// SPDX-License-Identifier: GPL-2.0-only

  /*
   * Copyright (C) ST-Ericsson AB 2010

   * Author:	Sjur Brendeland

   */

  #define pr_fmt(fmt) KBUILD_MODNAME ":%s(): " fmt, __func__

  #include <linux/fs.h>
  #include <linux/init.h>
  #include <linux/module.h>

  #include <linux/sched/signal.h>

  #include <linux/spinlock.h>
  #include <linux/mutex.h>
  #include <linux/list.h>
  #include <linux/wait.h>
  #include <linux/poll.h>
  #include <linux/tcp.h>
  #include <linux/uaccess.h>

  #include <linux/debugfs.h>

  #include <linux/caif/caif_socket.h>

  #include <linux/pkt_sched.h>

  #include <net/sock.h>
  #include <net/tcp_states.h>

  #include <net/caif/caif_layer.h>
  #include <net/caif/caif_dev.h>
  #include <net/caif/cfpkt.h>
  
  MODULE_LICENSE("GPL");

  MODULE_ALIAS_NETPROTO(AF_CAIF);

  /*
   * CAIF state is re-using the TCP socket states.
   * caif_states stored in sk_state reflect the state as reported by
   * the CAIF stack, while sk_socket->state is the state of the socket.
   */
  enum caif_states {
  	CAIF_CONNECTED		= TCP_ESTABLISHED,
  	CAIF_CONNECTING	= TCP_SYN_SENT,
  	CAIF_DISCONNECTED	= TCP_CLOSE
  };
  
  #define TX_FLOW_ON_BIT	1
  #define RX_FLOW_ON_BIT	2

  struct caifsock {

  	struct sock sk; /* must be first member */

  	struct cflayer layer;

  	u32 flow_state;

  	struct caif_connect_request conn_req;

  	struct mutex readlock;

  	struct dentry *debugfs_socket_dir;

  	int headroom, tailroom, maxframe;

  };

  static int rx_flow_is_on(struct caifsock *cf_sk)
  {
  	return test_bit(RX_FLOW_ON_BIT,
  			(void *) &cf_sk->flow_state);
  }
  
  static int tx_flow_is_on(struct caifsock *cf_sk)
  {
  	return test_bit(TX_FLOW_ON_BIT,
  			(void *) &cf_sk->flow_state);
  }

  static void set_rx_flow_off(struct caifsock *cf_sk)

  {

  	 clear_bit(RX_FLOW_ON_BIT,
  		 (void *) &cf_sk->flow_state);
  }

  static void set_rx_flow_on(struct caifsock *cf_sk)
  {
  	 set_bit(RX_FLOW_ON_BIT,
  			(void *) &cf_sk->flow_state);
  }

  static void set_tx_flow_off(struct caifsock *cf_sk)
  {
  	 clear_bit(TX_FLOW_ON_BIT,
  		(void *) &cf_sk->flow_state);
  }

  static void set_tx_flow_on(struct caifsock *cf_sk)
  {
  	 set_bit(TX_FLOW_ON_BIT,
  		(void *) &cf_sk->flow_state);
  }

  static void caif_read_lock(struct sock *sk)
  {
  	struct caifsock *cf_sk;
  	cf_sk = container_of(sk, struct caifsock, sk);
  	mutex_lock(&cf_sk->readlock);
  }

  static void caif_read_unlock(struct sock *sk)
  {
  	struct caifsock *cf_sk;
  	cf_sk = container_of(sk, struct caifsock, sk);
  	mutex_unlock(&cf_sk->readlock);
  }

  static int sk_rcvbuf_lowwater(struct caifsock *cf_sk)

  {
  	/* A quarter of full buffer is used a low water mark */
  	return cf_sk->sk.sk_rcvbuf / 4;
  }

  static void caif_flow_ctrl(struct sock *sk, int mode)

  {
  	struct caifsock *cf_sk;
  	cf_sk = container_of(sk, struct caifsock, sk);

  	if (cf_sk->layer.dn && cf_sk->layer.dn->modemcmd)

  		cf_sk->layer.dn->modemcmd(cf_sk->layer.dn, mode);
  }

  /*
   * Copied from sock.c:sock_queue_rcv_skb(), but changed so packets are
   * not dropped, but CAIF is sending flow off instead.
   */

  static void caif_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)

  {
  	int err;

  	unsigned long flags;
  	struct sk_buff_head *list = &sk->sk_receive_queue;
  	struct caifsock *cf_sk = container_of(sk, struct caifsock, sk);

  	bool queued = false;

  	if (atomic_read(&sk->sk_rmem_alloc) + skb->truesize >=

  		(unsigned int)sk->sk_rcvbuf && rx_flow_is_on(cf_sk)) {

  		net_dbg_ratelimited("sending flow OFF (queue len = %d %d)
  ",
  				    atomic_read(&cf_sk->sk.sk_rmem_alloc),
  				    sk_rcvbuf_lowwater(cf_sk));

  		set_rx_flow_off(cf_sk);

  		caif_flow_ctrl(sk, CAIF_MODEMCMD_FLOW_OFF_REQ);

