text: /*
   *	SUCS NET3:
   *
   *	Generic datagram handling routines. These are generic for all
   *	protocols. Possibly a generic IP version on top of these would
   *	make sense. Not tonight however 8-).
   *	This is used because UDP, RAW, PACKET, DDP, IPX, AX.25 and
   *	NetROM layer all have identical poll code and mostly
   *	identical recvmsg() code. So we share it here. The poll was
   *	shared before but buried in udp.c so I moved it.
   *
   *	Authors:	Alan Cox <alan@lxorguk.ukuu.org.uk>. (datagram_poll() from old
   *						     udp.c code)
   *
   *	Fixes:
   *		Alan Cox	:	NULL return from skb_peek_copy()
   *					understood
   *		Alan Cox	:	Rewrote skb_read_datagram to avoid the
   *					skb_peek_copy stuff.
   *		Alan Cox	:	Added support for SOCK_SEQPACKET.
   *					IPX can no longer use the SO_TYPE hack
   *					but AX.25 now works right, and SPX is
   *					feasible.
   *		Alan Cox	:	Fixed write poll of non IP protocol
   *					crash.
   *		Florian  La Roche:	Changed for my new skbuff handling.
   *		Darryl Miles	:	Fixed non-blocking SOCK_SEQPACKET.
   *		Linus Torvalds	:	BSD semantic fixes.
   *		Alan Cox	:	Datagram iovec handling
   *		Darryl Miles	:	Fixed non-blocking SOCK_STREAM.
   *		Alan Cox	:	POSIXisms
   *		Pete Wyckoff    :       Unconnected accept() fix.
   *
   */
  
  #include <linux/module.h>
  #include <linux/types.h>
  #include <linux/kernel.h>
  #include <asm/uaccess.h>
  #include <linux/mm.h>
  #include <linux/interrupt.h>
  #include <linux/errno.h>
  #include <linux/sched.h>
  #include <linux/inet.h>
  #include <linux/netdevice.h>
  #include <linux/rtnetlink.h>
  #include <linux/poll.h>
  #include <linux/highmem.h>
  #include <linux/spinlock.h>
  #include <linux/slab.h>
  #include <linux/pagemap.h>
  #include <linux/uio.h>
  
  #include <net/protocol.h>
  #include <linux/skbuff.h>
  
  #include <net/checksum.h>
  #include <net/sock.h>
  #include <net/tcp_states.h>
  #include <trace/events/skb.h>
  #include <net/busy_poll.h>
  
  /*
   *	Is a socket 'connection oriented' ?
   */
  static inline int connection_based(struct sock *sk)
  {
  	return sk->sk_type == SOCK_SEQPACKET || sk->sk_type == SOCK_STREAM;
  }
  
  static int receiver_wake_function(wait_queue_t *wait, unsigned int mode, int sync,
  				  void *key)
  {
  	unsigned long bits = (unsigned long)key;
  
  	/*
  	 * Avoid a wakeup if event not interesting for us
  	 */
  	if (bits && !(bits & (POLLIN | POLLERR)))
  		return 0;
  	return autoremove_wake_function(wait, mode, sync, key);
  }
  /*
   * Wait for the last received packet to be different from skb
   */
  int __skb_wait_for_more_packets(struct sock *sk, int *err, long *timeo_p,
  				const struct sk_buff *skb)
  {
  	int error;
  	DEFINE_WAIT_FUNC(wait, receiver_wake_function);
  
  	prepare_to_wait_exclusive(sk_sleep(sk), &wait, TASK_INTERRUPTIBLE);
  
  	/* Socket errors? */
  	error = sock_error(sk);
  	if (error)
  		goto out_err;
  
  	if (sk->sk_receive_queue.prev != skb)
  		goto out;
  
  	/* Socket shut down? */
  	if (sk->sk_shutdown & RCV_SHUTDOWN)
  		goto out_noerr;
  
  	/* Sequenced packets can come disconnected.
  	 * If so we report the problem
  	 */
  	error = -ENOTCONN;
  	if (connection_based(sk) &&
  	    !(sk->sk_state == TCP_ESTABLISHED || sk->sk_state == TCP_LISTEN))
  		goto out_err;
  
