[safe/jmp/linux-2.6] / drivers / net / ppp_generic.c

/*
 * Generic PPP layer for Linux.
 *
 * Copyright 1999-2002 Paul Mackerras.
 *
 *  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.
 *
 * The generic PPP layer handles the PPP network interfaces, the
 * /dev/ppp device, packet and VJ compression, and multilink.
 * It talks to PPP `channels' via the interface defined in
 * include/linux/ppp_channel.h.  Channels provide the basic means for
 * sending and receiving PPP frames on some kind of communications
 * channel.
 *
 * Part of the code in this driver was inspired by the old async-only
 * PPP driver, written by Michael Callahan and Al Longyear, and
 * subsequently hacked by Paul Mackerras.
 *
 * ==FILEVERSION 20041108==
 */

#include <linux/config.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/kmod.h>
#include <linux/init.h>
#include <linux/list.h>
#include <linux/devfs_fs_kernel.h>
#include <linux/netdevice.h>
#include <linux/poll.h>
#include <linux/ppp_defs.h>
#include <linux/filter.h>
#include <linux/if_ppp.h>
#include <linux/ppp_channel.h>
#include <linux/ppp-comp.h>
#include <linux/skbuff.h>
#include <linux/rtnetlink.h>
#include <linux/if_arp.h>
#include <linux/ip.h>
#include <linux/tcp.h>
#include <linux/spinlock.h>
#include <linux/smp_lock.h>
#include <linux/rwsem.h>
#include <linux/stddef.h>
#include <linux/device.h>
#include <linux/mutex.h>
#include <net/slhc_vj.h>
#include <asm/atomic.h>

#define PPP_VERSION     "2.4.2"

/*
 * Network protocols we support.
 */
#define NP_IP   0               /* Internet Protocol V4 */
#define NP_IPV6 1               /* Internet Protocol V6 */
#define NP_IPX  2               /* IPX protocol */
#define NP_AT   3               /* Appletalk protocol */
#define NP_MPLS_UC 4            /* MPLS unicast */
#define NP_MPLS_MC 5            /* MPLS multicast */
#define NUM_NP  6               /* Number of NPs. */

#define MPHDRLEN        6       /* multilink protocol header length */
#define MPHDRLEN_SSN    4       /* ditto with short sequence numbers */
#define MIN_FRAG_SIZE   64

/*
 * An instance of /dev/ppp can be associated with either a ppp
 * interface unit or a ppp channel.  In both cases, file->private_data
 * points to one of these.
 */
struct ppp_file {
        enum {
                INTERFACE=1, CHANNEL
        }               kind;
        struct sk_buff_head xq;         /* pppd transmit queue */
        struct sk_buff_head rq;         /* receive queue for pppd */
        wait_queue_head_t rwait;        /* for poll on reading /dev/ppp */
        atomic_t        refcnt;         /* # refs (incl /dev/ppp attached) */
        int             hdrlen;         /* space to leave for headers */
        int             index;          /* interface unit / channel number */
        int             dead;           /* unit/channel has been shut down */
};

#define PF_TO_X(pf, X)          ((X *)((char *)(pf) - offsetof(X, file)))

#define PF_TO_PPP(pf)           PF_TO_X(pf, struct ppp)
#define PF_TO_CHANNEL(pf)       PF_TO_X(pf, struct channel)

#define ROUNDUP(n, x)           (((n) + (x) - 1) / (x))

/*
 * Data structure describing one ppp unit.
 * A ppp unit corresponds to a ppp network interface device
 * and represents a multilink bundle.
 * It can have 0 or more ppp channels connected to it.
 */
struct ppp {
        struct ppp_file file;           /* stuff for read/write/poll 0 */
        struct file     *owner;         /* file that owns this unit 48 */
        struct list_head channels;      /* list of attached channels 4c */
        int             n_channels;     /* how many channels are attached 54 */
        spinlock_t      rlock;          /* lock for receive side 58 */
        spinlock_t      wlock;          /* lock for transmit side 5c */
        int             mru;            /* max receive unit 60 */
        unsigned int    flags;          /* control bits 64 */
        unsigned int    xstate;         /* transmit state bits 68 */
        unsigned int    rstate;         /* receive state bits 6c */
        int             debug;          /* debug flags 70 */
        struct slcompress *vj;          /* state for VJ header compression */
        enum NPmode     npmode[NUM_NP]; /* what to do with each net proto 78 */
        struct sk_buff  *xmit_pending;  /* a packet ready to go out 88 */
        struct compressor *xcomp;       /* transmit packet compressor 8c */
        void            *xc_state;      /* its internal state 90 */
        struct compressor *rcomp;       /* receive decompressor 94 */
        void            *rc_state;      /* its internal state 98 */
        unsigned long   last_xmit;      /* jiffies when last pkt sent 9c */
        unsigned long   last_recv;      /* jiffies when last pkt rcvd a0 */
        struct net_device *dev;         /* network interface device a4 */
#ifdef CONFIG_PPP_MULTILINK
        int             nxchan;         /* next channel to send something on */
        u32             nxseq;          /* next sequence number to send */
        int             mrru;           /* MP: max reconst. receive unit */
        u32             nextseq;        /* MP: seq no of next packet */
        u32             minseq;         /* MP: min of most recent seqnos */
        struct sk_buff_head mrq;        /* MP: receive reconstruction queue */
#endif /* CONFIG_PPP_MULTILINK */
        struct net_device_stats stats;  /* statistics */
#ifdef CONFIG_PPP_FILTER
        struct sock_filter *pass_filter;        /* filter for packets to pass */
        struct sock_filter *active_filter;/* filter for pkts to reset idle */
        unsigned pass_len, active_len;
#endif /* CONFIG_PPP_FILTER */
};

/*
 * Bits in flags: SC_NO_TCP_CCID, SC_CCP_OPEN, SC_CCP_UP, SC_LOOP_TRAFFIC,
 * SC_MULTILINK, SC_MP_SHORTSEQ, SC_MP_XSHORTSEQ, SC_COMP_TCP, SC_REJ_COMP_TCP,
 * SC_MUST_COMP
 * Bits in rstate: SC_DECOMP_RUN, SC_DC_ERROR, SC_DC_FERROR.
 * Bits in xstate: SC_COMP_RUN
 */
#define SC_FLAG_BITS    (SC_NO_TCP_CCID|SC_CCP_OPEN|SC_CCP_UP|SC_LOOP_TRAFFIC \
                         |SC_MULTILINK|SC_MP_SHORTSEQ|SC_MP_XSHORTSEQ \
                         |SC_COMP_TCP|SC_REJ_COMP_TCP|SC_MUST_COMP)

/*
 * Private data structure for each channel.
 * This includes the data structure used for multilink.
 */
struct channel {
        struct ppp_file file;           /* stuff for read/write/poll */
        struct list_head list;          /* link in all/new_channels list */
        struct ppp_channel *chan;       /* public channel data structure */
        struct rw_semaphore chan_sem;   /* protects `chan' during chan ioctl */
        spinlock_t      downl;          /* protects `chan', file.xq dequeue */
        struct ppp      *ppp;           /* ppp unit we're connected to */
        struct list_head clist;         /* link in list of channels per unit */
        rwlock_t        upl;            /* protects `ppp' */
#ifdef CONFIG_PPP_MULTILINK
        u8              avail;          /* flag used in multilink stuff */
        u8              had_frag;       /* >= 1 fragments have been sent */
        u32             lastseq;        /* MP: last sequence # received */
#endif /* CONFIG_PPP_MULTILINK */
};

/*
 * SMP locking issues:
 * Both the ppp.rlock and ppp.wlock locks protect the ppp.channels
 * list and the ppp.n_channels field, you need to take both locks
 * before you modify them.
 * The lock ordering is: channel.upl -> ppp.wlock -> ppp.rlock ->
 * channel.downl.
 */

/*
 * A cardmap represents a mapping from unsigned integers to pointers,
 * and provides a fast "find lowest unused number" operation.
 * It uses a broad (32-way) tree with a bitmap at each level.
 * It is designed to be space-efficient for small numbers of entries
 * and time-efficient for large numbers of entries.
 */
#define CARDMAP_ORDER   5
#define CARDMAP_WIDTH   (1U << CARDMAP_ORDER)
#define CARDMAP_MASK    (CARDMAP_WIDTH - 1)

struct cardmap {
        int shift;
        unsigned long inuse;
        struct cardmap *parent;
        void *ptr[CARDMAP_WIDTH];
};
static void *cardmap_get(struct cardmap *map, unsigned int nr);
static void cardmap_set(struct cardmap **map, unsigned int nr, void *ptr);
static unsigned int cardmap_find_first_free(struct cardmap *map);
static void cardmap_destroy(struct cardmap **map);

/*
 * all_ppp_mutex protects the all_ppp_units mapping.
 * It also ensures that finding a ppp unit in the all_ppp_units map
 * and updating its file.refcnt field is atomic.
 */
static DEFINE_MUTEX(all_ppp_mutex);
static struct cardmap *all_ppp_units;
static atomic_t ppp_unit_count = ATOMIC_INIT(0);

/*
 * all_channels_lock protects all_channels and last_channel_index,
 * and the atomicity of find a channel and updating its file.refcnt
 * field.
 */
static DEFINE_SPINLOCK(all_channels_lock);
static LIST_HEAD(all_channels);
static LIST_HEAD(new_channels);
static int last_channel_index;
static atomic_t channel_count = ATOMIC_INIT(0);

/* Get the PPP protocol number from a skb */
#define PPP_PROTO(skb)  (((skb)->data[0] << 8) + (skb)->data[1])

/* We limit the length of ppp->file.rq to this (arbitrary) value */
#define PPP_MAX_RQLEN   32

/*
 * Maximum number of multilink fragments queued up.
 * This has to be large enough to cope with the maximum latency of
 * the slowest channel relative to the others.  Strictly it should
 * depend on the number of channels and their characteristics.
 */
#define PPP_MP_MAX_QLEN 128

/* Multilink header bits. */
#define B       0x80            /* this fragment begins a packet */
#define E       0x40            /* this fragment ends a packet */

/* Compare multilink sequence numbers (assumed to be 32 bits wide) */
#define seq_before(a, b)        ((s32)((a) - (b)) < 0)
#define seq_after(a, b)         ((s32)((a) - (b)) > 0)