  	}

  	err = sk_filter(sk, skb);
  	if (err)

  		goto out;

  	if (!sk_rmem_schedule(sk, skb, skb->truesize) && rx_flow_is_on(cf_sk)) {

  		set_rx_flow_off(cf_sk);

  		net_dbg_ratelimited("sending flow OFF due to rmem_schedule
  ");

  		caif_flow_ctrl(sk, CAIF_MODEMCMD_FLOW_OFF_REQ);

  	}
  	skb->dev = NULL;
  	skb_set_owner_r(skb, sk);

  	spin_lock_irqsave(&list->lock, flags);

  	queued = !sock_flag(sk, SOCK_DEAD);
  	if (queued)

  		__skb_queue_tail(list, skb);
  	spin_unlock_irqrestore(&list->lock, flags);

  out:
  	if (queued)

  		sk->sk_data_ready(sk);

  	else
  		kfree_skb(skb);

  }

  /* Packet Receive Callback function called from CAIF Stack */
  static int caif_sktrecv_cb(struct cflayer *layr, struct cfpkt *pkt)

  {
  	struct caifsock *cf_sk;

  	struct sk_buff *skb;

  
  	cf_sk = container_of(layr, struct caifsock, layer);

  	skb = cfpkt_tonative(pkt);
  
  	if (unlikely(cf_sk->sk.sk_state != CAIF_CONNECTED)) {

  		kfree_skb(skb);

  		return 0;
  	}
  	caif_queue_rcv_skb(&cf_sk->sk, skb);
  	return 0;
  }

  static void cfsk_hold(struct cflayer *layr)
  {
  	struct caifsock *cf_sk = container_of(layr, struct caifsock, layer);
  	sock_hold(&cf_sk->sk);
  }
  
  static void cfsk_put(struct cflayer *layr)
  {
  	struct caifsock *cf_sk = container_of(layr, struct caifsock, layer);
  	sock_put(&cf_sk->sk);
  }

  /* Packet Control Callback function called from CAIF */
  static void caif_ctrl_cb(struct cflayer *layr,

  			 enum caif_ctrlcmd flow,
  			 int phyid)

  {
  	struct caifsock *cf_sk = container_of(layr, struct caifsock, layer);

  	switch (flow) {
  	case CAIF_CTRLCMD_FLOW_ON_IND:

  		/* OK from modem to start sending again */

  		set_tx_flow_on(cf_sk);
  		cf_sk->sk.sk_state_change(&cf_sk->sk);

  		break;
  
  	case CAIF_CTRLCMD_FLOW_OFF_IND:

  		/* Modem asks us to shut up */

  		set_tx_flow_off(cf_sk);
  		cf_sk->sk.sk_state_change(&cf_sk->sk);

  		break;
  
  	case CAIF_CTRLCMD_INIT_RSP:

  		/* We're now connected */

  		caif_client_register_refcnt(&cf_sk->layer,
  						cfsk_hold, cfsk_put);

  		cf_sk->sk.sk_state = CAIF_CONNECTED;
  		set_tx_flow_on(cf_sk);

  		cf_sk->sk.sk_shutdown = 0;

  		cf_sk->sk.sk_state_change(&cf_sk->sk);

  		break;
  
  	case CAIF_CTRLCMD_DEINIT_RSP:

  		/* We're now disconnected */
  		cf_sk->sk.sk_state = CAIF_DISCONNECTED;
  		cf_sk->sk.sk_state_change(&cf_sk->sk);

  		break;
  
  	case CAIF_CTRLCMD_INIT_FAIL_RSP:

  		/* Connect request failed */

  		cf_sk->sk.sk_err = ECONNREFUSED;
  		cf_sk->sk.sk_state = CAIF_DISCONNECTED;
  		cf_sk->sk.sk_shutdown = SHUTDOWN_MASK;
  		/*
  		 * Socket "standards" seems to require POLLOUT to
  		 * be set at connect failure.
  		 */
  		set_tx_flow_on(cf_sk);
  		cf_sk->sk.sk_state_change(&cf_sk->sk);

  		break;
  
  	case CAIF_CTRLCMD_REMOTE_SHUTDOWN_IND:

  		/* Modem has closed this connection, or device is down. */

  		cf_sk->sk.sk_shutdown = SHUTDOWN_MASK;
  		cf_sk->sk.sk_err = ECONNRESET;
  		set_rx_flow_on(cf_sk);
  		cf_sk->sk.sk_error_report(&cf_sk->sk);

  		break;
  
  	default:

  		pr_debug("Unexpected flow command %d
  ", flow);

  	}
  }

  static void caif_check_flow_release(struct sock *sk)

  {

  	struct caifsock *cf_sk = container_of(sk, struct caifsock, sk);

  	if (rx_flow_is_on(cf_sk))
  		return;

  	if (atomic_read(&sk->sk_rmem_alloc) <= sk_rcvbuf_lowwater(cf_sk)) {

  			set_rx_flow_on(cf_sk);

  			caif_flow_ctrl(sk, CAIF_MODEMCMD_FLOW_ON_REQ);

  	}
  }

  /*

   * Copied from unix_dgram_recvmsg, but removed credit checks,
   * changed locking, address handling and added MSG_TRUNC.

