altq (9)
Leading comments
$NetBSD: altq.9,v 1.8 2002/05/28 11:41:45 wiz Exp $
$OpenBSD: altq.9,v 1.4 2001/07/12 12:41:42 itojun Exp $
Copyright (C) 2004 Max Laier. All rights reserved.
Copyright (C) 2001
Sony Computer Science Laboratories Inc. All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
1. Redistributions of source code must retain the above copyright
notice, this list of conditions a...
NAME
ALTQ - kernel interfaces for manipulating output queues on network interfacesSYNOPSIS
In sys/types.h In sys/socket.h In net/if.h In net/if_var.hEnqueue macros
Fn IFQ_ENQUEUE struct ifaltq *ifq struct mbuf *m int error Fn IFQ_HANDOFF struct ifnet *ifp struct mbuf *m int error Fo IFQ_HANDOFF_ADJ Fa struct ifnet *ifp struct mbuf *m int adjust int error FcDequeue macros
Fn IFQ_DEQUEUE struct ifaltq *ifq struct mbuf *m Fn IFQ_POLL_NOLOCK struct ifaltq *ifq struct mbuf *m Fn IFQ_PURGE struct ifaltq *ifq Fn IFQ_IS_EMPTY struct ifaltq *ifqDriver managed dequeue macros
Fn IFQ_DRV_DEQUEUE struct ifaltq *ifq struct mbuf *m Fn IFQ_DRV_PREPEND struct ifaltq *ifq struct mbuf *m Fn IFQ_DRV_PURGE struct ifaltq *ifq Fn IFQ_DRV_IS_EMPTY struct ifaltq *ifqGeneral setup macros
Fn IFQ_SET_MAXLEN struct ifaltq *ifq int len Fn IFQ_INC_LEN struct ifaltq *ifq Fn IFQ_DEC_LEN struct ifaltq *ifq Fn IFQ_INC_DROPS struct ifaltq *ifq Fn IFQ_SET_READY struct ifaltq *ifqDESCRIPTION
The ifconfig system is a framework to manage queuing disciplines on network interfaces. ifconfig introduces new macros to manipulate output queues. The output queue macros are used to abstract queue operations and not to touch the internal fields of the output queue structure. The macros are independent from the ifconfig implementation, and compatible with the traditional Vt ifqueue macros for ease of transition.Fn IFQ_ENQUEUE , Fn IFQ_HANDOFF and Fn IFQ_HANDOFF_ADJ enqueue a packet Fa m to the queue Fa ifq . The underlying queuing discipline may discard the packet. The Fa error argument is set to 0 on success, or Er ENOBUFS if the packet is discarded. The packet pointed to by Fa m will be freed by the device driver on success, or by the queuing discipline on failure, so the caller should not touch Fa m after enqueuing. Fn IFQ_HANDOFF and Fn IFQ_HANDOFF_ADJ combine the enqueue operation with statistic generation and call Fn if_start upon successful enqueue to initiate the actual send.
Fn IFQ_DEQUEUE dequeues a packet from the queue. The dequeued packet is returned in Fa m , or Fa m is set to NULL if no packet is dequeued. The caller must always check Fa m since a non-empty queue could return NULL under rate-limiting.
Fn IFQ_POLL_NOLOCK returns the next packet without removing it from the queue. The caller must hold the queue mutex when calling Fn IFQ_POLL_NOLOCK in order to guarantee that a subsequent call to Fn IFQ_DEQUEUE_NOLOCK dequeues the same packet.
Fn IFQ_*_NOLOCK variants (if available) always assume that the caller holds the queue mutex. They can be grabbed with Fn IFQ_LOCK and released with Fn IFQ_UNLOCK .
Fn IFQ_PURGE discards all the packets in the queue. The purge operation is needed since a non-work conserving queue cannot be emptied by a dequeue loop.