  	/* handle signals */
  	if (signal_pending(current))
  		goto interrupted;
  
  	error = 0;
  	*timeo_p = schedule_timeout(*timeo_p);
  out:
  	finish_wait(sk_sleep(sk), &wait);
  	return error;
  interrupted:
  	error = sock_intr_errno(*timeo_p);
  out_err:
  	*err = error;
  	goto out;
  out_noerr:
  	*err = 0;
  	error = 1;
  	goto out;
  }
  EXPORT_SYMBOL(__skb_wait_for_more_packets);
  
  static struct sk_buff *skb_set_peeked(struct sk_buff *skb)
  {
  	struct sk_buff *nskb;
  
  	if (skb->peeked)
  		return skb;
  
  	/* We have to unshare an skb before modifying it. */
  	if (!skb_shared(skb))
  		goto done;
  
  	nskb = skb_clone(skb, GFP_ATOMIC);
  	if (!nskb)
  		return ERR_PTR(-ENOMEM);
  
  	skb->prev->next = nskb;
  	skb->next->prev = nskb;
  	nskb->prev = skb->prev;
  	nskb->next = skb->next;
  
  	consume_skb(skb);
  	skb = nskb;
  
  done:
  	skb->peeked = 1;
  
  	return skb;
  }
  
  /**
   *	__skb_try_recv_datagram - Receive a datagram skbuff
   *	@sk: socket
   *	@flags: MSG_ flags
   *	@peeked: returns non-zero if this packet has been seen before
   *	@off: an offset in bytes to peek skb from. Returns an offset
   *	      within an skb where data actually starts
   *	@err: error code returned
   *	@last: set to last peeked message to inform the wait function
   *	       what to look for when peeking
   *
   *	Get a datagram skbuff, understands the peeking, nonblocking wakeups
   *	and possible races. This replaces identical code in packet, raw and
   *	udp, as well as the IPX AX.25 and Appletalk. It also finally fixes
   *	the long standing peek and read race for datagram sockets. If you
   *	alter this routine remember it must be re-entrant.
   *
   *	This function will lock the socket if a skb is returned, so
   *	the caller needs to unlock the socket in that case (usually by
   *	calling skb_free_datagram). Returns NULL with *err set to
   *	-EAGAIN if no data was available or to some other value if an
   *	error was detected.
   *
   *	* It does not lock socket since today. This function is
   *	* free of race conditions. This measure should/can improve
   *	* significantly datagram socket latencies at high loads,
   *	* when data copying to user space takes lots of time.
   *	* (BTW I've just killed the last cli() in IP/IPv6/core/netlink/packet
   *	*  8) Great win.)
   *	*			                    --ANK (980729)
   *
   *	The order of the tests when we find no data waiting are specified
   *	quite explicitly by POSIX 1003.1g, don't change them without having
   *	the standard around please.
   */
  struct sk_buff *__skb_try_recv_datagram(struct sock *sk, unsigned int flags,
  					int *peeked, int *off, int *err,
  					struct sk_buff **last)
  {
  	struct sk_buff_head *queue = &sk->sk_receive_queue;
  	struct sk_buff *skb;
  	unsigned long cpu_flags;
  	/*
  	 * Caller is allowed not to check sk->sk_err before skb_recv_datagram()
  	 */
  	int error = sock_error(sk);
  
  	if (error)
  		goto no_packet;
  
  	do {
  		/* Again only user level code calls this function, so nothing
  		 * interrupt level will suddenly eat the receive_queue.
  		 *
  		 * Look at current nfs client by the way...
  		 * However, this function was correct in any case. 8)
  		 */
  		int _off = *off;
  
  		*last = (struct sk_buff *)queue;
  		spin_lock_irqsave(&queue->lock, cpu_flags);
  		skb_queue_walk(queue, skb) {
  			*last = skb;
  			*peeked = skb->peeked;
  			if (flags & MSG_PEEK) {
  				if (_off >= skb->len && (skb->len || _off ||
  							 skb->peeked)) {
  					_off -= skb->len;
  					continue;
  				}
  
  				skb = skb_set_peeked(skb);
  				error = PTR_ERR(skb);
  				if (IS_ERR(skb)) {
  					spin_unlock_irqrestore(&queue->lock,
  							       cpu_flags);
  					goto no_packet;
  				}
  
  				atomic_inc(&skb->users);
  			} else
  				__skb_unlink(skb, queue);
  
  			spin_unlock_irqrestore(&queue->lock, cpu_flags);
  			*off = _off;
  			return skb;
  		}
  
  		spin_unlock_irqrestore(&queue->lock, cpu_flags);
  	} while (sk_can_busy_loop(sk) &&
  		 sk_busy_loop(sk, flags & MSG_DONTWAIT));
  
