NAME

       ibv_poll_cq - poll a completion queue (CQ)

SYNOPSIS

       #include <infiniband/verbs.h>

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

DESCRIPTION

       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 */
               union {
                       __be32                  imm_data;         /* Immediate data (in network byte order) */
                       uint32_t                invalidated_rkey; /* Local RKey that was invalidated */
               };
               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) */
               unsigned 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

       IBV_WC_WITH_INV    Invalidated   RKey  data  value  is  valid  (cannot  be  combined  with
       IBV_WC_WITH_IMM)

       IBV_WC_IP_CSUM_OK  TCP/UDP checksum over IPv4 and IPv4 header checksum are
              verified.  Valid only when device_cap_flags in device_attr indicates current QP  is
              supported by checksum offload.

       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.

RETURN VALUE

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

NOTES

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

       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_WC_DRIVER1   will   be   reported   as   a   response   to   IBV_WR_DRIVER1    opcode;
       IBV_WC_DRIVER2/IBV_WC_DRIVER3 will be reported on specific driver operations.

SEE ALSO

       ibv_post_send(3), ibv_post_recv(3)

AUTHORS

       Dotan Barak <dotanba@gmail.com>