Fn IFQ_IS_EMPTY can be used to check if the queue is empty. Note that Fn IFQ_DEQUEUE could still return NULL if the queuing discipline is non-work conserving.
Fn IFQ_DRV_DEQUEUE moves up to Fa ifq->ifq_drv_maxlen packets from the queue to the ``driver managed'' queue and returns the first one via Fa m . As for Fn IFQ_DEQUEUE , Fa m can be NULL even for a non-empty queue. Subsequent calls to Fn IFQ_DRV_DEQUEUE pass the packets from the ``driver managed'' queue without obtaining the queue mutex. It is the responsibility of the caller to protect against concurrent access. Enabling ifconfig for a given queue sets ifq_drv_maxlen to 0 as the ``bulk dequeue'' performed by Fn IFQ_DRV_DEQUEUE for higher values of ifq_drv_maxlen is adverse to ALTQ 's internal timing. Note that a driver must not mix Fn IFQ_DRV_* macros with the default dequeue macros as the default macros do not look at the ``driver managed'' queue which might lead to an mbuf leak.
Fn IFQ_DRV_PREPEND prepends Fa m to the ``driver managed'' queue from where it will be obtained with the next call to Fn IFQ_DRV_DEQUEUE .
Fn IFQ_DRV_PURGE flushes all packets in the ``driver managed'' queue and calls to Fn IFQ_PURGE afterwards.
Fn IFQ_DRV_IS_EMPTY checks for packets in the ``driver managed'' part of the queue. If it is empty, it forwards to Fn IFQ_IS_EMPTY .
Fn IFQ_SET_MAXLEN sets the queue length limit to the default FIFO queue. The ifq_drv_maxlen member of the Vt ifaltq structure controls the length limit of the ``driver managed'' queue.
Fn IFQ_INC_LEN and Fn IFQ_DEC_LEN increment or decrement the current queue length in packets. This is mostly for internal purposes.
Fn IFQ_INC_DROPS increments the drop counter and is identical to Fn IF_DROP . It is defined for naming consistency only.
Fn IFQ_SET_READY sets a flag to indicate that a driver was converted to use the new macros. ifconfig can be enabled only on interfaces with this flag.
COMPATIBILITY
Vt ifaltq
structure
In order to keep compatibility with the existing code, the new
output queue structure
Vt ifaltq
has the same fields.
The traditional
Fn IF_*
macros and the code directly referencing the fields within
if_snd
still work with
Vt ifaltq .
##old-style## ##new-style##
|
struct ifqueue { | struct ifaltq {
struct mbuf *ifq_head; | struct mbuf *ifq_head;
struct mbuf *ifq_tail; | struct mbuf *ifq_tail;
int ifq_len; | int ifq_len;
int ifq_maxlen; | int ifq_maxlen;
int ifq_drops; | int ifq_drops;
}; | /* driver queue fields */
| ......
| /* altq related fields */
| ......
| };
|
The new structure replaces
Vt struct ifqueue
in
Vt struct ifnet .
##old-style## ##new-style##
|
struct ifnet { | struct ifnet {
.... | ....
|
struct ifqueue if_snd; | struct ifaltq if_snd;
|
.... | ....
}; | };
|
The (simplified) new
Fn IFQ_*
macros look like:
#define IFQ_DEQUEUE(ifq, m) \
if (ALTQ_IS_ENABLED((ifq)) \
ALTQ_DEQUEUE((ifq), (m)); \
else \
IF_DEQUEUE((ifq), (m));
Enqueue operation
The semantics of the enqueue operation is changed. In the new style, enqueue and packet drop are combined since they cannot be easily separated in many queuing disciplines. The new enqueue operation corresponds to the following macro that is written with the old macros.
#define IFQ_ENQUEUE(ifq, m, error) \
do { \
if (IF_QFULL((ifq))) { \
m_freem((m)); \
(error) = ENOBUFS; \
IF_DROP(ifq); \
} else { \
IF_ENQUEUE((ifq), (m)); \
(error) = 0; \
} \
} while (0)
Fn IFQ_ENQUEUE does the following:
- queue a packet,
- drop (and free) a packet if the enqueue operation fails.
