// SPDX-License-Identifier: GPL-2.0-only
/*
 * Generic HDLC support routines for Linux
 * Point-to-point protocol support
 *
 * Copyright (C) 1999 - 2008 Krzysztof Halasa <khc@pm.waw.pl>
 */

#include <linux/errno.h>
#include <linux/hdlc.h>
#include <linux/if_arp.h>
#include <linux/inetdevice.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/pkt_sched.h>
#include <linux/poll.h>
#include <linux/skbuff.h>
#include <linux/slab.h>
#include <linux/spinlock.h>

#define DEBUG_CP                0 /* also bytes# to dump */
#define DEBUG_STATE             0
#define DEBUG_HARD_HEADER       0

#define HDLC_ADDR_ALLSTATIONS   0xFF
#define HDLC_CTRL_UI            0x03

#define PID_LCP                 0xC021
#define PID_IP                  0x0021
#define PID_IPCP                0x8021
#define PID_IPV6                0x0057
#define PID_IPV6CP              0x8057

enum {IDX_LCP = 0, IDX_IPCP, IDX_IPV6CP, IDX_COUNT};
enum {CP_CONF_REQ = 1, CP_CONF_ACK, CP_CONF_NAK, CP_CONF_REJ, CP_TERM_REQ,
      CP_TERM_ACK, CP_CODE_REJ, LCP_PROTO_REJ, LCP_ECHO_REQ, LCP_ECHO_REPLY,
      LCP_DISC_REQ, CP_CODES};
#if DEBUG_CP
static const char *const code_names[CP_CODES] = {
        "0", "ConfReq", "ConfAck", "ConfNak", "ConfRej", "TermReq",
        "TermAck", "CodeRej", "ProtoRej", "EchoReq", "EchoReply", "Discard"
};

static char debug_buffer[64 + 3 * DEBUG_CP];
#endif

enum {LCP_OPTION_MRU = 1, LCP_OPTION_ACCM, LCP_OPTION_MAGIC = 5};

struct hdlc_header {
        u8 address;
        u8 control;
        __be16 protocol;
};

struct cp_header {
        u8 code;
        u8 id;
        __be16 len;
};

struct proto {
        struct net_device *dev;
        struct timer_list timer;
        unsigned long timeout;
        u16 pid;                /* protocol ID */
        u8 state;
        u8 cr_id;               /* ID of last Configuration-Request */
        u8 restart_counter;
};

struct ppp {
        struct proto protos[IDX_COUNT];
        spinlock_t lock;
        unsigned long last_pong;
        unsigned int req_timeout, cr_retries, term_retries;
        unsigned int keepalive_interval, keepalive_timeout;
        u8 seq;                 /* local sequence number for requests */
        u8 echo_id;             /* ID of last Echo-Request (LCP) */
};

enum {CLOSED = 0, STOPPED, STOPPING, REQ_SENT, ACK_RECV, ACK_SENT, OPENED,
      STATES, STATE_MASK = 0xF};
enum {START = 0, STOP, TO_GOOD, TO_BAD, RCR_GOOD, RCR_BAD, RCA, RCN, RTR, RTA,
      RUC, RXJ_GOOD, RXJ_BAD, EVENTS};
enum {INV = 0x10, IRC = 0x20, ZRC = 0x40, SCR = 0x80, SCA = 0x100,
      SCN = 0x200, STR = 0x400, STA = 0x800, SCJ = 0x1000};

