/* 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 *);
  	void (*old_release_cb)(struct atm_vcc *);
  	struct module *old_owner;
  					/* 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);
  }
  
  static void pppoatm_release_cb(struct atm_vcc *atmvcc)
  {
  	struct pppoatm_vcc *pvcc = atmvcc_to_pvcc(atmvcc);
  
  	/*
  	 * As in pppoatm_pop(), it's safe to clear the BLOCKED bit here because
  	 * the wakeup *can't* race with pppoatm_send(). They both hold the PPP
  	 * channel's ->downl lock. And the potential race with *setting* it,
  	 * which leads to the double-check dance in pppoatm_may_send(), doesn't
  	 * exist here. In the sock_owned_by_user() case in pppoatm_send(), we
  	 * set the BLOCKED bit while the socket is still locked. We know that
  	 * ->release_cb() can't be called until that's done.
  	 */
  	if (test_and_clear_bit(BLOCKED, &pvcc->blocked))
  		tasklet_schedule(&pvcc->wakeup_tasklet);
  	if (pvcc->old_release_cb)
  		pvcc->old_release_cb(atmvcc);
  }
  /*
   * 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;
  	atmvcc->release_cb = pvcc->old_release_cb;
  	tasklet_kill(&pvcc->wakeup_tasklet);
  	ppp_unregister_channel(&pvcc->chan);
  	atmvcc->user_back = NULL;
  	kfree(pvcc);
  }
  
  /* 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("
  ");
  	if (skb == NULL) {			/* VCC was closed */
  		struct module *module;
  
  		pr_debug("removing ATMPPP VCC %p
  ", pvcc);
  		module = pvcc->old_owner;
  		pppoatm_unassign_vcc(atmvcc);
  		atmvcc->push(atmvcc, NULL);	/* Pass along bad news */
  		module_put(module);
  		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)
  ",
  			 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 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);
  	struct atm_vcc *vcc;
  	int ret;
  
  	ATM_SKB(skb)->vcc = pvcc->atmvcc;
  	pr_debug("(skb=0x%p, vcc=0x%p)
  ", skb, pvcc->atmvcc);
  	if (skb->data[0] == '\0' && (pvcc->flags & SC_COMP_PROT))
  		(void) skb_pull(skb, 1);
  
  	vcc = ATM_SKB(skb)->vcc;
  	bh_lock_sock(sk_atm(vcc));
  	if (sock_owned_by_user(sk_atm(vcc))) {
  		/*
  		 * Needs to happen (and be flushed, hence test_and_) before we unlock
  		 * the socket. It needs to be seen by the time our ->release_cb gets
  		 * called.
  		 */
  		test_and_set_bit(BLOCKED, &pvcc->blocked);
  		goto nospace;
  	}
  	if (test_bit(ATM_VF_RELEASED, &vcc->flags) ||
  	    test_bit(ATM_VF_CLOSE, &vcc->flags) ||
  	    !test_bit(ATM_VF_READY, &vcc->flags)) {
  		bh_unlock_sock(sk_atm(vcc));
  		kfree_skb(skb);
  		return DROP_PACKET;
  	}
  
  	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;
  			}
  			consume_skb(skb);
  			skb = n;
  			if (skb == NULL) {
  				bh_unlock_sock(sk_atm(vcc));
  				return DROP_PACKET;
  			}
  		} else if (!pppoatm_may_send(pvcc, skb->truesize))
  			goto nospace;
  		memcpy(skb_push(skb, LLC_LEN), pppllc, LLC_LEN);
  		break;
  	case e_vc:
  		if (!pppoatm_may_send(pvcc, skb->truesize))
  			goto nospace;
  		break;
  	case e_autodetect:
  		bh_unlock_sock(sk_atm(vcc));
  		pr_debug("Trying to send without setting encaps!
  ");
  		kfree_skb(skb);
  		return 1;
  	}
  
  	atomic_add(skb->truesize, &sk_atm(ATM_SKB(skb)->vcc)->sk_wmem_alloc);
  	ATM_SKB(skb)->atm_options = ATM_SKB(skb)->vcc->atm_options;
  	pr_debug("atm_skb(%p)->vcc(%p)->dev(%p)
  ",
  		 skb, ATM_SKB(skb)->vcc, ATM_SKB(skb)->vcc->dev);
  	ret = ATM_SKB(skb)->vcc->send(ATM_SKB(skb)->vcc, skb)
  	    ? DROP_PACKET : 1;
  	bh_unlock_sock(sk_atm(vcc));
  	return ret;
  nospace:
  	bh_unlock_sock(sk_atm(vcc));
  	/*
  	 * We don't have space to send this SKB now, but we might have
  	 * already applied SC_COMP_PROT compression, so may need to undo
  	 */
  	if ((pvcc->flags & SC_COMP_PROT) && skb_headroom(skb) > 0 &&
  	    skb->data[-1] == '\0')
  		(void) skb_push(skb, 1);
  	return 0;
  }
  
