);
-    } else {
-        /* Save some space */
-        migrate_send_rp_req_pages(mis, NULL, aligned_rbo, pagesize);
-    }
+    migrate_send_rp_req_pages(mis, rb, aligned_rbo);
     return 0;
 }
 
@@ -986,20 +979,7 @@ retry:
              * Send the request to the source - we want to request one
              * of our host page sizes (which is >= TPS)
              */
-            if (rb != mis->last_rb) {
-                mis->last_rb = rb;
-                ret = migrate_send_rp_req_pages(mis,
-                                                qemu_ram_get_idstr(rb),
-                                                rb_offset,
-                                                qemu_ram_pagesize(rb));
-            } else {
-                /* Save some space */
-                ret = migrate_send_rp_req_pages(mis,
-                                                NULL,
-                                                rb_offset,
-                                                qemu_ram_pagesize(rb));
-            }
-
+            ret = migrate_send_rp_req_pages(mis, rb, rb_offset);
             if (ret) {
                 /* May be network failure, try to wait for recovery */
                 if (ret == -EIO && postcopy_pause_fault_thread(mis)) {