ppp_generic.c

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/*
 * 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/module.h>
#include <linux/kernel.h>
#include <linux/kmod.h>
#include <linux/init.h>
#include <linux/list.h>
#include <linux/idr.h>
#include <linux/netdevice.h>
#include <linux/poll.h>
#include <linux/ppp_defs.h>
#include <linux/filter.h>
#include <linux/ppp-ioctl.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/rwsem.h>
#include <linux/stddef.h>
#include <linux/device.h>
#include <linux/mutex.h>
#include <linux/slab.h>
#include <asm/unaligned.h>
#include <net/slhc_vj.h>
#include <linux/atomic.h>

#include <linux/nsproxy.h>
#include <net/net_namespace.h>
#include <net/netns/generic.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 */

/*
 * 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)      container_of(pf, X, file)

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

/*
 * Data structure to hold primary network stats for which
 * we want to use 64 bit storage.  Other network stats
 * are stored in dev->stats of the ppp strucute.
 */
struct ppp_link_stats {
    u64 rx_packets;
    u64 tx_packets;
    u64 rx_bytes;
    u64 tx_bytes;
};

/*
 * 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 */
    int     closing;    /* is device closing down? a8 */
#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 */
#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 */
    struct net  *ppp_net;   /* the net we belong to */
    struct ppp_link_stats stats64;  /* 64 bit network stats */
};

/*
 * 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 net  *chan_net;  /* the net channel belongs 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 */
    int     speed;      /* speed of the corresponding ppp channel*/
#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.
 */

static DEFINE_MUTEX(ppp_mutex);
static atomic_t ppp_unit_count = ATOMIC_INIT(0);
static atomic_t channel_count = ATOMIC_INIT(0);

/* per-net private data for this module */
static int ppp_net_id __read_mostly;
struct ppp_net {
    /* units to ppp mapping */
    struct idr units_idr;

    /*
     * all_ppp_mutex protects the units_idr mapping.
     * It also ensures that finding a ppp unit in the units_idr
     * map and updating its file.refcnt field is atomic.
     */
    struct mutex all_ppp_mutex;

    /* channels */
    struct list_head all_channels;
    struct list_head new_channels;
    int last_channel_index;

    /*
     * all_channels_lock protects all_channels and
     * last_channel_index, and the atomicity of find
     * a channel and updating its file.refcnt field.
     */
    spinlock_t all_channels_lock;
};

/* Get the PPP protocol number from a skb */
#define PPP_PROTO(skb)  get_unaligned_be16((skb)->data)

/* 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 net *net, 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(struct net *net, 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(struct ppp_net *pn, int unit);
static struct channel *ppp_find_channel(struct ppp_net *pn, 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 int unit_get(struct idr *p, void *ptr);
static int unit_set(struct idr *p, void *ptr, int n);
static void unit_put(struct idr *p, int n);
static void *unit_find(struct idr *p, int n);

static struct class *ppp_class;

/* per net-namespace data */
static inline struct ppp_net *ppp_pernet(struct net *net)
{
    BUG_ON(!net);

    return net_generic(net, ppp_net_id);
}

/* 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 *unused, struct file *file)
{
    struct ppp_file *pf = file->private_data;
    struct ppp *ppp;

    if (pf) {
        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;
    struct iovec iov;

    ret = count;

    if (!pf)
        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)
        goto out;

    ret = -EOVERFLOW;
    if (skb->len > count)
        goto outf;
    ret = -EFAULT;
    iov.iov_base = buf;
    iov.iov_len = count;
    if (skb_copy_datagram_iovec(skb, 0, &iov, 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)
        return -ENXIO;
    ret = -ENOMEM;
    skb = alloc_skb(count + pf->hdrlen, GFP_KERNEL);
    if (!skb)
        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)
        return 0;
    poll_wait(file, &pf->rwait, wait);
    mask = POLLOUT | POLLWRNORM;
    if (skb_peek(&pf->rq))
        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 = memdup_user(uprog.filter, len);
    if (IS_ERR(code))
        return PTR_ERR(code);