  	error = -EAGAIN;
  
  no_packet:
  	*err = error;
  	return NULL;
  }
  EXPORT_SYMBOL(__skb_try_recv_datagram);
  
  struct sk_buff *__skb_recv_datagram(struct sock *sk, unsigned int flags,
  				    int *peeked, int *off, int *err)
  {
  	struct sk_buff *skb, *last;
  	long timeo;
  
  	timeo = sock_rcvtimeo(sk, flags & MSG_DONTWAIT);
  
  	do {
  		skb = __skb_try_recv_datagram(sk, flags, peeked, off, err,
  					      &last);
  		if (skb)
  			return skb;
  
  		if (*err != -EAGAIN)
  			break;
  	} while (timeo &&
  		!__skb_wait_for_more_packets(sk, err, &timeo, last));
  
  	return NULL;
  }
  EXPORT_SYMBOL(__skb_recv_datagram);
  
  struct sk_buff *skb_recv_datagram(struct sock *sk, unsigned int flags,
  				  int noblock, int *err)
  {
  	int peeked, off = 0;
  
  	return __skb_recv_datagram(sk, flags | (noblock ? MSG_DONTWAIT : 0),
  				   &peeked, &off, err);
  }
  EXPORT_SYMBOL(skb_recv_datagram);
  
  void skb_free_datagram(struct sock *sk, struct sk_buff *skb)
  {
  	consume_skb(skb);
  	sk_mem_reclaim_partial(sk);
  }
  EXPORT_SYMBOL(skb_free_datagram);
  
  void __skb_free_datagram_locked(struct sock *sk, struct sk_buff *skb, int len)
  {
  	bool slow;
  
  	if (likely(atomic_read(&skb->users) == 1))
  		smp_rmb();
  	else if (likely(!atomic_dec_and_test(&skb->users))) {
  		sk_peek_offset_bwd(sk, len);
  		return;
  	}
  
  	slow = lock_sock_fast(sk);
  	sk_peek_offset_bwd(sk, len);
  	skb_orphan(skb);
  	sk_mem_reclaim_partial(sk);
  	unlock_sock_fast(sk, slow);
  
  	/* skb is now orphaned, can be freed outside of locked section */
  	__kfree_skb(skb);
  }
  EXPORT_SYMBOL(__skb_free_datagram_locked);
  
  /**
   *	skb_kill_datagram - Free a datagram skbuff forcibly
   *	@sk: socket
   *	@skb: datagram skbuff
   *	@flags: MSG_ flags
   *
   *	This function frees a datagram skbuff that was received by
   *	skb_recv_datagram.  The flags argument must match the one
   *	used for skb_recv_datagram.
   *
   *	If the MSG_PEEK flag is set, and the packet is still on the
   *	receive queue of the socket, it will be taken off the queue
   *	before it is freed.
   *
   *	This function currently only disables BH when acquiring the
   *	sk_receive_queue lock.  Therefore it must not be used in a
   *	context where that lock is acquired in an IRQ context.
   *
   *	It returns 0 if the packet was removed by us.
   */
  
  int skb_kill_datagram(struct sock *sk, struct sk_buff *skb, unsigned int flags)
  {
  	int err = 0;
  
  	if (flags & MSG_PEEK) {
  		err = -ENOENT;
  		spin_lock_bh(&sk->sk_receive_queue.lock);
  		if (skb == skb_peek(&sk->sk_receive_queue)) {
  			__skb_unlink(skb, &sk->sk_receive_queue);
  			atomic_dec(&skb->users);
  			err = 0;
  		}
  		spin_unlock_bh(&sk->sk_receive_queue.lock);
  	}
  
  	kfree_skb(skb);
  	atomic_inc(&sk->sk_drops);
  	sk_mem_reclaim_partial(sk);
  
  	return err;
  }
  EXPORT_SYMBOL(skb_kill_datagram);
  
  /**
   *	skb_copy_datagram_iter - Copy a datagram to an iovec iterator.
   *	@skb: buffer to copy
   *	@offset: offset in the buffer to start copying from
   *	@to: iovec iterator to copy to
   *	@len: amount of data to copy from buffer to iovec
   */
  int skb_copy_datagram_iter(const struct sk_buff *skb, int offset,
  			   struct iov_iter *to, int len)
  {
  	int start = skb_headlen(skb);
  	int i, copy = start - offset;
  	struct sk_buff *frag_iter;
  
  	trace_skb_copy_datagram_iovec(skb, len);
  
