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|
/* net/atm/pppoatm.c - RFC2364 PPP over ATM/AAL5 */
/* Copyright 1999-2000 by Mitchell Blank Jr */
/* Based on clip.c; 1995-1999 by Werner Almesberger, EPFL LRC/ICA */
/* And on ppp_async.c; Copyright 1999 Paul Mackerras */
/* And help from Jens Axboe */
/*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version
* 2 of the License, or (at your option) any later version.
*
* This driver provides the encapsulation and framing for sending
* and receiving PPP frames in ATM AAL5 PDUs.
*/
/*
* One shortcoming of this driver is that it does not comply with
* section 8 of RFC2364 - we are supposed to detect a change
* in encapsulation and immediately abort the connection (in order
* to avoid a black-hole being created if our peer loses state
* and changes encapsulation unilaterally. However, since the
* ppp_generic layer actually does the decapsulation, we need
* a way of notifying it when we _think_ there might be a problem)
* There's two cases:
* 1. LLC-encapsulation was missing when it was enabled. In
* this case, we should tell the upper layer "tear down
* this session if this skb looks ok to you"
* 2. LLC-encapsulation was present when it was disabled. Then
* we need to tell the upper layer "this packet may be
* ok, but if its in error tear down the session"
* These hooks are not yet available in ppp_generic
*/
#define pr_fmt(fmt) KBUILD_MODNAME ":%s: " fmt, __func__
#include <linux/module.h>
#include <linux/init.h>
#include <linux/interrupt.h>
#include <linux/skbuff.h>
#include <linux/slab.h>
#include <linux/atm.h>
#include <linux/atmdev.h>
#include <linux/capability.h>
#include <linux/ppp_defs.h>
#include <linux/ppp-ioctl.h>
#include <linux/ppp_channel.h>
#include <linux/atmppp.h>
#include "common.h"
enum pppoatm_encaps {
e_autodetect = PPPOATM_ENCAPS_AUTODETECT,
e_vc = PPPOATM_ENCAPS_VC,
e_llc = PPPOATM_ENCAPS_LLC,
};
struct pppoatm_vcc {
struct atm_vcc *atmvcc; /* VCC descriptor */
void (*old_push)(struct atm_vcc *, struct sk_buff *);
void (*old_pop)(struct atm_vcc *, struct sk_buff *);
/* keep old push/pop for detaching */
enum pppoatm_encaps encaps;
atomic_t inflight;
unsigned long blocked;
int flags; /* SC_COMP_PROT - compress protocol */
struct ppp_channel chan; /* interface to generic ppp layer */
struct tasklet_struct wakeup_tasklet;
};
/*
* We want to allow two packets in the queue. The one that's currently in
* flight, and *one* queued up ready for the ATM device to send immediately
* from its TX done IRQ. We want to be able to use atomic_inc_not_zero(), so
* inflight == -2 represents an empty queue, -1 one packet, and zero means
* there are two packets in the queue.
*/
#define NONE_INFLIGHT -2
#define BLOCKED 0
/*
* Header used for LLC Encapsulated PPP (4 bytes) followed by the LCP protocol
* ID (0xC021) used in autodetection
*/
static const unsigned char pppllc[6] = { 0xFE, 0xFE, 0x03, 0xCF, 0xC0, 0x21 };
#define LLC_LEN (4)
static inline struct pppoatm_vcc *atmvcc_to_pvcc(const struct atm_vcc *atmvcc)
{
return (struct pppoatm_vcc *) (atmvcc->user_back);
}
static inline struct pppoatm_vcc *chan_to_pvcc(const struct ppp_channel *chan)
{
return (struct pppoatm_vcc *) (chan->private);
}
/*
* We can't do this directly from our _pop handler, since the ppp code
* doesn't want to be called in interrupt context, so we do it from
* a tasklet
*/
static void pppoatm_wakeup_sender(unsigned long arg)
{
ppp_output_wakeup((struct ppp_channel *) arg);
}
/*
* This gets called every time the ATM card has finished sending our
* skb. The ->old_pop will take care up normal atm flow control,
* but we also need to wake up the device if we blocked it
*/
static void pppoatm_pop(struct atm_vcc *atmvcc, struct sk_buff *skb)
{
struct pppoatm_vcc *pvcc = atmvcc_to_pvcc(atmvcc);
pvcc->old_pop(atmvcc, skb);
atomic_dec(&pvcc->inflight);
/*
* We always used to run the wakeup tasklet unconditionally here, for
* fear of race conditions where we clear the BLOCKED flag just as we
* refuse another packet in pppoatm_send(). This was quite inefficient.
*
* In fact it's OK. The PPP core will only ever call pppoatm_send()
* while holding the channel->downl lock. And ppp_output_wakeup() as
* called by the tasklet will *also* grab that lock. So even if another
* CPU is in pppoatm_send() right now, the tasklet isn't going to race
* with it. The wakeup *will* happen after the other CPU is safely out
* of pppoatm_send() again.
*
* So if the CPU in pppoatm_send() has already set the BLOCKED bit and
* it about to return, that's fine. We trigger a wakeup which will
* happen later. And if the CPU in pppoatm_send() *hasn't* set the
* BLOCKED bit yet, that's fine too because of the double check in
* pppoatm_may_send() which is commented there.
