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) */
               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.

SEE ALSO

       ibv_post_send(3), ibv_post_recv(3)

AUTHORS

       Dotan Barak <dotanba@gmail.com>