[PATCH V1 05/26] migration: precreate vmstate

[Steve Sistare]

Provide the VMStateDescription precreate field to mark objects that must
be loaded on the incoming side before devices have been created, because
they provide properties that will be needed at creation time.  They will
be saved to and loaded from their own QEMUFile, via
qemu_savevm_precreate_save and qemu_savevm_precreate_load, but these
functions are not yet called in this patch.  Allow them to be called
before or after normal migration is active, when current_migration and
current_incoming are not valid.

Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
---
 include/migration/vmstate.h |  6 ++++
 migration/savevm.c          | 69 +++++++++++++++++++++++++++++++++++++++++----
 migration/savevm.h          |  3 ++
 3 files changed, 73 insertions(+), 5 deletions(-)

diff --git a/include/migration/vmstate.h b/include/migration/vmstate.h
index 294d2d8..4691334 100644
--- a/include/migration/vmstate.h
+++ b/include/migration/vmstate.h
@@ -198,6 +198,12 @@ struct VMStateDescription {
      * a QEMU_VM_SECTION_START section.
      */
     bool early_setup;
+
+    /*
+     * Send/receive this object in the precreate migration stream.
+     */
+    bool precreate;
+
     int version_id;
     int minimum_version_id;
     MigrationPriority priority;
diff --git a/migration/savevm.c b/migration/savevm.c
index 9789823..a30bcd9 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -239,6 +239,7 @@ static SaveState savevm_state = {
 
 #define SAVEVM_FOREACH(se, entry)                                    \
     QTAILQ_FOREACH(se, &savevm_state.handlers, entry)                \
+        if (!se->vmsd || !se->vmsd->precreate)
 
 #define SAVEVM_FOREACH_ALL(se, entry)                                \
     QTAILQ_FOREACH(se, &savevm_state.handlers, entry)
@@ -1006,13 +1007,19 @@ static void save_section_header(QEMUFile *f, 
SaveStateEntry *se,
     }
 }
 
+static bool send_section_footer(SaveStateEntry *se)
+{
+    return (se->vmsd && se->vmsd->precreate) ||
+           migrate_get_current()->send_section_footer;
+}
+
 /*
  * Write a footer onto device sections that catches cases misformatted device
  * sections.
  */
 static void save_section_footer(QEMUFile *f, SaveStateEntry *se)
 {
-    if (migrate_get_current()->send_section_footer) {
+    if (send_section_footer(se)) {
         qemu_put_byte(f, QEMU_VM_SECTION_FOOTER);
         qemu_put_be32(f, se->section_id);
     }
@@ -1319,6 +1326,52 @@ int qemu_savevm_state_prepare(Error **errp)
     return 0;
 }
 
+int qemu_savevm_precreate_save(QEMUFile *f, Error **errp)
+{
+    int ret;
+    SaveStateEntry *se;
+
+    qemu_put_be32(f, QEMU_VM_FILE_MAGIC);
+    qemu_put_be32(f, QEMU_VM_FILE_VERSION);
+
+    SAVEVM_FOREACH_ALL(se, entry) {
+        if (se->vmsd && se->vmsd->precreate) {
+            ret = vmstate_save(f, se, NULL, errp);
+            if (ret) {
+                qemu_file_set_error(f, ret);
+                return ret;
+            }
+        }
+    }
+    qemu_fflush(f);
+    return 0;
+}
+
+int qemu_savevm_precreate_load(QEMUFile *f, Error **errp)
+{
+    unsigned int v;
+    int ret;
+
+    v = qemu_get_be32(f);
+    if (v != QEMU_VM_FILE_MAGIC) {
+        error_setg(errp, "Not a migration stream");
+        return -EINVAL;
+    }
+
+    v = qemu_get_be32(f);
+    if (v != QEMU_VM_FILE_VERSION) {
+        error_setg(errp, "Unsupported migration stream version");
+        return -ENOTSUP;
+    }
+
+    ret = qemu_loadvm_state_main(f, NULL);
+    if (ret) {
+        error_setg_errno(errp, -ret, "qemu_savevm_precreate_load");
+    }
+
+    return ret;
+}
+
 int qemu_savevm_state_setup(QEMUFile *f, Error **errp)
 {
     ERRP_GUARD();
@@ -2559,7 +2612,7 @@ static bool check_section_footer(QEMUFile *f, 
SaveStateEntry *se)
     uint8_t read_mark;
     uint32_t read_section_id;
 
-    if (!migrate_get_current()->send_section_footer) {
+    if (!send_section_footer(se)) {
         /* No footer to check */
         return true;
     }
@@ -2895,9 +2948,12 @@ retry:
     while (true) {
         section_type = qemu_get_byte(f);
 
-        ret = qemu_file_get_error_obj_any(f, mis->postcopy_qemufile_dst, NULL);
-        if (ret) {
-            break;
+        if (mis) {
+            ret = qemu_file_get_error_obj_any(f, mis->postcopy_qemufile_dst,
+                                              NULL);
+            if (ret) {
+                break;
+            }
         }
 
         trace_qemu_loadvm_state_section(section_type);
@@ -2936,6 +2992,9 @@ retry:
 out:
     if (ret < 0) {
         qemu_file_set_error(f, ret);
+        if (!mis) {
+            return ret;
+        }
 
         /* Cancel bitmaps incoming regardless of recovery */
         dirty_bitmap_mig_cancel_incoming();
diff --git a/migration/savevm.h b/migration/savevm.h
index 9ec96a9..6f207b5 100644
--- a/migration/savevm.h
+++ b/migration/savevm.h
@@ -70,4 +70,7 @@ int qemu_loadvm_approve_switchover(void);
 int qemu_savevm_state_complete_precopy_non_iterable(QEMUFile *f,
         bool in_postcopy, bool inactivate_disks);
 
+int qemu_savevm_precreate_save(QEMUFile *f, Error **errp);
+int qemu_savevm_precreate_load(QEMUFile *f, Error **errp);
+
 #endif
-- 
1.8.3.1