nbd_aio_in_flight - Man Page

check how many aio commands are still in flight

Synopsis

 #include <libnbd.h>

 int nbd_aio_in_flight (struct nbd_handle *h);

Description

Return the number of in-flight aio commands that are still awaiting a response from the server before they can be retired.  If this returns a non-zero value when requesting a disconnect from the server (see nbd_aio_disconnect(3) and nbd_shutdown(3)), libnbd does not try to wait for those commands to complete gracefully; if the server strands commands while shutting down, nbd_aio_command_completed(3) will report those commands as failed with a status of ENOTCONN.

Return Value

This call returns an integer ≥ 0.

Errors

On error -1 is returned.

Refer to “ERROR HANDLING” in libnbd(3) for how to get further details of the error.

Handle State

The handle must be connected with the server, or shut down, or dead, otherwise this call will return an error.

Version

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:

 #define LIBNBD_HAVE_NBD_AIO_IN_FLIGHT 1

Example

This example is also available as examples/aio-connect-read.c in the libnbd source code.

 /* This example shows how to use the AIO (asynchronous) low
  * level API to connect to a server and read the disk.
  *
  * Here are a few ways to try this example:
  *
  * nbdkit -U - linuxdisk . \
  *   --run './aio-connect-read $unixsocket'
  *
  * nbdkit -U - floppy . \
  *   --run './aio-connect-read $unixsocket'
  *
  * nbdkit -U - pattern size=1M \
  *   --run './aio-connect-read $unixsocket'
  */
 
 #include <stdio.h>
 #include <stdlib.h>
 #include <stdint.h>
 #include <inttypes.h>
 #include <assert.h>
 
 #include <libnbd.h>
 
 #define NR_SECTORS 32
 #define SECTOR_SIZE 512
 
 struct data {
   uint64_t offset;
   char sector[SECTOR_SIZE];
 };
 
 static int
 hexdump (void *user_data, int *error)
 {
   struct data *data = user_data;
   FILE *pp;
 
   printf ("sector at offset 0x%" PRIx64 ":\n",
           data->offset);
   pp = popen ("hexdump -C", "w");
   if (pp == NULL) {
     perror ("popen: hexdump");
     exit (EXIT_FAILURE);
   }
   fwrite (data->sector, SECTOR_SIZE, 1, pp);
   pclose (pp);
   printf ("\n");
 
   /* Returning 1 from the callback automatically retires
    * the command.
    */
   return 1;
 }
 
 int
 main (int argc, char *argv[])
 {
   struct nbd_handle *nbd;
   struct data data[NR_SECTORS];
   size_t i;
 
   if (argc != 2) {
     fprintf (stderr, "%s socket\n", argv[0]);
     exit (EXIT_FAILURE);
   }
 
   /* Create the libnbd handle. */
   nbd = nbd_create ();
   if (nbd == NULL) {
     fprintf (stderr, "%s\n", nbd_get_error ());
     exit (EXIT_FAILURE);
   }
 
   /* Connect to the NBD server over a Unix domain socket.
    * This only starts the connection.
    */
   if (nbd_aio_connect_unix (nbd, argv[1]) == -1) {
     fprintf (stderr, "%s\n", nbd_get_error ());
     exit (EXIT_FAILURE);
   }
 
   /* Wait for the connection to complete.  The use of
    * nbd_poll here is only as an example.  You could also
    * integrate this with poll(2), glib or another main
    * loop.  Read libnbd(3) and the source file lib/poll.c.
    */
   while (!nbd_aio_is_ready (nbd)) {
     if (nbd_poll (nbd, -1) == -1) {
       fprintf (stderr, "%s\n", nbd_get_error ());
       exit (EXIT_FAILURE);
     }
   }
 
   assert (nbd_get_size (nbd) >= NR_SECTORS * SECTOR_SIZE);
 
   /* Issue read commands for the first NR sectors. */
   for (i = 0; i < NR_SECTORS; ++i) {
     data[i].offset = i * SECTOR_SIZE;
 
     /* The callback (hexdump) is called when the command
      * completes.  The buffer must continue to exist while
      * the command is running.
      */
     if (nbd_aio_pread (nbd, data[i].sector, SECTOR_SIZE,
                        data[i].offset,
                        (nbd_completion_callback) {
                          .callback = hexdump,
                          .user_data = &data[i],
                        }, 0) == -1) {
       fprintf (stderr, "%s\n", nbd_get_error ());
       exit (EXIT_FAILURE);
     }
   }
 
   /* Run the main loop until all the commands have
    * completed and retired.  Again the use of nbd_poll
    * here is only as an example.
    */
   while (nbd_aio_in_flight (nbd) > 0) {
     if (nbd_poll (nbd, -1) == -1) {
       fprintf (stderr, "%s\n", nbd_get_error ());
       exit (EXIT_FAILURE);
     }
   }
 
   /* Close the libnbd handle. */
   nbd_close (nbd);
 
   exit (EXIT_SUCCESS);
 }

See Also

nbd_aio_command_completed(3), nbd_aio_disconnect(3), nbd_create(3), nbd_shutdown(3), libnbd(3).

Authors

Eric Blake

Richard W.M. Jones

License

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

Referenced By

libnbd(3), NBD(3), nbd_aio_disconnect(3), nbd_aio_get_direction(3), nbd_shutdown(3).

2020-10-05 libnbd-1.5.4