/* Prototypes. */
static int ppp_unattached_ioctl(struct ppp_file *pf, struct file *file,
                                unsigned int cmd, unsigned long arg);
static void ppp_xmit_process(struct ppp *ppp);
static void ppp_send_frame(struct ppp *ppp, struct sk_buff *skb);
static void ppp_push(struct ppp *ppp);
static void ppp_channel_push(struct channel *pch);
static void ppp_receive_frame(struct ppp *ppp, struct sk_buff *skb,
                              struct channel *pch);
static void ppp_receive_error(struct ppp *ppp);
static void ppp_receive_nonmp_frame(struct ppp *ppp, struct sk_buff *skb);
static struct sk_buff *ppp_decompress_frame(struct ppp *ppp,
                                            struct sk_buff *skb);
#ifdef CONFIG_PPP_MULTILINK
static void ppp_receive_mp_frame(struct ppp *ppp, struct sk_buff *skb,
                                struct channel *pch);
static void ppp_mp_insert(struct ppp *ppp, struct sk_buff *skb);
static struct sk_buff *ppp_mp_reconstruct(struct ppp *ppp);
static int ppp_mp_explode(struct ppp *ppp, struct sk_buff *skb);
#endif /* CONFIG_PPP_MULTILINK */
static int ppp_set_compress(struct ppp *ppp, unsigned long arg);
static void ppp_ccp_peek(struct ppp *ppp, struct sk_buff *skb, int inbound);
static void ppp_ccp_closed(struct ppp *ppp);
static struct compressor *find_compressor(int type);
static void ppp_get_stats(struct ppp *ppp, struct ppp_stats *st);
static struct ppp *ppp_create_interface(int unit, int *retp);
static void init_ppp_file(struct ppp_file *pf, int kind);
static void ppp_shutdown_interface(struct ppp *ppp);
static void ppp_destroy_interface(struct ppp *ppp);
static struct ppp *ppp_find_unit(int unit);
static struct channel *ppp_find_channel(int unit);
static int ppp_connect_channel(struct channel *pch, int unit);
static int ppp_disconnect_channel(struct channel *pch);
static void ppp_destroy_channel(struct channel *pch);

static struct class *ppp_class;

/* Translates a PPP protocol number to a NP index (NP == network protocol) */
static inline int proto_to_npindex(int proto)
{
        switch (proto) {
        case PPP_IP:
                return NP_IP;
        case PPP_IPV6:
                return NP_IPV6;
        case PPP_IPX:
                return NP_IPX;
        case PPP_AT:
                return NP_AT;
        case PPP_MPLS_UC:
                return NP_MPLS_UC;
        case PPP_MPLS_MC:
                return NP_MPLS_MC;
        }
        return -EINVAL;
}

/* Translates an NP index into a PPP protocol number */
static const int npindex_to_proto[NUM_NP] = {
        PPP_IP,
        PPP_IPV6,
        PPP_IPX,
        PPP_AT,
        PPP_MPLS_UC,
        PPP_MPLS_MC,
};
        
/* Translates an ethertype into an NP index */
static inline int ethertype_to_npindex(int ethertype)
{
        switch (ethertype) {
        case ETH_P_IP:
                return NP_IP;
        case ETH_P_IPV6:
                return NP_IPV6;
        case ETH_P_IPX:
                return NP_IPX;
        case ETH_P_PPPTALK:
        case ETH_P_ATALK:
                return NP_AT;
        case ETH_P_MPLS_UC:
                return NP_MPLS_UC;
        case ETH_P_MPLS_MC:
                return NP_MPLS_MC;
        }
        return -1;
}

/* Translates an NP index into an ethertype */
static const int npindex_to_ethertype[NUM_NP] = {
        ETH_P_IP,
        ETH_P_IPV6,
        ETH_P_IPX,
        ETH_P_PPPTALK,
        ETH_P_MPLS_UC,
        ETH_P_MPLS_MC,
};

/*
 * Locking shorthand.
 */
#define ppp_xmit_lock(ppp)      spin_lock_bh(&(ppp)->wlock)
#define ppp_xmit_unlock(ppp)    spin_unlock_bh(&(ppp)->wlock)
#define ppp_recv_lock(ppp)      spin_lock_bh(&(ppp)->rlock)
#define ppp_recv_unlock(ppp)    spin_unlock_bh(&(ppp)->rlock)
#define ppp_lock(ppp)           do { ppp_xmit_lock(ppp); \
                                     ppp_recv_lock(ppp); } while (0)
#define ppp_unlock(ppp)         do { ppp_recv_unlock(ppp); \
                                     ppp_xmit_unlock(ppp); } while (0)

/*
 * /dev/ppp device routines.
 * The /dev/ppp device is used by pppd to control the ppp unit.
 * It supports the read, write, ioctl and poll functions.
 * Open instances of /dev/ppp can be in one of three states:
 * unattached, attached to a ppp unit, or attached to a ppp channel.
 */
static int ppp_open(struct inode *inode, struct file *file)
{
        /*
         * This could (should?) be enforced by the permissions on /dev/ppp.
         */
        if (!capable(CAP_NET_ADMIN))
                return -EPERM;
        return 0;
}

static int ppp_release(struct inode *inode, struct file *file)
{
        struct ppp_file *pf = file->private_data;
        struct ppp *ppp;

        if (pf != 0) {
                file->private_data = NULL;
                if (pf->kind == INTERFACE) {
                        ppp = PF_TO_PPP(pf);
                        if (file == ppp->owner)
                                ppp_shutdown_interface(ppp);
                }
                if (atomic_dec_and_test(&pf->refcnt)) {
                        switch (pf->kind) {
                        case INTERFACE:
                                ppp_destroy_interface(PF_TO_PPP(pf));
                                break;
                        case CHANNEL:
                                ppp_destroy_channel(PF_TO_CHANNEL(pf));
                                break;
                        }
                }
        }
        return 0;
}

static ssize_t ppp_read(struct file *file, char __user *buf,
                        size_t count, loff_t *ppos)
{
        struct ppp_file *pf = file->private_data;
        DECLARE_WAITQUEUE(wait, current);
        ssize_t ret;
        struct sk_buff *skb = NULL;

        ret = count;

        if (pf == 0)
                return -ENXIO;
        add_wait_queue(&pf->rwait, &wait);
        for (;;) {
                set_current_state(TASK_INTERRUPTIBLE);
                skb = skb_dequeue(&pf->rq);
                if (skb)
                        break;
                ret = 0;
                if (pf->dead)
                        break;
                if (pf->kind == INTERFACE) {
                        /*
                         * Return 0 (EOF) on an interface that has no
                         * channels connected, unless it is looping
                         * network traffic (demand mode).
                         */
                        struct ppp *ppp = PF_TO_PPP(pf);
                        if (ppp->n_channels == 0
                            && (ppp->flags & SC_LOOP_TRAFFIC) == 0)
                                break;
                }
                ret = -EAGAIN;
                if (file->f_flags & O_NONBLOCK)
                        break;
                ret = -ERESTARTSYS;
                if (signal_pending(current))
                        break;
                schedule();
        }
        set_current_state(TASK_RUNNING);
        remove_wait_queue(&pf->rwait, &wait);

        if (skb == 0)
                goto out;

        ret = -EOVERFLOW;
        if (skb->len > count)
                goto outf;
        ret = -EFAULT;
        if (copy_to_user(buf, skb->data, skb->len))
                goto outf;
        ret = skb->len;

 outf:
        kfree_skb(skb);
 out:
        return ret;
}

static ssize_t ppp_write(struct file *file, const char __user *buf,
                         size_t count, loff_t *ppos)
{
        struct ppp_file *pf = file->private_data;
        struct sk_buff *skb;
        ssize_t ret;

        if (pf == 0)
                return -ENXIO;
        ret = -ENOMEM;
        skb = alloc_skb(count + pf->hdrlen, GFP_KERNEL);
        if (skb == 0)
                goto out;
        skb_reserve(skb, pf->hdrlen);
        ret = -EFAULT;
        if (copy_from_user(skb_put(skb, count), buf, count)) {
                kfree_skb(skb);
                goto out;
        }

        skb_queue_tail(&pf->xq, skb);

        switch (pf->kind) {
        case INTERFACE:
                ppp_xmit_process(PF_TO_PPP(pf));
                break;
        case CHANNEL:
                ppp_channel_push(PF_TO_CHANNEL(pf));
                break;
        }

        ret = count;

 out:
        return ret;
}

/* No kernel lock - fine */
static unsigned int ppp_poll(struct file *file, poll_table *wait)
{
        struct ppp_file *pf = file->private_data;
        unsigned int mask;

        if (pf == 0)
                return 0;
        poll_wait(file, &pf->rwait, wait);
        mask = POLLOUT | POLLWRNORM;
        if (skb_peek(&pf->rq) != 0)
                mask |= POLLIN | POLLRDNORM;
        if (pf->dead)
                mask |= POLLHUP;
        else if (pf->kind == INTERFACE) {
                /* see comment in ppp_read */
                struct ppp *ppp = PF_TO_PPP(pf);
                if (ppp->n_channels == 0
                    && (ppp->flags & SC_LOOP_TRAFFIC) == 0)
                        mask |= POLLIN | POLLRDNORM;
        }

        return mask;
}

#ifdef CONFIG_PPP_FILTER
static int get_filter(void __user *arg, struct sock_filter **p)
{
        struct sock_fprog uprog;
        struct sock_filter *code = NULL;
        int len, err;

        if (copy_from_user(&uprog, arg, sizeof(uprog)))
                return -EFAULT;

        if (!uprog.len) {
                *p = NULL;
                return 0;
        }

        len = uprog.len * sizeof(struct sock_filter);
        code = kmalloc(len, GFP_KERNEL);
        if (code == NULL)
                return -ENOMEM;

        if (copy_from_user(code, uprog.filter, len)) {
                kfree(code);
                return -EFAULT;
        }

        err = sk_chk_filter(code, uprog.len);
        if (err) {
                kfree(code);
                return err;
        }

        *p = code;
        return uprog.len;
}
#endif /* CONFIG_PPP_FILTER */

static int ppp_ioctl(struct inode *inode, struct file *file,
                     unsigned int cmd, unsigned long arg)
{
        struct ppp_file *pf = file->private_data;
        struct ppp *ppp;
        int err = -EFAULT, val, val2, i;
        struct ppp_idle idle;
        struct npioctl npi;
        int unit, cflags;
        struct slcompress *vj;
        void __user *argp = (void __user *)arg;
        int __user *p = argp;

        if (pf == 0)
                return ppp_unattached_ioctl(pf, file, cmd, arg);

        if (cmd == PPPIOCDETACH) {
                /*
                 * We have to be careful here... if the file descriptor
                 * has been dup'd, we could have another process in the
                 * middle of a poll using the same file *, so we had
                 * better not free the interface data structures -
                 * instead we fail the ioctl.  Even in this case, we
                 * shut down the interface if we are the owner of it.
                 * Actually, we should get rid of PPPIOCDETACH, userland
                 * (i.e. pppd) could achieve the same effect by closing
                 * this fd and reopening /dev/ppp.
                 */
                err = -EINVAL;
                if (pf->kind == INTERFACE) {
                        ppp = PF_TO_PPP(pf);
                        if (file == ppp->owner)
                                ppp_shutdown_interface(ppp);
                }
                if (atomic_read(&file->f_count) <= 2) {
                        ppp_release(inode, file);
                        err = 0;
                } else
                        printk(KERN_DEBUG "PPPIOCDETACH file->f_count=%d\n",
                               atomic_read(&file->f_count));
                return err;
        }

        if (pf->kind == CHANNEL) {
                struct channel *pch = PF_TO_CHANNEL(pf);
                struct ppp_channel *chan;

                switch (cmd) {
                case PPPIOCCONNECT:
                        if (get_user(unit, p))
                                break;
                        err = ppp_connect_channel(pch, unit);
                        break;

                case PPPIOCDISCONN:
                        err = ppp_disconnect_channel(pch);
                        break;

                default:
                        down_read(&pch->chan_sem);
                        chan = pch->chan;
                        err = -ENOTTY;
                        if (chan && chan->ops->ioctl)
                                err = chan->ops->ioctl(chan, cmd, arg);
                        up_read(&pch->chan_sem);
                }
                return err;
        }

