void
IFQ_ENQUEUE(
struct ifaltq *ifq
, struct mbuf *m
, struct altq_pktattr *pattr
, int err
)
void
IFQ_DEQUEUE(
struct ifaltq *ifq
, struct mbuf *m
)
void
IFQ_POLL(
struct ifaltq *ifq
, struct mbuf *m
)
void
IFQ_PURGE(
struct ifaltq *ifq
)
void
IFQ_CLASSIFY(
struct ifaltq *ifq
, struct mbuf *m
, int af
, struct altq_pktattr *pattr
)
void
IFQ_IS_EMPTY(
struct ifaltq *ifq
)
void
IFQ_SET_MAXLEN(
struct ifaltq *ifq
, int len
)
void
IFQ_INC_LEN(
struct ifaltq *ifq
)
void
IFQ_DEC_LEN(
struct ifaltq *ifq
)
void
IFQ_INC_DROPS(
struct ifaltq *ifq
)
void
IFQ_SET_READY(
struct ifaltq *ifq
)
ifqueue
macros for ease of transition.
IFQ_ENQUEUE()
enqueues a packet
m
to the queue
ifq
.
The underlying queueing discipline may discard the packet.
err
is set to 0 on success, or
ENOBUFS
if the packet is discarded.
m
will be freed by the device driver on success or by the queueing discipline on
failure, so that the caller should not touch
m
after calling
IFQ_ENQUEUE().
IFQ_DEQUEUE()
dequeues a packet from the queue.
The dequeued packet is returned in
m
,
or
m
is set to
NULL
if no packet is dequeued.
The caller must always check
m
since a non-empty queue could return
NULL
under rate-limiting.
IFQ_POLL()
returns the next packet without removing it from the queue.
It is guaranteed by the underlying queueing discipline that
IFQ_DEQUEUE(
)
immediately after
IFQ_POLL(
)
returns the same packet.
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.
IFQ_CLASSIFY()
classifies a packet to a scheduling class, and returns the result in
pattr
.
IFQ_IS_EMPTY()
can be used to check if the queue is empty.
Note that
IFQ_DEQUEUE(
)
could still return
NULL
if the queueing discipline is non-work conserving.
IFQ_SET_MAXLEN()
sets the queue length limit to the default FIFO queue.
IFQ_INC_LEN()
and
IFQ_DEC_LEN(
)
increment or decrement the current queue length in packets.
IFQ_INC_DROPS()
increments the drop counter and is equal to
IF_DROP(
).
It is defined for naming consistency.
IFQ_SET_READY()
sets a flag to indicate this driver is converted to use the new macros.
ALTQ
can be enabled only on interfaces with this flag.
ifaltq
has the same fields.
The traditional
IF_XXX(
)
macros and the code directly referencing the fields within
if_snd
still work with
ifaltq
.
(Once we finish conversions of all the drivers, we no longer need
these fields.)
##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;
}; | /* altq related fields */
| ......
| };
|
The new structure replaces
struct
ifqueue
in
struct
ifnet
.
##old-style## ##new-style##
|
struct ifnet { | struct ifnet {
.... | ....
|
struct ifqueue if_snd; | struct ifaltq if_snd;
|
.... | ....
}; | };
|
The (simplified) new
IFQ_XXX(
)
macros looks like:
#ifdef ALTQ
#define IFQ_DEQUEUE(ifq, m) \
if (ALTQ_IS_ENABLED((ifq)) \
ALTQ_DEQUEUE((ifq), (m)); \
else \
IF_DEQUEUE((ifq), (m));
#else
#define IFQ_DEQUEUE(ifq, m) IF_DEQUEUE((ifq), (m));
#endif
#define IFQ_ENQUEUE(ifq, m, pattr, err) \
do { \
if (ALTQ_IS_ENABLED((ifq))) \
ALTQ_ENQUEUE((ifq), (m), (pattr), (err)); \
else { \
if (IF_QFULL((ifq))) { \
m_freem((m)); \
(err) = ENOBUFS; \
} else { \
IF_ENQUEUE((ifq), (m)); \
(err) = 0; \
} \
} \
if ((err)) \
(ifq)->ifq_drops++; \
} while (/*CONSTCOND*/ 0)
IFQ_ENQUEUE()
does the following:
err
is set to
ENOBUFS
.
m
is freed by the queueing discipline.
The caller should not touch mbuf after calling
IFQ_ENQUEUE(
)
so that the caller may need to copy
m_pkthdr.len
or
m_flags
field beforehand for statistics.
The caller should not use
senderr(
)
since mbuf was already freed.
The new style
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,
| NULL, 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);
} | }
|
).
struct
altq_pktattr
is used to store the classifier result, and it is passed to the enqueue
function.
(We will change the method to tag the classifier result to mbuf in the future.)
int
ether_output(ifp, m0, dst, rt0)
{
......
struct altq_pktattr pktattr;
......
/* classify the packet before prepending link-headers */
IFQ_CLASSIFY(&ifp->if_snd, m, dst->sa_family, &pktattr);
/* prepend link-level headers */
......
IFQ_ENQUEUE(&ifp->if_snd, m, &pktattr, error);
......
}
)
is already converted to the new style.
Look for
if_snd
in the driver.
You will probably need to make changes to the lines that include
if_snd
.
ifq_head
to see whether the queue is empty or not, use
IFQ_IS_EMPTY(
).
