RDMA/uverbs: Export ib_open_qp() capability to user space

Allow processes that share the same XRC domain to open an existing
shareable QP.  This permits those processes to receive events on the
shared QP and transfer ownership, so that any process may modify the
QP.  The latter allows the creating process to exit, while a remaining
process can still transition it for path migration purposes.

Signed-off-by: Sean Hefty <sean.hefty@intel.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>
diff --git a/include/rdma/ib_user_verbs.h b/include/rdma/ib_user_verbs.h
index 100abbb..81aba3a 100644
--- a/include/rdma/ib_user_verbs.h
+++ b/include/rdma/ib_user_verbs.h
@@ -84,7 +84,8 @@
 	IB_USER_VERBS_CMD_POST_SRQ_RECV,
 	IB_USER_VERBS_CMD_OPEN_XRCD,
 	IB_USER_VERBS_CMD_CLOSE_XRCD,
-	IB_USER_VERBS_CMD_CREATE_XSRQ
+	IB_USER_VERBS_CMD_CREATE_XSRQ,
+	IB_USER_VERBS_CMD_OPEN_QP
 };
 
 /*
@@ -422,6 +423,17 @@
 	__u64 driver_data[0];
 };
 
+struct ib_uverbs_open_qp {
+	__u64 response;
+	__u64 user_handle;
+	__u32 pd_handle;
+	__u32 qpn;
+	__u8  qp_type;
+	__u8  reserved[7];
+	__u64 driver_data[0];
+};
+
+/* also used for open response */
 struct ib_uverbs_create_qp_resp {
 	__u32 qp_handle;
 	__u32 qpn;