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|
/* Example usage with nbdkit:
*
* nbdkit -U - --filter=noparallel memory 2M \
* --run './batched-read-write $unixsocket'
*
* This will attempt to batch a large aio read request immediately
* followed by a large aio write request, prior to waiting for any
* command replies from the server. A naive client that does not check
* for available read data related to the first command while trying
* to write data for the second command, coupled with a server that
* only processes commands serially, would cause deadlock (both
* processes fill up their write buffers waiting for a reader); thus,
* this tests that libnbd is smart enough to always respond to replies
* for in-flight requests even when it has batched up other commands
* to write.
*
* To run it against a remote server over TCP:
*
* ./batched-read-write hostname port
* or
* ./batched-read-write nbd://hostname:port
*/
#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <stdint.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <poll.h>
#include <time.h>
#include <assert.h>
#include <signal.h>
#include <libnbd.h>
/* The single NBD handle. */
static struct nbd_handle *nbd;
/* Buffers used for the test. */
static char *in, *out;
static int64_t packetsize;
static int
try_deadlock (void *arg)
{
struct pollfd fds[1];
size_t i;
int64_t cookies[2], done;
unsigned dir;
int r;
/* Issue commands. */
cookies[0] = nbd_aio_pread (nbd, in, packetsize, 0,
NBD_NULL_COMPLETION, 0);
if (cookies[0] == -1) {
fprintf (stderr, "%s\n", nbd_get_error ());
goto error;
}
cookies[1] = nbd_aio_pwrite (nbd, out, packetsize, packetsize,
NBD_NULL_COMPLETION, 0);
if (cookies[1] == -1) {
fprintf (stderr, "%s\n", nbd_get_error ());
goto error;
}
/* Now wait for commands to retire, or for deadlock to occur */
while (nbd_aio_in_flight (nbd) > 0) {
if (nbd_aio_is_dead (nbd) || nbd_aio_is_closed (nbd)) {
fprintf (stderr, "connection is dead or closed\n");
goto error;
}
fds[0].fd = nbd_aio_get_fd (nbd);
fds[0].events = 0;
fds[0].revents = 0;
dir = nbd_aio_get_direction (nbd);
if ((dir & LIBNBD_AIO_DIRECTION_READ) != 0)
fds[0].events |= POLLIN;
if ((dir & LIBNBD_AIO_DIRECTION_WRITE) != 0)
fds[0].events |= POLLOUT;
if (poll (fds, 1, -1) == -1) {
perror ("poll");
goto error;
}
if ((dir & LIBNBD_AIO_DIRECTION_READ) != 0 &&
(fds[0].revents & POLLIN) != 0)
nbd_aio_notify_read (nbd);
else if ((dir & LIBNBD_AIO_DIRECTION_WRITE) != 0 &&
(fds[0].revents & POLLOUT) != 0)
nbd_aio_notify_write (nbd);
/* If a command is ready to retire, retire it. */
while ((done = nbd_aio_peek_command_completed (nbd)) > 0) {
for (i = 0; i < sizeof cookies / sizeof cookies[0]; ++i) {
if (cookies[i] == done) {
r = nbd_aio_command_completed (nbd, cookies[i]);
if (r == -1) {
fprintf (stderr, "%s\n", nbd_get_error ());
goto error;
}
assert (r == 1);
cookies[i] = 0;
}
}
}
}
assert (nbd_aio_in_flight (nbd) == 0);
printf ("finished OK\n");
return 0;
error:
fprintf (stderr, "failed\n");
return -1;
}
static void
alarm_handler (int sig)
{
fprintf (stderr, "alarm fired; deadlock probably occurred\n");
_exit (EXIT_FAILURE);
}
int
main (int argc, char *argv[])
{
int64_t exportsize;
if (argc < 2 || argc > 3) {
fprintf (stderr, "%s uri | socket | hostname port\n", argv[0]);
exit (EXIT_FAILURE);
}
nbd = nbd_create ();
if (nbd == NULL) {
fprintf (stderr, "%s\n", nbd_get_error ());
exit (EXIT_FAILURE);
}
/* Connect synchronously as this is simpler. */
if (argc == 2) {
if (strstr (argv[1], "://")) {
if (nbd_connect_uri (nbd, argv[1]) == -1) {
fprintf (stderr, "%s\n", nbd_get_error ());
exit (EXIT_FAILURE);
}
}
else if (nbd_connect_unix (nbd, argv[1]) == -1) {
fprintf (stderr, "%s\n", nbd_get_error ());
exit (EXIT_FAILURE);
}
}
else {
if (nbd_connect_tcp (nbd, argv[1], argv[2]) == -1) {
fprintf (stderr, "%s\n", nbd_get_error ());
exit (EXIT_FAILURE);
}
}
if (nbd_is_read_only (nbd) == 1) {
fprintf (stderr, "%s: error: this NBD export is read-only\n", argv[0]);
exit (EXIT_FAILURE);
}
exportsize = nbd_get_size (nbd);
if (exportsize == -1) {
fprintf (stderr, "%s\n", nbd_get_error ());
exit (EXIT_FAILURE);
}
packetsize = exportsize / 2;
if (packetsize > 2 * 1024 * 1024)
packetsize = 2 * 1024 * 1024;
in = malloc (packetsize);
out = malloc (packetsize);
if (!in || !out) {
fprintf (stderr, "insufficient memory\n");
exit (EXIT_FAILURE);
}
/* Attempt to be non-destructive, by writing what file already contains */
if (nbd_pread (nbd, out, packetsize, packetsize, 0) == -1) {
fprintf (stderr, "sync read failed: %s\n", nbd_get_error ());
exit (EXIT_FAILURE);
}
/* When not debugging, set an alarm, in case this test deadlocks
* instead of succeeding
*/
if (nbd_get_debug (nbd) < 1) {
signal (SIGALRM, alarm_handler);
alarm (10);
}
if (try_deadlock (NULL) == -1)
exit (EXIT_FAILURE);
if (nbd_shutdown (nbd, 0) == -1) {
fprintf (stderr, "%s\n", nbd_get_error ());
exit (EXIT_FAILURE);
}
nbd_close (nbd);
return EXIT_SUCCESS;
}
|