  	/* Copy header. */
  	if (copy > 0) {
  		if (copy > len)
  			copy = len;
  		if (copy_to_iter(skb->data + offset, copy, to) != copy)
  			goto short_copy;
  		if ((len -= copy) == 0)
  			return 0;
  		offset += copy;
  	}
  
  	/* Copy paged appendix. Hmm... why does this look so complicated? */
  	for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
  		int end;
  		const skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
  
  		WARN_ON(start > offset + len);
  
  		end = start + skb_frag_size(frag);
  		if ((copy = end - offset) > 0) {
  			if (copy > len)
  				copy = len;
  			if (copy_page_to_iter(skb_frag_page(frag),
  					      frag->page_offset + offset -
  					      start, copy, to) != copy)
  				goto short_copy;
  			if (!(len -= copy))
  				return 0;
  			offset += copy;
  		}
  		start = end;
  	}
  
  	skb_walk_frags(skb, frag_iter) {
  		int end;
  
  		WARN_ON(start > offset + len);
  
  		end = start + frag_iter->len;
  		if ((copy = end - offset) > 0) {
  			if (copy > len)
  				copy = len;
  			if (skb_copy_datagram_iter(frag_iter, offset - start,
  						   to, copy))
  				goto fault;
  			if ((len -= copy) == 0)
  				return 0;
  			offset += copy;
  		}
  		start = end;
  	}
  	if (!len)
  		return 0;
  
  	/* This is not really a user copy fault, but rather someone
  	 * gave us a bogus length on the skb.  We should probably
  	 * print a warning here as it may indicate a kernel bug.
  	 */
  
  fault:
  	return -EFAULT;
  
  short_copy:
  	if (iov_iter_count(to))
  		goto fault;
  
  	return 0;
  }
  EXPORT_SYMBOL(skb_copy_datagram_iter);
  
  /**
   *	skb_copy_datagram_from_iter - Copy a datagram from an iov_iter.
   *	@skb: buffer to copy
   *	@offset: offset in the buffer to start copying to
   *	@from: the copy source
   *	@len: amount of data to copy to buffer from iovec
   *
   *	Returns 0 or -EFAULT.
   */
  int skb_copy_datagram_from_iter(struct sk_buff *skb, int offset,
  				 struct iov_iter *from,
  				 int len)
  {
  	int start = skb_headlen(skb);
  	int i, copy = start - offset;
  	struct sk_buff *frag_iter;
  
  	/* Copy header. */
  	if (copy > 0) {
  		if (copy > len)
  			copy = len;
  		if (copy_from_iter(skb->data + offset, copy, from) != copy)
  			goto fault;
  		if ((len -= copy) == 0)
  			return 0;
  		offset += copy;
  	}
  
  	/* Copy paged appendix. Hmm... why does this look so complicated? */
  	for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
  		int end;
  		const skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
  
  		WARN_ON(start > offset + len);
  
  		end = start + skb_frag_size(frag);
  		if ((copy = end - offset) > 0) {
  			size_t copied;
  
  			if (copy > len)
  				copy = len;
  			copied = copy_page_from_iter(skb_frag_page(frag),
  					  frag->page_offset + offset - start,
  					  copy, from);
  			if (copied != copy)
  				goto fault;
  
  			if (!(len -= copy))
  				return 0;
  			offset += copy;
  		}
  		start = end;
  	}
  
  	skb_walk_frags(skb, frag_iter) {
  		int end;
  
  		WARN_ON(start > offset + len);
  
  		end = start + frag_iter->len;
  		if ((copy = end - offset) > 0) {
  			if (copy > len)
  				copy = len;
  			if (skb_copy_datagram_from_iter(frag_iter,
  							offset - start,
  							from, copy))
  				goto fault;
  			if ((len -= copy) == 0)
  				return 0;
  			offset += copy;
  		}
  		start = end;
  	}
  	if (!len)
  		return 0;
  
  fault:
  	return -EFAULT;
  }
  EXPORT_SYMBOL(skb_copy_datagram_from_iter);
  
  /**
   *	zerocopy_sg_from_iter - Build a zerocopy datagram from an iov_iter
   *	@skb: buffer to copy
   *	@from: the source to copy from
   *
   *	The function will first copy up to headlen, and then pin the userspace
   *	pages and build frags through them.
   *
   *	Returns 0, -EFAULT or -EMSGSIZE.
   */
  int zerocopy_sg_from_iter(struct sk_buff *skb, struct iov_iter *from)
  {
  	int len = iov_iter_count(from);
  	int copy = min_t(int, skb_headlen(skb), len);
  	int frag = 0;
  