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

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

static long ppp_ioctl(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)
        return ppp_unattached_ioctl(current->nsproxy->net_ns,
                    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;
        mutex_lock(&ppp_mutex);
        if (pf->kind == INTERFACE) {
            ppp = PF_TO_PPP(pf);
            if (file == ppp->owner)
                ppp_shutdown_interface(ppp);
        }
        if (atomic_long_read(&file->f_count) <= 2) {
            ppp_release(NULL, file);
            err = 0;
        } else
            pr_warn("PPPIOCDETACH file->f_count=%ld\n",
                atomic_long_read(&file->f_count));
        mutex_unlock(&ppp_mutex);
        return err;
    }

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

        mutex_lock(&ppp_mutex);
        pch = PF_TO_CHANNEL(pf);

        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);
        }
        mutex_unlock(&ppp_mutex);
        return err;
    }

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

    mutex_lock(&ppp_mutex);
    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) {
            netdev_err(ppp->dev,
                   "PPP: no memory (VJ compressor)\n");
            err = -ENOMEM;
            break;
        }
        ppp_lock(ppp);
        if (ppp->vj)
            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;
    }
    mutex_unlock(&ppp_mutex);
    return err;
}

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

    mutex_lock(&ppp_mutex);
    switch (cmd) {
    case PPPIOCNEWUNIT:
        /* Create a new ppp unit */
        if (get_user(unit, p))
            break;
        ppp = ppp_create_interface(net, unit, &err);
        if (!ppp)
            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;
        err = -ENXIO;
        pn = ppp_pernet(net);
        mutex_lock(&pn->all_ppp_mutex);
        ppp = ppp_find_unit(pn, unit);
        if (ppp) {
            atomic_inc(&ppp->file.refcnt);
            file->private_data = &ppp->file;
            err = 0;
        }
        mutex_unlock(&pn->all_ppp_mutex);
        break;

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

    default:
        err = -ENOTTY;
    }
    mutex_unlock(&ppp_mutex);
    return err;
}

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

static __net_init int ppp_init_net(struct net *net)
{
    struct ppp_net *pn = net_generic(net, ppp_net_id);

    idr_init(&pn->units_idr);
    mutex_init(&pn->all_ppp_mutex);

    INIT_LIST_HEAD(&pn->all_channels);
    INIT_LIST_HEAD(&pn->new_channels);

    spin_lock_init(&pn->all_channels_lock);

    return 0;
}

static __net_exit void ppp_exit_net(struct net *net)
{
    struct ppp_net *pn = net_generic(net, ppp_net_id);

    idr_destroy(&pn->units_idr);
}

static struct pernet_operations ppp_net_ops = {
    .init = ppp_init_net,
    .exit = ppp_exit_net,
    .id   = &ppp_net_id,
    .size = sizeof(struct ppp_net),
};

#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;

    pr_info("PPP generic driver version " PPP_VERSION "\n");

    err = register_pernet_device(&ppp_net_ops);
    if (err) {
        pr_err("failed to register PPP pernet device (%d)\n", err);
        goto out;
    }

    err = register_chrdev(PPP_MAJOR, "ppp", &ppp_device_fops);
    if (err) {
        pr_err("failed to register PPP device (%d)\n", err);
        goto out_net;
    }

    ppp_class = class_create(THIS_MODULE, "ppp");
    if (IS_ERR(ppp_class)) {
        err = PTR_ERR(ppp_class);
        goto out_chrdev;
    }

    /* not a big deal if we fail here :-) */
    device_create(ppp_class, NULL, MKDEV(PPP_MAJOR, 0), NULL, "ppp");

    return 0;

out_chrdev:
    unregister_chrdev(PPP_MAJOR, "ppp");
out_net:
    unregister_pernet_device(&ppp_net_ops);
out:
    return err;
}

