ibv_get_cq_event, ibv_ack_cq_events

#include <rdma/verbs.h>
int ibv_get_cq_event(struct ibv_comp_channel *channel, struct ibv_cq **cq, void **cq_context); 
void ibv_ack_cq_events(struct ibv_cq *cq, unsigned int nevents);

1. The following code example demonstrates one possible way to work with completion events. It performs the following steps:
   1. Preparation
      1. Creates a CQ.
      2. Requests for notification upon a new (first) completion event.
   2. Completion handling routine
      1. Waits for the completion event and ack it.
      2. Requests for notification upon the next completion event.
      3. Empties the CQ.
      Note: An extra event might be triggered without having a corresponding completion entry in the CQ. This occurs if a completion entry is added to the CQ between requesting for notification and emptying the CQ, and then the CQ is emptied.

   		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 */
   		if (ibv_req_notify_cq(cq, 0)) {
   				fprintf(stderr, "Couldn't request CQ notification\n");
   				return 1;
   		}
   
   		.
   		.
   		.
   		/* Wait for the completion event */
   		if (ibv_get_cq_event(channel, &ev_cq, &ev_ctx)) {
   				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 */ 
   		if (ibv_req_notify_cq(cq, 0)) {
   				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\n");
   						return 1;
   				}
   				if (wc.status != IBV_WC_SUCCESS) {
   						fprintf(stderr, "Completion with status 0x%x was found\n", wc.status);
   						return 1;
   				}
   		} while (ne);

2. The following code example demonstrates one possible way to work with completion events in nonblocking mode. It performs the following steps:
   1. Sets the completion event channel in the non-blocked mode.
   2. Polls the channel until there it has a completion event.
   3. Gets the completion event and acknowledges it.

   /* 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; 
   } 
   /*
   * 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_polfd;, 1, ms_timeout);
   		} while (rc == 0);
   		if (rc &lt; 0){  fprintf(stderr, "poll failed\n");
   		return 1;
   		}
    ev_cq = cq;
    /* Wait for the completion event */
    if (ibv_get_cq_event(channel, &ev_cq, &ev_ctx)) {
    		fprintf(stderr, "Failed to get cq_event\n");
    		return 1;
    }
     /* Ack the event */
    ibv_ack_cq_events(ev_cq, 1);