[PATCH v2 3/5] migration: Add .save_prepare() handler to struct SaveVMHandlers

[Avihai Horon]

Add a new .save_prepare() handler to struct SaveVMHandlers. This handler
is called early, even before migration starts, and can be used by
devices to perform early checks.

Suggested-by: Peter Xu <pet...@redhat.com>
Signed-off-by: Avihai Horon <avih...@nvidia.com>
---
 include/migration/register.h |  5 +++++
 migration/savevm.h           |  1 +
 migration/migration.c        |  4 ++++
 migration/savevm.c           | 29 +++++++++++++++++++++++++++++
 4 files changed, 39 insertions(+)

diff --git a/include/migration/register.h b/include/migration/register.h
index 90914f32f5..2b12c6adec 100644
--- a/include/migration/register.h
+++ b/include/migration/register.h
@@ -20,6 +20,11 @@ typedef struct SaveVMHandlers {
     /* This runs inside the iothread lock.  */
     SaveStateHandler *save_state;
 
+    /*
+     * save_prepare is called early, even before migration starts, and can be
+     * used to perform early checks.
+     */
+    int (*save_prepare)(void *opaque, Error **errp);
     void (*save_cleanup)(void *opaque);
     int (*save_live_complete_postcopy)(QEMUFile *f, void *opaque);
     int (*save_live_complete_precopy)(QEMUFile *f, void *opaque);
diff --git a/migration/savevm.h b/migration/savevm.h
index e894bbc143..74669733dd 100644
--- a/migration/savevm.h
+++ b/migration/savevm.h
@@ -31,6 +31,7 @@
 
 bool qemu_savevm_state_blocked(Error **errp);
 void qemu_savevm_non_migratable_list(strList **reasons);
+int qemu_savevm_state_prepare(Error **errp);
 void qemu_savevm_state_setup(QEMUFile *f);
 bool qemu_savevm_state_guest_unplug_pending(void);
 int qemu_savevm_state_resume_prepare(MigrationState *s);
diff --git a/migration/migration.c b/migration/migration.c
index 92866a8f49..914783f07b 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -1634,6 +1634,10 @@ static bool migrate_prepare(MigrationState *s, bool blk, 
bool blk_inc,
         migrate_set_block_incremental(true);
     }
 
+    if (qemu_savevm_state_prepare(errp)) {
+        return false;
+    }
+
     migrate_init(s);
     /*
      * set mig_stats compression_counters memory to zero for a
diff --git a/migration/savevm.c b/migration/savevm.c
index 5bf8b59a7d..818510ec57 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -1233,6 +1233,30 @@ bool qemu_savevm_state_guest_unplug_pending(void)
     return false;
 }
 
+int qemu_savevm_state_prepare(Error **errp)
+{
+    SaveStateEntry *se;
+    int ret;
+
+    QTAILQ_FOREACH(se, &savevm_state.handlers, entry) {
+        if (!se->ops || !se->ops->save_prepare) {
+            continue;
+        }
+        if (se->ops->is_active) {
+            if (!se->ops->is_active(se->opaque)) {
+                continue;
+            }
+        }
+
+        ret = se->ops->save_prepare(se->opaque, errp);
+        if (ret < 0) {
+            return ret;
+        }
+    }
+
+    return 0;
+}
+
 void qemu_savevm_state_setup(QEMUFile *f)
 {
     MigrationState *ms = migrate_get_current();
@@ -1619,6 +1643,11 @@ static int qemu_savevm_state(QEMUFile *f, Error **errp)
         return -EINVAL;
     }
 
+    ret = qemu_savevm_state_prepare(errp);
+    if (ret) {
+        return ret;
+    }
+
     migrate_init(ms);
     memset(&mig_stats, 0, sizeof(mig_stats));
     memset(&compression_counters, 0, sizeof(compression_counters));
-- 
2.26.3