From: Alexandr Moshkov <dtalexundeer@yandex-team.ru>

Prepare for future inflight region migration for vhost-user-blk.
We need to migrate size, queue_size, and inner buffer.

So firstly it migrate size and queue_size fields, then allocate memory
for buffer with
migrated size, then migrate inner buffer itself.

Signed-off-by: Alexandr Moshkov <dtalexundeer@yandex-team.ru>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Message-Id: <20260115081103.655749-5-dtalexundeer@yandex-team.ru>
---
 hw/virtio/vhost.c | 56 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 56 insertions(+)

diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
index c6a5928cb1..52801c1796 100644
--- a/hw/virtio/vhost.c
+++ b/hw/virtio/vhost.c
@@ -1918,6 +1918,62 @@ void vhost_get_features_ex(struct vhost_dev *hdev,
     }
 }
 
+static bool vhost_inflight_buffer_pre_load(void *opaque, Error **errp)
+{
+    struct vhost_inflight *inflight = opaque;
+
+    int fd = -1;
+    void *addr = qemu_memfd_alloc("vhost-inflight", inflight->size,
+                                  F_SEAL_GROW | F_SEAL_SHRINK | F_SEAL_SEAL,
+                                  &fd, errp);
+    if (*errp) {
+        return -ENOMEM;
+    }
+
+    inflight->offset = 0;
+    inflight->addr = addr;
+    inflight->fd = fd;
+
+    return true;
+}
+
+const VMStateDescription vmstate_vhost_inflight_region_buffer = {
+    .name = "vhost-inflight-region/buffer",
+    .pre_load_errp = vhost_inflight_buffer_pre_load,
+    .fields = (const VMStateField[]) {
+        VMSTATE_VBUFFER_UINT64(addr, struct vhost_inflight, 0, NULL, size),
+        VMSTATE_END_OF_LIST()
+    }
+};
+
+static bool vhost_inflight_region_post_load(void *opaque,
+                                           int version_id,
+                                           Error **errp)
+{
+    struct vhost_inflight *inflight = opaque;
+
+    if (inflight->addr == NULL) {
+        error_setg(errp, "inflight buffer subsection has not been loaded");
+        return false;
+    }
+
+    return true;
+}
+
+const VMStateDescription vmstate_vhost_inflight_region = {
+    .name = "vhost-inflight-region",
+    .post_load_errp = vhost_inflight_region_post_load,
+    .fields = (const VMStateField[]) {
+        VMSTATE_UINT64(size, struct vhost_inflight),
+        VMSTATE_UINT16(queue_size, struct vhost_inflight),
+        VMSTATE_END_OF_LIST()
+    },
+    .subsections = (const VMStateDescription * const []) {
+        &vmstate_vhost_inflight_region_buffer,
+        NULL
+    }
+};
+
 void vhost_ack_features_ex(struct vhost_dev *hdev, const int *feature_bits,
                            const uint64_t *features)
 {
-- 
MST