jiffies_round-jiffies_round_relative-conversion-rt2x00-checkpatch-fixes

[linux-2.6/linux-trees-mm.git] / drivers / net / pppol2tp.c

/*****************************************************************************
 * Linux PPP over L2TP (PPPoX/PPPoL2TP) Sockets
 *
 * PPPoX    --- Generic PPP encapsulation socket family
 * PPPoL2TP --- PPP over L2TP (RFC 2661)
 *
 * Version:     1.0.0
 *
 * Authors:     Martijn van Oosterhout <kleptog@svana.org>
 *              James Chapman (jchapman@katalix.com)
 * Contributors:
 *              Michal Ostrowski <mostrows@speakeasy.net>
 *              Arnaldo Carvalho de Melo <acme@xconectiva.com.br>
 *              David S. Miller (davem@redhat.com)
 *
 * License:
 *              This program is free software; you can redistribute it and/or
 *              modify it under the terms of the GNU General Public License
 *              as published by the Free Software Foundation; either version
 *              2 of the License, or (at your option) any later version.
 *
 */

/* This driver handles only L2TP data frames; control frames are handled by a
 * userspace application.
 *
 * To send data in an L2TP session, userspace opens a PPPoL2TP socket and
 * attaches it to a bound UDP socket with local tunnel_id / session_id and
 * peer tunnel_id / session_id set. Data can then be sent or received using
 * regular socket sendmsg() / recvmsg() calls. Kernel parameters of the socket
 * can be read or modified using ioctl() or [gs]etsockopt() calls.
 *
 * When a PPPoL2TP socket is connected with local and peer session_id values
 * zero, the socket is treated as a special tunnel management socket.
 *
 * Here's example userspace code to create a socket for sending/receiving data
 * over an L2TP session:-
 *
 *      struct sockaddr_pppol2tp sax;
 *      int fd;
 *      int session_fd;
 *
 *      fd = socket(AF_PPPOX, SOCK_DGRAM, PX_PROTO_OL2TP);
 *
 *      sax.sa_family = AF_PPPOX;
 *      sax.sa_protocol = PX_PROTO_OL2TP;
 *      sax.pppol2tp.fd = tunnel_fd;    // bound UDP socket
 *      sax.pppol2tp.addr.sin_addr.s_addr = addr->sin_addr.s_addr;
 *      sax.pppol2tp.addr.sin_port = addr->sin_port;
 *      sax.pppol2tp.addr.sin_family = AF_INET;
 *      sax.pppol2tp.s_tunnel  = tunnel_id;
 *      sax.pppol2tp.s_session = session_id;
 *      sax.pppol2tp.d_tunnel  = peer_tunnel_id;
 *      sax.pppol2tp.d_session = peer_session_id;
 *
 *      session_fd = connect(fd, (struct sockaddr *)&sax, sizeof(sax));
 *
 * A pppd plugin that allows PPP traffic to be carried over L2TP using
 * this driver is available from the OpenL2TP project at
 * http://openl2tp.sourceforge.net.
 */

#include <linux/module.h>
#include <linux/version.h>
#include <linux/string.h>
#include <linux/list.h>
#include <asm/uaccess.h>

#include <linux/kernel.h>
#include <linux/spinlock.h>
#include <linux/kthread.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/errno.h>
#include <linux/jiffies.h>

#include <linux/netdevice.h>
#include <linux/net.h>
#include <linux/inetdevice.h>
#include <linux/skbuff.h>
#include <linux/init.h>
#include <linux/ip.h>
#include <linux/udp.h>
#include <linux/if_pppox.h>
#include <linux/if_pppol2tp.h>
#include <net/sock.h>
#include <linux/ppp_channel.h>
#include <linux/ppp_defs.h>
#include <linux/if_ppp.h>
#include <linux/file.h>
#include <linux/hash.h>
#include <linux/sort.h>
#include <linux/proc_fs.h>
#include <net/net_namespace.h>
#include <net/dst.h>
#include <net/ip.h>
#include <net/udp.h>
#include <net/xfrm.h>

#include <asm/byteorder.h>
#include <asm/atomic.h>


#define PPPOL2TP_DRV_VERSION    "V1.0"

/* L2TP header constants */
#define L2TP_HDRFLAG_T     0x8000
#define L2TP_HDRFLAG_L     0x4000
#define L2TP_HDRFLAG_S     0x0800
#define L2TP_HDRFLAG_O     0x0200
#define L2TP_HDRFLAG_P     0x0100

#define L2TP_HDR_VER_MASK  0x000F
#define L2TP_HDR_VER       0x0002

/* Space for UDP, L2TP and PPP headers */
#define PPPOL2TP_HEADER_OVERHEAD        40

/* Just some random numbers */
#define L2TP_TUNNEL_MAGIC       0x42114DDA
#define L2TP_SESSION_MAGIC      0x0C04EB7D

#define PPPOL2TP_HASH_BITS      4
#define PPPOL2TP_HASH_SIZE      (1 << PPPOL2TP_HASH_BITS)

/* Default trace flags */
#define PPPOL2TP_DEFAULT_DEBUG_FLAGS    0

#define PRINTK(_mask, _type, _lvl, _fmt, args...)                       \
        do {                                                            \
                if ((_mask) & (_type))                                  \
                        printk(_lvl "PPPOL2TP: " _fmt, ##args);         \
        } while(0)

/* Number of bytes to build transmit L2TP headers.
 * Unfortunately the size is different depending on whether sequence numbers
 * are enabled.
 */
#define PPPOL2TP_L2TP_HDR_SIZE_SEQ              10
#define PPPOL2TP_L2TP_HDR_SIZE_NOSEQ            6

struct pppol2tp_tunnel;

/* Describes a session. It is the sk_user_data field in the PPPoL2TP
 * socket. Contains information to determine incoming packets and transmit
 * outgoing ones.
 */
struct pppol2tp_session
{
        int                     magic;          /* should be
                                                 * L2TP_SESSION_MAGIC */
        int                     owner;          /* pid that opened the socket */

        struct sock             *sock;          /* Pointer to the session
                                                 * PPPoX socket */
        struct sock             *tunnel_sock;   /* Pointer to the tunnel UDP
                                                 * socket */

        struct pppol2tp_addr    tunnel_addr;    /* Description of tunnel */

        struct pppol2tp_tunnel  *tunnel;        /* back pointer to tunnel
                                                 * context */

        char                    name[20];       /* "sess xxxxx/yyyyy", where
                                                 * x=tunnel_id, y=session_id */
        int                     mtu;
        int                     mru;
        int                     flags;          /* accessed by PPPIOCGFLAGS.
                                                 * Unused. */
        unsigned                recv_seq:1;     /* expect receive packets with
                                                 * sequence numbers? */
        unsigned                send_seq:1;     /* send packets with sequence
                                                 * numbers? */
        unsigned                lns_mode:1;     /* behave as LNS? LAC enables
                                                 * sequence numbers under
                                                 * control of LNS. */
        int                     debug;          /* bitmask of debug message
                                                 * categories */
        int                     reorder_timeout; /* configured reorder timeout
                                                  * (in jiffies) */
        u16                     nr;             /* session NR state (receive) */
        u16                     ns;             /* session NR state (send) */
        struct sk_buff_head     reorder_q;      /* receive reorder queue */
        struct pppol2tp_ioc_stats stats;
        struct hlist_node       hlist;          /* Hash list node */
};

/* The sk_user_data field of the tunnel's UDP socket. It contains info to track
 * all the associated sessions so incoming packets can be sorted out
 */
struct pppol2tp_tunnel
{
        int                     magic;          /* Should be L2TP_TUNNEL_MAGIC */
        rwlock_t                hlist_lock;     /* protect session_hlist */
        struct hlist_head       session_hlist[PPPOL2TP_HASH_SIZE];
                                                /* hashed list of sessions,
                                                 * hashed by id */
        int                     debug;          /* bitmask of debug message
                                                 * categories */
        char                    name[12];       /* "tunl xxxxx" */
        struct pppol2tp_ioc_stats stats;

        void (*old_sk_destruct)(struct sock *);

        struct sock             *sock;          /* Parent socket */
        struct list_head        list;           /* Keep a list of all open
                                                 * prepared sockets */

        atomic_t                ref_count;
};

/* Private data stored for received packets in the skb.
 */
struct pppol2tp_skb_cb {
        u16                     ns;
        u16                     nr;
        u16                     has_seq;
        u16                     length;
        unsigned long           expires;
};

#define PPPOL2TP_SKB_CB(skb)    ((struct pppol2tp_skb_cb *) &skb->cb[sizeof(struct inet_skb_parm)])

static int pppol2tp_xmit(struct ppp_channel *chan, struct sk_buff *skb);
static void pppol2tp_tunnel_free(struct pppol2tp_tunnel *tunnel);

static atomic_t pppol2tp_tunnel_count;
static atomic_t pppol2tp_session_count;
static struct ppp_channel_ops pppol2tp_chan_ops = { pppol2tp_xmit , NULL };
static struct proto_ops pppol2tp_ops;
static LIST_HEAD(pppol2tp_tunnel_list);
static DEFINE_RWLOCK(pppol2tp_tunnel_list_lock);

/* Helpers to obtain tunnel/session contexts from sockets.
 */
static inline struct pppol2tp_session *pppol2tp_sock_to_session(struct sock *sk)
{
        struct pppol2tp_session *session;

        if (sk == NULL)
                return NULL;

        session = (struct pppol2tp_session *)(sk->sk_user_data);
        if (session == NULL)
                return NULL;

        BUG_ON(session->magic != L2TP_SESSION_MAGIC);

        return session;
}

static inline struct pppol2tp_tunnel *pppol2tp_sock_to_tunnel(struct sock *sk)
{
        struct pppol2tp_tunnel *tunnel;

        if (sk == NULL)
                return NULL;

        tunnel = (struct pppol2tp_tunnel *)(sk->sk_user_data);
        if (tunnel == NULL)
                return NULL;

        BUG_ON(tunnel->magic != L2TP_TUNNEL_MAGIC);

        return tunnel;
}

/* Tunnel reference counts. Incremented per session that is added to
 * the tunnel.
 */
static inline void pppol2tp_tunnel_inc_refcount(struct pppol2tp_tunnel *tunnel)
{
        atomic_inc(&tunnel->ref_count);
}

static inline void pppol2tp_tunnel_dec_refcount(struct pppol2tp_tunnel *tunnel)
{
        if (atomic_dec_and_test(&tunnel->ref_count))
                pppol2tp_tunnel_free(tunnel);
}