        if (pf->kind != INTERFACE) {
                /* can't happen */
                printk(KERN_ERR "PPP: not interface or channel??\n");
                return -EINVAL;
        }

        ppp = PF_TO_PPP(pf);
        switch (cmd) {
        case PPPIOCSMRU:
                if (get_user(val, p))
                        break;
                ppp->mru = val;
                err = 0;
                break;

        case PPPIOCSFLAGS:
                if (get_user(val, p))
                        break;
                ppp_lock(ppp);
                cflags = ppp->flags & ~val;
                ppp->flags = val & SC_FLAG_BITS;
                ppp_unlock(ppp);
                if (cflags & SC_CCP_OPEN)
                        ppp_ccp_closed(ppp);
                err = 0;
                break;

        case PPPIOCGFLAGS:
                val = ppp->flags | ppp->xstate | ppp->rstate;
                if (put_user(val, p))
                        break;
                err = 0;
                break;

        case PPPIOCSCOMPRESS:
                err = ppp_set_compress(ppp, arg);
                break;

        case PPPIOCGUNIT:
                if (put_user(ppp->file.index, p))
                        break;
                err = 0;
                break;

        case PPPIOCSDEBUG:
                if (get_user(val, p))
                        break;
                ppp->debug = val;
                err = 0;
                break;

        case PPPIOCGDEBUG:
                if (put_user(ppp->debug, p))
                        break;
                err = 0;
                break;

        case PPPIOCGIDLE:
                idle.xmit_idle = (jiffies - ppp->last_xmit) / HZ;
                idle.recv_idle = (jiffies - ppp->last_recv) / HZ;
                if (copy_to_user(argp, &idle, sizeof(idle)))
                        break;
                err = 0;
                break;

        case PPPIOCSMAXCID:
                if (get_user(val, p))
                        break;
                val2 = 15;
                if ((val >> 16) != 0) {
                        val2 = val >> 16;
                        val &= 0xffff;
                }
                vj = slhc_init(val2+1, val+1);
                if (vj == 0) {
                        printk(KERN_ERR "PPP: no memory (VJ compressor)\n");
                        err = -ENOMEM;
                        break;
                }
                ppp_lock(ppp);
                if (ppp->vj != 0)
                        slhc_free(ppp->vj);
                ppp->vj = vj;
                ppp_unlock(ppp);
                err = 0;
                break;

        case PPPIOCGNPMODE:
        case PPPIOCSNPMODE:
                if (copy_from_user(&npi, argp, sizeof(npi)))
                        break;
                err = proto_to_npindex(npi.protocol);
                if (err < 0)
                        break;
                i = err;
                if (cmd == PPPIOCGNPMODE) {
                        err = -EFAULT;
                        npi.mode = ppp->npmode[i];
                        if (copy_to_user(argp, &npi, sizeof(npi)))
                                break;
                } else {
                        ppp->npmode[i] = npi.mode;
                        /* we may be able to transmit more packets now (??) */
                        netif_wake_queue(ppp->dev);
                }
                err = 0;
                break;

#ifdef CONFIG_PPP_FILTER
        case PPPIOCSPASS:
        {
                struct sock_filter *code;
                err = get_filter(argp, &code);
                if (err >= 0) {
                        ppp_lock(ppp);
                        kfree(ppp->pass_filter);
                        ppp->pass_filter = code;
                        ppp->pass_len = err;
                        ppp_unlock(ppp);
                        err = 0;
                }
                break;
        }
        case PPPIOCSACTIVE:
        {
                struct sock_filter *code;
                err = get_filter(argp, &code);
                if (err >= 0) {
                        ppp_lock(ppp);
                        kfree(ppp->active_filter);
                        ppp->active_filter = code;
                        ppp->active_len = err;
                        ppp_unlock(ppp);
                        err = 0;
                }
                break;
        }
#endif /* CONFIG_PPP_FILTER */

#ifdef CONFIG_PPP_MULTILINK
        case PPPIOCSMRRU:
                if (get_user(val, p))
                        break;
                ppp_recv_lock(ppp);
                ppp->mrru = val;
                ppp_recv_unlock(ppp);
                err = 0;
                break;
#endif /* CONFIG_PPP_MULTILINK */

        default:
                err = -ENOTTY;
        }

        return err;
}

static int ppp_unattached_ioctl(struct ppp_file *pf, struct file *file,
                                unsigned int cmd, unsigned long arg)
{
        int unit, err = -EFAULT;
        struct ppp *ppp;
        struct channel *chan;
        int __user *p = (int __user *)arg;

        switch (cmd) {
        case PPPIOCNEWUNIT:
                /* Create a new ppp unit */
                if (get_user(unit, p))
                        break;
                ppp = ppp_create_interface(unit, &err);
                if (ppp == 0)
                        break;
                file->private_data = &ppp->file;
                ppp->owner = file;
                err = -EFAULT;
                if (put_user(ppp->file.index, p))
                        break;
                err = 0;
                break;

        case PPPIOCATTACH:
                /* Attach to an existing ppp unit */
                if (get_user(unit, p))
                        break;
                mutex_lock(&all_ppp_mutex);
                err = -ENXIO;
                ppp = ppp_find_unit(unit);
                if (ppp != 0) {
                        atomic_inc(&ppp->file.refcnt);
                        file->private_data = &ppp->file;
                        err = 0;
                }
                mutex_unlock(&all_ppp_mutex);
                break;

        case PPPIOCATTCHAN:
                if (get_user(unit, p))
                        break;
                spin_lock_bh(&all_channels_lock);
                err = -ENXIO;
                chan = ppp_find_channel(unit);
                if (chan != 0) {
                        atomic_inc(&chan->file.refcnt);
                        file->private_data = &chan->file;
                        err = 0;
                }
                spin_unlock_bh(&all_channels_lock);
                break;

        default:
                err = -ENOTTY;
        }
        return err;
}

static struct file_operations ppp_device_fops = {
        .owner          = THIS_MODULE,
        .read           = ppp_read,
        .write          = ppp_write,
        .poll           = ppp_poll,
        .ioctl          = ppp_ioctl,
        .open           = ppp_open,
        .release        = ppp_release
};

#define PPP_MAJOR       108

/* Called at boot time if ppp is compiled into the kernel,
   or at module load time (from init_module) if compiled as a module. */
static int __init ppp_init(void)
{
        int err;

        printk(KERN_INFO "PPP generic driver version " PPP_VERSION "\n");
        err = register_chrdev(PPP_MAJOR, "ppp", &ppp_device_fops);
        if (!err) {
                ppp_class = class_create(THIS_MODULE, "ppp");
                if (IS_ERR(ppp_class)) {
                        err = PTR_ERR(ppp_class);
                        goto out_chrdev;
                }
                class_device_create(ppp_class, NULL, MKDEV(PPP_MAJOR, 0), NULL, "ppp");
        }

out:
        if (err)
                printk(KERN_ERR "failed to register PPP device (%d)\n", err);
        return err;

out_chrdev:
        unregister_chrdev(PPP_MAJOR, "ppp");
        goto out;
}

/*
 * Network interface unit routines.
 */
static int
ppp_start_xmit(struct sk_buff *skb, struct net_device *dev)
{
        struct ppp *ppp = (struct ppp *) dev->priv;
        int npi, proto;
        unsigned char *pp;

        npi = ethertype_to_npindex(ntohs(skb->protocol));
        if (npi < 0)
                goto outf;

        /* Drop, accept or reject the packet */
        switch (ppp->npmode[npi]) {
        case NPMODE_PASS:
                break;
        case NPMODE_QUEUE:
                /* it would be nice to have a way to tell the network
                   system to queue this one up for later. */
                goto outf;
        case NPMODE_DROP:
        case NPMODE_ERROR:
                goto outf;
        }

        /* Put the 2-byte PPP protocol number on the front,
           making sure there is room for the address and control fields. */
        if (skb_headroom(skb) < PPP_HDRLEN) {
                struct sk_buff *ns;

                ns = alloc_skb(skb->len + dev->hard_header_len, GFP_ATOMIC);
                if (ns == 0)
                        goto outf;
                skb_reserve(ns, dev->hard_header_len);
                skb_copy_bits(skb, 0, skb_put(ns, skb->len), skb->len);
                kfree_skb(skb);
                skb = ns;
        }
        pp = skb_push(skb, 2);
        proto = npindex_to_proto[npi];
        pp[0] = proto >> 8;
        pp[1] = proto;

        netif_stop_queue(dev);
        skb_queue_tail(&ppp->file.xq, skb);
        ppp_xmit_process(ppp);
        return 0;

 outf:
        kfree_skb(skb);
        ++ppp->stats.tx_dropped;
        return 0;
}

static struct net_device_stats *
ppp_net_stats(struct net_device *dev)
{
        struct ppp *ppp = (struct ppp *) dev->priv;

        return &ppp->stats;
}

static int
ppp_net_ioctl(struct net_device *dev, struct ifreq *ifr, int cmd)
{
        struct ppp *ppp = dev->priv;
        int err = -EFAULT;
        void __user *addr = (void __user *) ifr->ifr_ifru.ifru_data;
        struct ppp_stats stats;
        struct ppp_comp_stats cstats;
        char *vers;

        switch (cmd) {
        case SIOCGPPPSTATS:
                ppp_get_stats(ppp, &stats);
                if (copy_to_user(addr, &stats, sizeof(stats)))
                        break;
                err = 0;
                break;

        case SIOCGPPPCSTATS:
                memset(&cstats, 0, sizeof(cstats));
                if (ppp->xc_state != 0)
                        ppp->xcomp->comp_stat(ppp->xc_state, &cstats.c);
                if (ppp->rc_state != 0)
                        ppp->rcomp->decomp_stat(ppp->rc_state, &cstats.d);
                if (copy_to_user(addr, &cstats, sizeof(cstats)))
                        break;
                err = 0;
                break;

        case SIOCGPPPVER:
                vers = PPP_VERSION;
                if (copy_to_user(addr, vers, strlen(vers) + 1))
                        break;
                err = 0;
                break;

        default:
                err = -EINVAL;
        }

        return err;
}

static void ppp_setup(struct net_device *dev)
{
        dev->hard_header_len = PPP_HDRLEN;
        dev->mtu = PPP_MTU;
        dev->addr_len = 0;
        dev->tx_queue_len = 3;
        dev->type = ARPHRD_PPP;
        dev->flags = IFF_POINTOPOINT | IFF_NOARP | IFF_MULTICAST;
}

/*
 * Transmit-side routines.
 */

/*
 * Called to do any work queued up on the transmit side
 * that can now be done.
 */
static void
ppp_xmit_process(struct ppp *ppp)
{
        struct sk_buff *skb;

        ppp_xmit_lock(ppp);
        if (ppp->dev != 0) {
                ppp_push(ppp);
                while (ppp->xmit_pending == 0
                       && (skb = skb_dequeue(&ppp->file.xq)) != 0)
                        ppp_send_frame(ppp, skb);
                /* If there's no work left to do, tell the core net
                   code that we can accept some more. */
                if (ppp->xmit_pending == 0 && skb_peek(&ppp->file.xq) == 0)
                        netif_wake_queue(ppp->dev);
        }
        ppp_xmit_unlock(ppp);
}

static inline struct sk_buff *
pad_compress_skb(struct ppp *ppp, struct sk_buff *skb)
{
        struct sk_buff *new_skb;
        int len;
        int new_skb_size = ppp->dev->mtu +
                ppp->xcomp->comp_extra + ppp->dev->hard_header_len;
        int compressor_skb_size = ppp->dev->mtu +
                ppp->xcomp->comp_extra + PPP_HDRLEN;
        new_skb = alloc_skb(new_skb_size, GFP_ATOMIC);
        if (!new_skb) {
                if (net_ratelimit())
                        printk(KERN_ERR "PPP: no memory (comp pkt)\n");
                return NULL;
        }
        if (ppp->dev->hard_header_len > PPP_HDRLEN)
                skb_reserve(new_skb,
                            ppp->dev->hard_header_len - PPP_HDRLEN);