#if DEBUG_STATE
static const char *const state_names[STATES] = {
        "Closed", "Stopped", "Stopping", "ReqSent", "AckRecv", "AckSent",
        "Opened"
};

static const char *const event_names[EVENTS] = {
        "Start", "Stop", "TO+", "TO-", "RCR+", "RCR-", "RCA", "RCN",
        "RTR", "RTA", "RUC", "RXJ+", "RXJ-"
};
#endif

static struct sk_buff_head tx_queue; /* used when holding the spin lock */

static int ppp_ioctl(struct net_device *dev, struct if_settings *ifs);

static inline struct ppp *get_ppp(struct net_device *dev)
{
        return (struct ppp *)dev_to_hdlc(dev)->state;
}

static inline struct proto *get_proto(struct net_device *dev, u16 pid)
{
        struct ppp *ppp = get_ppp(dev);

        switch (pid) {
        case PID_LCP:
                return &ppp->protos[IDX_LCP];
        case PID_IPCP:
                return &ppp->protos[IDX_IPCP];
        case PID_IPV6CP:
                return &ppp->protos[IDX_IPV6CP];
        default:
                return NULL;
        }
}

static inline const char *proto_name(u16 pid)
{
        switch (pid) {
        case PID_IPCP:
                return "IPCP";
        case PID_IPV6CP:
                return "IPV6CP";
        default:
                return "LCP";
        }
}

static __be16 ppp_type_trans(struct sk_buff *skb, struct net_device *dev)
{
        struct hdlc_header *data = (struct hdlc_header *)skb->data;

        if (skb->len < sizeof(struct hdlc_header))
                return htons(ETH_P_HDLC);
        if (data->address != HDLC_ADDR_ALLSTATIONS ||
            data->control != HDLC_CTRL_UI)
                return htons(ETH_P_HDLC);

        switch (data->protocol) {
        case cpu_to_be16(PID_IP):
                skb_pull(skb, sizeof(struct hdlc_header));
                return htons(ETH_P_IP);

        case cpu_to_be16(PID_IPV6):
                skb_pull(skb, sizeof(struct hdlc_header));
                return htons(ETH_P_IPV6);

        default:
                return htons(ETH_P_HDLC);
        }
}

static int ppp_hard_header(struct sk_buff *skb, struct net_device *dev,
                           u16 type, const void *daddr, const void *saddr,
                           unsigned int len)
{
        struct hdlc_header *data;
#if DEBUG_HARD_HEADER
        printk(KERN_DEBUG "%s: ppp_hard_header() called\n", dev->name);
#endif

        skb_push(skb, sizeof(struct hdlc_header));
        data = (struct hdlc_header *)skb->data;

        data->address = HDLC_ADDR_ALLSTATIONS;
        data->control = HDLC_CTRL_UI;
        switch (type) {
        case ETH_P_IP:
                data->protocol = htons(PID_IP);
                break;
        case ETH_P_IPV6:
                data->protocol = htons(PID_IPV6);
                break;
        case PID_LCP:
        case PID_IPCP:
        case PID_IPV6CP:
                data->protocol = htons(type);
                break;
        default:                /* unknown protocol */
                data->protocol = 0;
        }
        return sizeof(struct hdlc_header);
}

static void ppp_tx_flush(void)
{
        struct sk_buff *skb;

        while ((skb = skb_dequeue(&tx_queue)) != NULL)
                dev_queue_xmit(skb);
}

static void ppp_tx_cp(struct net_device *dev, u16 pid, u8 code,
                      u8 id, unsigned int len, const void *data)
{
        struct sk_buff *skb;
        struct cp_header *cp;
        unsigned int magic_len = 0;
        static u32 magic;

#if DEBUG_CP
        int i;
        char *ptr;
#endif

        if (pid == PID_LCP && (code == LCP_ECHO_REQ || code == LCP_ECHO_REPLY))
                magic_len = sizeof(magic);

        skb = dev_alloc_skb(sizeof(struct hdlc_header) +
                            sizeof(struct cp_header) + magic_len + len);
        if (!skb)
                return;

        skb_reserve(skb, sizeof(struct hdlc_header));

        cp = skb_put(skb, sizeof(struct cp_header));
        cp->code = code;
        cp->id = id;
        cp->len = htons(sizeof(struct cp_header) + magic_len + len);

        if (magic_len)
                skb_put_data(skb, &magic, magic_len);
        if (len)
                skb_put_data(skb, data, len);