/* Session hash list.
 * The session_id SHOULD be random according to RFC2661, but several
 * L2TP implementations (Cisco and Microsoft) use incrementing
 * session_ids.  So we do a real hash on the session_id, rather than a
 * simple bitmask.
 */
static inline struct hlist_head *
pppol2tp_session_id_hash(struct pppol2tp_tunnel *tunnel, u16 session_id)
{
        unsigned long hash_val = (unsigned long) session_id;
        return &tunnel->session_hlist[hash_long(hash_val, PPPOL2TP_HASH_BITS)];
}

/* Lookup a session by id
 */
static struct pppol2tp_session *
pppol2tp_session_find(struct pppol2tp_tunnel *tunnel, u16 session_id)
{
        struct hlist_head *session_list =
                pppol2tp_session_id_hash(tunnel, session_id);
        struct pppol2tp_session *session;
        struct hlist_node *walk;

        read_lock(&tunnel->hlist_lock);
        hlist_for_each_entry(session, walk, session_list, hlist) {
                if (session->tunnel_addr.s_session == session_id) {
                        read_unlock(&tunnel->hlist_lock);
                        return session;
                }
        }
        read_unlock(&tunnel->hlist_lock);

        return NULL;
}

/* Lookup a tunnel by id
 */
static struct pppol2tp_tunnel *pppol2tp_tunnel_find(u16 tunnel_id)
{
        struct pppol2tp_tunnel *tunnel = NULL;

        read_lock(&pppol2tp_tunnel_list_lock);
        list_for_each_entry(tunnel, &pppol2tp_tunnel_list, list) {
                if (tunnel->stats.tunnel_id == tunnel_id) {
                        read_unlock(&pppol2tp_tunnel_list_lock);
                        return tunnel;
                }
        }
        read_unlock(&pppol2tp_tunnel_list_lock);

        return NULL;
}

/*****************************************************************************
 * Receive data handling
 *****************************************************************************/

/* Queue a skb in order. We come here only if the skb has an L2TP sequence
 * number.
 */
static void pppol2tp_recv_queue_skb(struct pppol2tp_session *session, struct sk_buff *skb)
{
        struct sk_buff *skbp;
        u16 ns = PPPOL2TP_SKB_CB(skb)->ns;

        spin_lock(&session->reorder_q.lock);
        skb_queue_walk(&session->reorder_q, skbp) {
                if (PPPOL2TP_SKB_CB(skbp)->ns > ns) {
                        __skb_insert(skb, skbp->prev, skbp, &session->reorder_q);
                        PRINTK(session->debug, PPPOL2TP_MSG_SEQ, KERN_DEBUG,
                               "%s: pkt %hu, inserted before %hu, reorder_q len=%d\n",
                               session->name, ns, PPPOL2TP_SKB_CB(skbp)->ns,
                               skb_queue_len(&session->reorder_q));
                        session->stats.rx_oos_packets++;
                        goto out;
                }
        }

        __skb_queue_tail(&session->reorder_q, skb);

out:
        spin_unlock(&session->reorder_q.lock);
}

/* Dequeue a single skb.
 */
static void pppol2tp_recv_dequeue_skb(struct pppol2tp_session *session, struct sk_buff *skb)
{
        struct pppol2tp_tunnel *tunnel = session->tunnel;
        int length = PPPOL2TP_SKB_CB(skb)->length;
        struct sock *session_sock = NULL;

        /* We're about to requeue the skb, so unlink it and return resources
         * to its current owner (a socket receive buffer).
         */
        skb_unlink(skb, &session->reorder_q);
        skb_orphan(skb);

        tunnel->stats.rx_packets++;
        tunnel->stats.rx_bytes += length;
        session->stats.rx_packets++;
        session->stats.rx_bytes += length;

        if (PPPOL2TP_SKB_CB(skb)->has_seq) {
                /* Bump our Nr */
                session->nr++;
                PRINTK(session->debug, PPPOL2TP_MSG_SEQ, KERN_DEBUG,
                       "%s: updated nr to %hu\n", session->name, session->nr);
        }

        /* If the socket is bound, send it in to PPP's input queue. Otherwise
         * queue it on the session socket.
         */
        session_sock = session->sock;
        if (session_sock->sk_state & PPPOX_BOUND) {
                struct pppox_sock *po;
                PRINTK(session->debug, PPPOL2TP_MSG_DATA, KERN_DEBUG,
                       "%s: recv %d byte data frame, passing to ppp\n",
                       session->name, length);

                /* We need to forget all info related to the L2TP packet
                 * gathered in the skb as we are going to reuse the same
                 * skb for the inner packet.
                 * Namely we need to:
                 * - reset xfrm (IPSec) information as it applies to
                 *   the outer L2TP packet and not to the inner one
                 * - release the dst to force a route lookup on the inner
                 *   IP packet since skb->dst currently points to the dst
                 *   of the UDP tunnel
                 * - reset netfilter information as it doesn't apply
                 *   to the inner packet either
                 */
                secpath_reset(skb);
                dst_release(skb->dst);
                skb->dst = NULL;
                nf_reset(skb);

                po = pppox_sk(session_sock);
                ppp_input(&po->chan, skb);
        } else {
                PRINTK(session->debug, PPPOL2TP_MSG_DATA, KERN_INFO,
                       "%s: socket not bound\n", session->name);

                /* Not bound. Nothing we can do, so discard. */
                session->stats.rx_errors++;
                kfree_skb(skb);
        }

        sock_put(session->sock);
}

/* Dequeue skbs from the session's reorder_q, subject to packet order.
 * Skbs that have been in the queue for too long are simply discarded.
 */
static void pppol2tp_recv_dequeue(struct pppol2tp_session *session)
{
        struct sk_buff *skb;
        struct sk_buff *tmp;

        /* If the pkt at the head of the queue has the nr that we
         * expect to send up next, dequeue it and any other
         * in-sequence packets behind it.
         */
        spin_lock(&session->reorder_q.lock);
        skb_queue_walk_safe(&session->reorder_q, skb, tmp) {
                if (time_after(jiffies, PPPOL2TP_SKB_CB(skb)->expires)) {
                        session->stats.rx_seq_discards++;
                        session->stats.rx_errors++;
                        PRINTK(session->debug, PPPOL2TP_MSG_SEQ, KERN_DEBUG,
                               "%s: oos pkt %hu len %d discarded (too old), "
                               "waiting for %hu, reorder_q_len=%d\n",
                               session->name, PPPOL2TP_SKB_CB(skb)->ns,
                               PPPOL2TP_SKB_CB(skb)->length, session->nr,
                               skb_queue_len(&session->reorder_q));
                        __skb_unlink(skb, &session->reorder_q);
                        kfree_skb(skb);
                        continue;
                }

                if (PPPOL2TP_SKB_CB(skb)->has_seq) {
                        if (PPPOL2TP_SKB_CB(skb)->ns != session->nr) {
                                PRINTK(session->debug, PPPOL2TP_MSG_SEQ, KERN_DEBUG,
                                       "%s: holding oos pkt %hu len %d, "
                                       "waiting for %hu, reorder_q_len=%d\n",
                                       session->name, PPPOL2TP_SKB_CB(skb)->ns,
                                       PPPOL2TP_SKB_CB(skb)->length, session->nr,
                                       skb_queue_len(&session->reorder_q));
                                goto out;
                        }
                }
                spin_unlock(&session->reorder_q.lock);
                pppol2tp_recv_dequeue_skb(session, skb);
                spin_lock(&session->reorder_q.lock);
        }

out:
        spin_unlock(&session->reorder_q.lock);
}

/* Internal receive frame. Do the real work of receiving an L2TP data frame
 * here. The skb is not on a list when we get here.
 * Returns 0 if the packet was a data packet and was successfully passed on.
 * Returns 1 if the packet was not a good data packet and could not be
 * forwarded.  All such packets are passed up to userspace to deal with.
 */
static int pppol2tp_recv_core(struct sock *sock, struct sk_buff *skb)
{
        struct pppol2tp_session *session = NULL;
        struct pppol2tp_tunnel *tunnel;
        unsigned char *ptr, *optr;
        u16 hdrflags;
        u16 tunnel_id, session_id;
        int length;
        int offset;

        tunnel = pppol2tp_sock_to_tunnel(sock);
        if (tunnel == NULL)
                goto no_tunnel;

        /* UDP always verifies the packet length. */
        __skb_pull(skb, sizeof(struct udphdr));

        /* Short packet? */
        if (!pskb_may_pull(skb, 12)) {
                PRINTK(tunnel->debug, PPPOL2TP_MSG_DATA, KERN_INFO,
                       "%s: recv short packet (len=%d)\n", tunnel->name, skb->len);
                goto error;
        }

        /* Point to L2TP header */
        optr = ptr = skb->data;

        /* Get L2TP header flags */
        hdrflags = ntohs(*(__be16*)ptr);

        /* Trace packet contents, if enabled */
        if (tunnel->debug & PPPOL2TP_MSG_DATA) {
                length = min(16u, skb->len);
                if (!pskb_may_pull(skb, length))
                        goto error;

                printk(KERN_DEBUG "%s: recv: ", tunnel->name);

                offset = 0;
                do {
                        printk(" %02X", ptr[offset]);
                } while (++offset < length);

                printk("\n");
        }

        /* Get length of L2TP packet */
        length = skb->len;

        /* If type is control packet, it is handled by userspace. */
        if (hdrflags & L2TP_HDRFLAG_T) {
                PRINTK(tunnel->debug, PPPOL2TP_MSG_DATA, KERN_DEBUG,
                       "%s: recv control packet, len=%d\n", tunnel->name, length);
                goto error;
        }

        /* Skip flags */
        ptr += 2;

        /* If length is present, skip it */
        if (hdrflags & L2TP_HDRFLAG_L)
                ptr += 2;

        /* Extract tunnel and session ID */
        tunnel_id = ntohs(*(__be16 *) ptr);
        ptr += 2;
        session_id = ntohs(*(__be16 *) ptr);
        ptr += 2;

        /* Find the session context */
        session = pppol2tp_session_find(tunnel, session_id);
        if (!session) {
                /* Not found? Pass to userspace to deal with */
                PRINTK(tunnel->debug, PPPOL2TP_MSG_DATA, KERN_INFO,
                       "%s: no socket found (%hu/%hu). Passing up.\n",
                       tunnel->name, tunnel_id, session_id);
                goto error;
        }
        sock_hold(session->sock);

        /* The ref count on the socket was increased by the above call since
         * we now hold a pointer to the session. Take care to do sock_put()
         * when exiting this function from now on...
         */