   */

  static int caif_seqpkt_recvmsg(struct socket *sock, struct msghdr *m,
  			       size_t len, int flags)

  
  {
  	struct sock *sk = sock->sk;

  	struct sk_buff *skb;

  	int ret;
  	int copylen;

  	ret = -EOPNOTSUPP;

  	if (flags & MSG_OOB)

  		goto read_error;

  	skb = skb_recv_datagram(sk, flags, 0 , &ret);
  	if (!skb)

  		goto read_error;

  	copylen = skb->len;
  	if (len < copylen) {
  		m->msg_flags |= MSG_TRUNC;
  		copylen = len;

  	}

  	ret = skb_copy_datagram_msg(skb, 0, m, copylen);

  	if (ret)

  		goto out_free;

  	ret = (flags & MSG_TRUNC) ? skb->len : copylen;
  out_free:

  	skb_free_datagram(sk, skb);

  	caif_check_flow_release(sk);

  	return ret;

  read_error:
  	return ret;
  }

  /* Copied from unix_stream_wait_data, identical except for lock call. */
  static long caif_stream_data_wait(struct sock *sk, long timeo)
  {
  	DEFINE_WAIT(wait);
  	lock_sock(sk);
  
  	for (;;) {
  		prepare_to_wait(sk_sleep(sk), &wait, TASK_INTERRUPTIBLE);
  
  		if (!skb_queue_empty(&sk->sk_receive_queue) ||
  			sk->sk_err ||
  			sk->sk_state != CAIF_CONNECTED ||
  			sock_flag(sk, SOCK_DEAD) ||
  			(sk->sk_shutdown & RCV_SHUTDOWN) ||
  			signal_pending(current) ||
  			!timeo)
  			break;

  		sk_set_bit(SOCKWQ_ASYNC_WAITDATA, sk);

  		release_sock(sk);
  		timeo = schedule_timeout(timeo);
  		lock_sock(sk);

  
  		if (sock_flag(sk, SOCK_DEAD))
  			break;

  		sk_clear_bit(SOCKWQ_ASYNC_WAITDATA, sk);

  	}

  	finish_wait(sk_sleep(sk), &wait);
  	release_sock(sk);
  	return timeo;
  }

  /*
   * Copied from unix_stream_recvmsg, but removed credit checks,
   * changed locking calls, changed address handling.
   */

  static int caif_stream_recvmsg(struct socket *sock, struct msghdr *msg,
  			       size_t size, int flags)

  {
  	struct sock *sk = sock->sk;
  	int copied = 0;
  	int target;
  	int err = 0;
  	long timeo;

  	err = -EOPNOTSUPP;
  	if (flags&MSG_OOB)
  		goto out;

  	/*
  	 * Lock the socket to prevent queue disordering
  	 * while sleeps in memcpy_tomsg
  	 */
  	err = -EAGAIN;
  	if (sk->sk_state == CAIF_CONNECTING)
  		goto out;

  	caif_read_lock(sk);
  	target = sock_rcvlowat(sk, flags&MSG_WAITALL, size);
  	timeo = sock_rcvtimeo(sk, flags&MSG_DONTWAIT);

  	do {
  		int chunk;
  		struct sk_buff *skb;

  		lock_sock(sk);

  		if (sock_flag(sk, SOCK_DEAD)) {
  			err = -ECONNRESET;
  			goto unlock;
  		}

  		skb = skb_dequeue(&sk->sk_receive_queue);
  		caif_check_flow_release(sk);

  		if (skb == NULL) {
  			if (copied >= target)
  				goto unlock;
  			/*
  			 *	POSIX 1003.1g mandates this order.
  			 */
  			err = sock_error(sk);
  			if (err)
  				goto unlock;
  			err = -ECONNRESET;
  			if (sk->sk_shutdown & RCV_SHUTDOWN)
  				goto unlock;

  			err = -EPIPE;
  			if (sk->sk_state != CAIF_CONNECTED)
  				goto unlock;
  			if (sock_flag(sk, SOCK_DEAD))
  				goto unlock;

  			release_sock(sk);

  			err = -EAGAIN;
  			if (!timeo)
  				break;

  			caif_read_unlock(sk);

  			timeo = caif_stream_data_wait(sk, timeo);

  			if (signal_pending(current)) {
  				err = sock_intr_errno(timeo);
  				goto out;
  			}
  			caif_read_lock(sk);
  			continue;
  unlock:
  			release_sock(sk);
  			break;

  		}

  		release_sock(sk);
  		chunk = min_t(unsigned int, skb->len, size);

  		if (memcpy_to_msg(msg, skb->data, chunk)) {

  			skb_queue_head(&sk->sk_receive_queue, skb);
  			if (copied == 0)
  				copied = -EFAULT;
  			break;
  		}
  		copied += chunk;
  		size -= chunk;

