[PULL 10/27] migration: Replace switchover_ack_needed SaveVMHandler

["Cédric Le Goater" <clg@redhat.com>]

From: Avihai Horon <avihaih@nvidia.com>

A new switchover-ack mechanism that will replace the existing one will
be added in the following patches. The new mechanism will not use
switchover_ack_needed SaveVMHandler, however, the old mechanism must
still be kept for backward compatibility.

To keep things clear and decrease API surface of old code, replace
switchover_ack_needed SaveVMHandler with a regular function
migration_request_switchover_ack().

No functional changes intended.

Acked-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Avihai Horon <avihaih@nvidia.com>
Link: https://lore.kernel.org/qemu-devel/20260706085211.13905-6-avihaih@nvidia.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>
---
 docs/devel/migration/vfio.rst |  3 ---
 include/migration/misc.h      |  2 ++
 include/migration/register.h  | 13 -------------
 hw/vfio/migration.c           | 18 ++++++++++--------
 migration/migration.c         | 15 +++++++++++++++
 migration/savevm.c            | 21 ---------------------
 migration/trace-events        |  2 +-
 7 files changed, 28 insertions(+), 46 deletions(-)

diff --git a/docs/devel/migration/vfio.rst b/docs/devel/migration/vfio.rst
index 691061d1820453a09df479f020abf0aab5fbabfd..854277b11ce64672f998ce1728bf8b5ddf1c129a 100644
--- a/docs/devel/migration/vfio.rst
+++ b/docs/devel/migration/vfio.rst
@@ -59,9 +59,6 @@ VFIO implements the device hooks for the iterative approach as follows:
 * A ``save_live_iterate`` function that reads the VFIO device's data from the
   vendor driver during iterative pre-copy phase.
 
-* A ``switchover_ack_needed`` function that checks if the VFIO device uses
-  "switchover-ack" migration capability when this capability is enabled.
-
 * A ``switchover_start`` function that in the multifd mode starts a thread that
   reassembles the multifd received data and loads it in-order into the device.
   In the non-multifd mode this function is a NOP.
diff --git a/include/migration/misc.h b/include/migration/misc.h
index d3d6e1f50d102d0f46f574423eb951232be9b86b..17b42949d4b68dc3ed9341d254e7ccc69e18735e 100644
--- a/include/migration/misc.h
+++ b/include/migration/misc.h
@@ -159,4 +159,6 @@ bool multifd_device_state_save_thread_should_exit(void);
 void multifd_abort_device_state_save_threads(void);
 bool multifd_join_device_state_save_threads(void);
 
+void migration_request_switchover_ack(const char *requester);
+
 #endif
diff --git a/include/migration/register.h b/include/migration/register.h
index 6f632123f1d0710de0556e68ba53e068a1e02640..a61c4236d22423a8477876971f1d73fe2e802f4a 100644
--- a/include/migration/register.h
+++ b/include/migration/register.h
@@ -302,19 +302,6 @@ typedef struct SaveVMHandlers {
      */
     int (*resume_prepare)(MigrationState *s, void *opaque);
 
-    /**
-     * @switchover_ack_needed
-     *
-     * Checks if switchover ack should be used. Called only on
-     * destination.
-     *
-     * @opaque: data pointer passed to register_savevm_live()
-     *
-     * Returns true if switchover ack should be used and false
-     * otherwise
-     */
-    bool (*switchover_ack_needed)(void *opaque);
-
     /**
      * @switchover_start
      *
diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
index 180b316baecb980fbd475b1426726697f340ccc8..7055cfbd3e04bd2b1e95c9be45b879cb0bf06212 100644
--- a/hw/vfio/migration.c
+++ b/hw/vfio/migration.c
@@ -487,6 +487,14 @@ static bool vfio_precopy_supported(VFIODevice *vbasedev)
     return migration->mig_flags & VFIO_MIGRATION_PRE_COPY;
 }
 
+static void vfio_request_switchover_ack(VFIODevice *vbasedev)
+{
+    if (vfio_precopy_supported(vbasedev)) {
+        /* Precopy support implies switchover-ack is needed */
+        migration_request_switchover_ack(vbasedev->name);
+    }
+}
+
 /* ---------------------------------------------------------------------- */
 
 static int vfio_save_prepare(void *opaque, Error **errp)
@@ -776,6 +784,8 @@ static int vfio_load_setup(QEMUFile *f, void *opaque, Error **errp)
         return ret;
     }
 
+    vfio_request_switchover_ack(vbasedev);
+
     return 0;
 }
 
@@ -874,13 +884,6 @@ static int vfio_load_state(QEMUFile *f, void *opaque, int version_id)
     return ret;
 }
 