        /* Handle the optional sequence numbers.  If we are the LAC,
         * enable/disable sequence numbers under the control of the LNS.  If
         * no sequence numbers present but we were expecting them, discard
         * frame.
         */
        if (hdrflags & L2TP_HDRFLAG_S) {
                u16 ns, nr;
                ns = ntohs(*(__be16 *) ptr);
                ptr += 2;
                nr = ntohs(*(__be16 *) ptr);
                ptr += 2;

                /* Received a packet with sequence numbers. If we're the LNS,
                 * check if we sre sending sequence numbers and if not,
                 * configure it so.
                 */
                if ((!session->lns_mode) && (!session->send_seq)) {
                        PRINTK(session->debug, PPPOL2TP_MSG_SEQ, KERN_INFO,
                               "%s: requested to enable seq numbers by LNS\n",
                               session->name);
                        session->send_seq = -1;
                }

                /* Store L2TP info in the skb */
                PPPOL2TP_SKB_CB(skb)->ns = ns;
                PPPOL2TP_SKB_CB(skb)->nr = nr;
                PPPOL2TP_SKB_CB(skb)->has_seq = 1;

                PRINTK(session->debug, PPPOL2TP_MSG_SEQ, KERN_DEBUG,
                       "%s: recv data ns=%hu, nr=%hu, session nr=%hu\n",
                       session->name, ns, nr, session->nr);
        } else {
                /* No sequence numbers.
                 * If user has configured mandatory sequence numbers, discard.
                 */
                if (session->recv_seq) {
                        PRINTK(session->debug, PPPOL2TP_MSG_SEQ, KERN_WARNING,
                               "%s: recv data has no seq numbers when required. "
                               "Discarding\n", session->name);
                        session->stats.rx_seq_discards++;
                        goto discard;
                }

                /* If we're the LAC and we're sending sequence numbers, the
                 * LNS has requested that we no longer send sequence numbers.
                 * If we're the LNS and we're sending sequence numbers, the
                 * LAC is broken. Discard the frame.
                 */
                if ((!session->lns_mode) && (session->send_seq)) {
                        PRINTK(session->debug, PPPOL2TP_MSG_SEQ, KERN_INFO,
                               "%s: requested to disable seq numbers by LNS\n",
                               session->name);
                        session->send_seq = 0;
                } else if (session->send_seq) {
                        PRINTK(session->debug, PPPOL2TP_MSG_SEQ, KERN_WARNING,
                               "%s: recv data has no seq numbers when required. "
                               "Discarding\n", session->name);
                        session->stats.rx_seq_discards++;
                        goto discard;
                }

                /* Store L2TP info in the skb */
                PPPOL2TP_SKB_CB(skb)->has_seq = 0;
        }

        /* If offset bit set, skip it. */
        if (hdrflags & L2TP_HDRFLAG_O) {
                offset = ntohs(*(__be16 *)ptr);
                ptr += 2 + offset;
        }

        offset = ptr - optr;
        if (!pskb_may_pull(skb, offset))
                goto discard;

        __skb_pull(skb, offset);

        /* Skip PPP header, if present.  In testing, Microsoft L2TP clients
         * don't send the PPP header (PPP header compression enabled), but
         * other clients can include the header. So we cope with both cases
         * here. The PPP header is always FF03 when using L2TP.
         *
         * Note that skb->data[] isn't dereferenced from a u16 ptr here since
         * the field may be unaligned.
         */
        if (!pskb_may_pull(skb, 2))
                goto discard;

        if ((skb->data[0] == 0xff) && (skb->data[1] == 0x03))
                skb_pull(skb, 2);

        /* Prepare skb for adding to the session's reorder_q.  Hold
         * packets for max reorder_timeout or 1 second if not
         * reordering.
         */
        PPPOL2TP_SKB_CB(skb)->length = length;
        PPPOL2TP_SKB_CB(skb)->expires = jiffies +
                (session->reorder_timeout ? session->reorder_timeout : HZ);

        /* Add packet to the session's receive queue. Reordering is done here, if
         * enabled. Saved L2TP protocol info is stored in skb->sb[].
         */
        if (PPPOL2TP_SKB_CB(skb)->has_seq) {
                if (session->reorder_timeout != 0) {
                        /* Packet reordering enabled. Add skb to session's
                         * reorder queue, in order of ns.
                         */
                        pppol2tp_recv_queue_skb(session, skb);
                } else {
                        /* Packet reordering disabled. Discard out-of-sequence
                         * packets
                         */
                        if (PPPOL2TP_SKB_CB(skb)->ns != session->nr) {
                                session->stats.rx_seq_discards++;
                                PRINTK(session->debug, PPPOL2TP_MSG_SEQ, KERN_DEBUG,
                                       "%s: oos pkt %hu len %d discarded, "
                                       "waiting for %hu, reorder_q_len=%d\n",
                                       session->name, PPPOL2TP_SKB_CB(skb)->ns,
                                       PPPOL2TP_SKB_CB(skb)->length, session->nr,
                                       skb_queue_len(&session->reorder_q));
                                goto discard;
                        }
                        skb_queue_tail(&session->reorder_q, skb);
                }
        } else {
                /* No sequence numbers. Add the skb to the tail of the
                 * reorder queue. This ensures that it will be
                 * delivered after all previous sequenced skbs.
                 */
                skb_queue_tail(&session->reorder_q, skb);
        }

        /* Try to dequeue as many skbs from reorder_q as we can. */
        pppol2tp_recv_dequeue(session);

        return 0;

discard:
        session->stats.rx_errors++;
        kfree_skb(skb);
        sock_put(session->sock);

        return 0;

error:
        /* Put UDP header back */
        __skb_push(skb, sizeof(struct udphdr));

no_tunnel:
        return 1;
}

/* UDP encapsulation receive handler. See net/ipv4/udp.c.
 * Return codes:
 * 0 : success.
 * <0: error
 * >0: skb should be passed up to userspace as UDP.
 */
static int pppol2tp_udp_encap_recv(struct sock *sk, struct sk_buff *skb)
{
        struct pppol2tp_tunnel *tunnel;

        tunnel = pppol2tp_sock_to_tunnel(sk);
        if (tunnel == NULL)
                goto pass_up;

        PRINTK(tunnel->debug, PPPOL2TP_MSG_DATA, KERN_DEBUG,
               "%s: received %d bytes\n", tunnel->name, skb->len);

        if (pppol2tp_recv_core(sk, skb))
                goto pass_up;

        return 0;

pass_up:
        return 1;
}

/* Receive message. This is the recvmsg for the PPPoL2TP socket.
 */
static int pppol2tp_recvmsg(struct kiocb *iocb, struct socket *sock,
                            struct msghdr *msg, size_t len,
                            int flags)
{
        int err;
        struct sk_buff *skb;
        struct sock *sk = sock->sk;

        err = -EIO;
        if (sk->sk_state & PPPOX_BOUND)
                goto end;

        msg->msg_namelen = 0;

        err = 0;
        skb = skb_recv_datagram(sk, flags & ~MSG_DONTWAIT,
                                flags & MSG_DONTWAIT, &err);
        if (skb) {
                err = memcpy_toiovec(msg->msg_iov, (unsigned char *) skb->data,
                                     skb->len);
                if (err < 0)
                        goto do_skb_free;
                err = skb->len;
        }
do_skb_free:
        kfree_skb(skb);
end:
        return err;
}

/************************************************************************
 * Transmit handling
 ***********************************************************************/

/* Tell how big L2TP headers are for a particular session. This
 * depends on whether sequence numbers are being used.
 */
static inline int pppol2tp_l2tp_header_len(struct pppol2tp_session *session)
{
        if (session->send_seq)
                return PPPOL2TP_L2TP_HDR_SIZE_SEQ;

        return PPPOL2TP_L2TP_HDR_SIZE_NOSEQ;
}

/* Build an L2TP header for the session into the buffer provided.
 */
static void pppol2tp_build_l2tp_header(struct pppol2tp_session *session,
                                       void *buf)
{
        __be16 *bufp = buf;
        u16 flags = L2TP_HDR_VER;

        if (session->send_seq)
                flags |= L2TP_HDRFLAG_S;

        /* Setup L2TP header.
         * FIXME: Can this ever be unaligned? Is direct dereferencing of
         * 16-bit header fields safe here for all architectures?
         */
        *bufp++ = htons(flags);
        *bufp++ = htons(session->tunnel_addr.d_tunnel);
        *bufp++ = htons(session->tunnel_addr.d_session);
        if (session->send_seq) {
                *bufp++ = htons(session->ns);
                *bufp++ = 0;
                session->ns++;
                PRINTK(session->debug, PPPOL2TP_MSG_SEQ, KERN_DEBUG,
                       "%s: updated ns to %hu\n", session->name, session->ns);
        }
}

/* This is the sendmsg for the PPPoL2TP pppol2tp_session socket.  We come here
 * when a user application does a sendmsg() on the session socket. L2TP and
 * PPP headers must be inserted into the user's data.
 */
static int pppol2tp_sendmsg(struct kiocb *iocb, struct socket *sock, struct msghdr *m,
                            size_t total_len)
{
        static const unsigned char ppph[2] = { 0xff, 0x03 };
        struct sock *sk = sock->sk;
        struct inet_sock *inet;
        __wsum csum = 0;
        struct sk_buff *skb;
        int error;
        int hdr_len;
        struct pppol2tp_session *session;
        struct pppol2tp_tunnel *tunnel;
        struct udphdr *uh;
        unsigned int len;

        error = -ENOTCONN;
        if (sock_flag(sk, SOCK_DEAD) || !(sk->sk_state & PPPOX_CONNECTED))
                goto error;

        /* Get session and tunnel contexts */
        error = -EBADF;
        session = pppol2tp_sock_to_session(sk);
        if (session == NULL)
                goto error;

        tunnel = pppol2tp_sock_to_tunnel(session->tunnel_sock);
        if (tunnel == NULL)
                goto error;

        /* What header length is configured for this session? */
        hdr_len = pppol2tp_l2tp_header_len(session);

        /* Allocate a socket buffer */
        error = -ENOMEM;
        skb = sock_wmalloc(sk, NET_SKB_PAD + sizeof(struct iphdr) +
                           sizeof(struct udphdr) + hdr_len +
                           sizeof(ppph) + total_len,
                           0, GFP_KERNEL);
        if (!skb)
                goto error;

        /* Reserve space for headers. */
        skb_reserve(skb, NET_SKB_PAD);
        skb_reset_network_header(skb);
        skb_reserve(skb, sizeof(struct iphdr));
        skb_reset_transport_header(skb);