        /* compressor still expects A/C bytes in hdr */
        len = ppp->xcomp->compress(ppp->xc_state, skb->data - 2,
                                   new_skb->data, skb->len + 2,
                                   compressor_skb_size);
        if (len > 0 && (ppp->flags & SC_CCP_UP)) {
                kfree_skb(skb);
                skb = new_skb;
                skb_put(skb, len);
                skb_pull(skb, 2);       /* pull off A/C bytes */
        } else if (len == 0) {
                /* didn't compress, or CCP not up yet */
                kfree_skb(new_skb);
                new_skb = skb;
        } else {
                /*
                 * (len < 0)
                 * MPPE requires that we do not send unencrypted
                 * frames.  The compressor will return -1 if we
                 * should drop the frame.  We cannot simply test
                 * the compress_proto because MPPE and MPPC share
                 * the same number.
                 */
                if (net_ratelimit())
                        printk(KERN_ERR "ppp: compressor dropped pkt\n");
                kfree_skb(skb);
                kfree_skb(new_skb);
                new_skb = NULL;
        }
        return new_skb;
}

/*
 * Compress and send a frame.
 * The caller should have locked the xmit path,
 * and xmit_pending should be 0.
 */
static void
ppp_send_frame(struct ppp *ppp, struct sk_buff *skb)
{
        int proto = PPP_PROTO(skb);
        struct sk_buff *new_skb;
        int len;
        unsigned char *cp;

        if (proto < 0x8000) {
#ifdef CONFIG_PPP_FILTER
                /* check if we should pass this packet */
                /* the filter instructions are constructed assuming
                   a four-byte PPP header on each packet */
                *skb_push(skb, 2) = 1;
                if (ppp->pass_filter
                    && sk_run_filter(skb, ppp->pass_filter,
                                     ppp->pass_len) == 0) {
                        if (ppp->debug & 1)
                                printk(KERN_DEBUG "PPP: outbound frame not passed\n");
                        kfree_skb(skb);
                        return;
                }
                /* if this packet passes the active filter, record the time */
                if (!(ppp->active_filter
                      && sk_run_filter(skb, ppp->active_filter,
                                       ppp->active_len) == 0))
                        ppp->last_xmit = jiffies;
                skb_pull(skb, 2);
#else
                /* for data packets, record the time */
                ppp->last_xmit = jiffies;
#endif /* CONFIG_PPP_FILTER */
        }

        ++ppp->stats.tx_packets;
        ppp->stats.tx_bytes += skb->len - 2;

        switch (proto) {
        case PPP_IP:
                if (ppp->vj == 0 || (ppp->flags & SC_COMP_TCP) == 0)
                        break;
                /* try to do VJ TCP header compression */
                new_skb = alloc_skb(skb->len + ppp->dev->hard_header_len - 2,
                                    GFP_ATOMIC);
                if (new_skb == 0) {
                        printk(KERN_ERR "PPP: no memory (VJ comp pkt)\n");
                        goto drop;
                }
                skb_reserve(new_skb, ppp->dev->hard_header_len - 2);
                cp = skb->data + 2;
                len = slhc_compress(ppp->vj, cp, skb->len - 2,
                                    new_skb->data + 2, &cp,
                                    !(ppp->flags & SC_NO_TCP_CCID));
                if (cp == skb->data + 2) {
                        /* didn't compress */
                        kfree_skb(new_skb);
                } else {
                        if (cp[0] & SL_TYPE_COMPRESSED_TCP) {
                                proto = PPP_VJC_COMP;
                                cp[0] &= ~SL_TYPE_COMPRESSED_TCP;
                        } else {
                                proto = PPP_VJC_UNCOMP;
                                cp[0] = skb->data[2];
                        }
                        kfree_skb(skb);
                        skb = new_skb;
                        cp = skb_put(skb, len + 2);
                        cp[0] = 0;
                        cp[1] = proto;
                }
                break;

        case PPP_CCP:
                /* peek at outbound CCP frames */
                ppp_ccp_peek(ppp, skb, 0);
                break;
        }

        /* try to do packet compression */
        if ((ppp->xstate & SC_COMP_RUN) && ppp->xc_state != 0
            && proto != PPP_LCP && proto != PPP_CCP) {
                if (!(ppp->flags & SC_CCP_UP) && (ppp->flags & SC_MUST_COMP)) {
                        if (net_ratelimit())
                                printk(KERN_ERR "ppp: compression required but down - pkt dropped.\n");
                        goto drop;
                }
                skb = pad_compress_skb(ppp, skb);
                if (!skb)
                        goto drop;
        }

        /*
         * If we are waiting for traffic (demand dialling),
         * queue it up for pppd to receive.
         */
        if (ppp->flags & SC_LOOP_TRAFFIC) {
                if (ppp->file.rq.qlen > PPP_MAX_RQLEN)
                        goto drop;
                skb_queue_tail(&ppp->file.rq, skb);
                wake_up_interruptible(&ppp->file.rwait);
                return;
        }

        ppp->xmit_pending = skb;
        ppp_push(ppp);
        return;

 drop:
        if (skb)
                kfree_skb(skb);
        ++ppp->stats.tx_errors;
}

/*
 * Try to send the frame in xmit_pending.
 * The caller should have the xmit path locked.
 */
static void
ppp_push(struct ppp *ppp)
{
        struct list_head *list;
        struct channel *pch;
        struct sk_buff *skb = ppp->xmit_pending;

        if (skb == 0)
                return;

        list = &ppp->channels;
        if (list_empty(list)) {
                /* nowhere to send the packet, just drop it */
                ppp->xmit_pending = NULL;
                kfree_skb(skb);
                return;
        }

        if ((ppp->flags & SC_MULTILINK) == 0) {
                /* not doing multilink: send it down the first channel */
                list = list->next;
                pch = list_entry(list, struct channel, clist);

                spin_lock_bh(&pch->downl);
                if (pch->chan) {
                        if (pch->chan->ops->start_xmit(pch->chan, skb))
                                ppp->xmit_pending = NULL;
                } else {
                        /* channel got unregistered */
                        kfree_skb(skb);
                        ppp->xmit_pending = NULL;
                }
                spin_unlock_bh(&pch->downl);
                return;
        }

#ifdef CONFIG_PPP_MULTILINK
        /* Multilink: fragment the packet over as many links
           as can take the packet at the moment. */
        if (!ppp_mp_explode(ppp, skb))
                return;
#endif /* CONFIG_PPP_MULTILINK */

        ppp->xmit_pending = NULL;
        kfree_skb(skb);
}

#ifdef CONFIG_PPP_MULTILINK
/*
 * Divide a packet to be transmitted into fragments and
 * send them out the individual links.
 */
static int ppp_mp_explode(struct ppp *ppp, struct sk_buff *skb)
{
        int len, fragsize;
        int i, bits, hdrlen, mtu;
        int flen;
        int navail, nfree;
        int nbigger;
        unsigned char *p, *q;
        struct list_head *list;
        struct channel *pch;
        struct sk_buff *frag;
        struct ppp_channel *chan;

        nfree = 0;      /* # channels which have no packet already queued */
        navail = 0;     /* total # of usable channels (not deregistered) */
        hdrlen = (ppp->flags & SC_MP_XSHORTSEQ)? MPHDRLEN_SSN: MPHDRLEN;
        i = 0;
        list_for_each_entry(pch, &ppp->channels, clist) {
                navail += pch->avail = (pch->chan != NULL);
                if (pch->avail) {
                        if (skb_queue_empty(&pch->file.xq) ||
                            !pch->had_frag) {
                                pch->avail = 2;
                                ++nfree;
                        }
                        if (!pch->had_frag && i < ppp->nxchan)
                                ppp->nxchan = i;
                }
                ++i;
        }

        /*
         * Don't start sending this packet unless at least half of
         * the channels are free.  This gives much better TCP
         * performance if we have a lot of channels.
         */
        if (nfree == 0 || nfree < navail / 2)
                return 0;       /* can't take now, leave it in xmit_pending */

        /* Do protocol field compression (XXX this should be optional) */
        p = skb->data;
        len = skb->len;
        if (*p == 0) {
                ++p;
                --len;
        }

        /*
         * Decide on fragment size.
         * We create a fragment for each free channel regardless of
         * how small they are (i.e. even 0 length) in order to minimize
         * the time that it will take to detect when a channel drops
         * a fragment.
         */
        fragsize = len;
        if (nfree > 1)
                fragsize = ROUNDUP(fragsize, nfree);
        /* nbigger channels get fragsize bytes, the rest get fragsize-1,
           except if nbigger==0, then they all get fragsize. */
        nbigger = len % nfree;

        /* skip to the channel after the one we last used
           and start at that one */
        list = &ppp->channels;
        for (i = 0; i < ppp->nxchan; ++i) {
                list = list->next;
                if (list == &ppp->channels) {
                        i = 0;
                        break;
                }
        }

        /* create a fragment for each channel */
        bits = B;
        while (nfree > 0 || len > 0) {
                list = list->next;
                if (list == &ppp->channels) {
                        i = 0;
                        continue;
                }
                pch = list_entry(list, struct channel, clist);
                ++i;
                if (!pch->avail)
                        continue;

                /*
                 * Skip this channel if it has a fragment pending already and
                 * we haven't given a fragment to all of the free channels.
                 */
                if (pch->avail == 1) {
                        if (nfree > 0)
                                continue;
                } else {
                        --nfree;
                        pch->avail = 1;
                }

                /* check the channel's mtu and whether it is still attached. */
                spin_lock_bh(&pch->downl);
                if (pch->chan == NULL) {
                        /* can't use this channel, it's being deregistered */
                        spin_unlock_bh(&pch->downl);
                        pch->avail = 0;
                        if (--navail == 0)
                                break;
                        continue;
                }

                /*
                 * Create a fragment for this channel of
                 * min(max(mtu+2-hdrlen, 4), fragsize, len) bytes.
                 * If mtu+2-hdrlen < 4, that is a ridiculously small
                 * MTU, so we use mtu = 2 + hdrlen.
                 */
                if (fragsize > len)
                        fragsize = len;
                flen = fragsize;
                mtu = pch->chan->mtu + 2 - hdrlen;
                if (mtu < 4)
                        mtu = 4;
                if (flen > mtu)
                        flen = mtu;
                if (flen == len && nfree == 0)
                        bits |= E;
                frag = alloc_skb(flen + hdrlen + (flen == 0), GFP_ATOMIC);
                if (frag == 0)
                        goto noskb;
                q = skb_put(frag, flen + hdrlen);