#if DEBUG_CP
        BUG_ON(code >= CP_CODES);
        ptr = debug_buffer;
        *ptr = '\x0';
        for (i = 0; i < min_t(unsigned int, magic_len + len, DEBUG_CP); i++) {
                sprintf(ptr, " %02X", skb->data[sizeof(struct cp_header) + i]);
                ptr += strlen(ptr);
        }
        printk(KERN_DEBUG "%s: TX %s [%s id 0x%X]%s\n", dev->name,
               proto_name(pid), code_names[code], id, debug_buffer);
#endif

        ppp_hard_header(skb, dev, pid, NULL, NULL, 0);

        skb->priority = TC_PRIO_CONTROL;
        skb->dev = dev;
        skb->protocol = htons(ETH_P_HDLC);
        skb_reset_network_header(skb);
        skb_queue_tail(&tx_queue, skb);
}

/* State transition table (compare STD-51)
   Events                                   Actions
   TO+  = Timeout with counter > 0          irc = Initialize-Restart-Count
   TO-  = Timeout with counter expired      zrc = Zero-Restart-Count

   RCR+ = Receive-Configure-Request (Good)  scr = Send-Configure-Request
   RCR- = Receive-Configure-Request (Bad)
   RCA  = Receive-Configure-Ack             sca = Send-Configure-Ack
   RCN  = Receive-Configure-Nak/Rej         scn = Send-Configure-Nak/Rej

   RTR  = Receive-Terminate-Request         str = Send-Terminate-Request
   RTA  = Receive-Terminate-Ack             sta = Send-Terminate-Ack

   RUC  = Receive-Unknown-Code              scj = Send-Code-Reject
   RXJ+ = Receive-Code-Reject (permitted)
       or Receive-Protocol-Reject
   RXJ- = Receive-Code-Reject (catastrophic)
       or Receive-Protocol-Reject
*/
static int cp_table[EVENTS][STATES] = {
        /* CLOSED     STOPPED STOPPING REQ_SENT ACK_RECV ACK_SENT OPENED
             0           1         2       3       4      5          6    */
        {IRC|SCR|3,     INV     , INV ,   INV   , INV ,  INV    ,   INV   }, /* START */
        {   INV   ,      0      ,  0  ,    0    ,  0  ,   0     ,    0    }, /* STOP */
        {   INV   ,     INV     ,STR|2,  SCR|3  ,SCR|3,  SCR|5  ,   INV   }, /* TO+ */
        {   INV   ,     INV     ,  1  ,    1    ,  1  ,    1    ,   INV   }, /* TO- */
        {  STA|0  ,IRC|SCR|SCA|5,  2  ,  SCA|5  ,SCA|6,  SCA|5  ,SCR|SCA|5}, /* RCR+ */
        {  STA|0  ,IRC|SCR|SCN|3,  2  ,  SCN|3  ,SCN|4,  SCN|3  ,SCR|SCN|3}, /* RCR- */
        {  STA|0  ,    STA|1    ,  2  ,  IRC|4  ,SCR|3,    6    , SCR|3   }, /* RCA */
        {  STA|0  ,    STA|1    ,  2  ,IRC|SCR|3,SCR|3,IRC|SCR|5, SCR|3   }, /* RCN */
        {  STA|0  ,    STA|1    ,STA|2,  STA|3  ,STA|3,  STA|3  ,ZRC|STA|2}, /* RTR */
        {    0    ,      1      ,  1  ,    3    ,  3  ,    5    ,  SCR|3  }, /* RTA */
        {  SCJ|0  ,    SCJ|1    ,SCJ|2,  SCJ|3  ,SCJ|4,  SCJ|5  ,  SCJ|6  }, /* RUC */
        {    0    ,      1      ,  2  ,    3    ,  3  ,    5    ,    6    }, /* RXJ+ */
        {    0    ,      1      ,  1  ,    1    ,  1  ,    1    ,IRC|STR|2}, /* RXJ- */
};

