.\" -*- nroff -*-
.\"
.TH IBV_POLL_CQ 3 2006-10-31 libibverbs "Libibverbs Programmer's Manual"
.SH "NAME"
ibv_poll_cq \- poll a completion queue (CQ)
.SH "SYNOPSIS"
.nf
.B #include <infiniband/verbs.h>
.sp
.BI "int ibv_poll_cq(struct ibv_cq " "*cq" ", int " "num_entries" ,
.BI "                struct ibv_wc " "*wc" );
.fi
.SH "DESCRIPTION"
.B ibv_poll_cq()
polls the CQ
.I cq
for work completions and returns the first
.I num_entries
(or all available completions if the CQ contains fewer than this number) in the array
.I wc\fR.
The argument
.I wc
is a pointer to an array of ibv_wc structs, as defined in <infiniband/verbs.h>.
.PP
.nf
struct ibv_wc {
.in +8
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) */
.in -8
};
.sp
.fi
.PP
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:
.PP
.TP
.B IBV_WC_GRH \fR      GRH is present (valid only for UD QPs)
.TP
.B IBV_WC_WITH_IMM \fR Immediate data value is valid
.TP
.B IBV_WC_IP_CSUM_OK \fR TCP/UDP checksum over IPv4 and IPv4 header checksum are
verified.
Valid only when \fBdevice_cap_flags\fR in device_attr indicates current QP is
supported by checksum offload.
.PP
Not all
.I wc
attributes are always valid. If the completion status is other than
.B IBV_WC_SUCCESS\fR,
only the following attributes are valid: wr_id, status, qp_num, and vendor_err.
.SH "RETURN VALUE"
On success, 
.B ibv_poll_cq()
returns a non-negative value equal to the number of completions
found.  On failure, a negative value is returned.
.SH "NOTES"
.PP
Each polled completion is removed from the CQ and cannot be returned to it.
.PP
The user should consume work completions at a rate that prevents CQ
overrun from occurrence.  In case of a CQ overrun, the async event
.B IBV_EVENT_CQ_ERR
will be triggered, and the CQ cannot be used.
.SH "SEE ALSO"
.BR ibv_post_send (3),
.BR ibv_post_recv (3)
.SH "AUTHORS"
.TP
Dotan Barak <dotanba@gmail.com>