ibv_poll_cq.3 - Online Linux Manual Page

IBV_POLL_CQ - Online Linux Manual PageSection : 3
Updated : 2006-10-31
Source : libibverbs
Note : Libibverbs Programmer's Manual

NAMEibv_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);

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

NOTESEach 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.

AUTHORSDotan Barak <dotanba@gmail.com> 0

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