/*
 * Network interface unit routines.
 */
static netdev_tx_t
ppp_start_xmit(struct sk_buff *skb, struct net_device *dev)
{
    struct ppp *ppp = netdev_priv(dev);
    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_cow_head(skb, PPP_HDRLEN))
        goto outf;

    pp = skb_push(skb, 2);
    proto = npindex_to_proto[npi];
    put_unaligned_be16(proto, pp);

    skb_queue_tail(&ppp->file.xq, skb);
    ppp_xmit_process(ppp);
    return NETDEV_TX_OK;

 outf:
    kfree_skb(skb);
    ++dev->stats.tx_dropped;
    return NETDEV_TX_OK;
}

static int
ppp_net_ioctl(struct net_device *dev, struct ifreq *ifr, int cmd)
{
    struct ppp *ppp = netdev_priv(dev);
    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)
            ppp->xcomp->comp_stat(ppp->xc_state, &cstats.c);
        if (ppp->rc_state)
            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;
}

struct rtnl_link_stats64*
ppp_get_stats64(struct net_device *dev, struct rtnl_link_stats64 *stats64)
{
    struct ppp *ppp = netdev_priv(dev);

    ppp_recv_lock(ppp);
    stats64->rx_packets = ppp->stats64.rx_packets;
    stats64->rx_bytes   = ppp->stats64.rx_bytes;
    ppp_recv_unlock(ppp);

    ppp_xmit_lock(ppp);
    stats64->tx_packets = ppp->stats64.tx_packets;
    stats64->tx_bytes   = ppp->stats64.tx_bytes;
    ppp_xmit_unlock(ppp);

    stats64->rx_errors        = dev->stats.rx_errors;
    stats64->tx_errors        = dev->stats.tx_errors;
    stats64->rx_dropped       = dev->stats.rx_dropped;
    stats64->tx_dropped       = dev->stats.tx_dropped;
    stats64->rx_length_errors = dev->stats.rx_length_errors;

    return stats64;
}

static const struct net_device_ops ppp_netdev_ops = {
    .ndo_start_xmit  = ppp_start_xmit,
    .ndo_do_ioctl    = ppp_net_ioctl,
    .ndo_get_stats64 = ppp_get_stats64,
};

static void ppp_setup(struct net_device *dev)
{
    dev->netdev_ops = &ppp_netdev_ops;
    dev->hard_header_len = PPP_HDRLEN;
    dev->mtu = PPP_MRU;
    dev->addr_len = 0;
    dev->tx_queue_len = 3;
    dev->type = ARPHRD_PPP;
    dev->flags = IFF_POINTOPOINT | IFF_NOARP | IFF_MULTICAST;
    dev->features |= NETIF_F_NETNS_LOCAL;
    dev->priv_flags &= ~IFF_XMIT_DST_RELEASE;
}

/*
 * 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->closing) {
        ppp_push(ppp);
        while (!ppp->xmit_pending &&
               (skb = skb_dequeue(&ppp->file.xq)))
            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 && !skb_peek(&ppp->file.xq))
            netif_wake_queue(ppp->dev);
        else
            netif_stop_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())
            netdev_err(ppp->dev, "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)) {
        consume_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 */
        consume_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())
            netdev_err(ppp->dev, "ppp: compressor dropped pkt\n");
        kfree_skb(skb);
        consume_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) == 0) {
            if (ppp->debug & 1)
                netdev_printk(KERN_DEBUG, ppp->dev,
                          "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) == 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->stats64.tx_packets;
    ppp->stats64.tx_bytes += skb->len - 2;

    switch (proto) {
    case PPP_IP:
        if (!ppp->vj || (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) {
            netdev_err(ppp->dev, "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 */
            consume_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];
            }
            consume_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 &&
        proto != PPP_LCP && proto != PPP_CCP) {
        if (!(ppp->flags & SC_CCP_UP) && (ppp->flags & SC_MUST_COMP)) {
            if (net_ratelimit())
                netdev_err(ppp->dev,
                       "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:
    kfree_skb(skb);
    ++ppp->dev->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)
        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
static bool mp_protocol_compress __read_mostly = true;
module_param(mp_protocol_compress, bool, S_IRUGO | S_IWUSR);
MODULE_PARM_DESC(mp_protocol_compress,
         "compress protocol id in multilink fragments");