  		/* Mark read part of skb as used */
  		if (!(flags & MSG_PEEK)) {
  			skb_pull(skb, chunk);

  			/* put the skb back if we didn't use it up. */
  			if (skb->len) {
  				skb_queue_head(&sk->sk_receive_queue, skb);
  				break;
  			}
  			kfree_skb(skb);

  		} else {

  			/*
  			 * It is questionable, see note in unix_dgram_recvmsg.
  			 */
  			/* put message back and return */
  			skb_queue_head(&sk->sk_receive_queue, skb);
  			break;

  		}

  	} while (size);
  	caif_read_unlock(sk);

  out:
  	return copied ? : err;
  }

  /*
   * Copied from sock.c:sock_wait_for_wmem, but change to wait for
   * CAIF flow-on and sock_writable.
   */
  static long caif_wait_for_flow_on(struct caifsock *cf_sk,

  				  int wait_writeable, long timeo, int *err)

  {
  	struct sock *sk = &cf_sk->sk;
  	DEFINE_WAIT(wait);
  	for (;;) {
  		*err = 0;
  		if (tx_flow_is_on(cf_sk) &&
  			(!wait_writeable || sock_writeable(&cf_sk->sk)))
  			break;
  		*err = -ETIMEDOUT;
  		if (!timeo)
  			break;
  		*err = -ERESTARTSYS;
  		if (signal_pending(current))
  			break;
  		prepare_to_wait(sk_sleep(sk), &wait, TASK_INTERRUPTIBLE);
  		*err = -ECONNRESET;
  		if (sk->sk_shutdown & SHUTDOWN_MASK)
  			break;
  		*err = -sk->sk_err;
  		if (sk->sk_err)
  			break;
  		*err = -EPIPE;
  		if (cf_sk->sk.sk_state != CAIF_CONNECTED)
  			break;
  		timeo = schedule_timeout(timeo);

  	}

  	finish_wait(sk_sleep(sk), &wait);
  	return timeo;
  }

  /*
   * Transmit a SKB. The device may temporarily request re-transmission
   * by returning EAGAIN.
   */
  static int transmit_skb(struct sk_buff *skb, struct caifsock *cf_sk,
  			int noblock, long timeo)
  {
  	struct cfpkt *pkt;

  	pkt = cfpkt_fromnative(CAIF_DIR_OUT, skb);

  	memset(skb->cb, 0, sizeof(struct caif_payload_info));

  	cfpkt_set_prio(pkt, cf_sk->sk.sk_priority);

  	if (cf_sk->layer.dn == NULL) {
  		kfree_skb(skb);

  		return -EINVAL;

  	}

  	return cf_sk->layer.dn->transmit(cf_sk->layer.dn, pkt);

  }

  /* Copied from af_unix:unix_dgram_sendmsg, and adapted to CAIF */

  static int caif_seqpkt_sendmsg(struct socket *sock, struct msghdr *msg,
  			       size_t len)

  {
  	struct sock *sk = sock->sk;
  	struct caifsock *cf_sk = container_of(sk, struct caifsock, sk);
  	int buffer_size;
  	int ret = 0;
  	struct sk_buff *skb = NULL;
  	int noblock;
  	long timeo;
  	caif_assert(cf_sk);
  	ret = sock_error(sk);
  	if (ret)
  		goto err;
  
  	ret = -EOPNOTSUPP;
  	if (msg->msg_flags&MSG_OOB)
  		goto err;
  
  	ret = -EOPNOTSUPP;
  	if (msg->msg_namelen)
  		goto err;
  
  	ret = -EINVAL;

  	if (unlikely(msg->msg_iter.iov->iov_base == NULL))

  		goto err;
  	noblock = msg->msg_flags & MSG_DONTWAIT;

  	timeo = sock_sndtimeo(sk, noblock);
  	timeo = caif_wait_for_flow_on(container_of(sk, struct caifsock, sk),
  				1, timeo, &ret);

  	if (ret)
  		goto err;

  	ret = -EPIPE;
  	if (cf_sk->sk.sk_state != CAIF_CONNECTED ||
  		sock_flag(sk, SOCK_DEAD) ||
  		(sk->sk_shutdown & RCV_SHUTDOWN))
  		goto err;

  	/* Error if trying to write more than maximum frame size. */
  	ret = -EMSGSIZE;
  	if (len > cf_sk->maxframe && cf_sk->sk.sk_protocol != CAIFPROTO_RFM)
  		goto err;
  
  	buffer_size = len + cf_sk->headroom + cf_sk->tailroom;

  	ret = -ENOMEM;
  	skb = sock_alloc_send_skb(sk, buffer_size, noblock, &ret);

  
  	if (!skb || skb_tailroom(skb) < buffer_size)

  		goto err;

  
  	skb_reserve(skb, cf_sk->headroom);

  	ret = memcpy_from_msg(skb_put(skb, len), msg, len);

  
  	if (ret)
  		goto err;
  	ret = transmit_skb(skb, cf_sk, noblock, timeo);
  	if (ret < 0)

