From: Fabiano Rosas <farosas@suse.de>

The QAPI converts an empty list on the block-bitmap-mapping input into
a NULL BitmapMigrationNodeAliasList. The empty list is a valid input
for the block-bitmap-mapping option, so commit 3cba22c9ad ("migration:
Fix block_bitmap_mapping migration") started using the
s->parameters.has_block_bitmap_mapping field to tell when the user has
passed in an empty list vs. when no list has been passed at all.

Using s->parameters.has_block_bitmap_mapping field is only possible
because MigrationParameters has had its members made optional due to
historical reasons.

In order to make improvements to the way configuration options are set
for a migration, we'd like to reduce the open-coded usage of the has_*
fields of the global configuration object (s->parameters).

Add a separate boolean to track the status of the block_bitmap_mapping
option.

No functional change intended.

(this was verified to not regress iotest 300, which is the test that
3cba22c9ad refers to)

CC: Kevin Wolf <kwolf@redhat.com>
Acked-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
Link: https://lore.kernel.org/r/20251215220041.12657-10-farosas@suse.de
Signed-off-by: Peter Xu <peterx@redhat.com>
---
 migration/migration.h          | 7 +++++++
 migration/migration-hmp-cmds.c | 3 ++-
 migration/options.c            | 6 +++---
 3 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/migration/migration.h b/migration/migration.h
index e4b4f25deb..4d42e8f9a7 100644
--- a/migration/migration.h
+++ b/migration/migration.h
@@ -514,6 +514,13 @@ struct MigrationState {
     QemuEvent postcopy_package_loaded_event;
 
     GSource *hup_source;
+
+    /*
+     * The block-bitmap-mapping option is allowed to be an empty list,
+     * therefore we need a way to know whether the user has given
+     * anything as input.
+     */
+    bool has_block_bitmap_mapping;
 };
 
 void migrate_set_state(MigrationStatus *state, MigrationStatus old_state,
diff --git a/migration/migration-hmp-cmds.c b/migration/migration-hmp-cmds.c
index 8b1096db86..a2863e6a2f 100644
--- a/migration/migration-hmp-cmds.c
+++ b/migration/migration-hmp-cmds.c
@@ -321,6 +321,7 @@ static void monitor_print_cpr_exec_command(Monitor *mon, strList *args)
 void hmp_info_migrate_parameters(Monitor *mon, const QDict *qdict)
 {
     MigrationParameters *params;
+    MigrationState *s = migrate_get_current();
 
     params = qmp_query_migrate_parameters(NULL);
 
@@ -404,7 +405,7 @@ void hmp_info_migrate_parameters(Monitor *mon, const QDict *qdict)
             MigrationParameter_str(MIGRATION_PARAMETER_XBZRLE_CACHE_SIZE),
             params->xbzrle_cache_size);
 
-        if (params->has_block_bitmap_mapping) {
+        if (s->has_block_bitmap_mapping) {
             const BitmapMigrationNodeAliasList *bmnal;
 
             monitor_printf(mon, "%s:\n",
diff --git a/migration/options.c b/migration/options.c
index cb127e9c72..20e9438656 100644
--- a/migration/options.c
+++ b/migration/options.c
@@ -786,7 +786,7 @@ bool migrate_has_block_bitmap_mapping(void)
 {
     MigrationState *s = migrate_get_current();
 
-    return s->parameters.has_block_bitmap_mapping;
+    return s->has_block_bitmap_mapping;
 }
 
 uint32_t migrate_checkpoint_delay(void)
@@ -1071,7 +1071,7 @@ MigrationParameters *qmp_query_migrate_parameters(Error **errp)
     params->has_announce_step = true;
     params->announce_step = s->parameters.announce_step;
 
-    if (s->parameters.has_block_bitmap_mapping) {
+    if (s->has_block_bitmap_mapping) {
         params->has_block_bitmap_mapping = true;
         params->block_bitmap_mapping =
             QAPI_CLONE(BitmapMigrationNodeAliasList,
@@ -1559,7 +1559,7 @@ static void migrate_params_apply(MigrationParameters *params)
         qapi_free_BitmapMigrationNodeAliasList(
             s->parameters.block_bitmap_mapping);
 
-        s->parameters.has_block_bitmap_mapping = true;
+        s->has_block_bitmap_mapping = true;
         s->parameters.block_bitmap_mapping =
             QAPI_CLONE(BitmapMigrationNodeAliasList,
                        params->block_bitmap_mapping);
-- 
2.50.1