.\"     $OpenBSD: ifq_enqueue.9,v 1.9 2015/12/10 06:58:56 jmc Exp $
.\"
.\"  Copyright (c) 2015 David Gwynne <dlg@openbsd.org>
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.Dd $Mdocdate: December 10 2015 $
.Dt IFQ_ENQUEUE 9
.Os
.Sh NAME
.Nm ifq_enqueue ,
.Nm ifq_dequeue ,
.Nm ifq_purge ,
.Nm ifq_len ,
.Nm ifq_empty ,
.Nm ifq_set_oactive ,
.Nm ifq_clr_oactive ,
.Nm ifq_is_oactive ,
.Nm ifq_restart ,
.Nm ifq_barrier
.Nd interface send queue API
.Sh SYNOPSIS
.In net/if_var.h
.Ft int
.Fn ifq_enqueue "struct ifqueue *ifq" "struct mbuf *m"
.Ft struft mbuf *
.Fn ifq_dequeue "struct ifqueue *ifq"
.Ft unsigned int
.Fn ifq_purge "struct ifqueue *ifq"
.Ft unsigned int
.Fn ifq_len "struct ifqueue *ifq"
.Ft unsigned int
.Fn ifq_empty "struct ifqueue *ifq"
.Ft void
.Fn ifq_set_oactive "struct ifqueue *ifq"
.Ft void
.Fn ifq_clr_oactive "struct ifqueue *ifq"
.Ft unsigned int
.Fn ifq_is_oactive "struct ifqueue *ifq"
.Ft void
.Fn ifq_restart "struct ifqueue *ifq"
.Ft void
.Fn ifq_barrier "struct ifqueue *ifq"
.Sh DESCRIPTION
The ifqueue API provides implementions of data structures and
operations for the network stack to queue mbufs for a network driver
to dequeue from its start routine for transmission.
.Bl -tag -width Ds
.It Fn ifq_enqueue "struct ifqueue *ifq" "struct mbuf *m"
Enqueue mbuf
.Fa m
on the
.Fa ifq
interface send queue.
If the queue rejects the packet it will be freed with
.Xr m_freem 9
and counted as a drop.
.It Fn ifq_dequeue "struct ifqueue *ifq"
Dequeue the next mbuf to be transmitted from the
.Fa ifq
interface send queue.
.It Fn ifq_purge "struct ifqueue *ifq"
Free all the mbufs on the interface send queue
.Fa ifq .
Freed mbufs will be accounted as drops.
.It Fn ifq_len "struct ifqueue *ifq"
Return the number of mbufs on the interface send queue
.Fa ifq .
Note that while
.Fn ifq_len
may report that mbufs are on the queue, the current queue
discipline may not make them available for dequeueing with
.Fn ifq_dequeue
or
.Fn ifq_deq_begin .
.It Fn ifq_empty "struct ifqueue *ifq"
Return if the interface send queue
.Fa ifq
is empty.
.It Fn ifq_set_oactive "struct ifqueue *ifq"
.Fn ifq_set_oactive
is called by the relevant driver to mark the hardware associated
with the interface send queue
.Fa ifq
as unable to transmit more packets.
.It Fn ifq_clr_oactive "struct ifqueue *ifq"
.Fn ifq_clr_oactive
is called by the relevant driver to clear the "active" mark on the
hardware associated with the interface send queue
.Fa ifq ,
meaning it is now able to transmit packets.
.It Fn ifq_is_oactive "struct ifqueue *ifq"
Return if the hardware associated with the interface send queue
.Fa ifq
is unable to transmit more packets.
.It Fn ifq_restart "struct ifqueue *ifq"
Dispatch a call to
.Fn ifq_clr_oactive
and the interface's start routine.
This call is serialised with other calls to the start routine via
.Fn if_start
and therefore provides race free modification of the "active" mark.
.It Fn ifq_barrier "struct ifqueue *ifq"
.Fn ifq_barrier
guarantees that any work currently running in the interface queue
serialiser (e.g. work dispatched by
.Fn ifq_restart
or the interface's start routine) has finished before
.Fn ifq_barrier
returns.
.El
.Sh CONTEXT
.Fn ifq_enqueue ,
.Fn ifq_dequeue ,
.Fn ifq_purge ,
.Fn ifq_len ,
.Fn ifq_empty ,
.Fn ifq_set_oactive ,
.Fn ifq_clr_oactive ,
.Fn ifq_is_oactive ,
and
.Fn ifq_restart
can be called during autoconf, from process context, or from interrupt context.
.Pp
.Fn ifq_barrier
can be called from process context.
.Sh RETURN VALUES
.Fn ifq_enqueue
returns 0 if the mbuf was successfully queued, or non-zero if mbuf was freed.
.Pp
.Fn ifq_dequeue
returns the next mbuf to be transmitted by the interface.
If no packet is available for transmission,
.Dv NULL
is returned.
.Pp
.Fn ifq_purge
returns the number of mbufs that were removed from the queue and freed.
.Pp
.Fn ifq_len
returns the number of mbufs on the queue.
.Pp
.Fn ifq_empty
returns a non-zero value if the queue is empty, otherwise 0.
.Pp
.Fn ifq_is_oactive
returns a non-zero value if the hardware associated with the interface
send queue is unable to transmit more packets, otherwise 0.
.Sh SEE ALSO
.Xr ifq_deq_begin 9 ,
.Xr m_freem 9