Hi Pavel,

> We don't even allow not plain data msg_control, which is disallowed in __sys_{send,revb}msg_sock().

Can't we better remove these checks and allow msg_control?
For me it's a limitation that I would like to be removed.

If there's a cost using IO_WQ_WORK_FS, would it be possible to use IO_WQ_WORK_FS only it msg_control is actually used?

  if (msg->msg_control || msg->msg_controllen)
      static const struct io_op_def sendmsg_control_op_def = {
         ...
      };

      something = &sendmsg_control_op_def;
  }

metze