int ibv_get_cq_event(struct ibv_comp_channel *channel,
                     struct ibv_cq **cq, void **cq_context);

struct ibv_context *context;
struct ibv_cq *cq;
void *ev_ctx = NULL; /* can be initialized with other values for the CQ context */
 
/* Create a CQ, which is associated with a Completion Event Channel */
cq = ibv_create_cq(ctx, 1, ev_ctx, channel, 0);
if (!cq) {
        fprintf(stderr, "Failed to create CQ\n");
        return -1;
}
 
/* Request notification before any completion can be created (to prevent races) */
ret = ibv_req_notify_cq(cq, 0);
if (ret) {
        fprintf(stderr, "Couldn't request CQ notification\n");
        return -1;
}
 
.
. /* Perform an operation that will eventually end with Work Completion */
.
 
/* The following code will be called each time you need to read a Work Completion */
struct ibv_cq *ev_cq;
void *ev_ctx;
int ret;
int ne;
 
/* Wait for the Completion event */
ret = ibv_get_cq_event(channel, &ev_cq, &ev_ctx);
if (ret) {
        fprintf(stderr, "Failed to get CQ event\n");
        return -1;
}
/* Ack the event */
ibv_ack_cq_events(ev_cq, 1);
 
/* Request notification upon the next completion event */
ret = ibv_req_notify_cq(ev_cq, 0);
if (ret) {
        fprintf(stderr, "Couldn't request CQ notification\n");
        return -1;
}
 
/* Empty the CQ: poll all of the completions from the CQ (if any exist) */
do {
        ne = ibv_poll_cq(cq, 1, &wc);
        if (ne < 0) {
                fprintf(stderr, "Failed to poll completions from the CQ: ret = %d\n",
                        ne);
                return -1;
        }
        /* there may be an extra event with no completion in the CQ */
        if (ne == 0)
                continue;
 
        if (wc.status != IBV_WC_SUCCESS) {
                fprintf(stderr, "Completion with status 0x%x was found\n",
wc.status);
                return -1;
        }
} while (ne);

struct ibv_context *context;
struct ibv_cq *cq;
void *ev_ctx = NULL; /* can be initialized with other values for the CQ context */
 
/* Create a CQ, which is associated with a Completion Event Channel */
cq = ibv_create_cq(ctx, 1, ev_ctx, channel, 0);
if (!cq) {
        fprintf(stderr, "Failed to create CQ\n");
        return -1;
}
 
/* Request notification before any completion can be created (to prevent races) */
ret = ibv_req_notify_cq(cq, 0);
if (ret) {
        fprintf(stderr, "Couldn't request CQ notification\n");
        return -1;
}
 
int flags;
int ret;
 
/* The following code will be called only once, after the Completion Event Channel 
was created */
printf("Changing the mode of Completion events to be read in non-blocking\n");
 
/* change the blocking mode of the completion channel */
flags = fcntl(channel->fd, F_GETFL);
rc = fcntl(channel->fd, F_SETFL, flags | O_NONBLOCK);
if (rc < 0) {
        fprintf(stderr, "Failed to change file descriptor of Completion Event Channel\n");
        return -1;
}
 
.
. /* Perform an operation that will eventually end with Work Completion */
.
 
/* The following code will be called each time you need to read a Work Completion */
 
struct pollfd my_pollfd;
struct ibv_cq *ev_cq;
void *ev_ctx;
int ne;
int ms_timeout = 10;
 
/*
 * poll the channel until it has an event and sleep ms_timeout
 * milliseconds between any iteration
 */
my_pollfd.fd      = channel->fd;
my_pollfd.events  = POLLIN;
my_pollfd.revents = 0;
do {
        rc = poll(&my_pollfd, 1, ms_timeout);
} while (rc == 0);
if (rc < 0) {
        fprintf(stderr, "poll failed\n");
        return -1;
}
ev_cq = cq;
/* Wait for the completion event */
ret = ibv_get_cq_event(channel, &ev_cq, &ev_ctx);
if (ret) {
        fprintf(stderr, "Failed to get cq_event\n");
        return -1;
}
/* Ack the event */
ibv_ack_cq_events(ev_cq, 1);
 
/* Request notification upon the next completion event */
ret = ibv_req_notify_cq(ev_cq, 0);
if (ret) {
        fprintf(stderr, "Couldn't request CQ notification\n");
        return -1;
}
 
/* Empty the CQ: poll all of the completions from the CQ (if any exist) */
do {
        ne = ibv_poll_cq(cq, 1, &wc);
        if (ne < 0) {
                fprintf(stderr, "Failed to poll completions from the CQ: ret = %d\n",
                        ne);
                return -1;
        }
        /* there may be an extra event with no completion in the CQ */
        if (ne == 0)
                continue;
 
        if (wc.status != IBV_WC_SUCCESS) {
                fprintf(stderr, "Completion with status 0x%x was found\n",
wc.status);
                return -1;
        }
} while (ne);