The documentation of qemu_file_get_return_path() states that it can
return NULL on failure. However, a review of the current implementation
reveals that it is guaranteed that it will always succeed and will never
return NULL.

As a result, the NULL checks post calling the function become redundant.
This commit updates the documentation for the function and removes all
NULL checks throughout the migration code.

Signed-off-by: Arun Menon <armenon@redhat.com>
---
 migration/colo.c      |  4 ----
 migration/migration.c | 12 ++----------
 migration/qemu-file.c |  1 -
 migration/savevm.c    |  4 ----
 4 files changed, 2 insertions(+), 19 deletions(-)

diff --git a/migration/colo.c b/migration/colo.c
index e0f713c837f5da25d67afbd02ceb6c54024ca3af..981bd4bf9ced8b45b4c5d494acae119a174ee974 100644
--- a/migration/colo.c
+++ b/migration/colo.c
@@ -849,10 +849,6 @@ static void *colo_process_incoming_thread(void *opaque)
     failover_init_state();
 
     mis->to_src_file = qemu_file_get_return_path(mis->from_src_file);
-    if (!mis->to_src_file) {
-        error_report("COLO incoming thread: Open QEMUFile to_src_file failed");
-        goto out;
-    }
     /*
      * Note: the communication between Primary side and Secondary side
      * should be sequential, we set the fd to unblocked in migration incoming
diff --git a/migration/migration.c b/migration/migration.c
index 10c216d25dec01f206eacad2edd24d21f00e614c..b3bccaeaee806abd01595863f6475057049b0688 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -2646,12 +2646,9 @@ out:
     return NULL;
 }
 
-static int open_return_path_on_source(MigrationState *ms)
+static void open_return_path_on_source(MigrationState *ms)
 {
     ms->rp_state.from_dst_file = qemu_file_get_return_path(ms->to_dst_file);
-    if (!ms->rp_state.from_dst_file) {
-        return -1;
-    }
 
     trace_open_return_path_on_source();
 
@@ -2660,8 +2657,6 @@ static int open_return_path_on_source(MigrationState *ms)
     ms->rp_state.rp_thread_created = true;
 
     trace_open_return_path_on_source_continue();
-
-    return 0;
 }
 
 /* Return true if error detected, or false otherwise */
@@ -4010,10 +4005,7 @@ void migration_connect(MigrationState *s, Error *error_in)
      * QEMU uses the return path.
      */
     if (migrate_postcopy_ram() || migrate_return_path()) {
-        if (open_return_path_on_source(s)) {
-            error_setg(&local_err, "Unable to open return-path for postcopy");
-            goto fail;
-        }
+        open_return_path_on_source(s);
     }
 
     /*
diff --git a/migration/qemu-file.c b/migration/qemu-file.c
index b6ac190034f777dbde0da1598483a892089d7538..f9ccee9a1091ecbd37e6b7d2081a4446442b544d 100644
--- a/migration/qemu-file.c
+++ b/migration/qemu-file.c
@@ -125,7 +125,6 @@ static QEMUFile *qemu_file_new_impl(QIOChannel *ioc, bool is_writable)
 
 /*
  * Result: QEMUFile* for a 'return path' for comms in the opposite direction
- *         NULL if not available
  */
 QEMUFile *qemu_file_get_return_path(QEMUFile *f)
 {
diff --git a/migration/savevm.c b/migration/savevm.c
index bef2236799945ed63124b3a41559ca4ab02e094e..96af7b412f2ed43468f4bcac8b833cda223f8321 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -2583,10 +2583,6 @@ static int loadvm_process_command(QEMUFile *f)
             return 0;
         }
         mis->to_src_file = qemu_file_get_return_path(f);
-        if (!mis->to_src_file) {
-            error_report("CMD_OPEN_RETURN_PATH failed");
-            return -1;
-        }
 
         /*
          * Switchover ack is enabled but no device uses it, so send an ACK to

-- 
2.50.0

On Mon, Jul 21, 2025 at 04:59:12PM +0530, Arun Menon wrote:
> The documentation of qemu_file_get_return_path() states that it can
> return NULL on failure. However, a review of the current implementation
> reveals that it is guaranteed that it will always succeed and will never
> return NULL.
> 
> As a result, the NULL checks post calling the function become redundant.
> This commit updates the documentation for the function and removes all
> NULL checks throughout the migration code.
> 
> Signed-off-by: Arun Menon <armenon@redhat.com>
> ---
>  migration/colo.c      |  4 ----
>  migration/migration.c | 12 ++----------
>  migration/qemu-file.c |  1 -
>  migration/savevm.c    |  4 ----
>  4 files changed, 2 insertions(+), 19 deletions(-)

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>


With regards,
Daniel
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