        /* Build UDP header */
        inet = inet_sk(session->tunnel_sock);
        uh = (struct udphdr *) skb->data;
        uh->source = inet->sport;
        uh->dest = inet->dport;
        uh->len = htons(hdr_len + sizeof(ppph) + total_len);
        uh->check = 0;
        skb_put(skb, sizeof(struct udphdr));

        /* Build L2TP header */
        pppol2tp_build_l2tp_header(session, skb->data);
        skb_put(skb, hdr_len);

        /* Add PPP header */
        skb->data[0] = ppph[0];
        skb->data[1] = ppph[1];
        skb_put(skb, 2);

        /* Copy user data into skb */
        error = memcpy_fromiovec(skb->data, m->msg_iov, total_len);
        if (error < 0) {
                kfree_skb(skb);
                goto error;
        }
        skb_put(skb, total_len);

        /* Calculate UDP checksum if configured to do so */
        if (session->tunnel_sock->sk_no_check != UDP_CSUM_NOXMIT)
                csum = udp_csum_outgoing(sk, skb);

        /* Debug */
        if (session->send_seq)
                PRINTK(session->debug, PPPOL2TP_MSG_DATA, KERN_DEBUG,
                       "%s: send %Zd bytes, ns=%hu\n", session->name,
                       total_len, session->ns - 1);
        else
                PRINTK(session->debug, PPPOL2TP_MSG_DATA, KERN_DEBUG,
                       "%s: send %Zd bytes\n", session->name, total_len);

        if (session->debug & PPPOL2TP_MSG_DATA) {
                int i;
                unsigned char *datap = skb->data;

                printk(KERN_DEBUG "%s: xmit:", session->name);
                for (i = 0; i < total_len; i++) {
                        printk(" %02X", *datap++);
                        if (i == 15) {
                                printk(" ...");
                                break;
                        }
                }
                printk("\n");
        }

        /* Queue the packet to IP for output */
        len = skb->len;
        error = ip_queue_xmit(skb, 1);

        /* Update stats */
        if (error >= 0) {
                tunnel->stats.tx_packets++;
                tunnel->stats.tx_bytes += len;
                session->stats.tx_packets++;
                session->stats.tx_bytes += len;
        } else {
                tunnel->stats.tx_errors++;
                session->stats.tx_errors++;
        }

error:
        return error;
}

/* Transmit function called by generic PPP driver.  Sends PPP frame
 * over PPPoL2TP socket.
 *
 * This is almost the same as pppol2tp_sendmsg(), but rather than
 * being called with a msghdr from userspace, it is called with a skb
 * from the kernel.
 *
 * The supplied skb from ppp doesn't have enough headroom for the
 * insertion of L2TP, UDP and IP headers so we need to allocate more
 * headroom in the skb. This will create a cloned skb. But we must be
 * careful in the error case because the caller will expect to free
 * the skb it supplied, not our cloned skb. So we take care to always
 * leave the original skb unfreed if we return an error.
 */
static int pppol2tp_xmit(struct ppp_channel *chan, struct sk_buff *skb)
{
        static const u8 ppph[2] = { 0xff, 0x03 };
        struct sock *sk = (struct sock *) chan->private;
        struct sock *sk_tun;
        int hdr_len;
        struct pppol2tp_session *session;
        struct pppol2tp_tunnel *tunnel;
        int rc;
        int headroom;
        int data_len = skb->len;
        struct inet_sock *inet;
        __wsum csum = 0;
        struct udphdr *uh;
        unsigned int len;

        if (sock_flag(sk, SOCK_DEAD) || !(sk->sk_state & PPPOX_CONNECTED))
                goto abort;

        /* Get session and tunnel contexts from the socket */
        session = pppol2tp_sock_to_session(sk);
        if (session == NULL)
                goto abort;

        sk_tun = session->tunnel_sock;
        if (sk_tun == NULL)
                goto abort;
        tunnel = pppol2tp_sock_to_tunnel(sk_tun);
        if (tunnel == NULL)
                goto abort;

        /* What header length is configured for this session? */
        hdr_len = pppol2tp_l2tp_header_len(session);

        /* Check that there's enough headroom in the skb to insert IP,
         * UDP and L2TP and PPP headers. If not enough, expand it to
         * make room. Note that a new skb (or a clone) is
         * allocated. If we return an error from this point on, make
         * sure we free the new skb but do not free the original skb
         * since that is done by the caller for the error case.
         */
        headroom = NET_SKB_PAD + sizeof(struct iphdr) +
                sizeof(struct udphdr) + hdr_len + sizeof(ppph);
        if (skb_cow_head(skb, headroom))
                goto abort;

        /* Setup PPP header */
        __skb_push(skb, sizeof(ppph));
        skb->data[0] = ppph[0];
        skb->data[1] = ppph[1];

        /* Setup L2TP header */
        pppol2tp_build_l2tp_header(session, __skb_push(skb, hdr_len));

        /* Setup UDP header */
        inet = inet_sk(sk_tun);
        __skb_push(skb, sizeof(*uh));
        skb_reset_transport_header(skb);
        uh = udp_hdr(skb);
        uh->source = inet->sport;
        uh->dest = inet->dport;
        uh->len = htons(sizeof(struct udphdr) + hdr_len + sizeof(ppph) + data_len);
        uh->check = 0;

        /* *BROKEN* Calculate UDP checksum if configured to do so */
        if (sk_tun->sk_no_check != UDP_CSUM_NOXMIT)
                csum = udp_csum_outgoing(sk_tun, skb);

        /* Debug */
        if (session->send_seq)
                PRINTK(session->debug, PPPOL2TP_MSG_DATA, KERN_DEBUG,
                       "%s: send %d bytes, ns=%hu\n", session->name,
                       data_len, session->ns - 1);
        else
                PRINTK(session->debug, PPPOL2TP_MSG_DATA, KERN_DEBUG,
                       "%s: send %d bytes\n", session->name, data_len);

        if (session->debug & PPPOL2TP_MSG_DATA) {
                int i;
                unsigned char *datap = skb->data;

                printk(KERN_DEBUG "%s: xmit:", session->name);
                for (i = 0; i < data_len; i++) {
                        printk(" %02X", *datap++);
                        if (i == 31) {
                                printk(" ...");
                                break;
                        }
                }
                printk("\n");
        }

        memset(&(IPCB(skb)->opt), 0, sizeof(IPCB(skb)->opt));
        IPCB(skb)->flags &= ~(IPSKB_XFRM_TUNNEL_SIZE | IPSKB_XFRM_TRANSFORMED |
                              IPSKB_REROUTED);
        nf_reset(skb);

        /* Get routing info from the tunnel socket */
        dst_release(skb->dst);
        skb->dst = sk_dst_get(sk_tun);
        skb_orphan(skb);
        skb->sk = sk_tun;

        /* Queue the packet to IP for output */
        len = skb->len;
        rc = ip_queue_xmit(skb, 1);

        /* Update stats */
        if (rc >= 0) {
                tunnel->stats.tx_packets++;
                tunnel->stats.tx_bytes += len;
                session->stats.tx_packets++;
                session->stats.tx_bytes += len;
        } else {
                tunnel->stats.tx_errors++;
                session->stats.tx_errors++;
        }

        return 1;

abort:
        /* Free the original skb */
        kfree_skb(skb);
        return 1;
}

/*****************************************************************************
 * Session (and tunnel control) socket create/destroy.
 *****************************************************************************/

/* When the tunnel UDP socket is closed, all the attached sockets need to go
 * too.
 */
static void pppol2tp_tunnel_closeall(struct pppol2tp_tunnel *tunnel)
{
        int hash;
        struct hlist_node *walk;
        struct hlist_node *tmp;
        struct pppol2tp_session *session;
        struct sock *sk;

        if (tunnel == NULL)
                BUG();

        PRINTK(tunnel->debug, PPPOL2TP_MSG_CONTROL, KERN_INFO,
               "%s: closing all sessions...\n", tunnel->name);

        write_lock(&tunnel->hlist_lock);
        for (hash = 0; hash < PPPOL2TP_HASH_SIZE; hash++) {
again:
                hlist_for_each_safe(walk, tmp, &tunnel->session_hlist[hash]) {
                        session = hlist_entry(walk, struct pppol2tp_session, hlist);

                        sk = session->sock;

                        PRINTK(session->debug, PPPOL2TP_MSG_CONTROL, KERN_INFO,
                               "%s: closing session\n", session->name);

                        hlist_del_init(&session->hlist);

                        /* Since we should hold the sock lock while
                         * doing any unbinding, we need to release the
                         * lock we're holding before taking that lock.
                         * Hold a reference to the sock so it doesn't
                         * disappear as we're jumping between locks.
                         */
                        sock_hold(sk);
                        write_unlock(&tunnel->hlist_lock);
                        lock_sock(sk);

                        if (sk->sk_state & (PPPOX_CONNECTED | PPPOX_BOUND)) {
                                pppox_unbind_sock(sk);
                                sk->sk_state = PPPOX_DEAD;
                                sk->sk_state_change(sk);
                        }

                        /* Purge any queued data */
                        skb_queue_purge(&sk->sk_receive_queue);
                        skb_queue_purge(&sk->sk_write_queue);
                        skb_queue_purge(&session->reorder_q);

                        release_sock(sk);
                        sock_put(sk);

                        /* Now restart from the beginning of this hash
                         * chain.  We always remove a session from the
                         * list so we are guaranteed to make forward
                         * progress.
                         */
                        write_lock(&tunnel->hlist_lock);
                        goto again;
                }
        }
        write_unlock(&tunnel->hlist_lock);
}

/* Really kill the tunnel.
 * Come here only when all sessions have been cleared from the tunnel.
 */
static void pppol2tp_tunnel_free(struct pppol2tp_tunnel *tunnel)
{
        /* Remove from socket list */
        write_lock(&pppol2tp_tunnel_list_lock);
        list_del_init(&tunnel->list);
        write_unlock(&pppol2tp_tunnel_list_lock);

        atomic_dec(&pppol2tp_tunnel_count);
        kfree(tunnel);
}

/* Tunnel UDP socket destruct hook.
 * The tunnel context is deleted only when all session sockets have been
 * closed.
 */
static void pppol2tp_tunnel_destruct(struct sock *sk)
{
        struct pppol2tp_tunnel *tunnel;

        tunnel = pppol2tp_sock_to_tunnel(sk);
        if (tunnel == NULL)
                goto end;

        PRINTK(tunnel->debug, PPPOL2TP_MSG_CONTROL, KERN_INFO,
               "%s: closing...\n", tunnel->name);

