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       ibv_poll_cq - poll a completion queue (CQ)


       #include <infiniband/verbs.h>

       int ibv_poll_cq(struct ibv_cq *cq, int num_entries,
                       struct ibv_wc *wc);


       ibv_poll_cq()  polls  the  CQ  cq  for work completions and returns the
       first num_entries (or all available  completions  if  the  CQ  contains
       fewer  than this number) in the array wc.  The argument wc is a pointer
       to an array of ibv_wc structs, as defined in <infiniband/verbs.h>.

       struct ibv_wc {
               uint64_t                wr_id;          /* ID of the completed Work Request (WR) */
               enum ibv_wc_status      status;         /* Status of the operation */
               enum ibv_wc_opcode      opcode;         /* Operation type specified in the completed WR */
               uint32_t                vendor_err;     /* Vendor error syndrome */
               uint32_t                byte_len;       /* Number of bytes transferred */
               uint32_t                imm_data;       /* Immediate data (in network byte order) */
               uint32_t                qp_num;         /* Local QP number of completed WR */
               uint32_t                src_qp;         /* Source QP number (remote QP number) of completed WR (valid only for UD QPs) */
               int                     wc_flags;       /* Flags of the completed WR */
               uint16_t                pkey_index;     /* P_Key index (valid only for GSI QPs) */
               uint16_t                slid;           /* Source LID */
               uint8_t                 sl;             /* Service Level */
               uint8_t                 dlid_path_bits; /* DLID path bits (not applicable for multicast messages) */

       The attribute wc_flags describes the properties of the work completion.
       It is either 0 or the bitwise OR of one or more of the following flags:

       IBV_WC_GRH  GRH is present (valid only for UD QPs)

       IBV_WC_WITH_IMM  Immediate data value is valid

       Not all wc attributes are always valid. If  the  completion  status  is
       other  than  IBV_WC_SUCCESS,  only  the following attributes are valid:
       wr_id, status, qp_num, and vendor_err.


       On success, ibv_poll_cq() returns a non-negative  value  equal  to  the
       number of completions found.  On failure, a negative value is returned.


       Each polled completion is removed from the CQ and cannot be returned to

       The  user  should  consume  work completions at a rate that prevents CQ
       overrun from occurrence.  In case of a  CQ  overrun,  the  async  event
       IBV_EVENT_CQ_ERR will be triggered, and the CQ cannot be used.


       ibv_post_send(3), ibv_post_recv(3)


       Dotan Barak <>