  	/* copy up to skb headlen */
  	if (skb_copy_datagram_from_iter(skb, 0, from, copy))
  		return -EFAULT;
  
  	while (iov_iter_count(from)) {
  		struct page *pages[MAX_SKB_FRAGS];
  		size_t start;
  		ssize_t copied;
  		unsigned long truesize;
  		int n = 0;
  
  		if (frag == MAX_SKB_FRAGS)
  			return -EMSGSIZE;
  
  		copied = iov_iter_get_pages(from, pages, ~0U,
  					    MAX_SKB_FRAGS - frag, &start);
  		if (copied < 0)
  			return -EFAULT;
  
  		iov_iter_advance(from, copied);
  
  		truesize = PAGE_ALIGN(copied + start);
  		skb->data_len += copied;
  		skb->len += copied;
  		skb->truesize += truesize;
  		atomic_add(truesize, &skb->sk->sk_wmem_alloc);
  		while (copied) {
  			int size = min_t(int, copied, PAGE_SIZE - start);
  			skb_fill_page_desc(skb, frag++, pages[n], start, size);
  			start = 0;
  			copied -= size;
  			n++;
  		}
  	}
  	return 0;
  }
  EXPORT_SYMBOL(zerocopy_sg_from_iter);
  
  static int skb_copy_and_csum_datagram(const struct sk_buff *skb, int offset,
  				      struct iov_iter *to, int len,
  				      __wsum *csump)
  {
  	int start = skb_headlen(skb);
  	int i, copy = start - offset;
  	struct sk_buff *frag_iter;
  	int pos = 0;
  	int n;
  
  	/* Copy header. */
  	if (copy > 0) {
  		if (copy > len)
  			copy = len;
  		n = csum_and_copy_to_iter(skb->data + offset, copy, csump, to);
  		if (n != copy)
  			goto fault;
  		if ((len -= copy) == 0)
  			return 0;
  		offset += copy;
  		pos = copy;
  	}
  
  	for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
  		int end;
  		const skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
  
  		WARN_ON(start > offset + len);
  
  		end = start + skb_frag_size(frag);
  		if ((copy = end - offset) > 0) {
  			__wsum csum2 = 0;
  			struct page *page = skb_frag_page(frag);
  			u8  *vaddr = kmap(page);
  
  			if (copy > len)
  				copy = len;
  			n = csum_and_copy_to_iter(vaddr + frag->page_offset +
  						  offset - start, copy,
  						  &csum2, to);
  			kunmap(page);
  			if (n != copy)
  				goto fault;
  			*csump = csum_block_add(*csump, csum2, pos);
  			if (!(len -= copy))
  				return 0;
  			offset += copy;
  			pos += copy;
  		}
  		start = end;
  	}
  
  	skb_walk_frags(skb, frag_iter) {
  		int end;
  
  		WARN_ON(start > offset + len);
  
  		end = start + frag_iter->len;
  		if ((copy = end - offset) > 0) {
  			__wsum csum2 = 0;
  			if (copy > len)
  				copy = len;
  			if (skb_copy_and_csum_datagram(frag_iter,
  						       offset - start,
  						       to, copy,
  						       &csum2))
  				goto fault;
  			*csump = csum_block_add(*csump, csum2, pos);
  			if ((len -= copy) == 0)
  				return 0;
  			offset += copy;
  			pos += copy;
  		}
  		start = end;
  	}
  	if (!len)
  		return 0;
  
  fault:
  	return -EFAULT;
  }
  
  __sum16 __skb_checksum_complete_head(struct sk_buff *skb, int len)
  {
  	__sum16 sum;
  
  	sum = csum_fold(skb_checksum(skb, 0, len, skb->csum));
  	if (likely(!sum)) {
  		if (unlikely(skb->ip_summed == CHECKSUM_COMPLETE) &&
  		    !skb->csum_complete_sw)
  			netdev_rx_csum_fault(skb->dev);
  	}
  	if (!skb_shared(skb))
  		skb->csum_valid = !sum;
  	return sum;
  }
  EXPORT_SYMBOL(__skb_checksum_complete_head);
  