/*
 * 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, totlen;
    int i, bits, hdrlen, mtu;
    int flen;
    int navail, nfree, nzero;
    int nbigger;
    int totspeed;
    int totfree;
    unsigned char *p, *q;
    struct list_head *list;
    struct channel *pch;
    struct sk_buff *frag;
    struct ppp_channel *chan;

    totspeed = 0; /*total bitrate of the bundle*/
    nfree = 0; /* # channels which have no packet already queued */
    navail = 0; /* total # of usable channels (not deregistered) */
    nzero = 0; /* number of channels with zero speed associated*/
    totfree = 0; /*total # of channels available and
                  *having no queued packets before
                  *starting the fragmentation*/

    hdrlen = (ppp->flags & SC_MP_XSHORTSEQ)? MPHDRLEN_SSN: MPHDRLEN;
    i = 0;
    list_for_each_entry(pch, &ppp->channels, clist) {
        if (pch->chan) {
            pch->avail = 1;
            navail++;
            pch->speed = pch->chan->speed;
        } else {
            pch->avail = 0;
        }
        if (pch->avail) {
            if (skb_queue_empty(&pch->file.xq) ||
                !pch->had_frag) {
                    if (pch->speed == 0)
                        nzero++;
                    else
                        totspeed += pch->speed;

                    pch->avail = 2;
                    ++nfree;
                    ++totfree;
                }
            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 */
    p = skb->data;
    len = skb->len;
    if (*p == 0 && mp_protocol_compress) {
        ++p;
        --len;
    }

    totlen = len;
    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 (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 {
            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 */
            if (pch->speed == 0)
                nzero--;
            else
                totspeed -= pch->speed;

            spin_unlock_bh(&pch->downl);
            pch->avail = 0;
            totlen = len;
            totfree--;
            nfree--;
            if (--navail == 0)
                break;
            continue;
        }

        /*
        *if the channel speed is not set divide
        *the packet evenly among the free channels;
        *otherwise divide it according to the speed
        *of the channel we are going to transmit on
        */
        flen = len;
        if (nfree > 0) {
            if (pch->speed == 0) {
                flen = len/nfree;
                if (nbigger > 0) {
                    flen++;
                    nbigger--;
                }
            } else {
                flen = (((totfree - nzero)*(totlen + hdrlen*totfree)) /
                    ((totspeed*totfree)/pch->speed)) - hdrlen;
                if (nbigger > 0) {
                    flen += ((totfree - nzero)*pch->speed)/totspeed;
                    nbigger -= ((totfree - nzero)*pch->speed)/
                            totspeed;
                }
            }
            nfree--;
        }

        /*
         *check if we are on the last channel or
         *we exceded the length of the data to
         *fragment
         */
        if ((nfree <= 0) || (flen > len))
            flen = len;
        /*
         *it is not worth to tx on slow channels:
         *in that case from the resulting flen according to the
         *above formula will be equal or less than zero.
         *Skip the channel in this case
         */
        if (flen <= 0) {
            pch->avail = 2;
            spin_unlock_bh(&pch->downl);
            continue;
        }

        /*
         * hdrlen includes the 2-byte PPP protocol field, but the
         * MTU counts only the payload excluding the protocol field.
         * (RFC1661 Section 2)
         */
        mtu = pch->chan->mtu - (hdrlen - 2);
        if (mtu < 4)
            mtu = 4;
        if (flen > mtu)
            flen = mtu;
        if (flen == len)
            bits |= E;
        frag = alloc_skb(flen + hdrlen + (flen == 0), GFP_ATOMIC);
        if (!frag)
            goto noskb;
        q = skb_put(frag, flen + hdrlen);

        /* make the MP header */
        put_unaligned_be16(PPP_MP, q);
        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;
        }

        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);
    }
    ppp->nxchan = i;

    return 1;

 noskb:
    spin_unlock_bh(&pch->downl);
    if (ppp->debug & 1)
        netdev_err(ppp->dev, "PPP: no memory (fragment)\n");
    ++ppp->dev->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) {
        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)
            ppp_xmit_process(ppp);
        read_unlock_bh(&pch->upl);
    }
}

