.\" -*- nroff -*-
.\" Licensed under the OpenIB.org BSD license (FreeBSD Variant) - See COPYING.md
.\"
.TH IBV_ATTACH_MCAST 3 2006-10-31 libibverbs "Libibverbs Programmer's Manual"
.SH "NAME"
ibv_attach_mcast, ibv_detach_mcast \- attach and detach a queue pair
(QPs) to/from a multicast group
.SH "SYNOPSIS"
.nf
.B #include <infiniband/verbs.h>
.sp
.BI "int ibv_attach_mcast(struct ibv_qp " "*qp" ", const union ibv_gid " "*gid" ",
.BI "                     uint16_t " "lid" ");
.sp
.BI "int ibv_detach_mcast(struct ibv_qp " "*qp" ", const union ibv_gid " "*gid" ",
.BI "                     uint16_t " "lid" ");
.fi
.SH "DESCRIPTION"
.B ibv_attach_mcast()
attaches the QP 
.I qp
to the multicast group having MGID
.I gid
and MLID 
.I lid\fR.
.PP
.B ibv_detach_mcast()
detaches the QP
.I qp
to the multicast group having MGID
.I gid
and MLID
.I lid\fR.
.SH "RETURN VALUE"
.B ibv_attach_mcast()
and
.B ibv_detach_mcast()
returns 0 on success, or the value of errno on failure (which indicates the failure reason).
.SH "NOTES"
Only QPs of Transport Service Type
.BR IBV_QPT_UD
may be attached to multicast groups.
.PP
If a QP is attached to the same multicast group multiple times, the QP will still receive a single copy of a multicast message.
.PP
In order to receive multicast messages, a join request for the
multicast group must be sent to the subnet administrator (SA), so that
the fabric's multicast routing is configured to deliver messages to
the local port.
.SH "SEE ALSO"
.BR ibv_create_qp (3)
.SH "AUTHORS"
.TP
Dotan Barak <dotanba@gmail.com>