-static bool vfio_switchover_ack_needed(void *opaque)
-{
-    VFIODevice *vbasedev = opaque;
-
-    return vfio_precopy_supported(vbasedev);
-}
-
 static int vfio_switchover_start(void *opaque)
 {
     VFIODevice *vbasedev = opaque;
@@ -904,7 +907,6 @@ static const SaveVMHandlers savevm_vfio_handlers = {
     .load_setup = vfio_load_setup,
     .load_cleanup = vfio_load_cleanup,
     .load_state = vfio_load_state,
-    .switchover_ack_needed = vfio_switchover_ack_needed,
     /*
      * Multifd support
      */
diff --git a/migration/migration.c b/migration/migration.c
index 442f950c43cef47ed23856a16bdda3af5549a5bf..9a8d47ba9637eb57ee9f3bc6cfe8f580161fb36c 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -2202,6 +2202,21 @@ void migration_rp_kick(MigrationState *s)
     qemu_sem_post(&s->rp_state.rp_sem);
 }
 
+/* This is called only on destination side */
+void migration_request_switchover_ack(const char *requester)
+{
+    MigrationIncomingState *mis = migration_incoming_get_current();
+
+    if (!migrate_switchover_ack()) {
+        return;
+    }
+
+    mis->switchover_ack_pending_num++;
+
+    trace_migration_request_switchover_ack(requester,
+                                           mis->switchover_ack_pending_num);
+}
+
 static struct rp_cmd_args {
     ssize_t     len; /* -1 = variable */
     const char *name;
diff --git a/migration/savevm.c b/migration/savevm.c
index be81de26160d195488e5fb09a88dc37a7a06a3fe..98639630277b7543db7400ec97d6b009603a03bc 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -2800,23 +2800,6 @@ static int qemu_loadvm_state_header(QEMUFile *f, Error **errp)
     return 0;
 }
 
-static void qemu_loadvm_state_switchover_ack_needed(MigrationIncomingState *mis)
-{
-    SaveStateEntry *se;
-
-    QTAILQ_FOREACH(se, &savevm_state.handlers, entry) {
-        if (!se->ops || !se->ops->switchover_ack_needed) {
-            continue;
-        }
-
-        if (se->ops->switchover_ack_needed(se->opaque)) {
-            mis->switchover_ack_pending_num++;
-        }
-    }
-
-    trace_loadvm_state_switchover_ack_needed(mis->switchover_ack_pending_num);
-}
-
 static int qemu_loadvm_state_setup(QEMUFile *f, Error **errp)
 {
     ERRP_GUARD();
@@ -3078,10 +3061,6 @@ int qemu_loadvm_state(QEMUFile *f, Error **errp)
         return -EINVAL;
     }
 
-    if (migrate_switchover_ack()) {
-        qemu_loadvm_state_switchover_ack_needed(mis);
-    }
-
     cpu_synchronize_all_pre_loadvm();
 
     ret = qemu_loadvm_state_main(f, mis, errp);
diff --git a/migration/trace-events b/migration/trace-events
index c0c433744cd33d7e28496831bb8ce93c65670bf5..5955befcc66128b72dfdbc9711e5749f19b9faf8 100644
--- a/migration/trace-events
+++ b/migration/trace-events
@@ -8,7 +8,6 @@ qemu_loadvm_state_post_main(int ret) "%d"
 qemu_loadvm_state_section_startfull(uint32_t section_id, const char *idstr, uint32_t instance_id, uint32_t version_id) "%u(%s) %u %u"
 qemu_savevm_send_packaged(void) ""
 qemu_savevm_query_pending(bool exact, bool final, uint64_t precopy, uint64_t stopcopy, uint64_t postcopy, uint64_t total) "exact=%d, final=%d, precopy=%"PRIu64", stopcopy=%"PRIu64", postcopy=%"PRIu64", total=%"PRIu64
-loadvm_state_switchover_ack_needed(unsigned int switchover_ack_pending_num) "Switchover ack pending num=%u"
 loadvm_state_setup(void) ""
 loadvm_state_cleanup(void) ""
 loadvm_handle_cmd_packaged(unsigned int length) "%u"
@@ -199,6 +198,7 @@ process_incoming_migration_co_postcopy_end_main(void) ""
 postcopy_preempt_enabled(bool value) "%d"
 migration_precopy_complete(void) ""
 migration_call_notifiers(int type) "type=%d"
+migration_request_switchover_ack(const char *requester, unsigned int switchover_ack_pending_num) "Requester %s, switchover_ack_pending_num %u"
 
 # migration-stats
 migration_transferred_bytes(uint64_t qemu_file, uint64_t multifd, uint64_t rdma) "qemu_file %" PRIu64 " multifd %" PRIu64 " RDMA %" PRIu64
-- 
2.54.0