  		/* skb is already freed */
  		return ret;

  	return len;
  err:
  	kfree_skb(skb);
  	return ret;
  }

  /*
   * Copied from unix_stream_sendmsg and adapted to CAIF:
   * Changed removed permission handling and added waiting for flow on
   * and other minor adaptations.
   */

  static int caif_stream_sendmsg(struct socket *sock, struct msghdr *msg,
  			       size_t len)

  {
  	struct sock *sk = sock->sk;
  	struct caifsock *cf_sk = container_of(sk, struct caifsock, sk);
  	int err, size;
  	struct sk_buff *skb;
  	int sent = 0;
  	long timeo;

  	err = -EOPNOTSUPP;

  	if (unlikely(msg->msg_flags&MSG_OOB))
  		goto out_err;

  	if (unlikely(msg->msg_namelen))
  		goto out_err;

  	timeo = sock_sndtimeo(sk, msg->msg_flags & MSG_DONTWAIT);
  	timeo = caif_wait_for_flow_on(cf_sk, 1, timeo, &err);

  	if (unlikely(sk->sk_shutdown & SEND_SHUTDOWN))
  		goto pipe_err;

  	while (sent < len) {

  		size = len-sent;

  		if (size > cf_sk->maxframe)
  			size = cf_sk->maxframe;

  		/* If size is more than half of sndbuf, chop up message */
  		if (size > ((sk->sk_sndbuf >> 1) - 64))
  			size = (sk->sk_sndbuf >> 1) - 64;

  		if (size > SKB_MAX_ALLOC)
  			size = SKB_MAX_ALLOC;

  		skb = sock_alloc_send_skb(sk,

  					size + cf_sk->headroom +
  					cf_sk->tailroom,

  					msg->msg_flags&MSG_DONTWAIT,
  					&err);
  		if (skb == NULL)
  			goto out_err;

  		skb_reserve(skb, cf_sk->headroom);

  		/*
  		 *	If you pass two values to the sock_alloc_send_skb
  		 *	it tries to grab the large buffer with GFP_NOFS
  		 *	(which can fail easily), and if it fails grab the
  		 *	fallback size buffer which is under a page and will
  		 *	succeed. [Alan]
  		 */
  		size = min_t(int, size, skb_tailroom(skb));

  		err = memcpy_from_msg(skb_put(skb, size), msg, size);

  		if (err) {
  			kfree_skb(skb);
  			goto out_err;
  		}
  		err = transmit_skb(skb, cf_sk,
  				msg->msg_flags&MSG_DONTWAIT, timeo);

  		if (err < 0)
  			/* skb is already freed */

  			goto pipe_err;

  		sent += size;

  	}

  	return sent;

  pipe_err:
  	if (sent == 0 && !(msg->msg_flags&MSG_NOSIGNAL))
  		send_sig(SIGPIPE, current, 0);
  	err = -EPIPE;
  out_err:
  	return sent ? : err;

  }

  static int setsockopt(struct socket *sock, int lvl, int opt, sockptr_t ov,
  		unsigned int ol)

  {
  	struct sock *sk = sock->sk;
  	struct caifsock *cf_sk = container_of(sk, struct caifsock, sk);

  	int linksel;

  	if (cf_sk->sk.sk_socket->state != SS_UNCONNECTED)

  		return -ENOPROTOOPT;

  	switch (opt) {
  	case CAIFSO_LINK_SELECT:

  		if (ol < sizeof(int))

  			return -EINVAL;

  		if (lvl != SOL_CAIF)
  			goto bad_sol;

  		if (copy_from_sockptr(&linksel, ov, sizeof(int)))

  			return -EINVAL;
  		lock_sock(&(cf_sk->sk));
  		cf_sk->conn_req.link_selector = linksel;
  		release_sock(&cf_sk->sk);
  		return 0;

  	case CAIFSO_REQ_PARAM:
  		if (lvl != SOL_CAIF)
  			goto bad_sol;
  		if (cf_sk->sk.sk_protocol != CAIFPROTO_UTIL)
  			return -ENOPROTOOPT;

  		lock_sock(&(cf_sk->sk));

  		if (ol > sizeof(cf_sk->conn_req.param.data) ||

  		    copy_from_sockptr(&cf_sk->conn_req.param.data, ov, ol)) {

  			release_sock(&cf_sk->sk);

  			return -EINVAL;
  		}

  		cf_sk->conn_req.param.size = ol;

  		release_sock(&cf_sk->sk);
  		return 0;
  
  	default:

  		return -ENOPROTOOPT;

  	}
  
  	return 0;
  bad_sol:

  	return -ENOPROTOOPT;
  
