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.\" -*- 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
.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>