*/
if (test_and_clear_bit(BLOCKED, &pvcc->blocked))
tasklet_schedule(&pvcc->wakeup_tasklet);
}
/*
* Unbind from PPP - currently we only do this when closing the socket,
* but we could put this into an ioctl if need be
*/
static void pppoatm_unassign_vcc(struct atm_vcc *atmvcc)
{
struct pppoatm_vcc *pvcc;
pvcc = atmvcc_to_pvcc(atmvcc);
atmvcc->push = pvcc->old_push;
atmvcc->pop = pvcc->old_pop;
tasklet_kill(&pvcc->wakeup_tasklet);
ppp_unregister_channel(&pvcc->chan);
atmvcc->user_back = NULL;
kfree(pvcc);
/* Gee, I hope we have the big kernel lock here... */
module_put(THIS_MODULE);
}
/* Called when an AAL5 PDU comes in */
static void pppoatm_push(struct atm_vcc *atmvcc, struct sk_buff *skb)
{
struct pppoatm_vcc *pvcc = atmvcc_to_pvcc(atmvcc);
pr_debug("\n");
if (skb == NULL) { /* VCC was closed */
pr_debug("removing ATMPPP VCC %p\n", pvcc);
pppoatm_unassign_vcc(atmvcc);
atmvcc->push(atmvcc, NULL); /* Pass along bad news */
return;
}
atm_return(atmvcc, skb->truesize);
switch (pvcc->encaps) {
case e_llc:
if (skb->len < LLC_LEN ||
memcmp(skb->data, pppllc, LLC_LEN))
goto error;
skb_pull(skb, LLC_LEN);
break;
case e_autodetect:
if (pvcc->chan.ppp == NULL) { /* Not bound yet! */
kfree_skb(skb);
return;
}
if (skb->len >= sizeof(pppllc) &&
!memcmp(skb->data, pppllc, sizeof(pppllc))) {
pvcc->encaps = e_llc;
skb_pull(skb, LLC_LEN);
break;
}
if (skb->len >= (sizeof(pppllc) - LLC_LEN) &&
!memcmp(skb->data, &pppllc[LLC_LEN],
sizeof(pppllc) - LLC_LEN)) {
pvcc->encaps = e_vc;
pvcc->chan.mtu += LLC_LEN;
break;
}
pr_debug("Couldn't autodetect yet (skb: %02X %02X %02X %02X %02X %02X)\n",
skb->data[0], skb->data[1], skb->data[2],
skb->data[3], skb->data[4], skb->data[5]);
goto error;
case e_vc:
break;
}
ppp_input(&pvcc->chan, skb);
return;
error:
kfree_skb(skb);
ppp_input_error(&pvcc->chan, 0);
}
static inline int pppoatm_may_send(struct pppoatm_vcc *pvcc, int size)
{
/*
* It's not clear that we need to bother with using atm_may_send()
* to check we don't exceed sk->sk_sndbuf. If userspace sets a
* value of sk_sndbuf which is lower than the MTU, we're going to
* block for ever. But the code always did that before we introduced
* the packet count limit, so...
*/
if (atm_may_send(pvcc->atmvcc, size) &&
atomic_inc_not_zero_hint(&pvcc->inflight, NONE_INFLIGHT))
return 1;
/*
* We use test_and_set_bit() rather than set_bit() here because
* we need to ensure there's a memory barrier after it. The bit
* *must* be set before we do the atomic_inc() on pvcc->inflight.
* There's no smp_mb__after_set_bit(), so it's this or abuse
* smp_mb__after_clear_bit().
*/
test_and_set_bit(BLOCKED, &pvcc->blocked);
/*
* We may have raced with pppoatm_pop(). If it ran for the
* last packet in the queue, *just* before we set the BLOCKED
* bit, then it might never run again and the channel could
* remain permanently blocked. Cope with that race by checking
* *again*. If it did run in that window, we'll have space on
* the queue now and can return success. It's harmless to leave
* the BLOCKED flag set, since it's only used as a trigger to
* run the wakeup tasklet. Another wakeup will never hurt.
* If pppoatm_pop() is running but hasn't got as far as making
* space on the queue yet, then it hasn't checked the BLOCKED
* flag yet either, so we're safe in that case too. It'll issue
* an "immediate" wakeup... where "immediate" actually involves
* taking the PPP channel's ->downl lock, which is held by the
* code path that calls pppoatm_send(), and is thus going to
* wait for us to finish.
*/
if (atm_may_send(pvcc->atmvcc, size) &&
atomic_inc_not_zero(&pvcc->inflight))
return 1;
return 0;
}
/*
* Called by the ppp_generic.c to send a packet - returns true if packet
* was accepted. If we return false, then it's our job to call
* ppp_output_wakeup(chan) when we're feeling more up to it.
* Note that in the ENOMEM case (as opposed to the !atm_may_send case)
* we should really drop the packet, but the generic layer doesn't
* support this yet. We just return 'DROP_PACKET' which we actually define
* as success, just to be clear what we're really doing.
*/
#define DROP_PACKET 1
static int pppoatm_send(struct ppp_channel *chan, struct sk_buff *skb)
{
struct pppoatm_vcc *pvcc = chan_to_pvcc(chan);
ATM_SKB(skb)->vcc = pvcc->atmvcc;
pr_debug("(skb=0x%p, vcc=0x%p)\n", skb, pvcc->atmvcc);
if (skb->data[0] == '\0' && (pvcc->flags & SC_COMP_PROT))
(void) skb_pull(skb, 1);
switch (pvcc->encaps) { /* LLC encapsulation needed */
case e_llc:
if (skb_headroom(skb) < LLC_LEN) {
struct sk_buff *n;
n = skb_realloc_headroom(skb, LLC_LEN);
if (n != NULL &&
!pppoatm_may_send(pvcc, n->truesize)) {
kfree_skb(n);
goto nospace;
}
kfree_skb(skb);
skb = n;
if (skb == NULL)
return DROP_PACKET;
} else if (!pppoatm_may_send(pvcc, skb->truesize))
goto nospace;
memcpy(skb_push(skb, LLC_LEN), pppllc
|