migration/rdma: Convert qemu_rdma_exchange_recv() to Error

Functions that use an Error **errp parameter to return errors should
not also report them to the user, because reporting is the caller's
job.  When the caller does, the error is reported twice.  When it
doesn't (because it recovered from the error), there is no error to
report, i.e. the report is bogus.

qio_channel_rdma_readv() violates this principle: it calls
error_report() via qemu_rdma_exchange_recv().  I elected not to
investigate how callers handle the error, i.e. precise impact is not
known.

Clean this up by converting qemu_rdma_exchange_recv() to Error.

Necessitates setting an error when qemu_rdma_exchange_get_response()
failed.  Since this error will go away later in this series, simply
use "FIXME temporary error message" there.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Li Zhijian <lizhijian@fujitsu.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
Message-ID: <20230928132019.2544702-36-armbru@redhat.com>

migration/rdma.c

@@ -1980,7 +1980,7 @@ static int qemu_rdma_exchange_send(RDMAContext *rdma, RDMAControlHeader *head,
  * control-channel message.
  */
 static int qemu_rdma_exchange_recv(RDMAContext *rdma, RDMAControlHeader *head,
-                                   uint32_t expecting)
+                                   uint32_t expecting, Error **errp)
 {
     RDMAControlHeader ready = {
                                 .len = 0,
@@ -1995,7 +1995,7 @@ static int qemu_rdma_exchange_recv(RDMAContext *rdma, RDMAControlHeader *head,
     ret = qemu_rdma_post_send_control(rdma, NULL, &ready);
 
     if (ret < 0) {
-        error_report("Failed to send control buffer!");
+        error_setg(errp, "Failed to send control buffer!");
         return -1;
     }
 
@@ -2006,6 +2006,7 @@ static int qemu_rdma_exchange_recv(RDMAContext *rdma, RDMAControlHeader *head,
                                           expecting, RDMA_WRID_READY);
 
     if (ret < 0) {
+        error_setg(errp, "FIXME temporary error message");
         return -1;
     }
 
@@ -2016,7 +2017,7 @@ static int qemu_rdma_exchange_recv(RDMAContext *rdma, RDMAControlHeader *head,
      */
     ret = qemu_rdma_post_recv_control(rdma, RDMA_WRID_READY);
     if (ret < 0) {
-        error_report("rdma migration: error posting second control recv!");
+        error_setg(errp, "rdma migration: error posting second control recv!");
         return -1;
     }
 
@@ -2957,11 +2958,11 @@ static ssize_t qio_channel_rdma_readv(QIOChannel *ioc,
         /* We've got nothing at all, so lets wait for
          * more to arrive
          */
-        ret = qemu_rdma_exchange_recv(rdma, &head, RDMA_CONTROL_QEMU_FILE);
+        ret = qemu_rdma_exchange_recv(rdma, &head, RDMA_CONTROL_QEMU_FILE,
+                                      errp);
 
         if (ret < 0) {
             rdma->errored = true;
-            error_setg(errp, "qemu_rdma_exchange_recv failed");
             return -1;
         }
 
@@ -3575,6 +3576,7 @@ static int qemu_rdma_registration_handle(QEMUFile *f)
     RDMAControlHeader blocks = { .type = RDMA_CONTROL_RAM_BLOCKS_RESULT,
                                  .repeat = 1 };
     QIOChannelRDMA *rioc = QIO_CHANNEL_RDMA(qemu_file_get_ioc(f));
+    Error *err = NULL;
     RDMAContext *rdma;
     RDMALocalBlocks *local;
     RDMAControlHeader head;
@@ -3604,9 +3606,10 @@ static int qemu_rdma_registration_handle(QEMUFile *f)
     do {
         trace_qemu_rdma_registration_handle_wait();
 
-        ret = qemu_rdma_exchange_recv(rdma, &head, RDMA_CONTROL_NONE);
+        ret = qemu_rdma_exchange_recv(rdma, &head, RDMA_CONTROL_NONE, &err);
 
         if (ret < 0) {
+            error_report_err(err);
             break;
         }