Currently, x-blockdev-set-iothread changes the AioContext but does not
track the IOThread object itself within the block layer. This makes it
difficult to manage IOThread reference counting (put/get) during
dynamic context switching.

Introduce an 'iothread' field to BlockDriverState to store the current
assigned IOThread. Update qmp_x_blockdev_set_iothread to perform
proper reference counting using iothread_ref/put when moving nodes
between an IOThread and the main loop.

This ensures 'info iothreads' (holders) accurately reflects the block
device attachment state after dynamic migrations.

Signed-off-by: Zhang Chen <zhangckid@gmail.com>
---
 blockdev.c                       | 6 +++++-
 include/block/block_int-common.h | 5 +++++
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/blockdev.c b/blockdev.c
index 6e86c6262f..6e20579187 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -3683,8 +3683,12 @@ void qmp_x_blockdev_set_iothread(const char *node_name, StrOrNull *iothread,
             goto out;
         }
 
-        new_context = iothread_get_aio_context(obj);
+        new_context = iothread_ref_and_get_aio_context(obj, node_name);
+        bs->iothread = obj;
     } else {
+        if (bs->iothread) {
+            iothread_put_aio_context(bs->iothread, node_name);
+        }
         new_context = qemu_get_aio_context();
     }
 
diff --git a/include/block/block_int-common.h b/include/block/block_int-common.h
index 147c08155f..6edaf53377 100644
--- a/include/block/block_int-common.h
+++ b/include/block/block_int-common.h
@@ -1101,6 +1101,8 @@ typedef struct BdrvBlockStatusCache {
     int64_t data_end;
 } BdrvBlockStatusCache;
 
+typedef struct IOThread IOThread;
+
 struct BlockDriverState {
     /*
      * Protected by big QEMU lock or read-only after opening.  No special
@@ -1289,6 +1291,9 @@ struct BlockDriverState {
 
     /* array of write pointers' location of each zone in the zoned device. */
     BlockZoneWps *wps;
+
+    /* Track the iothread for detach aio context*/
+    IOThread *iothread;
 };
 
 struct BlockBackendRootState {
-- 
2.49.0