        /* Close all sessions */
        pppol2tp_tunnel_closeall(tunnel);

        /* No longer an encapsulation socket. See net/ipv4/udp.c */
        (udp_sk(sk))->encap_type = 0;
        (udp_sk(sk))->encap_rcv = NULL;

        /* Remove hooks into tunnel socket */
        tunnel->sock = NULL;
        sk->sk_destruct = tunnel->old_sk_destruct;
        sk->sk_user_data = NULL;

        /* Call original (UDP) socket descructor */
        if (sk->sk_destruct != NULL)
                (*sk->sk_destruct)(sk);

        pppol2tp_tunnel_dec_refcount(tunnel);

end:
        return;
}

/* Really kill the session socket. (Called from sock_put() if
 * refcnt == 0.)
 */
static void pppol2tp_session_destruct(struct sock *sk)
{
        struct pppol2tp_session *session = NULL;

        if (sk->sk_user_data != NULL) {
                struct pppol2tp_tunnel *tunnel;

                session = pppol2tp_sock_to_session(sk);
                if (session == NULL)
                        goto out;

                /* Don't use pppol2tp_sock_to_tunnel() here to
                 * get the tunnel context because the tunnel
                 * socket might have already been closed (its
                 * sk->sk_user_data will be NULL) so use the
                 * session's private tunnel ptr instead.
                 */
                tunnel = session->tunnel;
                if (tunnel != NULL) {
                        BUG_ON(tunnel->magic != L2TP_TUNNEL_MAGIC);

                        /* If session_id is zero, this is a null
                         * session context, which was created for a
                         * socket that is being used only to manage
                         * tunnels.
                         */
                        if (session->tunnel_addr.s_session != 0) {
                                /* Delete the session socket from the
                                 * hash
                                 */
                                write_lock(&tunnel->hlist_lock);
                                hlist_del_init(&session->hlist);
                                write_unlock(&tunnel->hlist_lock);

                                atomic_dec(&pppol2tp_session_count);
                        }

                        /* This will delete the tunnel context if this
                         * is the last session on the tunnel.
                         */
                        session->tunnel = NULL;
                        session->tunnel_sock = NULL;
                        pppol2tp_tunnel_dec_refcount(tunnel);
                }
        }

        kfree(session);
out:
        return;
}

/* Called when the PPPoX socket (session) is closed.
 */
static int pppol2tp_release(struct socket *sock)
{
        struct sock *sk = sock->sk;
        int error;

        if (!sk)
                return 0;

        error = -EBADF;
        lock_sock(sk);
        if (sock_flag(sk, SOCK_DEAD) != 0)
                goto error;

        pppox_unbind_sock(sk);

        /* Signal the death of the socket. */
        sk->sk_state = PPPOX_DEAD;
        sock_orphan(sk);
        sock->sk = NULL;

        /* Purge any queued data */
        skb_queue_purge(&sk->sk_receive_queue);
        skb_queue_purge(&sk->sk_write_queue);

        release_sock(sk);

        /* This will delete the session context via
         * pppol2tp_session_destruct() if the socket's refcnt drops to
         * zero.
         */
        sock_put(sk);

        return 0;

error:
        release_sock(sk);
        return error;
}

/* Internal function to prepare a tunnel (UDP) socket to have PPPoX
 * sockets attached to it.
 */
static struct sock *pppol2tp_prepare_tunnel_socket(int fd, u16 tunnel_id,
                                                   int *error)
{
        int err;
        struct socket *sock = NULL;
        struct sock *sk;
        struct pppol2tp_tunnel *tunnel;
        struct sock *ret = NULL;

        /* Get the tunnel UDP socket from the fd, which was opened by
         * the userspace L2TP daemon.
         */
        err = -EBADF;
        sock = sockfd_lookup(fd, &err);
        if (!sock) {
                PRINTK(-1, PPPOL2TP_MSG_CONTROL, KERN_ERR,
                       "tunl %hu: sockfd_lookup(fd=%d) returned %d\n",
                       tunnel_id, fd, err);
                goto err;
        }

        sk = sock->sk;

        /* Quick sanity checks */
        err = -EPROTONOSUPPORT;
        if (sk->sk_protocol != IPPROTO_UDP) {
                PRINTK(-1, PPPOL2TP_MSG_CONTROL, KERN_ERR,
                       "tunl %hu: fd %d wrong protocol, got %d, expected %d\n",
                       tunnel_id, fd, sk->sk_protocol, IPPROTO_UDP);
                goto err;
        }
        err = -EAFNOSUPPORT;
        if (sock->ops->family != AF_INET) {
                PRINTK(-1, PPPOL2TP_MSG_CONTROL, KERN_ERR,
                       "tunl %hu: fd %d wrong family, got %d, expected %d\n",
                       tunnel_id, fd, sock->ops->family, AF_INET);
                goto err;
        }

        err = -ENOTCONN;

        /* Check if this socket has already been prepped */
        tunnel = (struct pppol2tp_tunnel *)sk->sk_user_data;
        if (tunnel != NULL) {
                /* User-data field already set */
                err = -EBUSY;
                BUG_ON(tunnel->magic != L2TP_TUNNEL_MAGIC);

                /* This socket has already been prepped */
                ret = tunnel->sock;
                goto out;
        }

        /* This socket is available and needs prepping. Create a new tunnel
         * context and init it.
         */
        sk->sk_user_data = tunnel = kzalloc(sizeof(struct pppol2tp_tunnel), GFP_KERNEL);
        if (sk->sk_user_data == NULL) {
                err = -ENOMEM;
                goto err;
        }

        tunnel->magic = L2TP_TUNNEL_MAGIC;
        sprintf(&tunnel->name[0], "tunl %hu", tunnel_id);

        tunnel->stats.tunnel_id = tunnel_id;
        tunnel->debug = PPPOL2TP_DEFAULT_DEBUG_FLAGS;

        /* Hook on the tunnel socket destructor so that we can cleanup
         * if the tunnel socket goes away.
         */
        tunnel->old_sk_destruct = sk->sk_destruct;
        sk->sk_destruct = &pppol2tp_tunnel_destruct;

        tunnel->sock = sk;
        sk->sk_allocation = GFP_ATOMIC;

        /* Misc init */
        rwlock_init(&tunnel->hlist_lock);

        /* Add tunnel to our list */
        INIT_LIST_HEAD(&tunnel->list);
        write_lock(&pppol2tp_tunnel_list_lock);
        list_add(&tunnel->list, &pppol2tp_tunnel_list);
        write_unlock(&pppol2tp_tunnel_list_lock);
        atomic_inc(&pppol2tp_tunnel_count);

        /* Bump the reference count. The tunnel context is deleted
         * only when this drops to zero.
         */
        pppol2tp_tunnel_inc_refcount(tunnel);

        /* Mark socket as an encapsulation socket. See net/ipv4/udp.c */
        (udp_sk(sk))->encap_type = UDP_ENCAP_L2TPINUDP;
        (udp_sk(sk))->encap_rcv = pppol2tp_udp_encap_recv;

        ret = tunnel->sock;

        *error = 0;
out:
        if (sock)
                sockfd_put(sock);

        return ret;

err:
        *error = err;
        goto out;
}

static struct proto pppol2tp_sk_proto = {
        .name     = "PPPOL2TP",
        .owner    = THIS_MODULE,
        .obj_size = sizeof(struct pppox_sock),
};

/* socket() handler. Initialize a new struct sock.
 */
static int pppol2tp_create(struct net *net, struct socket *sock)
{
        int error = -ENOMEM;
        struct sock *sk;

        sk = sk_alloc(net, PF_PPPOX, GFP_KERNEL, &pppol2tp_sk_proto);
        if (!sk)
                goto out;

        sock_init_data(sock, sk);

        sock->state  = SS_UNCONNECTED;
        sock->ops    = &pppol2tp_ops;

        sk->sk_backlog_rcv = pppol2tp_recv_core;
        sk->sk_protocol    = PX_PROTO_OL2TP;
        sk->sk_family      = PF_PPPOX;
        sk->sk_state       = PPPOX_NONE;
        sk->sk_type        = SOCK_STREAM;
        sk->sk_destruct    = pppol2tp_session_destruct;

        error = 0;

out:
        return error;
}

/* connect() handler. Attach a PPPoX socket to a tunnel UDP socket
 */
static int pppol2tp_connect(struct socket *sock, struct sockaddr *uservaddr,
                            int sockaddr_len, int flags)
{
        struct sock *sk = sock->sk;
        struct sockaddr_pppol2tp *sp = (struct sockaddr_pppol2tp *) uservaddr;
        struct pppox_sock *po = pppox_sk(sk);
        struct sock *tunnel_sock = NULL;
        struct pppol2tp_session *session = NULL;
        struct pppol2tp_tunnel *tunnel;
        struct dst_entry *dst;
        int error = 0;

        lock_sock(sk);

        error = -EINVAL;
        if (sp->sa_protocol != PX_PROTO_OL2TP)
                goto end;

        /* Check for already bound sockets */
        error = -EBUSY;
        if (sk->sk_state & PPPOX_CONNECTED)
                goto end;

        /* We don't supporting rebinding anyway */
        error = -EALREADY;
        if (sk->sk_user_data)
                goto end; /* socket is already attached */

        /* Don't bind if s_tunnel is 0 */
        error = -EINVAL;
        if (sp->pppol2tp.s_tunnel == 0)
                goto end;

        /* Special case: prepare tunnel socket if s_session and
         * d_session is 0. Otherwise look up tunnel using supplied
         * tunnel id.
         */
        if ((sp->pppol2tp.s_session == 0) && (sp->pppol2tp.d_session == 0)) {
                tunnel_sock = pppol2tp_prepare_tunnel_socket(sp->pppol2tp.fd,
                                                             sp->pppol2tp.s_tunnel,
                                                             &error);
                if (tunnel_sock == NULL)
                        goto end;

                tunnel = tunnel_sock->sk_user_data;
        } else {
                tunnel = pppol2tp_tunnel_find(sp->pppol2tp.s_tunnel);

                /* Error if we can't find the tunnel */
                error = -ENOENT;
                if (tunnel == NULL)
                        goto end;

                tunnel_sock = tunnel->sock;
        }

        /* Check that this session doesn't already exist */
        error = -EEXIST;
        session = pppol2tp_session_find(tunnel, sp->pppol2tp.s_session);
        if (session != NULL)
                goto end;