  }

  /*
   * caif_connect() - Connect a CAIF Socket
   * Copied and modified af_irda.c:irda_connect().
   *
   * Note : by consulting "errno", the user space caller may learn the cause
   * of the failure. Most of them are visible in the function, others may come
   * from subroutines called and are listed here :
   *  o -EAFNOSUPPORT: bad socket family or type.
   *  o -ESOCKTNOSUPPORT: bad socket type or protocol
   *  o -EINVAL: bad socket address, or CAIF link type
   *  o -ECONNREFUSED: remote end refused the connection.
   *  o -EINPROGRESS: connect request sent but timed out (or non-blocking)
   *  o -EISCONN: already connected.
   *  o -ETIMEDOUT: Connection timed out (send timeout)
   *  o -ENODEV: No link layer to send request
   *  o -ECONNRESET: Received Shutdown indication or lost link layer
   *  o -ENOMEM: Out of memory
   *
   *  State Strategy:
   *  o sk_state: holds the CAIF_* protocol state, it's updated by
   *	caif_ctrl_cb.
   *  o sock->state: holds the SS_* socket state and is updated by connect and
   *	disconnect.
   */
  static int caif_connect(struct socket *sock, struct sockaddr *uaddr,
  			int addr_len, int flags)

  {

  	struct sock *sk = sock->sk;

  	struct caifsock *cf_sk = container_of(sk, struct caifsock, sk);
  	long timeo;
  	int err;

  	int ifindex, headroom, tailroom;

  	unsigned int mtu;

  	struct net_device *dev;

  	lock_sock(sk);

  	err = -EINVAL;
  	if (addr_len < offsetofend(struct sockaddr, sa_family))
  		goto out;

  	err = -EAFNOSUPPORT;
  	if (uaddr->sa_family != AF_CAIF)

  		goto out;

  	switch (sock->state) {
  	case SS_UNCONNECTED:
  		/* Normal case, a fresh connect */
  		caif_assert(sk->sk_state == CAIF_DISCONNECTED);
  		break;
  	case SS_CONNECTING:
  		switch (sk->sk_state) {
  		case CAIF_CONNECTED:
  			sock->state = SS_CONNECTED;
  			err = -EISCONN;
  			goto out;
  		case CAIF_DISCONNECTED:
  			/* Reconnect allowed */
  			break;
  		case CAIF_CONNECTING:
  			err = -EALREADY;
  			if (flags & O_NONBLOCK)
  				goto out;
  			goto wait_connect;
  		}
  		break;
  	case SS_CONNECTED:
  		caif_assert(sk->sk_state == CAIF_CONNECTED ||
  				sk->sk_state == CAIF_DISCONNECTED);
  		if (sk->sk_shutdown & SHUTDOWN_MASK) {
  			/* Allow re-connect after SHUTDOWN_IND */

  			caif_disconnect_client(sock_net(sk), &cf_sk->layer);

  			caif_free_client(&cf_sk->layer);

  			break;
  		}
  		/* No reconnect on a seqpacket socket */
  		err = -EISCONN;
  		goto out;
  	case SS_DISCONNECTING:
  	case SS_FREE:
  		caif_assert(1); /*Should never happen */
  		break;

  	}

  	sk->sk_state = CAIF_DISCONNECTED;
  	sock->state = SS_UNCONNECTED;
  	sk_stream_kill_queues(&cf_sk->sk);

  	err = -EINVAL;

  	if (addr_len != sizeof(struct sockaddr_caif))

  		goto out;

  	memcpy(&cf_sk->conn_req.sockaddr, uaddr,

  		sizeof(struct sockaddr_caif));

  	/* Move to connecting socket, start sending Connect Requests */
  	sock->state = SS_CONNECTING;
  	sk->sk_state = CAIF_CONNECTING;

  	/* Check priority value comming from socket */

  	/* if priority value is out of range it will be ajusted */
  	if (cf_sk->sk.sk_priority > CAIF_PRIO_MAX)
  		cf_sk->conn_req.priority = CAIF_PRIO_MAX;
  	else if (cf_sk->sk.sk_priority < CAIF_PRIO_MIN)
  		cf_sk->conn_req.priority = CAIF_PRIO_MIN;
  	else
  		cf_sk->conn_req.priority = cf_sk->sk.sk_priority;
  
  	/*ifindex = id of the interface.*/
  	cf_sk->conn_req.ifindex = cf_sk->sk.sk_bound_dev_if;

  	cf_sk->layer.receive = caif_sktrecv_cb;

  	err = caif_connect_client(sock_net(sk), &cf_sk->conn_req,

  				&cf_sk->layer, &ifindex, &headroom, &tailroom);

  	if (err < 0) {
  		cf_sk->sk.sk_socket->state = SS_UNCONNECTED;
  		cf_sk->sk.sk_state = CAIF_DISCONNECTED;
  		goto out;