/*
 * Receive-side routines.
 */

struct ppp_mp_skb_parm {
    u32     sequence;
    u8      BEbits;
};
#define PPP_MP_CB(skb)  ((struct ppp_mp_skb_parm *)((skb)->cb))

static inline void
ppp_do_recv(struct ppp *ppp, struct sk_buff *skb, struct channel *pch)
{
    ppp_recv_lock(ppp);
    if (!ppp->closing)
        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) {
        kfree_skb(skb);
        return;
    }

    read_lock_bh(&pch->upl);
    if (!pskb_may_pull(skb, 2)) {
        kfree_skb(skb);
        if (pch->ppp) {
            ++pch->ppp->dev->stats.rx_length_errors;
            ppp_receive_error(pch->ppp);
        }
        goto done;
    }

    proto = PPP_PROTO(skb);
    if (!pch->ppp || 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)))
            kfree_skb(skb);
        wake_up_interruptible(&pch->file.rwait);
    } else {
        ppp_do_recv(pch->ppp, skb, pch);
    }

done:
    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)
        return;

    read_lock_bh(&pch->upl);
    if (pch->ppp) {
        skb = alloc_skb(0, GFP_ATOMIC);
        if (skb) {
            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)
{
    /* note: a 0-length skb is used as an error indication */
    if (skb->len > 0) {
#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);
    } else {
        kfree_skb(skb);
        ppp_receive_error(ppp);
    }
}

static void
ppp_receive_error(struct ppp *ppp)
{
    ++ppp->dev->stats.rx_errors;
    if (ppp->vj)
        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 && (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 || (ppp->flags & SC_REJ_COMP_TCP))
            goto err;

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

        len = slhc_uncompress(ppp->vj, skb->data + 2, skb->len - 2);
        if (len <= 0) {
            netdev_printk(KERN_DEBUG, ppp->dev,
                      "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 || (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) {
            netdev_err(ppp->dev, "PPP: VJ uncompressed error\n");
            goto err;
        }
        proto = PPP_IP;
        break;

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

    ++ppp->stats64.rx_packets;
    ppp->stats64.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)))
            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 */
        if (ppp->pass_filter || ppp->active_filter) {
            if (skb_cloned(skb) &&
                pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
                goto err;

            *skb_push(skb, 2) = 0;
            if (ppp->pass_filter &&
                sk_run_filter(skb, ppp->pass_filter) == 0) {
                if (ppp->debug & 1)
                    netdev_printk(KERN_DEBUG, ppp->dev,
                              "PPP: inbound frame "
                              "not passed\n");
                kfree_skb(skb);
                return;
            }
            if (!(ppp->active_filter &&
                  sk_run_filter(skb, ppp->active_filter) == 0))
                ppp->last_recv = jiffies;
            __skb_pull(skb, 2);
        } else
#endif /* CONFIG_PPP_FILTER */
            ppp->last_recv = jiffies;

        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_reset_mac_header(skb);
            netif_rx(skb);
        }
    }
    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) {
        int obuff_size;

        switch(ppp->rcomp->compress_proto) {
        case CI_MPPE:
            obuff_size = ppp->mru + PPP_HDRLEN + 1;
            break;
        default:
            obuff_size = ppp->mru + PPP_HDRLEN;
            break;
        }

        ns = dev_alloc_skb(obuff_size);
        if (!ns) {
            netdev_err(ppp->dev, "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, obuff_size);
        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;
        }

        consume_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 + 1) || 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;
    }
    PPP_MP_CB(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 ((PPP_MP_CB(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 */
    PPP_MP_CB(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->dev->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) {
        struct sk_buff *mskb = skb_peek(&ppp->mrq);
        if (seq_before(ppp->minseq, PPP_MP_CB(mskb)->sequence))
            ppp->minseq = PPP_MP_CB(mskb)->sequence;
    }

    /* Pull completed packets off the queue and receive them. */
    while ((skb = ppp_mp_reconstruct(ppp))) {
        if (pskb_may_pull(skb, 2))
            ppp_receive_nonmp_frame(ppp, skb);
        else {
            ++ppp->dev->stats.rx_length_errors;
            kfree_skb(skb);
            ppp_receive_error(ppp);
        }
    }