/* SCA: RCR+ must supply id, len and data
   SCN: RCR- must supply code, id, len and data
   STA: RTR must supply id
   SCJ: RUC must supply CP packet len and data */
static void ppp_cp_event(struct net_device *dev, u16 pid, u16 event, u8 code,
                         u8 id, unsigned int len, const void *data)
{
        int old_state, action;
        struct ppp *ppp = get_ppp(dev);
        struct proto *proto = get_proto(dev, pid);

        old_state = proto->state;
        BUG_ON(old_state >= STATES);
        BUG_ON(event >= EVENTS);

#if DEBUG_STATE
        printk(KERN_DEBUG "%s: %s ppp_cp_event(%s) %s ...\n", dev->name,
               proto_name(pid), event_names[event], state_names[proto->state]);
#endif

        action = cp_table[event][old_state];

        proto->state = action & STATE_MASK;
        if (action & (SCR | STR)) /* set Configure-Req/Terminate-Req timer */
                mod_timer(&proto->timer, proto->timeout =
                          jiffies + ppp->req_timeout * HZ);
        if (action & ZRC)
                proto->restart_counter = 0;
        if (action & IRC)
                proto->restart_counter = (proto->state == STOPPING) ?
                        ppp->term_retries : ppp->cr_retries;

        if (action & SCR)       /* send Configure-Request */
                ppp_tx_cp(dev, pid, CP_CONF_REQ, proto->cr_id = ++ppp->seq,
                          0, NULL);
        if (action & SCA)       /* send Configure-Ack */
                ppp_tx_cp(dev, pid, CP_CONF_ACK, id, len, data);
        if (action & SCN)       /* send Configure-Nak/Reject */
                ppp_tx_cp(dev, pid, code, id, len, data);
        if (action & STR)       /* send Terminate-Request */
                ppp_tx_cp(dev, pid, CP_TERM_REQ, ++ppp->seq, 0, NULL);
        if (action & STA)       /* send Terminate-Ack */
                ppp_tx_cp(dev, pid, CP_TERM_ACK, id, 0, NULL);
        if (action & SCJ)       /* send Code-Reject */
                ppp_tx_cp(dev, pid, CP_CODE_REJ, ++ppp->seq, len, data);

        if (old_state != OPENED && proto->state == OPENED) {
                netdev_info(dev, "%s up\n", proto_name(pid));
                if (pid == PID_LCP) {
                        netif_dormant_off(dev);
                        ppp_cp_event(dev, PID_IPCP, START, 0, 0, 0, NULL);
                        ppp_cp_event(dev, PID_IPV6CP, START, 0, 0, 0, NULL);
                        ppp->last_pong = jiffies;
                        mod_timer(&proto->timer, proto->timeout =
                                  jiffies + ppp->keepalive_interval * HZ);
                }
        }
        if (old_state == OPENED && proto->state != OPENED) {
                netdev_info(dev, "%s down\n", proto_name(pid));
                if (pid == PID_LCP) {
                        netif_dormant_on(dev);
                        ppp_cp_event(dev, PID_IPCP, STOP, 0, 0, 0, NULL);
                        ppp_cp_event(dev, PID_IPV6CP, STOP, 0, 0, 0, NULL);
                }
        }
        if (old_state != CLOSED && proto->state == CLOSED)
                timer_delete(&proto->timer);

#if DEBUG_STATE
        printk(KERN_DEBUG "%s: %s ppp_cp_event(%s) ... %s\n", dev->name,
               proto_name(pid), event_names[event], state_names[proto->state]);
#endif
}

static void ppp_cp_parse_cr(struct net_device *dev, u16 pid, u8 id,
                            unsigned int req_len, const u8 *data)
{
        static u8 const valid_accm[6] = { LCP_OPTION_ACCM, 6, 0, 0, 0, 0 };
        const u8 *opt;
        u8 *out;
        unsigned int len = req_len, nak_len = 0, rej_len = 0;

        out = kmalloc(len, GFP_ATOMIC);
        if (!out) {
                dev->stats.rx_dropped++;
                return; /* out of memory, ignore CR packet */
        }

        for (opt = data; len; len -= opt[1], opt += opt[1]) {
                if (len < 2 || opt[1] < 2 || len < opt[1])
                        goto err_out;

                if (pid == PID_LCP)
                        switch (opt[0]) {
                        case LCP_OPTION_MRU:
                                continue; /* MRU always OK and > 1500 bytes? */

