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.\" $OpenBSD: ifq_enqueue.9,v 1.11 2020/08/28 09:15:16 fcambus 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: August 28 2020 $
.Dt IFQ_ENQUEUE 9
.Os
.Sh NAME
.Nm ifq_enqueue ,
.Nm ifq_dequeue ,
.Nm ifq_purge ,
.Nm ifq_len ,
.Nm ifq_empty ,
.Nm ifq_hdatalen ,
.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 int
.Fn ifq_hdatalen "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 implementations 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_hdatalen "struct ifqueue *ifq"
Return the number of bytes in the mbuf at the head of the interface
send queue
.Fa ifq .
.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_hdatalen ,
.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_hdatalen
returns the size of a packet on the queue, or 0 if the queue is empty;
.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
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