  	}

  
  	err = -ENODEV;
  	rcu_read_lock();
  	dev = dev_get_by_index_rcu(sock_net(sk), ifindex);
  	if (!dev) {
  		rcu_read_unlock();
  		goto out;
  	}

  	cf_sk->headroom = LL_RESERVED_SPACE_EXTRA(dev, headroom);

  	mtu = dev->mtu;
  	rcu_read_unlock();

  	cf_sk->tailroom = tailroom;

  	cf_sk->maxframe = mtu - (headroom + tailroom);

  	if (cf_sk->maxframe < 1) {

  		pr_warn("CAIF Interface MTU too small (%d)
  ", dev->mtu);

  		err = -ENODEV;

  		goto out;
  	}

  	err = -EINPROGRESS;
  wait_connect:

  	if (sk->sk_state != CAIF_CONNECTED && (flags & O_NONBLOCK))
  		goto out;

  	timeo = sock_sndtimeo(sk, flags & O_NONBLOCK);
  
  	release_sock(sk);

  	err = -ERESTARTSYS;
  	timeo = wait_event_interruptible_timeout(*sk_sleep(sk),

  			sk->sk_state != CAIF_CONNECTING,
  			timeo);
  	lock_sock(sk);

  	if (timeo < 0)

  		goto out; /* -ERESTARTSYS */

  	err = -ETIMEDOUT;
  	if (timeo == 0 && sk->sk_state != CAIF_CONNECTED)
  		goto out;

  	if (sk->sk_state != CAIF_CONNECTED) {
  		sock->state = SS_UNCONNECTED;
  		err = sock_error(sk);
  		if (!err)
  			err = -ECONNREFUSED;
  		goto out;
  	}
  	sock->state = SS_CONNECTED;
  	err = 0;

  out:

  	release_sock(sk);
  	return err;

  }

  /*
   * caif_release() - Disconnect a CAIF Socket
   * Copied and modified af_irda.c:irda_release().
   */
  static int caif_release(struct socket *sock)

  {

  	struct sock *sk = sock->sk;

  	struct caifsock *cf_sk = container_of(sk, struct caifsock, sk);

  	if (!sk)
  		return 0;

  	set_tx_flow_off(cf_sk);

  
  	/*

  	 * Ensure that packets are not queued after this point in time.
  	 * caif_queue_rcv_skb checks SOCK_DEAD holding the queue lock,
  	 * this ensures no packets when sock is dead.

  	 */

  	spin_lock_bh(&sk->sk_receive_queue.lock);

  	sock_set_flag(sk, SOCK_DEAD);

  	spin_unlock_bh(&sk->sk_receive_queue.lock);

  	sock->sk = NULL;

  	WARN_ON(IS_ERR(cf_sk->debugfs_socket_dir));

  	debugfs_remove_recursive(cf_sk->debugfs_socket_dir);

  	lock_sock(&(cf_sk->sk));

  	sk->sk_state = CAIF_DISCONNECTED;
  	sk->sk_shutdown = SHUTDOWN_MASK;

  	caif_disconnect_client(sock_net(sk), &cf_sk->layer);

  	cf_sk->sk.sk_socket->state = SS_DISCONNECTING;

  	wake_up_interruptible_poll(sk_sleep(sk), EPOLLERR|EPOLLHUP);

  	sock_orphan(sk);

  	sk_stream_kill_queues(&cf_sk->sk);
  	release_sock(sk);
  	sock_put(sk);

  	return 0;

  }

  /* Copied from af_unix.c:unix_poll(), added CAIF tx_flow handling */

  static __poll_t caif_poll(struct file *file,
  			      struct socket *sock, poll_table *wait)

  {
  	struct sock *sk = sock->sk;

  	__poll_t mask;

  	struct caifsock *cf_sk = container_of(sk, struct caifsock, sk);

  	sock_poll_wait(file, sock, wait);

  	mask = 0;

  	/* exceptional events? */
  	if (sk->sk_err)

  		mask |= EPOLLERR;

  	if (sk->sk_shutdown == SHUTDOWN_MASK)

  		mask |= EPOLLHUP;

  	if (sk->sk_shutdown & RCV_SHUTDOWN)

  		mask |= EPOLLRDHUP;

  	/* readable? */

  	if (!skb_queue_empty_lockless(&sk->sk_receive_queue) ||

  		(sk->sk_shutdown & RCV_SHUTDOWN))

  		mask |= EPOLLIN | EPOLLRDNORM;

  	/*

  	 * we set writable also when the other side has shut down the
  	 * connection. This prevents stuck sockets.

  	 */

  	if (sock_writeable(sk) && tx_flow_is_on(cf_sk))

  		mask |= EPOLLOUT | EPOLLWRNORM | EPOLLWRBAND;

  
  	return mask;

  }

  static const struct proto_ops caif_seqpacket_ops = {
  	.family = PF_CAIF,
  	.owner = THIS_MODULE,
  	.release = caif_release,
  	.bind = sock_no_bind,
  	.connect = caif_connect,
  	.socketpair = sock_no_socketpair,
  	.accept = sock_no_accept,
  	.getname = sock_no_getname,

  	.poll = caif_poll,

  	.ioctl = sock_no_ioctl,
  	.listen = sock_no_listen,
  	.shutdown = sock_no_shutdown,
  	.setsockopt = setsockopt,