        /* Allocate and initialize a new session context. */
        session = kzalloc(sizeof(struct pppol2tp_session), GFP_KERNEL);
        if (session == NULL) {
                error = -ENOMEM;
                goto end;
        }

        skb_queue_head_init(&session->reorder_q);

        session->magic       = L2TP_SESSION_MAGIC;
        session->owner       = current->pid;
        session->sock        = sk;
        session->tunnel      = tunnel;
        session->tunnel_sock = tunnel_sock;
        session->tunnel_addr = sp->pppol2tp;
        sprintf(&session->name[0], "sess %hu/%hu",
                session->tunnel_addr.s_tunnel,
                session->tunnel_addr.s_session);

        session->stats.tunnel_id  = session->tunnel_addr.s_tunnel;
        session->stats.session_id = session->tunnel_addr.s_session;

        INIT_HLIST_NODE(&session->hlist);

        /* Inherit debug options from tunnel */
        session->debug = tunnel->debug;

        /* Default MTU must allow space for UDP/L2TP/PPP
         * headers.
         */
        session->mtu = session->mru = 1500 - PPPOL2TP_HEADER_OVERHEAD;

        /* If PMTU discovery was enabled, use the MTU that was discovered */
        dst = sk_dst_get(sk);
        if (dst != NULL) {
                u32 pmtu = dst_mtu(__sk_dst_get(sk));
                if (pmtu != 0)
                        session->mtu = session->mru = pmtu -
                                PPPOL2TP_HEADER_OVERHEAD;
                dst_release(dst);
        }

        /* Special case: if source & dest session_id == 0x0000, this socket is
         * being created to manage the tunnel. Don't add the session to the
         * session hash list, just set up the internal context for use by
         * ioctl() and sockopt() handlers.
         */
        if ((session->tunnel_addr.s_session == 0) &&
            (session->tunnel_addr.d_session == 0)) {
                error = 0;
                sk->sk_user_data = session;
                goto out_no_ppp;
        }

        /* Get tunnel context from the tunnel socket */
        tunnel = pppol2tp_sock_to_tunnel(tunnel_sock);
        if (tunnel == NULL) {
                error = -EBADF;
                goto end;
        }

        /* Right now, because we don't have a way to push the incoming skb's
         * straight through the UDP layer, the only header we need to worry
         * about is the L2TP header. This size is different depending on
         * whether sequence numbers are enabled for the data channel.
         */
        po->chan.hdrlen = PPPOL2TP_L2TP_HDR_SIZE_NOSEQ;

        po->chan.private = sk;
        po->chan.ops     = &pppol2tp_chan_ops;
        po->chan.mtu     = session->mtu;

        error = ppp_register_channel(&po->chan);
        if (error)
                goto end;

        /* This is how we get the session context from the socket. */
        sk->sk_user_data = session;

        /* Add session to the tunnel's hash list */
        write_lock(&tunnel->hlist_lock);
        hlist_add_head(&session->hlist,
                       pppol2tp_session_id_hash(tunnel,
                                                session->tunnel_addr.s_session));
        write_unlock(&tunnel->hlist_lock);

        atomic_inc(&pppol2tp_session_count);

out_no_ppp:
        pppol2tp_tunnel_inc_refcount(tunnel);
        sk->sk_state = PPPOX_CONNECTED;
        PRINTK(session->debug, PPPOL2TP_MSG_CONTROL, KERN_INFO,
               "%s: created\n", session->name);

end:
        release_sock(sk);

        if (error != 0)
                PRINTK(session ? session->debug : -1, PPPOL2TP_MSG_CONTROL, KERN_WARNING,
                       "%s: connect failed: %d\n", session->name, error);

        return error;
}

/* getname() support.
 */
static int pppol2tp_getname(struct socket *sock, struct sockaddr *uaddr,
                            int *usockaddr_len, int peer)
{
        int len = sizeof(struct sockaddr_pppol2tp);
        struct sockaddr_pppol2tp sp;
        int error = 0;
        struct pppol2tp_session *session;

        error = -ENOTCONN;
        if (sock->sk->sk_state != PPPOX_CONNECTED)
                goto end;

        session = pppol2tp_sock_to_session(sock->sk);
        if (session == NULL) {
                error = -EBADF;
                goto end;
        }

        sp.sa_family    = AF_PPPOX;
        sp.sa_protocol  = PX_PROTO_OL2TP;
        memcpy(&sp.pppol2tp, &session->tunnel_addr,
               sizeof(struct pppol2tp_addr));

        memcpy(uaddr, &sp, len);

        *usockaddr_len = len;

        error = 0;

end:
        return error;
}

/****************************************************************************
 * ioctl() handlers.
 *
 * The PPPoX socket is created for L2TP sessions: tunnels have their own UDP
 * sockets. However, in order to control kernel tunnel features, we allow
 * userspace to create a special "tunnel" PPPoX socket which is used for
 * control only.  Tunnel PPPoX sockets have session_id == 0 and simply allow
 * the user application to issue L2TP setsockopt(), getsockopt() and ioctl()
 * calls.
 ****************************************************************************/

/* Session ioctl helper.
 */
static int pppol2tp_session_ioctl(struct pppol2tp_session *session,
                                  unsigned int cmd, unsigned long arg)
{
        struct ifreq ifr;
        int err = 0;
        struct sock *sk = session->sock;
        int val = (int) arg;

        PRINTK(session->debug, PPPOL2TP_MSG_CONTROL, KERN_DEBUG,
               "%s: pppol2tp_session_ioctl(cmd=%#x, arg=%#lx)\n",
               session->name, cmd, arg);

        sock_hold(sk);

        switch (cmd) {
        case SIOCGIFMTU:
                err = -ENXIO;
                if (!(sk->sk_state & PPPOX_CONNECTED))
                        break;

                err = -EFAULT;
                if (copy_from_user(&ifr, (void __user *) arg, sizeof(struct ifreq)))
                        break;
                ifr.ifr_mtu = session->mtu;
                if (copy_to_user((void __user *) arg, &ifr, sizeof(struct ifreq)))
                        break;

                PRINTK(session->debug, PPPOL2TP_MSG_CONTROL, KERN_INFO,
                       "%s: get mtu=%d\n", session->name, session->mtu);
                err = 0;
                break;

        case SIOCSIFMTU:
                err = -ENXIO;
                if (!(sk->sk_state & PPPOX_CONNECTED))
                        break;

                err = -EFAULT;
                if (copy_from_user(&ifr, (void __user *) arg, sizeof(struct ifreq)))
                        break;

                session->mtu = ifr.ifr_mtu;

                PRINTK(session->debug, PPPOL2TP_MSG_CONTROL, KERN_INFO,
                       "%s: set mtu=%d\n", session->name, session->mtu);
                err = 0;
                break;

        case PPPIOCGMRU:
                err = -ENXIO;
                if (!(sk->sk_state & PPPOX_CONNECTED))
                        break;

                err = -EFAULT;
                if (put_user(session->mru, (int __user *) arg))
                        break;

                PRINTK(session->debug, PPPOL2TP_MSG_CONTROL, KERN_INFO,
                       "%s: get mru=%d\n", session->name, session->mru);
                err = 0;
                break;

        case PPPIOCSMRU:
                err = -ENXIO;
                if (!(sk->sk_state & PPPOX_CONNECTED))
                        break;

                err = -EFAULT;
                if (get_user(val,(int __user *) arg))
                        break;

                session->mru = val;
                PRINTK(session->debug, PPPOL2TP_MSG_CONTROL, KERN_INFO,
                       "%s: set mru=%d\n", session->name, session->mru);
                err = 0;
                break;

        case PPPIOCGFLAGS:
                err = -EFAULT;
                if (put_user(session->flags, (int __user *) arg))
                        break;

                PRINTK(session->debug, PPPOL2TP_MSG_CONTROL, KERN_INFO,
                       "%s: get flags=%d\n", session->name, session->flags);
                err = 0;
                break;

        case PPPIOCSFLAGS:
                err = -EFAULT;
                if (get_user(val, (int __user *) arg))
                        break;
                session->flags = val;
                PRINTK(session->debug, PPPOL2TP_MSG_CONTROL, KERN_INFO,
                       "%s: set flags=%d\n", session->name, session->flags);
                err = 0;
                break;

        case PPPIOCGL2TPSTATS:
                err = -ENXIO;
                if (!(sk->sk_state & PPPOX_CONNECTED))
                        break;

                if (copy_to_user((void __user *) arg, &session->stats,
                                 sizeof(session->stats)))
                        break;
                PRINTK(session->debug, PPPOL2TP_MSG_CONTROL, KERN_INFO,
                       "%s: get L2TP stats\n", session->name);
                err = 0;
                break;

        default:
                err = -ENOSYS;
                break;
        }

        sock_put(sk);

        return err;
}

/* Tunnel ioctl helper.
 *
 * Note the special handling for PPPIOCGL2TPSTATS below. If the ioctl data
 * specifies a session_id, the session ioctl handler is called. This allows an
 * application to retrieve session stats via a tunnel socket.
 */
static int pppol2tp_tunnel_ioctl(struct pppol2tp_tunnel *tunnel,
                                 unsigned int cmd, unsigned long arg)
{
        int err = 0;
        struct sock *sk = tunnel->sock;
        struct pppol2tp_ioc_stats stats_req;

        PRINTK(tunnel->debug, PPPOL2TP_MSG_CONTROL, KERN_DEBUG,
               "%s: pppol2tp_tunnel_ioctl(cmd=%#x, arg=%#lx)\n", tunnel->name,
               cmd, arg);

        sock_hold(sk);

        switch (cmd) {
        case PPPIOCGL2TPSTATS:
                err = -ENXIO;
                if (!(sk->sk_state & PPPOX_CONNECTED))
                        break;

                if (copy_from_user(&stats_req, (void __user *) arg,
                                   sizeof(stats_req))) {
                        err = -EFAULT;
                        break;
                }
                if (stats_req.session_id != 0) {
                        /* resend to session ioctl handler */
                        struct pppol2tp_session *session =
                                pppol2tp_session_find(tunnel, stats_req.session_id);
                        if (session != NULL)
                                err = pppol2tp_session_ioctl(session, cmd, arg);
                        else
                                err = -EBADR;
                        break;
                }
#ifdef CONFIG_XFRM
                tunnel->stats.using_ipsec = (sk->sk_policy[0] || sk->sk_policy[1]) ? 1 : 0;
#endif
                if (copy_to_user((void __user *) arg, &tunnel->stats,
                                 sizeof(tunnel->stats))) {
                        err = -EFAULT;
                        break;
                }
                PRINTK(tunnel->debug, PPPOL2TP_MSG_CONTROL, KERN_INFO,
                       "%s: get L2TP stats\n", tunnel->name);
                err = 0;
                break;

        default:
                err = -ENOSYS;
                break;
        }

        sock_put(sk);

        return err;
}

/* Main ioctl() handler.
 * Dispatch to tunnel or session helpers depending on the socket.
 */
static int pppol2tp_ioctl(struct socket *sock, unsigned int cmd,
                          unsigned long arg)
{
        struct sock *sk = sock->sk;
        struct pppol2tp_session *session;
        struct pppol2tp_tunnel *tunnel;
        int err;

        if (!sk)
                return 0;

        err = -EBADF;
        if (sock_flag(sk, SOCK_DEAD) != 0)
                goto end;

        err = -ENOTCONN;
        if ((sk->sk_user_data == NULL) ||
            (!(sk->sk_state & (PPPOX_CONNECTED | PPPOX_BOUND))))
                goto end;