                /* make the MP header */
                q[0] = PPP_MP >> 8;
                q[1] = PPP_MP;
                if (ppp->flags & SC_MP_XSHORTSEQ) {
                        q[2] = bits + ((ppp->nxseq >> 8) & 0xf);
                        q[3] = ppp->nxseq;
                } else {
                        q[2] = bits;
                        q[3] = ppp->nxseq >> 16;
                        q[4] = ppp->nxseq >> 8;
                        q[5] = ppp->nxseq;
                }

                /*
                 * Copy the data in.
                 * Unfortunately there is a bug in older versions of
                 * the Linux PPP multilink reconstruction code where it
                 * drops 0-length fragments.  Therefore we make sure the
                 * fragment has at least one byte of data.  Any bytes
                 * we add in this situation will end up as padding on the
                 * end of the reconstructed packet.
                 */
                if (flen == 0)
                        *skb_put(frag, 1) = 0;
                else
                        memcpy(q + hdrlen, p, flen);

                /* try to send it down the channel */
                chan = pch->chan;
                if (!skb_queue_empty(&pch->file.xq) ||
                    !chan->ops->start_xmit(chan, frag))
                        skb_queue_tail(&pch->file.xq, frag);
                pch->had_frag = 1;
                p += flen;
                len -= flen;
                ++ppp->nxseq;
                bits = 0;
                spin_unlock_bh(&pch->downl);

                if (--nbigger == 0 && fragsize > 0)
                        --fragsize;
        }
        ppp->nxchan = i;

        return 1;

 noskb:
        spin_unlock_bh(&pch->downl);
        if (ppp->debug & 1)
                printk(KERN_ERR "PPP: no memory (fragment)\n");
        ++ppp->stats.tx_errors;
        ++ppp->nxseq;
        return 1;       /* abandon the frame */
}
#endif /* CONFIG_PPP_MULTILINK */

/*
 * Try to send data out on a channel.
 */
static void
ppp_channel_push(struct channel *pch)
{
        struct sk_buff *skb;
        struct ppp *ppp;

        spin_lock_bh(&pch->downl);
        if (pch->chan != 0) {
                while (!skb_queue_empty(&pch->file.xq)) {
                        skb = skb_dequeue(&pch->file.xq);
                        if (!pch->chan->ops->start_xmit(pch->chan, skb)) {
                                /* put the packet back and try again later */
                                skb_queue_head(&pch->file.xq, skb);
                                break;
                        }
                }
        } else {
                /* channel got deregistered */
                skb_queue_purge(&pch->file.xq);
        }
        spin_unlock_bh(&pch->downl);
        /* see if there is anything from the attached unit to be sent */
        if (skb_queue_empty(&pch->file.xq)) {
                read_lock_bh(&pch->upl);
                ppp = pch->ppp;
                if (ppp != 0)
                        ppp_xmit_process(ppp);
                read_unlock_bh(&pch->upl);
        }
}

/*
 * Receive-side routines.
 */

/* misuse a few fields of the skb for MP reconstruction */
#define sequence        priority
#define BEbits          cb[0]

static inline void
ppp_do_recv(struct ppp *ppp, struct sk_buff *skb, struct channel *pch)
{
        ppp_recv_lock(ppp);
        /* ppp->dev == 0 means interface is closing down */
        if (ppp->dev != 0)
                ppp_receive_frame(ppp, skb, pch);
        else
                kfree_skb(skb);
        ppp_recv_unlock(ppp);
}

void
ppp_input(struct ppp_channel *chan, struct sk_buff *skb)
{
        struct channel *pch = chan->ppp;
        int proto;

        if (pch == 0 || skb->len == 0) {
                kfree_skb(skb);
                return;
        }

        proto = PPP_PROTO(skb);
        read_lock_bh(&pch->upl);
        if (pch->ppp == 0 || proto >= 0xc000 || proto == PPP_CCPFRAG) {
                /* put it on the channel queue */
                skb_queue_tail(&pch->file.rq, skb);
                /* drop old frames if queue too long */
                while (pch->file.rq.qlen > PPP_MAX_RQLEN
                       && (skb = skb_dequeue(&pch->file.rq)) != 0)
                        kfree_skb(skb);
                wake_up_interruptible(&pch->file.rwait);
        } else {
                ppp_do_recv(pch->ppp, skb, pch);
        }
        read_unlock_bh(&pch->upl);
}

/* Put a 0-length skb in the receive queue as an error indication */
void
ppp_input_error(struct ppp_channel *chan, int code)
{
        struct channel *pch = chan->ppp;
        struct sk_buff *skb;

        if (pch == 0)
                return;

        read_lock_bh(&pch->upl);
        if (pch->ppp != 0) {
                skb = alloc_skb(0, GFP_ATOMIC);
                if (skb != 0) {
                        skb->len = 0;           /* probably unnecessary */
                        skb->cb[0] = code;
                        ppp_do_recv(pch->ppp, skb, pch);
                }
        }
        read_unlock_bh(&pch->upl);
}

/*
 * We come in here to process a received frame.
 * The receive side of the ppp unit is locked.
 */
static void
ppp_receive_frame(struct ppp *ppp, struct sk_buff *skb, struct channel *pch)
{
        if (skb->len >= 2) {
#ifdef CONFIG_PPP_MULTILINK
                /* XXX do channel-level decompression here */
                if (PPP_PROTO(skb) == PPP_MP)
                        ppp_receive_mp_frame(ppp, skb, pch);
                else
#endif /* CONFIG_PPP_MULTILINK */
                        ppp_receive_nonmp_frame(ppp, skb);
                return;
        }

        if (skb->len > 0)
                /* note: a 0-length skb is used as an error indication */
                ++ppp->stats.rx_length_errors;

        kfree_skb(skb);
        ppp_receive_error(ppp);
}

static void
ppp_receive_error(struct ppp *ppp)
{
        ++ppp->stats.rx_errors;
        if (ppp->vj != 0)
                slhc_toss(ppp->vj);
}

static void
ppp_receive_nonmp_frame(struct ppp *ppp, struct sk_buff *skb)
{
        struct sk_buff *ns;
        int proto, len, npi;

        /*
         * Decompress the frame, if compressed.
         * Note that some decompressors need to see uncompressed frames
         * that come in as well as compressed frames.
         */
        if (ppp->rc_state != 0 && (ppp->rstate & SC_DECOMP_RUN)
            && (ppp->rstate & (SC_DC_FERROR | SC_DC_ERROR)) == 0)
                skb = ppp_decompress_frame(ppp, skb);

        if (ppp->flags & SC_MUST_COMP && ppp->rstate & SC_DC_FERROR)
                goto err;

        proto = PPP_PROTO(skb);
        switch (proto) {
        case PPP_VJC_COMP:
                /* decompress VJ compressed packets */
                if (ppp->vj == 0 || (ppp->flags & SC_REJ_COMP_TCP))
                        goto err;

                if (skb_tailroom(skb) < 124) {
                        /* copy to a new sk_buff with more tailroom */
                        ns = dev_alloc_skb(skb->len + 128);
                        if (ns == 0) {
                                printk(KERN_ERR"PPP: no memory (VJ decomp)\n");
                                goto err;
                        }
                        skb_reserve(ns, 2);
                        skb_copy_bits(skb, 0, skb_put(ns, skb->len), skb->len);
                        kfree_skb(skb);
                        skb = ns;
                }
                else
                        skb->ip_summed = CHECKSUM_NONE;

                len = slhc_uncompress(ppp->vj, skb->data + 2, skb->len - 2);
                if (len <= 0) {
                        printk(KERN_DEBUG "PPP: VJ decompression error\n");
                        goto err;
                }
                len += 2;
                if (len > skb->len)
                        skb_put(skb, len - skb->len);
                else if (len < skb->len)
                        skb_trim(skb, len);
                proto = PPP_IP;
                break;

        case PPP_VJC_UNCOMP:
                if (ppp->vj == 0 || (ppp->flags & SC_REJ_COMP_TCP))
                        goto err;
                
                /* Until we fix the decompressor need to make sure
                 * data portion is linear.
                 */
                if (!pskb_may_pull(skb, skb->len)) 
                        goto err;

                if (slhc_remember(ppp->vj, skb->data + 2, skb->len - 2) <= 0) {
                        printk(KERN_ERR "PPP: VJ uncompressed error\n");
                        goto err;
                }
                proto = PPP_IP;
                break;

        case PPP_CCP:
                ppp_ccp_peek(ppp, skb, 1);
                break;
        }

        ++ppp->stats.rx_packets;
        ppp->stats.rx_bytes += skb->len - 2;

        npi = proto_to_npindex(proto);
        if (npi < 0) {
                /* control or unknown frame - pass it to pppd */
                skb_queue_tail(&ppp->file.rq, skb);
                /* limit queue length by dropping old frames */
                while (ppp->file.rq.qlen > PPP_MAX_RQLEN
                       && (skb = skb_dequeue(&ppp->file.rq)) != 0)
                        kfree_skb(skb);
                /* wake up any process polling or blocking on read */
                wake_up_interruptible(&ppp->file.rwait);

        } else {
                /* network protocol frame - give it to the kernel */

#ifdef CONFIG_PPP_FILTER
                /* check if the packet passes the pass and active filters */
                /* the filter instructions are constructed assuming
                   a four-byte PPP header on each packet */
                *skb_push(skb, 2) = 0;
                if (ppp->pass_filter
                    && sk_run_filter(skb, ppp->pass_filter,
                                     ppp->pass_len) == 0) {
                        if (ppp->debug & 1)
                                printk(KERN_DEBUG "PPP: inbound frame not passed\n");
                        kfree_skb(skb);
                        return;
                }
                if (!(ppp->active_filter
                      && sk_run_filter(skb, ppp->active_filter,
                                       ppp->active_len) == 0))
                        ppp->last_recv = jiffies;
                skb_pull(skb, 2);
#else
                ppp->last_recv = jiffies;
#endif /* CONFIG_PPP_FILTER */

                if ((ppp->dev->flags & IFF_UP) == 0
                    || ppp->npmode[npi] != NPMODE_PASS) {
                        kfree_skb(skb);
                } else {
                        /* chop off protocol */
                        skb_pull_rcsum(skb, 2);
                        skb->dev = ppp->dev;
                        skb->protocol = htons(npindex_to_ethertype[npi]);
                        skb->mac.raw = skb->data;
                        netif_rx(skb);
                        ppp->dev->last_rx = jiffies;
                }
        }
        return;

 err:
        kfree_skb(skb);
        ppp_receive_error(ppp);
}

static struct sk_buff *
ppp_decompress_frame(struct ppp *ppp, struct sk_buff *skb)
{
        int proto = PPP_PROTO(skb);
        struct sk_buff *ns;
        int len;

        /* Until we fix all the decompressor's need to make sure
         * data portion is linear.
         */
        if (!pskb_may_pull(skb, skb->len))
                goto err;

        if (proto == PPP_COMP) {
                ns = dev_alloc_skb(ppp->mru + PPP_HDRLEN);
                if (ns == 0) {
                        printk(KERN_ERR "ppp_decompress_frame: no memory\n");
                        goto err;
                }
                /* the decompressor still expects the A/C bytes in the hdr */
                len = ppp->rcomp->decompress(ppp->rc_state, skb->data - 2,
                                skb->len + 2, ns->data, ppp->mru + PPP_HDRLEN);
                if (len < 0) {
                        /* Pass the compressed frame to pppd as an
                           error indication. */
                        if (len == DECOMP_FATALERROR)
                                ppp->rstate |= SC_DC_FERROR;
                        kfree_skb(ns);
                        goto err;
                }

                kfree_skb(skb);
                skb = ns;
                skb_put(skb, len);
                skb_pull(skb, 2);       /* pull off the A/C bytes */