    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 = PPP_MP_CB(skb)->sequence;

    /* N.B. we don't need to lock the list lock because we have the
       ppp unit receive-side lock. */
    skb_queue_walk(list, p) {
        if (seq_before(seq, PPP_MP_CB(p)->sequence))
            break;
    }
    __skb_queue_before(list, p, skb);
}

/*
 * 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.
 */
static 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, *tmp;
    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;
    skb_queue_walk_safe(list, p, tmp) {
    again:
        if (seq_before(PPP_MP_CB(p)->sequence, seq)) {
            /* this can't happen, anyway ignore the skb */
            netdev_err(ppp->dev, "ppp_mp_reconstruct bad "
                   "seq %u < %u\n",
                   PPP_MP_CB(p)->sequence, seq);
            __skb_unlink(p, list);
            kfree_skb(p);
            continue;
        }
        if (PPP_MP_CB(p)->sequence != seq) {
            u32 oldseq;
            /* 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;
            oldseq = seq;
            seq = seq_before(minseq, PPP_MP_CB(p)->sequence)?
                minseq + 1: PPP_MP_CB(p)->sequence;

            if (ppp->debug & 1)
                netdev_printk(KERN_DEBUG, ppp->dev,
                          "lost frag %u..%u\n",
                          oldseq, seq-1);

            goto again;
        }

        /*
         * 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 (PPP_MP_CB(p)->BEbits & B) {
            head = p;
            lost = 0;
            len = 0;
        }

        len += p->len;

        /* Got a complete packet yet? */
        if (lost == 0 && (PPP_MP_CB(p)->BEbits & E) &&
            (PPP_MP_CB(head)->BEbits & B)) {
            if (len > ppp->mrru + 2) {
                ++ppp->dev->stats.rx_length_errors;
                netdev_printk(KERN_DEBUG, ppp->dev,
                          "PPP: reconstructed packet"
                          " is too long (%d)\n", len);
            } 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 (PPP_MP_CB(p)->BEbits & E) {
            struct sk_buff *tmp2;

            skb_queue_reverse_walk_from_safe(list, p, tmp2) {
                if (ppp->debug & 1)
                    netdev_printk(KERN_DEBUG, ppp->dev,
                              "discarding frag %u\n",
                              PPP_MP_CB(p)->sequence);
                __skb_unlink(p, list);
                kfree_skb(p);
            }
            head = skb_peek(list);
            if (!head)
                break;
        }
        ++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 (PPP_MP_CB(head)->sequence != ppp->nextseq) {
            skb_queue_walk_safe(list, p, tmp) {
                if (p == head)
                    break;
                if (ppp->debug & 1)
                    netdev_printk(KERN_DEBUG, ppp->dev,
                              "discarding frag %u\n",
                              PPP_MP_CB(p)->sequence);
                __skb_unlink(p, list);
                kfree_skb(p);
            }

            if (ppp->debug & 1)
                netdev_printk(KERN_DEBUG, ppp->dev,
                          "  missed pkts %u..%u\n",
                          ppp->nextseq,
                          PPP_MP_CB(head)->sequence-1);
            ++ppp->dev->stats.rx_dropped;
            ppp_receive_error(ppp);
        }

        skb = head;
        if (head != tail) {
            struct sk_buff **fragpp = &skb_shinfo(skb)->frag_list;
            p = skb_queue_next(list, head);
            __skb_unlink(skb, list);
            skb_queue_walk_from_safe(list, p, tmp) {
                __skb_unlink(p, list);
                *fragpp = p;
                p->next = NULL;
                fragpp = &p->next;

                skb->len += p->len;
                skb->data_len += p->len;
                skb->truesize += p->truesize;

                if (p == tail)
                    break;
            }
        } else {
            __skb_unlink(skb, list);
        }

        ppp->nextseq = PPP_MP_CB(tail)->sequence + 1;
    }

    return skb;
}
#endif /* CONFIG_PPP_MULTILINK */

/*
 * Channel interface.
 */

/* Create a new, unattached ppp channel. */
int ppp_register_channel(struct ppp_channel *chan)
{
    return ppp_register_net_channel(current->nsproxy->net_ns, chan);
}