                        case LCP_OPTION_ACCM: /* async control character map */
                                if (opt[1] < sizeof(valid_accm))
                                        goto err_out;
                                if (!memcmp(opt, valid_accm,
                                            sizeof(valid_accm)))
                                        continue;
                                if (!rej_len) { /* NAK it */
                                        memcpy(out + nak_len, valid_accm,
                                               sizeof(valid_accm));
                                        nak_len += sizeof(valid_accm);
                                        continue;
                                }
                                break;
                        case LCP_OPTION_MAGIC:
                                if (len < 6)
                                        goto err_out;
                                if (opt[1] != 6 || (!opt[2] && !opt[3] &&
                                                    !opt[4] && !opt[5]))
                                        break; /* reject invalid magic number */
                                continue;
                        }
                /* reject this option */
                memcpy(out + rej_len, opt, opt[1]);
                rej_len += opt[1];
        }

        if (rej_len)
                ppp_cp_event(dev, pid, RCR_BAD, CP_CONF_REJ, id, rej_len, out);
        else if (nak_len)
                ppp_cp_event(dev, pid, RCR_BAD, CP_CONF_NAK, id, nak_len, out);
        else
                ppp_cp_event(dev, pid, RCR_GOOD, CP_CONF_ACK, id, req_len, data);

        kfree(out);
        return;

err_out:
        dev->stats.rx_errors++;
        kfree(out);
}

static int ppp_rx(struct sk_buff *skb)
{
        struct hdlc_header *hdr = (struct hdlc_header *)skb->data;
        struct net_device *dev = skb->dev;
        struct ppp *ppp = get_ppp(dev);
        struct proto *proto;
        struct cp_header *cp;
        unsigned long flags;
        unsigned int len;
        u16 pid;
#if DEBUG_CP
        int i;
        char *ptr;
#endif

        spin_lock_irqsave(&ppp->lock, flags);
        /* Check HDLC header */
        if (skb->len < sizeof(struct hdlc_header))
                goto rx_error;
        cp = skb_pull(skb, sizeof(struct hdlc_header));
        if (hdr->address != HDLC_ADDR_ALLSTATIONS ||
            hdr->control != HDLC_CTRL_UI)
                goto rx_error;

        pid = ntohs(hdr->protocol);
        proto = get_proto(dev, pid);
        if (!proto) {
                if (ppp->protos[IDX_LCP].state == OPENED)
                        ppp_tx_cp(dev, PID_LCP, LCP_PROTO_REJ,
                                  ++ppp->seq, skb->len + 2, &hdr->protocol);
                goto rx_error;
        }

        len = ntohs(cp->len);
        if (len < sizeof(struct cp_header) /* no complete CP header? */ ||
            skb->len < len /* truncated packet? */)
                goto rx_error;
        skb_pull(skb, sizeof(struct cp_header));
        len -= sizeof(struct cp_header);

        /* HDLC and CP headers stripped from skb */
#if DEBUG_CP
        if (cp->code < CP_CODES)
                sprintf(debug_buffer, "[%s id 0x%X]", code_names[cp->code],
                        cp->id);
        else
                sprintf(debug_buffer, "[code %u id 0x%X]", cp->code, cp->id);
        ptr = debug_buffer + strlen(debug_buffer);
        for (i = 0; i < min_t(unsigned int, len, DEBUG_CP); i++) {
                sprintf(ptr, " %02X", skb->data[i]);
                ptr += strlen(ptr);
        }
        printk(KERN_DEBUG "%s: RX %s %s\n", dev->name, proto_name(pid),
               debug_buffer);
#endif