        } else {
                /* Uncompressed frame - pass to decompressor so it
                   can update its dictionary if necessary. */
                if (ppp->rcomp->incomp)
                        ppp->rcomp->incomp(ppp->rc_state, skb->data - 2,
                                           skb->len + 2);
        }

        return skb;

 err:
        ppp->rstate |= SC_DC_ERROR;
        ppp_receive_error(ppp);
        return skb;
}

#ifdef CONFIG_PPP_MULTILINK
/*
 * Receive a multilink frame.
 * We put it on the reconstruction queue and then pull off
 * as many completed frames as we can.
 */
static void
ppp_receive_mp_frame(struct ppp *ppp, struct sk_buff *skb, struct channel *pch)
{
        u32 mask, seq;
        struct channel *ch;
        int mphdrlen = (ppp->flags & SC_MP_SHORTSEQ)? MPHDRLEN_SSN: MPHDRLEN;

        if (!pskb_may_pull(skb, mphdrlen) || ppp->mrru == 0)
                goto err;               /* no good, throw it away */

        /* Decode sequence number and begin/end bits */
        if (ppp->flags & SC_MP_SHORTSEQ) {
                seq = ((skb->data[2] & 0x0f) << 8) | skb->data[3];
                mask = 0xfff;
        } else {
                seq = (skb->data[3] << 16) | (skb->data[4] << 8)| skb->data[5];
                mask = 0xffffff;
        }
        skb->BEbits = skb->data[2];
        skb_pull(skb, mphdrlen);        /* pull off PPP and MP headers */

        /*
         * Do protocol ID decompression on the first fragment of each packet.
         */
        if ((skb->BEbits & B) && (skb->data[0] & 1))
                *skb_push(skb, 1) = 0;

        /*
         * Expand sequence number to 32 bits, making it as close
         * as possible to ppp->minseq.
         */
        seq |= ppp->minseq & ~mask;
        if ((int)(ppp->minseq - seq) > (int)(mask >> 1))
                seq += mask + 1;
        else if ((int)(seq - ppp->minseq) > (int)(mask >> 1))
                seq -= mask + 1;        /* should never happen */
        skb->sequence = seq;
        pch->lastseq = seq;

        /*
         * If this packet comes before the next one we were expecting,
         * drop it.
         */
        if (seq_before(seq, ppp->nextseq)) {
                kfree_skb(skb);
                ++ppp->stats.rx_dropped;
                ppp_receive_error(ppp);
                return;
        }

        /*
         * Reevaluate minseq, the minimum over all channels of the
         * last sequence number received on each channel.  Because of
         * the increasing sequence number rule, we know that any fragment
         * before `minseq' which hasn't arrived is never going to arrive.
         * The list of channels can't change because we have the receive
         * side of the ppp unit locked.
         */
        list_for_each_entry(ch, &ppp->channels, clist) {
                if (seq_before(ch->lastseq, seq))
                        seq = ch->lastseq;
        }
        if (seq_before(ppp->minseq, seq))
                ppp->minseq = seq;

        /* Put the fragment on the reconstruction queue */
        ppp_mp_insert(ppp, skb);

        /* If the queue is getting long, don't wait any longer for packets
           before the start of the queue. */
        if (skb_queue_len(&ppp->mrq) >= PPP_MP_MAX_QLEN
            && seq_before(ppp->minseq, ppp->mrq.next->sequence))
                ppp->minseq = ppp->mrq.next->sequence;

        /* Pull completed packets off the queue and receive them. */
        while ((skb = ppp_mp_reconstruct(ppp)) != 0)
                ppp_receive_nonmp_frame(ppp, skb);

        return;

 err:
        kfree_skb(skb);
        ppp_receive_error(ppp);
}

/*
 * Insert a fragment on the MP reconstruction queue.
 * The queue is ordered by increasing sequence number.
 */
static void
ppp_mp_insert(struct ppp *ppp, struct sk_buff *skb)
{
        struct sk_buff *p;
        struct sk_buff_head *list = &ppp->mrq;
        u32 seq = skb->sequence;

        /* N.B. we don't need to lock the list lock because we have the
           ppp unit receive-side lock. */
        for (p = list->next; p != (struct sk_buff *)list; p = p->next)
                if (seq_before(seq, p->sequence))
                        break;
        __skb_insert(skb, p->prev, p, list);
}

/*
 * Reconstruct a packet from the MP fragment queue.
 * We go through increasing sequence numbers until we find a
 * complete packet, or we get to the sequence number for a fragment
 * which hasn't arrived but might still do so.
 */
struct sk_buff *
ppp_mp_reconstruct(struct ppp *ppp)
{
        u32 seq = ppp->nextseq;
        u32 minseq = ppp->minseq;
        struct sk_buff_head *list = &ppp->mrq;
        struct sk_buff *p, *next;
        struct sk_buff *head, *tail;
        struct sk_buff *skb = NULL;
        int lost = 0, len = 0;

        if (ppp->mrru == 0)     /* do nothing until mrru is set */
                return NULL;
        head = list->next;
        tail = NULL;
        for (p = head; p != (struct sk_buff *) list; p = next) {
                next = p->next;
                if (seq_before(p->sequence, seq)) {
                        /* this can't happen, anyway ignore the skb */
                        printk(KERN_ERR "ppp_mp_reconstruct bad seq %u < %u\n",
                               p->sequence, seq);
                        head = next;
                        continue;
                }
                if (p->sequence != seq) {
                        /* Fragment `seq' is missing.  If it is after
                           minseq, it might arrive later, so stop here. */
                        if (seq_after(seq, minseq))
                                break;
                        /* Fragment `seq' is lost, keep going. */
                        lost = 1;
                        seq = seq_before(minseq, p->sequence)?
                                minseq + 1: p->sequence;
                        next = p;
                        continue;
                }

                /*
                 * At this point we know that all the fragments from
                 * ppp->nextseq to seq are either present or lost.
                 * Also, there are no complete packets in the queue
                 * that have no missing fragments and end before this
                 * fragment.
                 */

                /* B bit set indicates this fragment starts a packet */
                if (p->BEbits & B) {
                        head = p;
                        lost = 0;
                        len = 0;
                }

                len += p->len;

                /* Got a complete packet yet? */
                if (lost == 0 && (p->BEbits & E) && (head->BEbits & B)) {
                        if (len > ppp->mrru + 2) {
                                ++ppp->stats.rx_length_errors;
                                printk(KERN_DEBUG "PPP: reconstructed packet"
                                       " is too long (%d)\n", len);
                        } else if (p == head) {
                                /* fragment is complete packet - reuse skb */
                                tail = p;
                                skb = skb_get(p);
                                break;
                        } else if ((skb = dev_alloc_skb(len)) == NULL) {
                                ++ppp->stats.rx_missed_errors;
                                printk(KERN_DEBUG "PPP: no memory for "
                                       "reconstructed packet");
                        } else {
                                tail = p;
                                break;
                        }
                        ppp->nextseq = seq + 1;
                }

                /*
                 * If this is the ending fragment of a packet,
                 * and we haven't found a complete valid packet yet,
                 * we can discard up to and including this fragment.
                 */
                if (p->BEbits & E)
                        head = next;

                ++seq;
        }

        /* If we have a complete packet, copy it all into one skb. */
        if (tail != NULL) {
                /* If we have discarded any fragments,
                   signal a receive error. */
                if (head->sequence != ppp->nextseq) {
                        if (ppp->debug & 1)
                                printk(KERN_DEBUG "  missed pkts %u..%u\n",
                                       ppp->nextseq, head->sequence-1);
                        ++ppp->stats.rx_dropped;
                        ppp_receive_error(ppp);
                }

                if (head != tail)
                        /* copy to a single skb */
                        for (p = head; p != tail->next; p = p->next)
                                skb_copy_bits(p, 0, skb_put(skb, p->len), p->len);
                ppp->nextseq = tail->sequence + 1;
                head = tail->next;
        }

        /* Discard all the skbuffs that we have copied the data out of
           or that we can't use. */
        while ((p = list->next) != head) {
                __skb_unlink(p, list);
                kfree_skb(p);
        }

        return skb;
}
#endif /* CONFIG_PPP_MULTILINK */

/*
 * Channel interface.
 */

/*
 * Create a new, unattached ppp channel.
 */
int
ppp_register_channel(struct ppp_channel *chan)
{
        struct channel *pch;

        pch = kmalloc(sizeof(struct channel), GFP_KERNEL);
        if (pch == 0)
                return -ENOMEM;
        memset(pch, 0, sizeof(struct channel));
        pch->ppp = NULL;
        pch->chan = chan;
        chan->ppp = pch;
        init_ppp_file(&pch->file, CHANNEL);
        pch->file.hdrlen = chan->hdrlen;
#ifdef CONFIG_PPP_MULTILINK
        pch->lastseq = -1;
#endif /* CONFIG_PPP_MULTILINK */
        init_rwsem(&pch->chan_sem);
        spin_lock_init(&pch->downl);
        rwlock_init(&pch->upl);
        spin_lock_bh(&all_channels_lock);
        pch->file.index = ++last_channel_index;
        list_add(&pch->list, &new_channels);
        atomic_inc(&channel_count);
        spin_unlock_bh(&all_channels_lock);
        return 0;
}

/*
 * Return the index of a channel.
 */
int ppp_channel_index(struct ppp_channel *chan)
{
        struct channel *pch = chan->ppp;

        if (pch != 0)
                return pch->file.index;
        return -1;
}

/*
 * Return the PPP unit number to which a channel is connected.
 */
int ppp_unit_number(struct ppp_channel *chan)
{
        struct channel *pch = chan->ppp;
        int unit = -1;

        if (pch != 0) {
                read_lock_bh(&pch->upl);
                if (pch->ppp != 0)
                        unit = pch->ppp->file.index;
                read_unlock_bh(&pch->upl);
        }
        return unit;
}

/*
 * Disconnect a channel from the generic layer.
 * This must be called in process context.
 */
void
ppp_unregister_channel(struct ppp_channel *chan)
{
        struct channel *pch = chan->ppp;

        if (pch == 0)
                return;         /* should never happen */
        chan->ppp = NULL;

        /*
         * This ensures that we have returned from any calls into the
         * the channel's start_xmit or ioctl routine before we proceed.
         */
        down_write(&pch->chan_sem);
        spin_lock_bh(&pch->downl);
        pch->chan = NULL;
        spin_unlock_bh(&pch->downl);
        up_write(&pch->chan_sem);
        ppp_disconnect_channel(pch);
        spin_lock_bh(&all_channels_lock);
        list_del(&pch->list);
        spin_unlock_bh(&all_channels_lock);
        pch->file.dead = 1;
        wake_up_interruptible(&pch->file.rwait);
        if (atomic_dec_and_test(&pch->file.refcnt))
                ppp_destroy_channel(pch);
}