##old-style## ##new-style##
|
if (ifp->if_snd.ifq_head != NULL) | if (IFQ_IS_EMPTY(&ifp->if_snd) == 0)
|
Note that
IFQ_POLL(
)
can be used for the same purpose, but
IFQ_POLL(
)
could be costly for a complex scheduling algorithm since
IFQ_POLL(
)
needs to run the scheduling algorithm to select the next packet.
On the other hand,
IFQ_IS_EMPTY(
)
checks only if there is any packet stored in the queue.
Another difference is that even when
IFQ_IS_EMPTY(
)
is
false
,
IFQ_DEQUEUE(
)
could still return
NULL
if the queue is under rate-limiting.
)
by
IFQ_DEQUEUE(
).
Always check whether the dequeued mbuf is
NULL
or not.
Note that even when
IFQ_IS_EMPTY(
)
is
false
,
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
if_start(
)
from transmission complete interrupts in order to trigger the next dequeue.
)
and
IFQ_DEQUEUE(
).
##old-style## ##new-style##
|
m = ifp->if_snd.ifq_head; | IFQ_POLL(&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)
return; | return;
|
IF_DEQUEUE(&ifp->if_snd, m); | IFQ_DEQUEUE(&ifp->if_snd, m);
|
/* kick the hardware */ | /* kick the hardware */
} | }
|
It is guaranteed that
IFQ_DEQUEUE(
)
immediately after
IFQ_POLL(
)
returns the same packet.
Note that they need to be guarded by
splimp(
)
if called from outside of
if_start(
).
),
you have to eliminate it since the prepend operation is not possible for many
queueing disciplines.
A common use of
IF_PREPEND(
)
is to cancel the previous dequeue operation.
You have to convert the logic into poll-and-dequeue.
##old-style## ##new-style##
|
IF_DEQUEUE(&ifp->if_snd, m); | IFQ_POLL(&ifp->if_snd, m);
if (m != NULL) { | if (m != NULL) {
|
if (something_goes_wrong) { | if (something_goes_wrong) {
IF_PREPEND(&ifp->if_snd, m); |
return; | return;
} | }
|
| /* at this point, the driver
| * is committed to send this
| * packet.
| */
| IFQ_DEQUEUE(&ifp->if_snd, m);
|
/* kick the hardware */ | /* kick the hardware */
} | }
|
)
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); |
} |
|
)
to set
ifq_maxlen
to
len
.
Add
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);
| IFQ_SET_READY(&ifp->if_snd);
if_attach(ifp); | if_attach(ifp);
|
##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);
|
Some drivers instruct the hardware to invoke transmission complete
interrupts only when it thinks necessary.
Rate-limiting breaks its assumption.
ifqueue
to prioritize packets.
It is possible to eliminate the second queue
since
ALTQ
provides more flexible mechanisms but the following shows
how to keep the original behavior.
struct sl_softc {
struct ifnet sc_if; /* network-visible interface */
...
struct ifqueue sc_fastq; /* interactive output queue */
...
};
The driver doesn't compile in the new model since it has the following
line
struct
ifqueue
(
if_snd
is no longer a type of.)
struct ifqueue *ifq = &ifp->if_snd;
A simple way is to use the original
IF_XXX(
)
macros for
sc_fastq
and use the new
IFQ_XXX(
)
macros for
if_snd
.
The enqueue operation looks like:
##old-style## ##new-style##
|
struct ifqueue *ifq = &ifp->if_snd; | struct ifqueue *ifq = NULL;
|
if (ip->ip_tos & IPTOS_LOWDELAY) | if ((ip->ip_tos & IPTOS_LOWDELAY) &&
ifq = &sc->sc_fastq; | !ALTQ_IS_ENABLED(&sc->sc_if.if_snd)) {
| ifq = &sc->sc_fastq;
if (IF_QFULL(ifq)) { | if (IF_QFULL(ifq)) {
IF_DROP(ifq); | IF_DROP(ifq);
m_freem(m); | m_freem(m);
splx(s); | error = ENOBUFS;
sc->sc_if.if_oerrors++; | } else {
return (ENOBUFS); | IF_ENQUEUE(ifq, m);
} | error = 0;
IF_ENQUEUE(ifq, m); | }
| } else
| IFQ_ENQUEUE(&sc->sc_if.if_snd,
| m, NULL, error);
|
| if (error) {
| splx(s);
| sc->sc_if.if_oerrors++;
| return (error);
| }
if ((sc->sc_oqlen = | if ((sc->sc_oqlen =
sc->sc_ttyp->t_outq.c_cc) == 0) | sc->sc_ttyp->t_outq.c_cc) == 0)
slstart(sc->sc_ttyp); | slstart(sc->sc_ttyp);
splx(s); | splx(s);
|
The dequeue operations looks like:
##old-style## ##new-style##
|
s = splimp(); | s = splimp();
IF_DEQUEUE(&sc->sc_fastq, m); | IF_DEQUEUE(&sc->sc_fastq, m);
if (m == NULL) | if (m == NULL)
IF_DEQUEUE(&sc->sc_if.if_snd, m); | IFQ_DEQUEUE(&sc->sc_if.if_snd, m);
splx(s); | splx(s);
|
ifq_len
IFQ_IS_EMPTY(
)
(used by.)
Queueing disciplines also need to guarantee the same mbuf is returned if
IFQ_DEQUEUE(
)
is called immediately after
IFQ_POLL(
).