/* Create a new, unattached ppp channel for specified net. */
int ppp_register_net_channel(struct net *net, struct ppp_channel *chan)
{
    struct channel *pch;
    struct ppp_net *pn;

    pch = kzalloc(sizeof(struct channel), GFP_KERNEL);
    if (!pch)
        return -ENOMEM;

    pn = ppp_pernet(net);

    pch->ppp = NULL;
    pch->chan = chan;
    pch->chan_net = net;
    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(&pn->all_channels_lock);
    pch->file.index = ++pn->last_channel_index;
    list_add(&pch->list, &pn->new_channels);
    atomic_inc(&channel_count);
    spin_unlock_bh(&pn->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)
        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) {
        read_lock_bh(&pch->upl);
        if (pch->ppp)
            unit = pch->ppp->file.index;
        read_unlock_bh(&pch->upl);
    }
    return unit;
}

/*
 * Return the PPP device interface name of a channel.
 */
char *ppp_dev_name(struct ppp_channel *chan)
{
    struct channel *pch = chan->ppp;
    char *name = NULL;

    if (pch) {
        read_lock_bh(&pch->upl);
        if (pch->ppp && pch->ppp->dev)
            name = pch->ppp->dev->name;
        read_unlock_bh(&pch->upl);
    }
    return name;
}


/*
 * 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;
    struct ppp_net *pn;

    if (!pch)
        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);

    pn = ppp_pernet(pch->chan_net);
    spin_lock_bh(&pn->all_channels_lock);
    list_del(&pch->list);
    spin_unlock_bh(&pn->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)
        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 = try_then_request_module(
        find_compressor(ccp_option[0]),
        "ppp-compress-%d", ccp_option[0]);
    if (!cp)
        goto out;

    err = -ENOBUFS;
    if (data.transmit) {
        state = cp->comp_alloc(ccp_option, data.length);
        if (state) {
            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) {
                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) {
            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) {
                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)
                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)
                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))
        goto out;
    ret = -ENOMEM;
    ce = kmalloc(sizeof(struct compressor_entry), GFP_ATOMIC);
    if (!ce)
        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 && 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) {
        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->stats64.rx_packets;
    st->p.ppp_ierrors = ppp->dev->stats.rx_errors;
    st->p.ppp_ibytes = ppp->stats64.rx_bytes;
    st->p.ppp_opackets = ppp->stats64.tx_packets;
    st->p.ppp_oerrors = ppp->dev->stats.tx_errors;
    st->p.ppp_obytes = ppp->stats64.tx_bytes;
    if (!vj)
        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(struct net *net, int unit, int *retp)
{
    struct ppp *ppp;
    struct ppp_net *pn;
    struct net_device *dev = NULL;
    int ret = -ENOMEM;
    int i;

    dev = alloc_netdev(sizeof(struct ppp), "", ppp_setup);
    if (!dev)
        goto out1;

    pn = ppp_pernet(net);

    ppp = netdev_priv(dev);
    ppp->dev = dev;
    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 */

    /*
     * drum roll: don't forget to set
     * the net device is belong to
     */
    dev_net_set(dev, net);

    mutex_lock(&pn->all_ppp_mutex);

    if (unit < 0) {
        unit = unit_get(&pn->units_idr, ppp);
        if (unit < 0) {
            ret = unit;
            goto out2;
        }
    } else {
        ret = -EEXIST;
        if (unit_find(&pn->units_idr, unit))
            goto out2; /* unit already exists */
        /*
         * if caller need a specified unit number
         * lets try to satisfy him, otherwise --
         * he should better ask us for new unit number
         *
         * NOTE: yes I know that returning EEXIST it's not
         * fair but at least pppd will ask us to allocate
         * new unit in this case so user is happy :)
         */
        unit = unit_set(&pn->units_idr, ppp, unit);
        if (unit < 0)
            goto out2;
    }