  	.sendmsg = caif_seqpkt_sendmsg,
  	.recvmsg = caif_seqpkt_recvmsg,
  	.mmap = sock_no_mmap,
  	.sendpage = sock_no_sendpage,
  };
  
  static const struct proto_ops caif_stream_ops = {

  	.family = PF_CAIF,
  	.owner = THIS_MODULE,
  	.release = caif_release,
  	.bind = sock_no_bind,
  	.connect = caif_connect,
  	.socketpair = sock_no_socketpair,
  	.accept = sock_no_accept,
  	.getname = sock_no_getname,

  	.poll = caif_poll,

  	.ioctl = sock_no_ioctl,
  	.listen = sock_no_listen,

  	.shutdown = sock_no_shutdown,

  	.setsockopt = setsockopt,

  	.sendmsg = caif_stream_sendmsg,
  	.recvmsg = caif_stream_recvmsg,

  	.mmap = sock_no_mmap,

  	.sendpage = sock_no_sendpage,

  };
  
  /* This function is called when a socket is finally destroyed. */
  static void caif_sock_destructor(struct sock *sk)
  {

  	struct caifsock *cf_sk = container_of(sk, struct caifsock, sk);

  	caif_assert(!refcount_read(&sk->sk_wmem_alloc));

  	caif_assert(sk_unhashed(sk));
  	caif_assert(!sk->sk_socket);
  	if (!sock_flag(sk, SOCK_DEAD)) {

  		pr_debug("Attempt to release alive CAIF socket: %p
  ", sk);

  		return;
  	}

  	sk_stream_kill_queues(&cf_sk->sk);

  	caif_free_client(&cf_sk->layer);

  }
  
  static int caif_create(struct net *net, struct socket *sock, int protocol,

  		       int kern)

  {
  	struct sock *sk = NULL;
  	struct caifsock *cf_sk = NULL;

  	static struct proto prot = {.name = "PF_CAIF",
  		.owner = THIS_MODULE,
  		.obj_size = sizeof(struct caifsock),

  		.useroffset = offsetof(struct caifsock, conn_req.param),
  		.usersize = sizeof_field(struct caifsock, conn_req.param)

  	};

  	if (!capable(CAP_SYS_ADMIN) && !capable(CAP_NET_ADMIN))
  		return -EPERM;

  	/*
  	 * The sock->type specifies the socket type to use.

  	 * The CAIF socket is a packet stream in the sense
  	 * that it is packet based. CAIF trusts the reliability
  	 * of the link, no resending is implemented.

  	 */

  	if (sock->type == SOCK_SEQPACKET)
  		sock->ops = &caif_seqpacket_ops;
  	else if (sock->type == SOCK_STREAM)
  		sock->ops = &caif_stream_ops;
  	else

  		return -ESOCKTNOSUPPORT;

  	if (protocol < 0 || protocol >= CAIFPROTO_MAX)
  		return -EPROTONOSUPPORT;
  	/*

  	 * Set the socket state to unconnected.	 The socket state
  	 * is really not used at all in the net/core or socket.c but the

  	 * initialization makes sure that sock->state is not uninitialized.
  	 */

  	sk = sk_alloc(net, PF_CAIF, GFP_KERNEL, &prot, kern);

  	if (!sk)
  		return -ENOMEM;
  
  	cf_sk = container_of(sk, struct caifsock, sk);
  
  	/* Store the protocol */
  	sk->sk_protocol = (unsigned char) protocol;

  	/* Initialize default priority for well-known cases */
  	switch (protocol) {
  	case CAIFPROTO_AT:
  		sk->sk_priority = TC_PRIO_CONTROL;
  		break;
  	case CAIFPROTO_RFM:
  		sk->sk_priority = TC_PRIO_INTERACTIVE_BULK;
  		break;
  	default:
  		sk->sk_priority = TC_PRIO_BESTEFFORT;
  	}

  	/*
  	 * Lock in order to try to stop someone from opening the socket
  	 * too early.
  	 */
  	lock_sock(&(cf_sk->sk));
  
  	/* Initialize the nozero default sock structure data. */
  	sock_init_data(sock, sk);

  	sk->sk_destruct = caif_sock_destructor;

  	mutex_init(&cf_sk->readlock); /* single task reading lock */
  	cf_sk->layer.ctrlcmd = caif_ctrl_cb;
  	cf_sk->sk.sk_socket->state = SS_UNCONNECTED;
  	cf_sk->sk.sk_state = CAIF_DISCONNECTED;

  	set_tx_flow_off(cf_sk);
  	set_rx_flow_on(cf_sk);

  
  	/* Set default options on configuration */

  	cf_sk->conn_req.link_selector = CAIF_LINK_LOW_LATENCY;

  	cf_sk->conn_req.protocol = protocol;

  	release_sock(&cf_sk->sk);
  	return 0;

  }

  static const struct net_proto_family caif_family_ops = {

  	.family = PF_CAIF,
  	.create = caif_create,
  	.owner = THIS_MODULE,
  };

  static int __init caif_sktinit_module(void)

  {

  	return sock_register(&caif_family_ops);

  }

  static void __exit caif_sktexit_module(void)
  {
  	sock_unregister(PF_CAIF);

  }

  module_init(caif_sktinit_module);
  module_exit(caif_sktexit_module);