        /* Get session context from the socket */
        err = -EBADF;
        session = pppol2tp_sock_to_session(sk);
        if (session == NULL)
                goto end;

        /* Special case: if session's session_id is zero, treat ioctl as a
         * tunnel ioctl
         */
        if ((session->tunnel_addr.s_session == 0) &&
            (session->tunnel_addr.d_session == 0)) {
                err = -EBADF;
                tunnel = pppol2tp_sock_to_tunnel(session->tunnel_sock);
                if (tunnel == NULL)
                        goto end;

                err = pppol2tp_tunnel_ioctl(tunnel, cmd, arg);
                goto end;
        }

        err = pppol2tp_session_ioctl(session, cmd, arg);

end:
        return err;
}

/*****************************************************************************
 * setsockopt() / getsockopt() support.
 *
 * The PPPoX socket is created for L2TP sessions: tunnels have their own UDP
 * sockets. In order to control kernel tunnel features, we allow userspace to
 * create a special "tunnel" PPPoX socket which is used for control only.
 * Tunnel PPPoX sockets have session_id == 0 and simply allow the user
 * application to issue L2TP setsockopt(), getsockopt() and ioctl() calls.
 *****************************************************************************/

/* Tunnel setsockopt() helper.
 */
static int pppol2tp_tunnel_setsockopt(struct sock *sk,
                                      struct pppol2tp_tunnel *tunnel,
                                      int optname, int val)
{
        int err = 0;

        switch (optname) {
        case PPPOL2TP_SO_DEBUG:
                tunnel->debug = val;
                PRINTK(tunnel->debug, PPPOL2TP_MSG_CONTROL, KERN_INFO,
                       "%s: set debug=%x\n", tunnel->name, tunnel->debug);
                break;

        default:
                err = -ENOPROTOOPT;
                break;
        }

        return err;
}

/* Session setsockopt helper.
 */
static int pppol2tp_session_setsockopt(struct sock *sk,
                                       struct pppol2tp_session *session,
                                       int optname, int val)
{
        int err = 0;

        switch (optname) {
        case PPPOL2TP_SO_RECVSEQ:
                if ((val != 0) && (val != 1)) {
                        err = -EINVAL;
                        break;
                }
                session->recv_seq = val ? -1 : 0;
                PRINTK(session->debug, PPPOL2TP_MSG_CONTROL, KERN_INFO,
                       "%s: set recv_seq=%d\n", session->name,
                       session->recv_seq);
                break;

        case PPPOL2TP_SO_SENDSEQ:
                if ((val != 0) && (val != 1)) {
                        err = -EINVAL;
                        break;
                }
                session->send_seq = val ? -1 : 0;
                {
                        struct sock *ssk      = session->sock;
                        struct pppox_sock *po = pppox_sk(ssk);
                        po->chan.hdrlen = val ? PPPOL2TP_L2TP_HDR_SIZE_SEQ :
                                PPPOL2TP_L2TP_HDR_SIZE_NOSEQ;
                }
                PRINTK(session->debug, PPPOL2TP_MSG_CONTROL, KERN_INFO,
                       "%s: set send_seq=%d\n", session->name, session->send_seq);
                break;

        case PPPOL2TP_SO_LNSMODE:
                if ((val != 0) && (val != 1)) {
                        err = -EINVAL;
                        break;
                }
                session->lns_mode = val ? -1 : 0;
                PRINTK(session->debug, PPPOL2TP_MSG_CONTROL, KERN_INFO,
                       "%s: set lns_mode=%d\n", session->name,
                       session->lns_mode);
                break;

        case PPPOL2TP_SO_DEBUG:
                session->debug = val;
                PRINTK(session->debug, PPPOL2TP_MSG_CONTROL, KERN_INFO,
                       "%s: set debug=%x\n", session->name, session->debug);
                break;

        case PPPOL2TP_SO_REORDERTO:
                session->reorder_timeout = msecs_to_jiffies(val);
                PRINTK(session->debug, PPPOL2TP_MSG_CONTROL, KERN_INFO,
                       "%s: set reorder_timeout=%d\n", session->name,
                       session->reorder_timeout);
                break;

        default:
                err = -ENOPROTOOPT;
                break;
        }

        return err;
}

/* Main setsockopt() entry point.
 * Does API checks, then calls either the tunnel or session setsockopt
 * handler, according to whether the PPPoL2TP socket is a for a regular
 * session or the special tunnel type.
 */
static int pppol2tp_setsockopt(struct socket *sock, int level, int optname,
                               char __user *optval, int optlen)
{
        struct sock *sk = sock->sk;
        struct pppol2tp_session *session = sk->sk_user_data;
        struct pppol2tp_tunnel *tunnel;
        int val;
        int err;

        if (level != SOL_PPPOL2TP)
                return udp_prot.setsockopt(sk, level, optname, optval, optlen);

        if (optlen < sizeof(int))
                return -EINVAL;

        if (get_user(val, (int __user *)optval))
                return -EFAULT;

        err = -ENOTCONN;
        if (sk->sk_user_data == NULL)
                goto end;

        /* Get session context from the socket */
        err = -EBADF;
        session = pppol2tp_sock_to_session(sk);
        if (session == NULL)
                goto end;

        /* Special case: if session_id == 0x0000, treat as operation on tunnel
         */
        if ((session->tunnel_addr.s_session == 0) &&
            (session->tunnel_addr.d_session == 0)) {
                err = -EBADF;
                tunnel = pppol2tp_sock_to_tunnel(session->tunnel_sock);
                if (tunnel == NULL)
                        goto end;

                err = pppol2tp_tunnel_setsockopt(sk, tunnel, optname, val);
        } else
                err = pppol2tp_session_setsockopt(sk, session, optname, val);

        err = 0;

end:
        return err;
}

/* Tunnel getsockopt helper. Called with sock locked.
 */
static int pppol2tp_tunnel_getsockopt(struct sock *sk,
                                      struct pppol2tp_tunnel *tunnel,
                                      int optname, int *val)
{
        int err = 0;

        switch (optname) {
        case PPPOL2TP_SO_DEBUG:
                *val = tunnel->debug;
                PRINTK(tunnel->debug, PPPOL2TP_MSG_CONTROL, KERN_INFO,
                       "%s: get debug=%x\n", tunnel->name, tunnel->debug);
                break;

        default:
                err = -ENOPROTOOPT;
                break;
        }

        return err;
}

/* Session getsockopt helper. Called with sock locked.
 */
static int pppol2tp_session_getsockopt(struct sock *sk,
                                       struct pppol2tp_session *session,
                                       int optname, int *val)
{
        int err = 0;

        switch (optname) {
        case PPPOL2TP_SO_RECVSEQ:
                *val = session->recv_seq;
                PRINTK(session->debug, PPPOL2TP_MSG_CONTROL, KERN_INFO,
                       "%s: get recv_seq=%d\n", session->name, *val);
                break;

        case PPPOL2TP_SO_SENDSEQ:
                *val = session->send_seq;
                PRINTK(session->debug, PPPOL2TP_MSG_CONTROL, KERN_INFO,
                       "%s: get send_seq=%d\n", session->name, *val);
                break;

        case PPPOL2TP_SO_LNSMODE:
                *val = session->lns_mode;
                PRINTK(session->debug, PPPOL2TP_MSG_CONTROL, KERN_INFO,
                       "%s: get lns_mode=%d\n", session->name, *val);
                break;

        case PPPOL2TP_SO_DEBUG:
                *val = session->debug;
                PRINTK(session->debug, PPPOL2TP_MSG_CONTROL, KERN_INFO,
                       "%s: get debug=%d\n", session->name, *val);
                break;

        case PPPOL2TP_SO_REORDERTO:
                *val = (int) jiffies_to_msecs(session->reorder_timeout);
                PRINTK(session->debug, PPPOL2TP_MSG_CONTROL, KERN_INFO,
                       "%s: get reorder_timeout=%d\n", session->name, *val);
                break;

        default:
                err = -ENOPROTOOPT;
        }

        return err;
}

/* Main getsockopt() entry point.
 * Does API checks, then calls either the tunnel or session getsockopt
 * handler, according to whether the PPPoX socket is a for a regular session
 * or the special tunnel type.
 */
static int pppol2tp_getsockopt(struct socket *sock, int level,
                               int optname, char __user *optval, int __user *optlen)
{
        struct sock *sk = sock->sk;
        struct pppol2tp_session *session = sk->sk_user_data;
        struct pppol2tp_tunnel *tunnel;
        int val, len;
        int err;

        if (level != SOL_PPPOL2TP)
                return udp_prot.getsockopt(sk, level, optname, optval, optlen);

        if (get_user(len, (int __user *) optlen))
                return -EFAULT;

        len = min_t(unsigned int, len, sizeof(int));

        if (len < 0)
                return -EINVAL;

        err = -ENOTCONN;
        if (sk->sk_user_data == NULL)
                goto end;

        /* Get the session context */
        err = -EBADF;
        session = pppol2tp_sock_to_session(sk);
        if (session == NULL)
                goto end;

        /* Special case: if session_id == 0x0000, treat as operation on tunnel */
        if ((session->tunnel_addr.s_session == 0) &&
            (session->tunnel_addr.d_session == 0)) {
                err = -EBADF;
                tunnel = pppol2tp_sock_to_tunnel(session->tunnel_sock);
                if (tunnel == NULL)
                        goto end;

                err = pppol2tp_tunnel_getsockopt(sk, tunnel, optname, &val);
        } else
                err = pppol2tp_session_getsockopt(sk, session, optname, &val);

        err = -EFAULT;
        if (put_user(len, (int __user *) optlen))
                goto end;

        if (copy_to_user((void __user *) optval, &val, len))
                goto end;

        err = 0;
end:
        return err;
}

/*****************************************************************************
 * /proc filesystem for debug
 *****************************************************************************/

