Provided by: libnbd-dev_1.2.2-1ubuntu2_amd64 bug


       nbd_aio_get_direction - return the read or write direction


        #include <libnbd.h>

        unsigned nbd_aio_get_direction (struct nbd_handle *h);


       Return the current direction of this connection, which means whether we are next expecting
       to read data from the server, write data to the server, or both.  It returns

       0   We are not expected to interact with the server file descriptor from the current
           state. It is not worth attempting to use poll(2); if the connection is not dead, then
           state machine progress must instead come from some other means such as

           We are expected next to read from the server.  If using poll(2) you would set "events
           = POLLIN".  If "revents" returns "POLLIN" or "POLLHUP" you would then call

           Note that once libnbd reaches nbd_aio_is_ready(3), this direction is returned even
           when there are no commands in flight (see nbd_aio_in_flight(3)). In a single-threaded
           use of libnbd, it is not worth polling until after issuing a command, as otherwise the
           server will never wake up the poll. In a multi-threaded scenario, you can have one
           thread begin a polling loop prior to any commands, but any other thread that issues a
           command will need a way to kick the polling thread out of poll in case issuing the
           command changes the needed polling direction. Possible ways to do this include polling
           for activity on a pipe-to-self, or using pthread_kill(3) to send a signal that is
           masked except during ppoll(2).

           We are expected next to write to the server.  If using poll(2) you would set "events =
           POLLOUT".  If "revents" returns "POLLOUT" you would then call nbd_aio_notify_write(3).

           We are expected next to either read or write to the server.  If using poll(2) you
           would set "events = POLLIN|POLLOUT".  If only one of "POLLIN" or "POLLOUT" is
           returned, then see above.  However, if both are returned, it is better to call only
           nbd_aio_notify_read(3), as processing the server's reply may change the state of the
           connection and invalidate the need to write more commands.


       This call returns a bitmask.


       This function does not fail.


       This function first appeared in libnbd 1.0.

       If you need to test if this function is available at compile time check if the following
       macro is defined:



       nbd_aio_in_flight(3), nbd_create(3), libnbd(3).


       Eric Blake

       Richard W.M. Jones


       Copyright (C) 2019 Red Hat Inc.


       This library is free software; you can redistribute it and/or modify it under the terms of
       the GNU Lesser General Public License as published by the Free Software Foundation; either
       version 2 of the License, or (at your option) any later version.

       This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
       without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
       See the GNU Lesser General Public License for more details.

       You should have received a copy of the GNU Lesser General Public License along with this
       library; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth
       Floor, Boston, MA 02110-1301 USA