  /* This handles ioctls sent to the /dev/ppp interface */
  static int pppoatm_devppp_ioctl(struct ppp_channel *chan, unsigned int cmd,
  	unsigned long arg)
  {
  	switch (cmd) {
  	case PPPIOCGFLAGS:
  		return put_user(chan_to_pvcc(chan)->flags, (int __user *) arg)
  		    ? -EFAULT : 0;
  	case PPPIOCSFLAGS:
  		return get_user(chan_to_pvcc(chan)->flags, (int __user *) arg)
  		    ? -EFAULT : 0;
  	}
  	return -ENOTTY;
  }
  
  static const struct ppp_channel_ops pppoatm_ops = {
  	.start_xmit = pppoatm_send,
  	.ioctl = pppoatm_devppp_ioctl,
  };
  
  static int pppoatm_assign_vcc(struct atm_vcc *atmvcc, void __user *arg)
  {
  	struct atm_backend_ppp be;
  	struct pppoatm_vcc *pvcc;
  	int err;
  	/*
  	 * Each PPPoATM instance has its own tasklet - this is just a
  	 * prototypical one used to initialize them
  	 */
  	static const DECLARE_TASKLET(tasklet_proto, pppoatm_wakeup_sender, 0);
  	if (copy_from_user(&be, arg, sizeof be))
  		return -EFAULT;
  	if (be.encaps != PPPOATM_ENCAPS_AUTODETECT &&
  	    be.encaps != PPPOATM_ENCAPS_VC && be.encaps != PPPOATM_ENCAPS_LLC)
  		return -EINVAL;
  	pvcc = kzalloc(sizeof(*pvcc), GFP_KERNEL);
  	if (pvcc == NULL)
  		return -ENOMEM;
  	pvcc->atmvcc = atmvcc;
  
  	/* Maximum is zero, so that we can use atomic_inc_not_zero() */
  	atomic_set(&pvcc->inflight, NONE_INFLIGHT);
  	pvcc->old_push = atmvcc->push;
  	pvcc->old_pop = atmvcc->pop;
  	pvcc->old_owner = atmvcc->owner;
  	pvcc->old_release_cb = atmvcc->release_cb;
  	pvcc->encaps = (enum pppoatm_encaps) be.encaps;
  	pvcc->chan.private = pvcc;
  	pvcc->chan.ops = &pppoatm_ops;
  	pvcc->chan.mtu = atmvcc->qos.txtp.max_sdu - PPP_HDRLEN -
  	    (be.encaps == e_vc ? 0 : LLC_LEN);
  	pvcc->wakeup_tasklet = tasklet_proto;
  	pvcc->wakeup_tasklet.data = (unsigned long) &pvcc->chan;
  	err = ppp_register_channel(&pvcc->chan);
  	if (err != 0) {
  		kfree(pvcc);
  		return err;
  	}
  	atmvcc->user_back = pvcc;
  	atmvcc->push = pppoatm_push;
  	atmvcc->pop = pppoatm_pop;
  	atmvcc->release_cb = pppoatm_release_cb;
  	__module_get(THIS_MODULE);
  	atmvcc->owner = THIS_MODULE;
  
  	/* re-process everything received between connection setup and
  	   backend setup */
  	vcc_process_recv_queue(atmvcc);
  	return 0;
  }
  
  /*
   * This handles ioctls actually performed on our vcc - we must return
   * -ENOIOCTLCMD for any unrecognized ioctl
   */
  static int pppoatm_ioctl(struct socket *sock, unsigned int cmd,
  	unsigned long arg)
  {
  	struct atm_vcc *atmvcc = ATM_SD(sock);
  	void __user *argp = (void __user *)arg;
  
  	if (cmd != ATM_SETBACKEND && atmvcc->push != pppoatm_push)
  		return -ENOIOCTLCMD;
  	switch (cmd) {
  	case ATM_SETBACKEND: {
  		atm_backend_t b;
  		if (get_user(b, (atm_backend_t __user *) argp))
  			return -EFAULT;
  		if (b != ATM_BACKEND_PPP)
  			return -ENOIOCTLCMD;
  		if (!capable(CAP_NET_ADMIN))
  			return -EPERM;
  		if (sock->state != SS_CONNECTED)
  			return -EINVAL;
  		return pppoatm_assign_vcc(atmvcc, argp);
  		}
  	case PPPIOCGCHAN:
  		return put_user(ppp_channel_index(&atmvcc_to_pvcc(atmvcc)->
  		    chan), (int __user *) argp) ? -EFAULT : 0;
  	case PPPIOCGUNIT:
  		return put_user(ppp_unit_number(&atmvcc_to_pvcc(atmvcc)->
  		    chan), (int __user *) argp) ? -EFAULT : 0;
  	}
  	return -ENOIOCTLCMD;
  }
  
  static struct atm_ioctl pppoatm_ioctl_ops = {
  	.owner	= THIS_MODULE,
  	.ioctl	= pppoatm_ioctl,
  };
  
  static int __init pppoatm_init(void)
  {
  	register_atm_ioctl(&pppoatm_ioctl_ops);
  	return 0;
  }
  
  static void __exit pppoatm_exit(void)
  {
  	deregister_atm_ioctl(&pppoatm_ioctl_ops);
  }
  
  module_init(pppoatm_init);
  module_exit(pppoatm_exit);
  
  MODULE_AUTHOR("Mitchell Blank Jr <mitch@sfgoth.com>");
  MODULE_DESCRIPTION("RFC2364 PPP over ATM/AAL5");
  MODULE_LICENSE("GPL");