migration: Trivial cleanup on JSON writer of vmstate_save()

Two small cleanups in the same section of vmstate_save():

  - Check vmdesc before the "mixed null/non-null data in array" logic, to
  be crystal clear that it's only about the JSON writer, not the vmstate on
  its own in the migration stream.

  - Since we have is_null variable now, use that to replace a check.

Signed-off-by: Peter Xu <peterx@redhat.com>
Tested-by: Jiri Denemark <jdenemar@redhat.com>
Reviewed-by: Juraj Marcin <jmarcin@redhat.com>
Link: https://lore.kernel.org/r/20250114230746.3268797-17-peterx@redhat.com
Signed-off-by: Fabiano Rosas <farosas@suse.de>

diff --git a/migration/vmstate.c b/migration/vmstate.c
index 82bd005a832616d5946b4cd7e49bdf2a197b45fc..047a52af89e7a98627de6adb274643e16d9b6ed3 100644 (file)
--- a/migration/vmstate.c
+++ b/migration/vmstate.c
@@ -459,6 +459,8 @@ int vmstate_save_state_v(QEMUFile *f, const VMStateDescription *vmsd,
                 }
 
                 /*
+                 * This logic only matters when dumping VM Desc.
+                 *
                  * Due to the fake nullptr handling above, if there's mixed
                  * null/non-null data, it doesn't make sense to emit a
                  * compressed array representation spanning the entire array
@@ -466,7 +468,7 @@ int vmstate_save_state_v(QEMUFile *f, const VMStateDescription *vmsd,
                  * vs. nullptr). Search ahead for the next null/non-null element
                  * and start a new compressed array if found.
                  */
-                if (field->flags & VMS_ARRAY_OF_POINTER &&
+                if (vmdesc && (field->flags & VMS_ARRAY_OF_POINTER) &&
                     is_null != is_prev_null) {
 
                     is_prev_null = is_null;
@@ -504,7 +506,7 @@ int vmstate_save_state_v(QEMUFile *f, const VMStateDescription *vmsd,
                                     written_bytes);
 
                 /* If we used a fake temp field.. free it now */
-                if (inner_field != field) {
+                if (is_null) {
                     g_clear_pointer((gpointer *)&inner_field, g_free);
                 }