make migration state callback optionally asynchronous (#608)

Some devices need the migration state callback to be asynchronous. The simplest way to implement this is to require from the callback to return -1 and set errno to EBUSY, not process any other new messages (vfu_ctx_run returns -1 and sets errno to EBUSY), and provide a way to the user to complete migration (vfu_migr_done).

Signed-off-by: Thanos Makatos <thanos.makatos@nutanix.com>
Reviewed-by: John Levon <john.levon@nutanix.com>
Reviewed-by: Swapnil Ingle <swapnil.ingle@nutanix.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/lib/private.h b/lib/private.h
index 93a354b..05d2fa4 100644
--- a/lib/private.h
+++ b/lib/private.h
@@ -169,6 +169,8 @@ struct vfu_ctx {
     size_t                  client_max_data_xfer_size;
 
     struct migration        *migration;
+    bool                    migr_trans_pending;
+    vfu_msg_t               *migr_trans_msg;
 
     uint32_t                irq_count[VFU_DEV_NUM_IRQS];
     vfu_irqs_t              *irqs;