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.\" $OpenBSD: ifq_deq_begin.9,v 1.1 2015/11/23 10:45:26 mpi Exp $
.\"
.\" Copyright (c) 2015 David Gwynne <dlg@openbsd.org>
.\"
.\" Permission to use, copy, modify, and distribute this software for any
.\" purpose with or without fee is hereby granted, provided that the above
.\" copyright notice and this permission notice appear in all copies.
.\"
.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
.\"
.Dd $Mdocdate: November 23 2015 $
.Dt IFQ_DEQ_BEGIN 9
.Os
.Sh NAME
.Nm ifq_deq_begin ,
.Nm ifq_deq_commit ,
.Nm ifq_deq_rollback
.Nd dequeue a mbuf from an interface sending queue
.Sh SYNOPSIS
.In net/if_var.h
.Ft struft mbuf *
.Fn ifq_deq_begin "struct ifqueue *ifq"
.Ft void
.Fn ifq_deq_commit "struct ifqueue *ifq" "struct mbuf *m"
.Ft void
.Fn ifq_deq_rollback "struct ifqueue *ifq" "struct mbuf *m"
.Sh DESCRIPTION
The
.Fn ifq_deq_begin
set of functions provides a non-atomic alternative to
.Fn ifq_dequeue .
.Bl -tag -width Ds
.It Fn ifq_deq_begin "struct ifqueue *ifq"
Get a reference to the next mbuf to be transmitted from the
.Fa ifq
interface send queue.
If an mbuf is to be transmitted, also acquire a lock on the send queue
to exclude modification or freeing of the referenced mbuf.
Its packet header must not be modified until the mbuf has been dequeued with
.Fn ifq_deq_commit .
.It Fn ifq_deq_commit "struct ifqueue *ifq" "struct mbuf *m"
Dequeue the mbuf
.Fa m
that was referenced by a previous call to
.Fn ifq_deq_begin
and release the lock on
.Fa ifq .
.It Fn ifq_deq_rollback "struct ifqueue *ifq" "struct mbuf *m"
Release the lock on the interface send queue
.Fa ifq
that was acquired while a reference to
.Fa m
was being held.
.El
.Sh CONTEXT
.Fn ifq_deq_begin ,
.Fn ifq_deq_commit ,
and
.Fn ifq_deq_rollback
can be called during autoconf, from process context, or from interrupt context.
.Sh RETURN VALUES
.Fn ifq_deq_begin
return the next mbuf to be transmitted by the interface.
If no packet is available for transmission,
.Dv NULL
is returned.
.Sh SEE ALSO
.Xr ifq_dequeue 9
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