/*
 * Callback from a channel when it can accept more to transmit.
 * This should be called at BH/softirq level, not interrupt level.
 */
void
ppp_output_wakeup(struct ppp_channel *chan)
{
        struct channel *pch = chan->ppp;

        if (pch == 0)
                return;
        ppp_channel_push(pch);
}

/*
 * Compression control.
 */

/* Process the PPPIOCSCOMPRESS ioctl. */
static int
ppp_set_compress(struct ppp *ppp, unsigned long arg)
{
        int err;
        struct compressor *cp, *ocomp;
        struct ppp_option_data data;
        void *state, *ostate;
        unsigned char ccp_option[CCP_MAX_OPTION_LENGTH];

        err = -EFAULT;
        if (copy_from_user(&data, (void __user *) arg, sizeof(data))
            || (data.length <= CCP_MAX_OPTION_LENGTH
                && copy_from_user(ccp_option, (void __user *) data.ptr, data.length)))
                goto out;
        err = -EINVAL;
        if (data.length > CCP_MAX_OPTION_LENGTH
            || ccp_option[1] < 2 || ccp_option[1] > data.length)
                goto out;

        cp = find_compressor(ccp_option[0]);
#ifdef CONFIG_KMOD
        if (cp == 0) {
                request_module("ppp-compress-%d", ccp_option[0]);
                cp = find_compressor(ccp_option[0]);
        }
#endif /* CONFIG_KMOD */
        if (cp == 0)
                goto out;

        err = -ENOBUFS;
        if (data.transmit) {
                state = cp->comp_alloc(ccp_option, data.length);
                if (state != 0) {
                        ppp_xmit_lock(ppp);
                        ppp->xstate &= ~SC_COMP_RUN;
                        ocomp = ppp->xcomp;
                        ostate = ppp->xc_state;
                        ppp->xcomp = cp;
                        ppp->xc_state = state;
                        ppp_xmit_unlock(ppp);
                        if (ostate != 0) {
                                ocomp->comp_free(ostate);
                                module_put(ocomp->owner);
                        }
                        err = 0;
                } else
                        module_put(cp->owner);

        } else {
                state = cp->decomp_alloc(ccp_option, data.length);
                if (state != 0) {
                        ppp_recv_lock(ppp);
                        ppp->rstate &= ~SC_DECOMP_RUN;
                        ocomp = ppp->rcomp;
                        ostate = ppp->rc_state;
                        ppp->rcomp = cp;
                        ppp->rc_state = state;
                        ppp_recv_unlock(ppp);
                        if (ostate != 0) {
                                ocomp->decomp_free(ostate);
                                module_put(ocomp->owner);
                        }
                        err = 0;
                } else
                        module_put(cp->owner);
        }

 out:
        return err;
}

/*
 * Look at a CCP packet and update our state accordingly.
 * We assume the caller has the xmit or recv path locked.
 */
static void
ppp_ccp_peek(struct ppp *ppp, struct sk_buff *skb, int inbound)
{
        unsigned char *dp;
        int len;

        if (!pskb_may_pull(skb, CCP_HDRLEN + 2))
                return; /* no header */
        dp = skb->data + 2;

        switch (CCP_CODE(dp)) {
        case CCP_CONFREQ:

                /* A ConfReq starts negotiation of compression 
                 * in one direction of transmission,
                 * and hence brings it down...but which way?
                 *
                 * Remember:
                 * A ConfReq indicates what the sender would like to receive
                 */
                if(inbound)
                        /* He is proposing what I should send */
                        ppp->xstate &= ~SC_COMP_RUN;
                else    
                        /* I am proposing to what he should send */
                        ppp->rstate &= ~SC_DECOMP_RUN;
                
                break;
                
        case CCP_TERMREQ:
        case CCP_TERMACK:
                /*
                 * CCP is going down, both directions of transmission 
                 */
                ppp->rstate &= ~SC_DECOMP_RUN;
                ppp->xstate &= ~SC_COMP_RUN;
                break;

        case CCP_CONFACK:
                if ((ppp->flags & (SC_CCP_OPEN | SC_CCP_UP)) != SC_CCP_OPEN)
                        break;
                len = CCP_LENGTH(dp);
                if (!pskb_may_pull(skb, len + 2))
                        return;         /* too short */
                dp += CCP_HDRLEN;
                len -= CCP_HDRLEN;
                if (len < CCP_OPT_MINLEN || len < CCP_OPT_LENGTH(dp))
                        break;
                if (inbound) {
                        /* we will start receiving compressed packets */
                        if (ppp->rc_state == 0)
                                break;
                        if (ppp->rcomp->decomp_init(ppp->rc_state, dp, len,
                                        ppp->file.index, 0, ppp->mru, ppp->debug)) {
                                ppp->rstate |= SC_DECOMP_RUN;
                                ppp->rstate &= ~(SC_DC_ERROR | SC_DC_FERROR);
                        }
                } else {
                        /* we will soon start sending compressed packets */
                        if (ppp->xc_state == 0)
                                break;
                        if (ppp->xcomp->comp_init(ppp->xc_state, dp, len,
                                        ppp->file.index, 0, ppp->debug))
                                ppp->xstate |= SC_COMP_RUN;
                }
                break;

        case CCP_RESETACK:
                /* reset the [de]compressor */
                if ((ppp->flags & SC_CCP_UP) == 0)
                        break;
                if (inbound) {
                        if (ppp->rc_state && (ppp->rstate & SC_DECOMP_RUN)) {
                                ppp->rcomp->decomp_reset(ppp->rc_state);
                                ppp->rstate &= ~SC_DC_ERROR;
                        }
                } else {
                        if (ppp->xc_state && (ppp->xstate & SC_COMP_RUN))
                                ppp->xcomp->comp_reset(ppp->xc_state);
                }
                break;
        }
}

/* Free up compression resources. */
static void
ppp_ccp_closed(struct ppp *ppp)
{
        void *xstate, *rstate;
        struct compressor *xcomp, *rcomp;

        ppp_lock(ppp);
        ppp->flags &= ~(SC_CCP_OPEN | SC_CCP_UP);
        ppp->xstate = 0;
        xcomp = ppp->xcomp;
        xstate = ppp->xc_state;
        ppp->xc_state = NULL;
        ppp->rstate = 0;
        rcomp = ppp->rcomp;
        rstate = ppp->rc_state;
        ppp->rc_state = NULL;
        ppp_unlock(ppp);

        if (xstate) {
                xcomp->comp_free(xstate);
                module_put(xcomp->owner);
        }
        if (rstate) {
                rcomp->decomp_free(rstate);
                module_put(rcomp->owner);
        }
}

/* List of compressors. */
static LIST_HEAD(compressor_list);
static DEFINE_SPINLOCK(compressor_list_lock);

struct compressor_entry {
        struct list_head list;
        struct compressor *comp;
};

static struct compressor_entry *
find_comp_entry(int proto)
{
        struct compressor_entry *ce;

        list_for_each_entry(ce, &compressor_list, list) {
                if (ce->comp->compress_proto == proto)
                        return ce;
        }
        return NULL;
}

/* Register a compressor */
int
ppp_register_compressor(struct compressor *cp)
{
        struct compressor_entry *ce;
        int ret;
        spin_lock(&compressor_list_lock);
        ret = -EEXIST;
        if (find_comp_entry(cp->compress_proto) != 0)
                goto out;
        ret = -ENOMEM;
        ce = kmalloc(sizeof(struct compressor_entry), GFP_ATOMIC);
        if (ce == 0)
                goto out;
        ret = 0;
        ce->comp = cp;
        list_add(&ce->list, &compressor_list);
 out:
        spin_unlock(&compressor_list_lock);
        return ret;
}

/* Unregister a compressor */
void
ppp_unregister_compressor(struct compressor *cp)
{
        struct compressor_entry *ce;

        spin_lock(&compressor_list_lock);
        ce = find_comp_entry(cp->compress_proto);
        if (ce != 0 && ce->comp == cp) {
                list_del(&ce->list);
                kfree(ce);
        }
        spin_unlock(&compressor_list_lock);
}

/* Find a compressor. */
static struct compressor *
find_compressor(int type)
{
        struct compressor_entry *ce;
        struct compressor *cp = NULL;

        spin_lock(&compressor_list_lock);
        ce = find_comp_entry(type);
        if (ce != 0) {
                cp = ce->comp;
                if (!try_module_get(cp->owner))
                        cp = NULL;
        }
        spin_unlock(&compressor_list_lock);
        return cp;
}

/*
 * Miscelleneous stuff.
 */

static void
ppp_get_stats(struct ppp *ppp, struct ppp_stats *st)
{
        struct slcompress *vj = ppp->vj;

        memset(st, 0, sizeof(*st));
        st->p.ppp_ipackets = ppp->stats.rx_packets;
        st->p.ppp_ierrors = ppp->stats.rx_errors;
        st->p.ppp_ibytes = ppp->stats.rx_bytes;
        st->p.ppp_opackets = ppp->stats.tx_packets;
        st->p.ppp_oerrors = ppp->stats.tx_errors;
        st->p.ppp_obytes = ppp->stats.tx_bytes;
        if (vj == 0)
                return;
        st->vj.vjs_packets = vj->sls_o_compressed + vj->sls_o_uncompressed;
        st->vj.vjs_compressed = vj->sls_o_compressed;
        st->vj.vjs_searches = vj->sls_o_searches;
        st->vj.vjs_misses = vj->sls_o_misses;
        st->vj.vjs_errorin = vj->sls_i_error;
        st->vj.vjs_tossed = vj->sls_i_tossed;
        st->vj.vjs_uncompressedin = vj->sls_i_uncompressed;
        st->vj.vjs_compressedin = vj->sls_i_compressed;
}

/*
 * Stuff for handling the lists of ppp units and channels
 * and for initialization.
 */

/*
 * Create a new ppp interface unit.  Fails if it can't allocate memory
 * or if there is already a unit with the requested number.
 * unit == -1 means allocate a new number.
 */
static struct ppp *
ppp_create_interface(int unit, int *retp)
{
        struct ppp *ppp;
        struct net_device *dev = NULL;
        int ret = -ENOMEM;
        int i;

        ppp = kmalloc(sizeof(struct ppp), GFP_KERNEL);
        if (!ppp)
                goto out;
        dev = alloc_netdev(0, "", ppp_setup);
        if (!dev)
                goto out1;
        memset(ppp, 0, sizeof(struct ppp));

        ppp->mru = PPP_MRU;
        init_ppp_file(&ppp->file, INTERFACE);
        ppp->file.hdrlen = PPP_HDRLEN - 2;      /* don't count proto bytes */
        for (i = 0; i < NUM_NP; ++i)
                ppp->npmode[i] = NPMODE_PASS;
        INIT_LIST_HEAD(&ppp->channels);
        spin_lock_init(&ppp->rlock);
        spin_lock_init(&ppp->wlock);
#ifdef CONFIG_PPP_MULTILINK
        ppp->minseq = -1;
        skb_queue_head_init(&ppp->mrq);
#endif /* CONFIG_PPP_MULTILINK */
        ppp->dev = dev;
        dev->priv = ppp;

        dev->hard_start_xmit = ppp_start_xmit;
        dev->get_stats = ppp_net_stats;
        dev->do_ioctl = ppp_net_ioctl;

        ret = -EEXIST;
        mutex_lock(&all_ppp_mutex);
        if (unit < 0)
                unit = cardmap_find_first_free(all_ppp_units);
        else if (cardmap_get(all_ppp_units, unit) != NULL)
                goto out2;      /* unit already exists */