If the enqueue operation fails, Fa error is set to Er ENOBUFS . The Fa m mbuf is freed by the queuing discipline. The caller should not touch mbuf after calling Fn IFQ_ENQUEUE so that the caller may need to copy m_pkthdr.len or m_flags field beforehand for statistics. Fn IFQ_HANDOFF and Fn IFQ_HANDOFF_ADJ can be used if only default interface statistics and an immediate call to Fn if_start are desired. The caller should not use Fn senderr since mbuf was already freed.
The new style Fn if_output looks as follows:
##old-style## ##new-style##
|
int | int
ether_output(ifp, m0, dst, rt0) | ether_output(ifp, m0, dst, rt0)
{ | {
...... | ......
|
| mflags = m->m_flags;
| len = m->m_pkthdr.len;
s = splimp(); | s = splimp();
if (IF_QFULL(&ifp->if_snd)) { | IFQ_ENQUEUE(&ifp->if_snd, m,
| error);
IF_DROP(&ifp->if_snd); | if (error != 0) {
splx(s); | splx(s);
senderr(ENOBUFS); | return (error);
} | }
IF_ENQUEUE(&ifp->if_snd, m); |
ifp->if_obytes += | ifp->if_obytes += len;
m->m_pkthdr.len; |
if (m->m_flags & M_MCAST) | if (mflags & M_MCAST)
ifp->if_omcasts++; | ifp->if_omcasts++;
|
if ((ifp->if_flags & IFF_OACTIVE) | if ((ifp->if_flags & IFF_OACTIVE)
== 0) | == 0)
(*ifp->if_start)(ifp); | (*ifp->if_start)(ifp);
splx(s); | splx(s);
return (error); | return (error);
|
bad: | bad:
if (m) | if (m)
m_freem(m); | m_freem(m);
return (error); | return (error);
} | }
|
HOW TO CONVERT THE EXISTING DRIVERS
First, make sure the corresponding Fn if_output is already converted to the new style.Look for if_snd in the driver. Probably, you need to make changes to the lines that include if_snd
Empty check operation
If the code checks ifq_head to see whether the queue is empty or not, use Fn IFQ_IS_EMPTY .
##old-style## ##new-style##
|
if (ifp->if_snd.ifq_head != NULL) | if (!IFQ_IS_EMPTY(&ifp->if_snd))
|
Fn IFQ_IS_EMPTY
only checks if there is any packet stored in the queue.
Note that even when
Fn IFQ_IS_EMPTY
is
FALSE
Fn IFQ_DEQUEUE
could still return
NULL
if the queue is under rate-limiting.
Dequeue operation
Replace Fn IF_DEQUEUE by Fn IFQ_DEQUEUE . Always check whether the dequeued mbuf is NULL or not. Note that even when Fn IFQ_IS_EMPTY is FALSE Fn IFQ_DEQUEUE could return NULL due to rate-limiting.
##old-style## ##new-style##
|
IF_DEQUEUE(&ifp->if_snd, m); | IFQ_DEQUEUE(&ifp->if_snd, m);
| if (m == NULL)
| return;
|
A driver is supposed to call
Fn if_start
from transmission complete interrupts in order to trigger the next dequeue.
Poll-and-dequeue operation
If the code polls the packet at the head of the queue and actually uses the packet before dequeuing it, use Fn IFQ_POLL_NOLOCK and Fn IFQ_DEQUEUE_NOLOCK .