  __sum16 __skb_checksum_complete(struct sk_buff *skb)
  {
  	__wsum csum;
  	__sum16 sum;
  
  	csum = skb_checksum(skb, 0, skb->len, 0);
  
  	/* skb->csum holds pseudo checksum */
  	sum = csum_fold(csum_add(skb->csum, csum));
  	if (likely(!sum)) {
  		if (unlikely(skb->ip_summed == CHECKSUM_COMPLETE) &&
  		    !skb->csum_complete_sw)
  			netdev_rx_csum_fault(skb->dev);
  	}
  
  	if (!skb_shared(skb)) {
  		/* Save full packet checksum */
  		skb->csum = csum;
  		skb->ip_summed = CHECKSUM_COMPLETE;
  		skb->csum_complete_sw = 1;
  		skb->csum_valid = !sum;
  	}
  
  	return sum;
  }
  EXPORT_SYMBOL(__skb_checksum_complete);
  
  /**
   *	skb_copy_and_csum_datagram_msg - Copy and checksum skb to user iovec.
   *	@skb: skbuff
   *	@hlen: hardware length
   *	@msg: destination
   *
   *	Caller _must_ check that skb will fit to this iovec.
   *
   *	Returns: 0       - success.
   *		 -EINVAL - checksum failure.
   *		 -EFAULT - fault during copy.
   */
  int skb_copy_and_csum_datagram_msg(struct sk_buff *skb,
  				   int hlen, struct msghdr *msg)
  {
  	__wsum csum;
  	int chunk = skb->len - hlen;
  
  	if (!chunk)
  		return 0;
  
  	if (msg_data_left(msg) < chunk) {
  		if (__skb_checksum_complete(skb))
  			goto csum_error;
  		if (skb_copy_datagram_msg(skb, hlen, msg, chunk))
  			goto fault;
  	} else {
  		csum = csum_partial(skb->data, hlen, skb->csum);
  		if (skb_copy_and_csum_datagram(skb, hlen, &msg->msg_iter,
  					       chunk, &csum))
  			goto fault;
  		if (csum_fold(csum))
  			goto csum_error;
  		if (unlikely(skb->ip_summed == CHECKSUM_COMPLETE))
  			netdev_rx_csum_fault(skb->dev);
  	}
  	return 0;
  csum_error:
  	return -EINVAL;
  fault:
  	return -EFAULT;
  }
  EXPORT_SYMBOL(skb_copy_and_csum_datagram_msg);
  
  /**
   * 	datagram_poll - generic datagram poll
   *	@file: file struct
   *	@sock: socket
   *	@wait: poll table
   *
   *	Datagram poll: Again totally generic. This also handles
   *	sequenced packet sockets providing the socket receive queue
   *	is only ever holding data ready to receive.
   *
   *	Note: when you _don't_ use this routine for this protocol,
   *	and you use a different write policy from sock_writeable()
   *	then please supply your own write_space callback.
   */
  unsigned int datagram_poll(struct file *file, struct socket *sock,
  			   poll_table *wait)
  {
  	struct sock *sk = sock->sk;
  	unsigned int mask;
  
  	sock_poll_wait(file, sk_sleep(sk), wait);
  	mask = 0;
  
  	/* exceptional events? */
  	if (sk->sk_err || !skb_queue_empty(&sk->sk_error_queue))
  		mask |= POLLERR |
  			(sock_flag(sk, SOCK_SELECT_ERR_QUEUE) ? POLLPRI : 0);
  
  	if (sk->sk_shutdown & RCV_SHUTDOWN)
  		mask |= POLLRDHUP | POLLIN | POLLRDNORM;
  	if (sk->sk_shutdown == SHUTDOWN_MASK)
  		mask |= POLLHUP;
  
  	/* readable? */
  	if (!skb_queue_empty(&sk->sk_receive_queue))
  		mask |= POLLIN | POLLRDNORM;
  
  	/* Connection-based need to check for termination and startup */
  	if (connection_based(sk)) {
  		if (sk->sk_state == TCP_CLOSE)
  			mask |= POLLHUP;
  		/* connection hasn't started yet? */
  		if (sk->sk_state == TCP_SYN_SENT)
  			return mask;
  	}
  
  	/* writable? */
  	if (sock_writeable(sk))
  		mask |= POLLOUT | POLLWRNORM | POLLWRBAND;
  	else
  		sk_set_bit(SOCKWQ_ASYNC_NOSPACE, sk);
  
  	return mask;
  }
  EXPORT_SYMBOL(datagram_poll);
  