datagram.c

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/*
 *	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 <[e-mail]>. (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/types.h>
#include <linux/kernel.h>
#include <asm/uaccess.h>
#include <asm/system.h>
#include <linux/mm.h>
#include <linux/interrupt.h>
#include <linux/in.h>
#include <linux/errno.h>
#include <linux/sched.h>
#include <linux/inet.h>
#include <linux/netdevice.h>
#include <linux/poll.h>

#include <net/ip.h>
#include <net/protocol.h>
#include <net/route.h>
#include <net/tcp.h>
#include <net/udp.h>
#include <linux/skbuff.h>
#include <net/sock.h>


/*
 *	Is a socket 'connection oriented' ?
 */
 
static inline int connection_based(struct sock *sk)
{
	return (sk->type==SOCK_SEQPACKET || sk->type==SOCK_STREAM);
}


/*
 * Wait for a packet..
 */

static int wait_for_packet(struct sock * sk, int *err, long *timeo_p)
{
	int error;

	DECLARE_WAITQUEUE(wait, current);

	__set_current_state(TASK_INTERRUPTIBLE);
	add_wait_queue_exclusive(sk->sleep, &wait);

	/* Socket errors? */
	error = sock_error(sk);
	if (error)
		goto out;

	if (!skb_queue_empty(&sk->receive_queue))
		goto ready;

	/* Socket shut down? */
	if (sk->shutdown & RCV_SHUTDOWN)
		goto out;

	/* Sequenced packets can come disconnected. If so we report the problem */
	error = -ENOTCONN;
	if(connection_based(sk) && !(sk->state==TCP_ESTABLISHED || sk->state==TCP_LISTEN))
		goto out;

	/* handle signals */
	if (signal_pending(current))
		goto interrupted;

	*timeo_p = schedule_timeout(*timeo_p);

ready:
	current->state = TASK_RUNNING;
	remove_wait_queue(sk->sleep, &wait);
	return 0;

interrupted:
	error = sock_intr_errno(*timeo_p);
out:
	current->state = TASK_RUNNING;
	remove_wait_queue(sk->sleep, &wait);
	*err = error;
	return error;
}

/*
 *	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)
 *
 *	* 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_recv_datagram(struct sock *sk, unsigned flags, int noblock, int *err)
{
	int error;
	struct sk_buff *skb;
	long timeo;

	/* Caller is allowed not to check sk->err before skb_recv_datagram() */
	error = sock_error(sk);
	if (error)
		goto no_packet;

	timeo = sock_rcvtimeo(sk, noblock);

	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 corrent in any case. 8)
		 */
		if (flags & MSG_PEEK)
		{
			unsigned long cpu_flags;

			spin_lock_irqsave(&sk->receive_queue.lock, cpu_flags);
			skb = skb_peek(&sk->receive_queue);
			if(skb!=NULL)
				atomic_inc(&skb->users);
			spin_unlock_irqrestore(&sk->receive_queue.lock, cpu_flags);
		} else
			skb = skb_dequeue(&sk->receive_queue);

		if (skb)
			return skb;

		/* User doesn't want to wait */
		error = -EAGAIN;
		if (!timeo)
			goto no_packet;

	} while (wait_for_packet(sk, err, &timeo) == 0);

	return NULL;

no_packet:
	*err = error;
	return NULL;
}

void skb_free_datagram(struct sock * sk, struct sk_buff *skb)
{
	kfree_skb(skb);
}

/*
 *	Copy a datagram to a linear buffer.
 */

int skb_copy_datagram(struct sk_buff *skb, int offset, char *to, int size)
{
	int err = -EFAULT;

	if (!copy_to_user(to, skb->h.raw + offset, size))
		err = 0;
	return err;
}


/*
 *	Copy a datagram to an iovec.
 *	Note: the iovec is modified during the copy.
 */
 
int skb_copy_datagram_iovec(struct sk_buff *skb, int offset, struct iovec *to,
			    int size)
{
	return memcpy_toiovec(to, skb->h.raw + offset, size);
}

/*
 *	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;

	poll_wait(file, sk->sleep, wait);
	mask = 0;

	/* exceptional events? */
	if (sk->err || !skb_queue_empty(&sk->error_queue))
		mask |= POLLERR;
	if (sk->shutdown == SHUTDOWN_MASK)
		mask |= POLLHUP;

	/* readable? */
	if (!skb_queue_empty(&sk->receive_queue) || (sk->shutdown&RCV_SHUTDOWN))
		mask |= POLLIN | POLLRDNORM;

	/* Connection-based need to check for termination and startup */
	if (connection_based(sk)) {
		if (sk->state==TCP_CLOSE)
			mask |= POLLHUP;
		/* connection hasn't started yet? */
		if (sk->state == TCP_SYN_SENT)
			return mask;
	}

	/* writable? */
	if (sock_writeable(sk))
		mask |= POLLOUT | POLLWRNORM | POLLWRBAND;
	else
		set_bit(SOCK_ASYNC_NOSPACE, &sk->socket->flags);

	return mask;
}