##old-style## ##new-style##
|
| IFQ_LOCK(&ifp->if_snd);
m = ifp->if_snd.ifq_head; | IFQ_POLL_NOLOCK(&ifp->if_snd, m);
if (m != NULL) { | if (m != NULL) {
|
/* use m to get resources */ | /* use m to get resources */
if (something goes wrong) | if (something goes wrong)
| IFQ_UNLOCK(&ifp->if_snd);
return; | return;
|
IF_DEQUEUE(&ifp->if_snd, m); | IFQ_DEQUEUE_NOLOCK(&ifp->if_snd, m);
| IFQ_UNLOCK(&ifp->if_snd);
|
/* kick the hardware */ | /* kick the hardware */
} | }
|
It is guaranteed that
Fn IFQ_DEQUEUE_NOLOCK
under the same lock as a previous
Fn IFQ_POLL_NOLOCK
returns the same packet.
Note that they need to be guarded by
Fn IFQ_LOCK .
Eliminating Fn IF_PREPEND
If the code uses Fn IF_PREPEND , you have to eliminate it unless you can use a ``driver managed'' queue which allows the use of Fn IFQ_DRV_PREPEND as a substitute. A common usage of Fn IF_PREPEND is to cancel the previous dequeue operation. You have to convert the logic into poll-and-dequeue.
##old-style## ##new-style##
|
| IFQ_LOCK(&ifp->if_snd);
IF_DEQUEUE(&ifp->if_snd, m); | IFQ_POLL_NOLOCK(&ifp->if_snd, m);
if (m != NULL) { | if (m != NULL) {
|
if (something_goes_wrong) { | if (something_goes_wrong) {
IF_PREPEND(&ifp->if_snd, m); | IFQ_UNLOCK(&ifp->if_snd);
return; | return;
} | }
|
| /* at this point, the driver
| * is committed to send this
| * packet.
| */
| IFQ_DEQUEUE_NOLOCK(&ifp->if_snd, m);
| IFQ_UNLOCK(&ifp->if_snd);
|
/* kick the hardware */ | /* kick the hardware */
} | }
|
Purge operation
Use Fn IFQ_PURGE to empty the queue. Note that a non-work conserving queue cannot be emptied by a dequeue loop.
##old-style## ##new-style##
|
while (ifp->if_snd.ifq_head != NULL) {| IFQ_PURGE(&ifp->if_snd);
IF_DEQUEUE(&ifp->if_snd, m); |
m_freem(m); |
} |
|
Conversion using a driver managed queue
Convert Fn IF_* macros to their equivalent Fn IFQ_DRV_* and employ Fn IFQ_DRV_IS_EMPTY where appropriate.
##old-style## ##new-style##
|
if (ifp->if_snd.ifq_head != NULL) | if (!IFQ_DRV_IS_EMPTY(&ifp->if_snd))
|
Make sure that calls to
Fn IFQ_DRV_DEQUEUE ,
Fn IFQ_DRV_PREPEND
and
Fn IFQ_DRV_PURGE
are protected with a mutex of some kind.
Attach routine
Use Fn IFQ_SET_MAXLEN to set ifq_maxlen to Fa len . Initialize ifq_drv_maxlen with a sensible value if you plan to use the Fn IFQ_DRV_* macros. Add Fn IFQ_SET_READY to show this driver is converted to the new style. (This is used to distinguish new-style drivers.)
##old-style## ##new-style##
|
ifp->if_snd.ifq_maxlen = qsize; | IFQ_SET_MAXLEN(&ifp->if_snd, qsize);
| ifp->if_snd.ifq_drv_maxlen = qsize;
| IFQ_SET_READY(&ifp->if_snd);
if_attach(ifp); | if_attach(ifp);
|
Other issues
The new macros for statistics:
##old-style## ##new-style##
|
IF_DROP(&ifp->if_snd); | IFQ_INC_DROPS(&ifp->if_snd);
|
ifp->if_snd.ifq_len++; | IFQ_INC_LEN(&ifp->if_snd);
|
ifp->if_snd.ifq_len--; | IFQ_DEC_LEN(&ifp->if_snd);
|