#ifdef CONFIG_PROC_FS

#include <linux/seq_file.h>

struct pppol2tp_seq_data {
        struct pppol2tp_tunnel *tunnel; /* current tunnel */
        struct pppol2tp_session *session; /* NULL means get first session in tunnel */
};

static struct pppol2tp_session *next_session(struct pppol2tp_tunnel *tunnel, struct pppol2tp_session *curr)
{
        struct pppol2tp_session *session = NULL;
        struct hlist_node *walk;
        int found = 0;
        int next = 0;
        int i;

        read_lock(&tunnel->hlist_lock);
        for (i = 0; i < PPPOL2TP_HASH_SIZE; i++) {
                hlist_for_each_entry(session, walk, &tunnel->session_hlist[i], hlist) {
                        if (curr == NULL) {
                                found = 1;
                                goto out;
                        }
                        if (session == curr) {
                                next = 1;
                                continue;
                        }
                        if (next) {
                                found = 1;
                                goto out;
                        }
                }
        }
out:
        read_unlock(&tunnel->hlist_lock);
        if (!found)
                session = NULL;

        return session;
}

static struct pppol2tp_tunnel *next_tunnel(struct pppol2tp_tunnel *curr)
{
        struct pppol2tp_tunnel *tunnel = NULL;

        read_lock(&pppol2tp_tunnel_list_lock);
        if (list_is_last(&curr->list, &pppol2tp_tunnel_list)) {
                goto out;
        }
        tunnel = list_entry(curr->list.next, struct pppol2tp_tunnel, list);
out:
        read_unlock(&pppol2tp_tunnel_list_lock);

        return tunnel;
}

static void *pppol2tp_seq_start(struct seq_file *m, loff_t *offs)
{
        struct pppol2tp_seq_data *pd = SEQ_START_TOKEN;
        loff_t pos = *offs;

        if (!pos)
                goto out;

        BUG_ON(m->private == NULL);
        pd = m->private;

        if (pd->tunnel == NULL) {
                if (!list_empty(&pppol2tp_tunnel_list))
                        pd->tunnel = list_entry(pppol2tp_tunnel_list.next, struct pppol2tp_tunnel, list);
        } else {
                pd->session = next_session(pd->tunnel, pd->session);
                if (pd->session == NULL) {
                        pd->tunnel = next_tunnel(pd->tunnel);
                }
        }

        /* NULL tunnel and session indicates end of list */
        if ((pd->tunnel == NULL) && (pd->session == NULL))
                pd = NULL;

out:
        return pd;
}

static void *pppol2tp_seq_next(struct seq_file *m, void *v, loff_t *pos)
{
        (*pos)++;
        return NULL;
}

static void pppol2tp_seq_stop(struct seq_file *p, void *v)
{
        /* nothing to do */
}

static void pppol2tp_seq_tunnel_show(struct seq_file *m, void *v)
{
        struct pppol2tp_tunnel *tunnel = v;

        seq_printf(m, "\nTUNNEL '%s', %c %d\n",
                   tunnel->name,
                   (tunnel == tunnel->sock->sk_user_data) ? 'Y':'N',
                   atomic_read(&tunnel->ref_count) - 1);
        seq_printf(m, " %08x %llu/%llu/%llu %llu/%llu/%llu\n",
                   tunnel->debug,
                   tunnel->stats.tx_packets, tunnel->stats.tx_bytes,
                   tunnel->stats.tx_errors,
                   tunnel->stats.rx_packets, tunnel->stats.rx_bytes,
                   tunnel->stats.rx_errors);
}

static void pppol2tp_seq_session_show(struct seq_file *m, void *v)
{
        struct pppol2tp_session *session = v;

        seq_printf(m, "  SESSION '%s' %08X/%d %04X/%04X -> "
                   "%04X/%04X %d %c\n",
                   session->name,
                   ntohl(session->tunnel_addr.addr.sin_addr.s_addr),
                   ntohs(session->tunnel_addr.addr.sin_port),
                   session->tunnel_addr.s_tunnel,
                   session->tunnel_addr.s_session,
                   session->tunnel_addr.d_tunnel,
                   session->tunnel_addr.d_session,
                   session->sock->sk_state,
                   (session == session->sock->sk_user_data) ?
                   'Y' : 'N');
        seq_printf(m, "   %d/%d/%c/%c/%s %08x %u\n",
                   session->mtu, session->mru,
                   session->recv_seq ? 'R' : '-',
                   session->send_seq ? 'S' : '-',
                   session->lns_mode ? "LNS" : "LAC",
                   session->debug,
                   jiffies_to_msecs(session->reorder_timeout));
        seq_printf(m, "   %hu/%hu %llu/%llu/%llu %llu/%llu/%llu\n",
                   session->nr, session->ns,
                   session->stats.tx_packets,
                   session->stats.tx_bytes,
                   session->stats.tx_errors,
                   session->stats.rx_packets,
                   session->stats.rx_bytes,
                   session->stats.rx_errors);
}

static int pppol2tp_seq_show(struct seq_file *m, void *v)
{
        struct pppol2tp_seq_data *pd = v;

        /* display header on line 1 */
        if (v == SEQ_START_TOKEN) {
                seq_puts(m, "PPPoL2TP driver info, " PPPOL2TP_DRV_VERSION "\n");
                seq_puts(m, "TUNNEL name, user-data-ok session-count\n");
                seq_puts(m, " debug tx-pkts/bytes/errs rx-pkts/bytes/errs\n");
                seq_puts(m, "  SESSION name, addr/port src-tid/sid "
                         "dest-tid/sid state user-data-ok\n");
                seq_puts(m, "   mtu/mru/rcvseq/sendseq/lns debug reorderto\n");
                seq_puts(m, "   nr/ns tx-pkts/bytes/errs rx-pkts/bytes/errs\n");
                goto out;
        }

        /* Show the tunnel or session context.
         */
        if (pd->session == NULL)
                pppol2tp_seq_tunnel_show(m, pd->tunnel);
        else
                pppol2tp_seq_session_show(m, pd->session);

out:
        return 0;
}

static struct seq_operations pppol2tp_seq_ops = {
        .start          = pppol2tp_seq_start,
        .next           = pppol2tp_seq_next,
        .stop           = pppol2tp_seq_stop,
        .show           = pppol2tp_seq_show,
};

/* Called when our /proc file is opened. We allocate data for use when
 * iterating our tunnel / session contexts and store it in the private
 * data of the seq_file.
 */
static int pppol2tp_proc_open(struct inode *inode, struct file *file)
{
        struct seq_file *m;
        struct pppol2tp_seq_data *pd;
        int ret = 0;

        ret = seq_open(file, &pppol2tp_seq_ops);
        if (ret < 0)
                goto out;

        m = file->private_data;

        /* Allocate and fill our proc_data for access later */
        ret = -ENOMEM;
        m->private = kzalloc(sizeof(struct pppol2tp_seq_data), GFP_KERNEL);
        if (m->private == NULL)
                goto out;

        pd = m->private;
        ret = 0;

out:
        return ret;
}

/* Called when /proc file access completes.
 */
static int pppol2tp_proc_release(struct inode *inode, struct file *file)
{
        struct seq_file *m = (struct seq_file *)file->private_data;

        kfree(m->private);
        m->private = NULL;

        return seq_release(inode, file);
}

static struct file_operations pppol2tp_proc_fops = {
        .owner          = THIS_MODULE,
        .open           = pppol2tp_proc_open,
        .read           = seq_read,
        .llseek         = seq_lseek,
        .release        = pppol2tp_proc_release,
};

static struct proc_dir_entry *pppol2tp_proc;

#endif /* CONFIG_PROC_FS */

/*****************************************************************************
 * Init and cleanup
 *****************************************************************************/

static struct proto_ops pppol2tp_ops = {
        .family         = AF_PPPOX,
        .owner          = THIS_MODULE,
        .release        = pppol2tp_release,
        .bind           = sock_no_bind,
        .connect        = pppol2tp_connect,
        .socketpair     = sock_no_socketpair,
        .accept         = sock_no_accept,
        .getname        = pppol2tp_getname,
        .poll           = datagram_poll,
        .listen         = sock_no_listen,
        .shutdown       = sock_no_shutdown,
        .setsockopt     = pppol2tp_setsockopt,
        .getsockopt     = pppol2tp_getsockopt,
        .sendmsg        = pppol2tp_sendmsg,
        .recvmsg        = pppol2tp_recvmsg,
        .mmap           = sock_no_mmap,
        .ioctl          = pppox_ioctl,
};

static struct pppox_proto pppol2tp_proto = {
        .create         = pppol2tp_create,
        .ioctl          = pppol2tp_ioctl
};

static int __init pppol2tp_init(void)
{
        int err;

        err = proto_register(&pppol2tp_sk_proto, 0);
        if (err)
                goto out;
        err = register_pppox_proto(PX_PROTO_OL2TP, &pppol2tp_proto);
        if (err)
                goto out_unregister_pppol2tp_proto;

#ifdef CONFIG_PROC_FS
        pppol2tp_proc = create_proc_entry("pppol2tp", 0, init_net.proc_net);
        if (!pppol2tp_proc) {
                err = -ENOMEM;
                goto out_unregister_pppox_proto;
        }
        pppol2tp_proc->proc_fops = &pppol2tp_proc_fops;
#endif /* CONFIG_PROC_FS */
        printk(KERN_INFO "PPPoL2TP kernel driver, %s\n",
               PPPOL2TP_DRV_VERSION);

out:
        return err;

out_unregister_pppox_proto:
        unregister_pppox_proto(PX_PROTO_OL2TP);
out_unregister_pppol2tp_proto:
        proto_unregister(&pppol2tp_sk_proto);
        goto out;
}

static void __exit pppol2tp_exit(void)
{
        unregister_pppox_proto(PX_PROTO_OL2TP);

#ifdef CONFIG_PROC_FS
        remove_proc_entry("pppol2tp", init_net.proc_net);
#endif
        proto_unregister(&pppol2tp_sk_proto);
}

module_init(pppol2tp_init);
module_exit(pppol2tp_exit);

MODULE_AUTHOR("Martijn van Oosterhout <kleptog@svana.org>,"
              "James Chapman <jchapman@katalix.com>");
MODULE_DESCRIPTION("PPP over L2TP over UDP");
MODULE_LICENSE("GPL");
MODULE_VERSION(PPPOL2TP_DRV_VERSION);