migration: Drop return code for disgard ram process

It will just never fail.  Drop those return values where they're constantly
zeros.

A tiny touch-up on the tracepoint so trace_ram_postcopy_send_discard_bitmap()
is called after the logic itself (which sounds more reasonable).

Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>

migration/migration.c

@@ -2991,10 +2991,7 @@ static int postcopy_start(MigrationState *ms)
      * that are dirty
      */
     if (migrate_postcopy_ram()) {
-        if (ram_postcopy_send_discard_bitmap(ms)) {
+        ram_postcopy_send_discard_bitmap(ms);
-            error_report("postcopy send discard bitmap failed");
-            goto fail;
-        }
     }
 
     /*

migration/ram.c

@@ -2459,8 +2459,6 @@ static void postcopy_chunk_hostpages_pass(MigrationState *ms, RAMBlock *block);
 /**
  * postcopy_each_ram_send_discard: discard all RAMBlocks
  *
- * Returns 0 for success or negative for error
- *
  * Utility for the outgoing postcopy code.
  *   Calls postcopy_send_discard_bm_ram for each RAMBlock
  *   passing it bitmap indexes and name.
@@ -2469,10 +2467,9 @@ static void postcopy_chunk_hostpages_pass(MigrationState *ms, RAMBlock *block);
  *
  * @ms: current migration state
  */
-static int postcopy_each_ram_send_discard(MigrationState *ms)
+static void postcopy_each_ram_send_discard(MigrationState *ms)
 {
     struct RAMBlock *block;
-    int ret;
 
     RAMBLOCK_FOREACH_NOT_IGNORED(block) {
         postcopy_discard_send_init(ms, block->idstr);
@@ -2490,14 +2487,9 @@ static int postcopy_each_ram_send_discard(MigrationState *ms)
          * just needs indexes at this point, avoids it having
          * target page specific code.
          */
-        ret = postcopy_send_discard_bm_ram(ms, block);
+        postcopy_send_discard_bm_ram(ms, block);
         postcopy_discard_send_finish(ms);
-        if (ret) {
-            return ret;
-        }
     }
-
-    return 0;
 }
 
 /**
@@ -2570,8 +2562,6 @@ static void postcopy_chunk_hostpages_pass(MigrationState *ms, RAMBlock *block)
 /**
  * ram_postcopy_send_discard_bitmap: transmit the discard bitmap
  *
- * Returns zero on success
- *
  * Transmit the set of pages to be discarded after precopy to the target
  * these are pages that:
  *     a) Have been previously transmitted but are now dirty again
@@ -2582,7 +2572,7 @@ static void postcopy_chunk_hostpages_pass(MigrationState *ms, RAMBlock *block)
  *
  * @ms: current migration state
  */
-int ram_postcopy_send_discard_bitmap(MigrationState *ms)
+void ram_postcopy_send_discard_bitmap(MigrationState *ms)
 {
     RAMState *rs = ram_state;
 
@@ -2596,9 +2586,9 @@ int ram_postcopy_send_discard_bitmap(MigrationState *ms)
     rs->last_sent_block = NULL;
     rs->last_page = 0;
 
-    trace_ram_postcopy_send_discard_bitmap();
+    postcopy_each_ram_send_discard(ms);
 
-    return postcopy_each_ram_send_discard(ms);
+    trace_ram_postcopy_send_discard_bitmap();
 }
 
 /**

migration/ram.h

@@ -57,7 +57,7 @@ int ram_save_queue_pages(const char *rbname, ram_addr_t start, ram_addr_t len);
 void acct_update_position(QEMUFile *f, size_t size, bool zero);
 void ram_postcopy_migrated_memory_release(MigrationState *ms);
 /* For outgoing discard bitmap */
-int ram_postcopy_send_discard_bitmap(MigrationState *ms);
+void ram_postcopy_send_discard_bitmap(MigrationState *ms);
 /* For incoming postcopy discard */
 int ram_discard_range(const char *block_name, uint64_t start, size_t length);
 int ram_postcopy_incoming_init(MigrationIncomingState *mis);