        /* LCP only */
        if (pid == PID_LCP)
                switch (cp->code) {
                case LCP_PROTO_REJ:
                        pid = ntohs(*(__be16 *)skb->data);
                        if (pid == PID_LCP || pid == PID_IPCP ||
                            pid == PID_IPV6CP)
                                ppp_cp_event(dev, pid, RXJ_BAD, 0, 0,
                                             0, NULL);
                        goto out;

                case LCP_ECHO_REQ: /* send Echo-Reply */
                        if (len >= 4 && proto->state == OPENED)
                                ppp_tx_cp(dev, PID_LCP, LCP_ECHO_REPLY,
                                          cp->id, len - 4, skb->data + 4);
                        goto out;

                case LCP_ECHO_REPLY:
                        if (cp->id == ppp->echo_id)
                                ppp->last_pong = jiffies;
                        goto out;

                case LCP_DISC_REQ: /* discard */
                        goto out;
                }

        /* LCP, IPCP and IPV6CP */
        switch (cp->code) {
        case CP_CONF_REQ:
                ppp_cp_parse_cr(dev, pid, cp->id, len, skb->data);
                break;

        case CP_CONF_ACK:
                if (cp->id == proto->cr_id)
                        ppp_cp_event(dev, pid, RCA, 0, 0, 0, NULL);
                break;

        case CP_CONF_REJ:
        case CP_CONF_NAK:
                if (cp->id == proto->cr_id)
                        ppp_cp_event(dev, pid, RCN, 0, 0, 0, NULL);
                break;

        case CP_TERM_REQ:
                ppp_cp_event(dev, pid, RTR, 0, cp->id, 0, NULL);
                break;

        case CP_TERM_ACK:
                ppp_cp_event(dev, pid, RTA, 0, 0, 0, NULL);
                break;

        case CP_CODE_REJ:
                ppp_cp_event(dev, pid, RXJ_BAD, 0, 0, 0, NULL);
                break;

        default:
                len += sizeof(struct cp_header);
                if (len > dev->mtu)
                        len = dev->mtu;
                ppp_cp_event(dev, pid, RUC, 0, 0, len, cp);
                break;
        }
        goto out;

rx_error:
        dev->stats.rx_errors++;
out:
        spin_unlock_irqrestore(&ppp->lock, flags);
        dev_kfree_skb_any(skb);
        ppp_tx_flush();
        return NET_RX_DROP;
}

static void ppp_timer(struct timer_list *t)
{
        struct proto *proto = timer_container_of(proto, t, timer);
        struct ppp *ppp = get_ppp(proto->dev);
        unsigned long flags;

        spin_lock_irqsave(&ppp->lock, flags);
        /* mod_timer could be called after we entered this function but
         * before we got the lock.
         */
        if (timer_pending(&proto->timer)) {
                spin_unlock_irqrestore(&ppp->lock, flags);
                return;
        }
        switch (proto->state) {
        case STOPPING:
        case REQ_SENT:
        case ACK_RECV:
        case ACK_SENT:
                if (proto->restart_counter) {
                        ppp_cp_event(proto->dev, proto->pid, TO_GOOD, 0, 0,
                                     0, NULL);
                        proto->restart_counter--;
                } else if (netif_carrier_ok(proto->dev))
                        ppp_cp_event(proto->dev, proto->pid, TO_GOOD, 0, 0,
                                     0, NULL);
                else
                        ppp_cp_event(proto->dev, proto->pid, TO_BAD, 0, 0,
                                     0, NULL);
                break;

