multifd: multifd_send_sync_main now returns negative on error

Even though multifd_send_sync_main() currently emits error_reports, it's
callers don't really check it before continuing.

Change multifd_send_sync_main() to return -1 on error and 0 on success.
Also change all it's callers to make use of this change and possibly fail
earlier.

(This change is important to next patch on  multifd zero copy
implementation, to make it sure an error in zero-copy flush does not go
unnoticed.

Signed-off-by: Leonardo Bras <leobras@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Message-Id: <20220513062836.965425-7-leobras@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

1 files changed, 22 insertions, 7 deletions

diff --git a/migration/ram.c b/migration/ram.c
index a2489a2699..5f5e37f64d 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -2909,6 +2909,7 @@ static int ram_save_setup(QEMUFile *f, void *opaque)
 {
     RAMState **rsp = opaque;
     RAMBlock *block;
+    int ret;
 
     if (compress_threads_save_setup()) {
         return -1;
@@ -2943,7 +2944,11 @@ static int ram_save_setup(QEMUFile *f, void *opaque)
     ram_control_before_iterate(f, RAM_CONTROL_SETUP);
     ram_control_after_iterate(f, RAM_CONTROL_SETUP);
 
-    multifd_send_sync_main(f);
+    ret =  multifd_send_sync_main(f);
+    if (ret < 0) {
+        return ret;
+    }
+
     qemu_put_be64(f, RAM_SAVE_FLAG_EOS);
     qemu_fflush(f);
 
@@ -3052,7 +3057,11 @@ static int ram_save_iterate(QEMUFile *f, void *opaque)
 out:
     if (ret >= 0
         && migration_is_setup_or_active(migrate_get_current()->state)) {
-        multifd_send_sync_main(rs->f);
+        ret = multifd_send_sync_main(rs->f);
+        if (ret < 0) {
+            return ret;
+        }
+
         qemu_put_be64(f, RAM_SAVE_FLAG_EOS);
         qemu_fflush(f);
         ram_transferred_add(8);
@@ -3112,13 +3121,19 @@ static int ram_save_complete(QEMUFile *f, void *opaque)
         ram_control_after_iterate(f, RAM_CONTROL_FINISH);
     }
 
-    if (ret >= 0) {
-        multifd_send_sync_main(rs->f);
-        qemu_put_be64(f, RAM_SAVE_FLAG_EOS);
-        qemu_fflush(f);
+    if (ret < 0) {
+        return ret;
     }
 
-    return ret;
+    ret = multifd_send_sync_main(rs->f);
+    if (ret < 0) {
+        return ret;
+    }
+
+    qemu_put_be64(f, RAM_SAVE_FLAG_EOS);
+    qemu_fflush(f);
+
+    return 0;
 }
 
 static void ram_save_pending(QEMUFile *f, void *opaque, uint64_t max_size,