        /* Initialize the new ppp unit */
        ppp->file.index = unit;
        sprintf(dev->name, "ppp%d", unit);

        ret = register_netdev(dev);
        if (ret != 0) {
                printk(KERN_ERR "PPP: couldn't register device %s (%d)\n",
                       dev->name, ret);
                goto out2;
        }

        atomic_inc(&ppp_unit_count);
        cardmap_set(&all_ppp_units, unit, ppp);
        mutex_unlock(&all_ppp_mutex);
        *retp = 0;
        return ppp;

out2:
        mutex_unlock(&all_ppp_mutex);
        free_netdev(dev);
out1:
        kfree(ppp);
out:
        *retp = ret;
        return NULL;
}

/*
 * Initialize a ppp_file structure.
 */
static void
init_ppp_file(struct ppp_file *pf, int kind)
{
        pf->kind = kind;
        skb_queue_head_init(&pf->xq);
        skb_queue_head_init(&pf->rq);
        atomic_set(&pf->refcnt, 1);
        init_waitqueue_head(&pf->rwait);
}

/*
 * Take down a ppp interface unit - called when the owning file
 * (the one that created the unit) is closed or detached.
 */
static void ppp_shutdown_interface(struct ppp *ppp)
{
        struct net_device *dev;

        mutex_lock(&all_ppp_mutex);
        ppp_lock(ppp);
        dev = ppp->dev;
        ppp->dev = NULL;
        ppp_unlock(ppp);
        /* This will call dev_close() for us. */
        if (dev) {
                unregister_netdev(dev);
                free_netdev(dev);
        }
        cardmap_set(&all_ppp_units, ppp->file.index, NULL);
        ppp->file.dead = 1;
        ppp->owner = NULL;
        wake_up_interruptible(&ppp->file.rwait);
        mutex_unlock(&all_ppp_mutex);
}

/*
 * Free the memory used by a ppp unit.  This is only called once
 * there are no channels connected to the unit and no file structs
 * that reference the unit.
 */
static void ppp_destroy_interface(struct ppp *ppp)
{
        atomic_dec(&ppp_unit_count);

        if (!ppp->file.dead || ppp->n_channels) {
                /* "can't happen" */
                printk(KERN_ERR "ppp: destroying ppp struct %p but dead=%d "
                       "n_channels=%d !\n", ppp, ppp->file.dead,
                       ppp->n_channels);
                return;
        }

        ppp_ccp_closed(ppp);
        if (ppp->vj) {
                slhc_free(ppp->vj);
                ppp->vj = NULL;
        }
        skb_queue_purge(&ppp->file.xq);
        skb_queue_purge(&ppp->file.rq);
#ifdef CONFIG_PPP_MULTILINK
        skb_queue_purge(&ppp->mrq);
#endif /* CONFIG_PPP_MULTILINK */
#ifdef CONFIG_PPP_FILTER
        kfree(ppp->pass_filter);
        ppp->pass_filter = NULL;
        kfree(ppp->active_filter);
        ppp->active_filter = NULL;
#endif /* CONFIG_PPP_FILTER */

        kfree(ppp);
}

/*
 * Locate an existing ppp unit.
 * The caller should have locked the all_ppp_mutex.
 */
static struct ppp *
ppp_find_unit(int unit)
{
        return cardmap_get(all_ppp_units, unit);
}

/*
 * Locate an existing ppp channel.
 * The caller should have locked the all_channels_lock.
 * First we look in the new_channels list, then in the
 * all_channels list.  If found in the new_channels list,
 * we move it to the all_channels list.  This is for speed
 * when we have a lot of channels in use.
 */
static struct channel *
ppp_find_channel(int unit)
{
        struct channel *pch;

        list_for_each_entry(pch, &new_channels, list) {
                if (pch->file.index == unit) {
                        list_move(&pch->list, &all_channels);
                        return pch;
                }
        }
        list_for_each_entry(pch, &all_channels, list) {
                if (pch->file.index == unit)
                        return pch;
        }
        return NULL;
}

/*
 * Connect a PPP channel to a PPP interface unit.
 */
static int
ppp_connect_channel(struct channel *pch, int unit)
{
        struct ppp *ppp;
        int ret = -ENXIO;
        int hdrlen;

        mutex_lock(&all_ppp_mutex);
        ppp = ppp_find_unit(unit);
        if (ppp == 0)
                goto out;
        write_lock_bh(&pch->upl);
        ret = -EINVAL;
        if (pch->ppp != 0)
                goto outl;

        ppp_lock(ppp);
        if (pch->file.hdrlen > ppp->file.hdrlen)
                ppp->file.hdrlen = pch->file.hdrlen;
        hdrlen = pch->file.hdrlen + 2;  /* for protocol bytes */
        if (ppp->dev && hdrlen > ppp->dev->hard_header_len)
                ppp->dev->hard_header_len = hdrlen;
        list_add_tail(&pch->clist, &ppp->channels);
        ++ppp->n_channels;
        pch->ppp = ppp;
        atomic_inc(&ppp->file.refcnt);
        ppp_unlock(ppp);
        ret = 0;

 outl:
        write_unlock_bh(&pch->upl);
 out:
        mutex_unlock(&all_ppp_mutex);
        return ret;
}

/*
 * Disconnect a channel from its ppp unit.
 */
static int
ppp_disconnect_channel(struct channel *pch)
{
        struct ppp *ppp;
        int err = -EINVAL;

        write_lock_bh(&pch->upl);
        ppp = pch->ppp;
        pch->ppp = NULL;
        write_unlock_bh(&pch->upl);
        if (ppp != 0) {
                /* remove it from the ppp unit's list */
                ppp_lock(ppp);
                list_del(&pch->clist);
                if (--ppp->n_channels == 0)
                        wake_up_interruptible(&ppp->file.rwait);
                ppp_unlock(ppp);
                if (atomic_dec_and_test(&ppp->file.refcnt))
                        ppp_destroy_interface(ppp);
                err = 0;
        }
        return err;
}

/*
 * Free up the resources used by a ppp channel.
 */
static void ppp_destroy_channel(struct channel *pch)
{
        atomic_dec(&channel_count);

        if (!pch->file.dead) {
                /* "can't happen" */
                printk(KERN_ERR "ppp: destroying undead channel %p !\n",
                       pch);
                return;
        }
        skb_queue_purge(&pch->file.xq);
        skb_queue_purge(&pch->file.rq);
        kfree(pch);
}

static void __exit ppp_cleanup(void)
{
        /* should never happen */
        if (atomic_read(&ppp_unit_count) || atomic_read(&channel_count))
                printk(KERN_ERR "PPP: removing module but units remain!\n");
        cardmap_destroy(&all_ppp_units);
        if (unregister_chrdev(PPP_MAJOR, "ppp") != 0)
                printk(KERN_ERR "PPP: failed to unregister PPP device\n");
        class_device_destroy(ppp_class, MKDEV(PPP_MAJOR, 0));
        class_destroy(ppp_class);
}

/*
 * Cardmap implementation.
 */
static void *cardmap_get(struct cardmap *map, unsigned int nr)
{
        struct cardmap *p;
        int i;

        for (p = map; p != NULL; ) {
                if ((i = nr >> p->shift) >= CARDMAP_WIDTH)
                        return NULL;
                if (p->shift == 0)
                        return p->ptr[i];
                nr &= ~(CARDMAP_MASK << p->shift);
                p = p->ptr[i];
        }
        return NULL;
}

static void cardmap_set(struct cardmap **pmap, unsigned int nr, void *ptr)
{
        struct cardmap *p;
        int i;

        p = *pmap;
        if (p == NULL || (nr >> p->shift) >= CARDMAP_WIDTH) {
                do {
                        /* need a new top level */
                        struct cardmap *np = kmalloc(sizeof(*np), GFP_KERNEL);
                        memset(np, 0, sizeof(*np));
                        np->ptr[0] = p;
                        if (p != NULL) {
                                np->shift = p->shift + CARDMAP_ORDER;
                                p->parent = np;
                        } else
                                np->shift = 0;
                        p = np;
                } while ((nr >> p->shift) >= CARDMAP_WIDTH);
                *pmap = p;
        }
        while (p->shift > 0) {
                i = (nr >> p->shift) & CARDMAP_MASK;
                if (p->ptr[i] == NULL) {
                        struct cardmap *np = kmalloc(sizeof(*np), GFP_KERNEL);
                        memset(np, 0, sizeof(*np));
                        np->shift = p->shift - CARDMAP_ORDER;
                        np->parent = p;
                        p->ptr[i] = np;
                }
                if (ptr == NULL)
                        clear_bit(i, &p->inuse);
                p = p->ptr[i];
        }
        i = nr & CARDMAP_MASK;
        p->ptr[i] = ptr;
        if (ptr != NULL)
                set_bit(i, &p->inuse);
        else
                clear_bit(i, &p->inuse);
}

static unsigned int cardmap_find_first_free(struct cardmap *map)
{
        struct cardmap *p;
        unsigned int nr = 0;
        int i;

        if ((p = map) == NULL)
                return 0;
        for (;;) {
                i = find_first_zero_bit(&p->inuse, CARDMAP_WIDTH);
                if (i >= CARDMAP_WIDTH) {
                        if (p->parent == NULL)
                                return CARDMAP_WIDTH << p->shift;
                        p = p->parent;
                        i = (nr >> p->shift) & CARDMAP_MASK;
                        set_bit(i, &p->inuse);
                        continue;
                }
                nr = (nr & (~CARDMAP_MASK << p->shift)) | (i << p->shift);
                if (p->shift == 0 || p->ptr[i] == NULL)
                        return nr;
                p = p->ptr[i];
        }
}

static void cardmap_destroy(struct cardmap **pmap)
{
        struct cardmap *p, *np;
        int i;

        for (p = *pmap; p != NULL; p = np) {
                if (p->shift != 0) {
                        for (i = 0; i < CARDMAP_WIDTH; ++i)
                                if (p->ptr[i] != NULL)
                                        break;
                        if (i < CARDMAP_WIDTH) {
                                np = p->ptr[i];
                                p->ptr[i] = NULL;
                                continue;
                        }
                }
                np = p->parent;
                kfree(p);
        }
        *pmap = NULL;
}

/* Module/initialization stuff */

module_init(ppp_init);
module_exit(ppp_cleanup);

EXPORT_SYMBOL(ppp_register_channel);
EXPORT_SYMBOL(ppp_unregister_channel);
EXPORT_SYMBOL(ppp_channel_index);
EXPORT_SYMBOL(ppp_unit_number);
EXPORT_SYMBOL(ppp_input);
EXPORT_SYMBOL(ppp_input_error);
EXPORT_SYMBOL(ppp_output_wakeup);
EXPORT_SYMBOL(ppp_register_compressor);
EXPORT_SYMBOL(ppp_unregister_compressor);
MODULE_LICENSE("GPL");
MODULE_ALIAS_CHARDEV_MAJOR(PPP_MAJOR);
MODULE_ALIAS("/dev/ppp");