        case OPENED:
                if (proto->pid != PID_LCP)
                        break;
                if (time_after(jiffies, ppp->last_pong +
                               ppp->keepalive_timeout * HZ)) {
                        netdev_info(proto->dev, "Link down\n");
                        ppp_cp_event(proto->dev, PID_LCP, STOP, 0, 0, 0, NULL);
                        ppp_cp_event(proto->dev, PID_LCP, START, 0, 0, 0, NULL);
                } else {        /* send keep-alive packet */
                        ppp->echo_id = ++ppp->seq;
                        ppp_tx_cp(proto->dev, PID_LCP, LCP_ECHO_REQ,
                                  ppp->echo_id, 0, NULL);
                        proto->timer.expires = jiffies +
                                ppp->keepalive_interval * HZ;
                        add_timer(&proto->timer);
                }
                break;
        }
        spin_unlock_irqrestore(&ppp->lock, flags);
        ppp_tx_flush();
}

static void ppp_start(struct net_device *dev)
{
        struct ppp *ppp = get_ppp(dev);
        int i;

        for (i = 0; i < IDX_COUNT; i++) {
                struct proto *proto = &ppp->protos[i];

                proto->dev = dev;
                timer_setup(&proto->timer, ppp_timer, 0);
                proto->state = CLOSED;
        }
        ppp->protos[IDX_LCP].pid = PID_LCP;
        ppp->protos[IDX_IPCP].pid = PID_IPCP;
        ppp->protos[IDX_IPV6CP].pid = PID_IPV6CP;

        ppp_cp_event(dev, PID_LCP, START, 0, 0, 0, NULL);
}

static void ppp_stop(struct net_device *dev)
{
        ppp_cp_event(dev, PID_LCP, STOP, 0, 0, 0, NULL);
}

static void ppp_close(struct net_device *dev)
{
        ppp_tx_flush();
}

static struct hdlc_proto proto = {
        .start          = ppp_start,
        .stop           = ppp_stop,
        .close          = ppp_close,
        .type_trans     = ppp_type_trans,
        .ioctl          = ppp_ioctl,
        .netif_rx       = ppp_rx,
        .module         = THIS_MODULE,
};

static const struct header_ops ppp_header_ops = {
        .create = ppp_hard_header,
};

static int ppp_ioctl(struct net_device *dev, struct if_settings *ifs)
{
        hdlc_device *hdlc = dev_to_hdlc(dev);
        struct ppp *ppp;
        int result;

        switch (ifs->type) {
        case IF_GET_PROTO:
                if (dev_to_hdlc(dev)->proto != &proto)
                        return -EINVAL;
                ifs->type = IF_PROTO_PPP;
                return 0; /* return protocol only, no settable parameters */

        case IF_PROTO_PPP:
                if (!capable(CAP_NET_ADMIN))
                        return -EPERM;

                if (dev->flags & IFF_UP)
                        return -EBUSY;

                /* no settable parameters */

                result = hdlc->attach(dev, ENCODING_NRZ,
                                      PARITY_CRC16_PR1_CCITT);
                if (result)
                        return result;

                result = attach_hdlc_protocol(dev, &proto, sizeof(struct ppp));
                if (result)
                        return result;

                ppp = get_ppp(dev);
                spin_lock_init(&ppp->lock);
                ppp->req_timeout = 2;
                ppp->cr_retries = 10;
                ppp->term_retries = 2;
                ppp->keepalive_interval = 10;
                ppp->keepalive_timeout = 60;

                dev->hard_header_len = sizeof(struct hdlc_header);
                dev->header_ops = &ppp_header_ops;
                dev->type = ARPHRD_PPP;
                call_netdevice_notifiers(NETDEV_POST_TYPE_CHANGE, dev);
                netif_dormant_on(dev);
                return 0;
        }

        return -EINVAL;
}

static int __init hdlc_ppp_init(void)
{
        skb_queue_head_init(&tx_queue);
        register_hdlc_protocol(&proto);
        return 0;
}

static void __exit hdlc_ppp_exit(void)
{
        unregister_hdlc_protocol(&proto);
}

module_init(hdlc_ppp_init);
module_exit(hdlc_ppp_exit);

MODULE_AUTHOR("Krzysztof Halasa <khc@pm.waw.pl>");
MODULE_DESCRIPTION("PPP protocol support for generic HDLC");
MODULE_LICENSE("GPL v2");