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

    ret = register_netdev(dev);
    if (ret != 0) {
        unit_put(&pn->units_idr, unit);
        netdev_err(ppp->dev, "PPP: couldn't register device %s (%d)\n",
               dev->name, ret);
        goto out2;
    }

    ppp->ppp_net = net;

    atomic_inc(&ppp_unit_count);
    mutex_unlock(&pn->all_ppp_mutex);

    *retp = 0;
    return ppp;

out2:
    mutex_unlock(&pn->all_ppp_mutex);
    free_netdev(dev);
out1:
    *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 ppp_net *pn;

    pn = ppp_pernet(ppp->ppp_net);
    mutex_lock(&pn->all_ppp_mutex);

    /* This will call dev_close() for us. */
    ppp_lock(ppp);
    if (!ppp->closing) {
        ppp->closing = 1;
        ppp_unlock(ppp);
        unregister_netdev(ppp->dev);
        unit_put(&pn->units_idr, ppp->file.index);
    } else
        ppp_unlock(ppp);

    ppp->file.dead = 1;
    ppp->owner = NULL;
    wake_up_interruptible(&ppp->file.rwait);

    mutex_unlock(&pn->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" */
        netdev_err(ppp->dev, "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_skb(ppp->xmit_pending);

    free_netdev(ppp->dev);
}

/*
 * Locate an existing ppp unit.
 * The caller should have locked the all_ppp_mutex.
 */
static struct ppp *
ppp_find_unit(struct ppp_net *pn, int unit)
{
    return unit_find(&pn->units_idr, 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(struct ppp_net *pn, int unit)
{
    struct channel *pch;

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

    list_for_each_entry(pch, &pn->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;
    struct ppp_net *pn;
    int ret = -ENXIO;
    int hdrlen;

    pn = ppp_pernet(pch->chan_net);

    mutex_lock(&pn->all_ppp_mutex);
    ppp = ppp_find_unit(pn, unit);
    if (!ppp)
        goto out;
    write_lock_bh(&pch->upl);
    ret = -EINVAL;
    if (pch->ppp)
        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 (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(&pn->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) {
        /* 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" */
        pr_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))
        pr_err("PPP: removing module but units remain!\n");
    unregister_chrdev(PPP_MAJOR, "ppp");
    device_destroy(ppp_class, MKDEV(PPP_MAJOR, 0));
    class_destroy(ppp_class);
    unregister_pernet_device(&ppp_net_ops);
}

/*
 * Units handling. Caller must protect concurrent access
 * by holding all_ppp_mutex
 */

static int __unit_alloc(struct idr *p, void *ptr, int n)
{
    int unit, err;

again:
    if (!idr_pre_get(p, GFP_KERNEL)) {
        pr_err("PPP: No free memory for idr\n");
        return -ENOMEM;
    }

    err = idr_get_new_above(p, ptr, n, &unit);
    if (err < 0) {
        if (err == -EAGAIN)
            goto again;
        return err;
    }

    return unit;
}

/* associate pointer with specified number */
static int unit_set(struct idr *p, void *ptr, int n)
{
    int unit;

    unit = __unit_alloc(p, ptr, n);
    if (unit < 0)
        return unit;
    else if (unit != n) {
        idr_remove(p, unit);
        return -EINVAL;
    }

    return unit;
}

/* get new free unit number and associate pointer with it */
static int unit_get(struct idr *p, void *ptr)
{
    return __unit_alloc(p, ptr, 0);
}

/* put unit number back to a pool */
static void unit_put(struct idr *p, int n)
{
    idr_remove(p, n);
}

/* get pointer associated with the number */
static void *unit_find(struct idr *p, int n)
{
    return idr_find(p, n);
}

/* Module/initialization stuff */

module_init(ppp_init);
module_exit(ppp_cleanup);

EXPORT_SYMBOL(ppp_register_net_channel);
EXPORT_SYMBOL(ppp_register_channel);
EXPORT_SYMBOL(ppp_unregister_channel);
EXPORT_SYMBOL(ppp_channel_index);
EXPORT_SYMBOL(ppp_unit_number);
EXPORT_SYMBOL(ppp_dev_name);
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(PPP_MAJOR, 0);
MODULE_ALIAS("devname:ppp");