linux-2.1.101-ftcp.tgz:

	Linux kernel 2.1.101 source distribution with freeze TCP
	support.  To enable, select Freeze TCP support (CONFIG_FTCP)
	under Networking Options when compiling.

ftcp.h:

	Include file needed for user access to the ftcp system call.
	The behavior is meant to imitate a function declared as:

		int ftcp(func, ftcp_t *fp);

	and really just calls the sys_ftcp() function shown below.
	Type ftcp_t is defined by:

		typedef struct {
		  char *ifname;
		  int val;
		} ftcp_t;

	where ifname is a pointer to the name of the network interface
	to use (eth0, ppp0, etc.).  The result of the called function
	gets returned in val.  The return value of the function itself
	just reflects success (0) or failure (-1).  On failure the
	global variable errno can get set to the values below.

		EACCES user has insufficient privileges
		EINVAL for invalid function

	int sys_ftcp(int func, ftcp_t *fp);

	  System call interface to the kernel functions below.  The
	  func parameter can take any of the values below and selects
	  which kernel function gets called.

	    FTCP_FREEZE_CHECK
	    FTCP_FREEZE_OFF
	    FTCP_FREEZE_ON
	    FTCP_IF_CHECK
	    FTCP_IF_DISABLE
	    FTCP_IF_ENABLE
	    FTCP_DUP_ACKS1
	    FTCP_DUP_ACKS3

Kernel functions:

	The kernel functions that implement freeze TCP are described
	below.  All of them may return fp->val equal to -ENODEV if an
	invalid network interface is given.

	void ftcp_freeze_check(ftcp_t *fp);

	  Check if an interface is frozen.  Returns fp->val equal to 1
	  if so, 0 if not.

	void ftcp_freeze_on(ftcp_t *fp);

	  Turn freeze TCP on for an interface.  Returns fp->val equal
	  to 1 if interface was previously frozen, 0 otherwise.

	void ftcp_freeze_off(ftcp_t *fp);

	  Turn freeze TCP off for an interface.  Returns fp->val equal
	  to 1 if interface was previously frozen, 0 otherwise.

	void ftcp_if_check(ftcp_t *fp);

	  Check if an interface is enabled.  Returns fp->val equal to
	  1 if so, 0 if not.

	void ftcp_if_disable(ftcp_t *fp);

	  Disable an interface (drop all IP packets going through the
	  interface).  Returns fp->val equal to 1 if interface was
	  previously disabled, 0 otherwise.

	void ftcp_if_enable(ftcp_t *fp);

	  Enable an interface (pass IP packets through the interface).
	  Returns fp->val equal to 1 if interface was previously
	  disabled, 0 otherwise.

	void ftcp_send_dup_acks(ftcp_t *fp, int num);

	  Send num duplicate ACKs on all established TCP sockets.
	  Returns fp->val equal to the number of sockets where
	  duplicate ACKs were on.

example.c:

	An example program using the freeze TCP system call.  This
	simple program is meant to be run while TCP connections are
	active through network interface IFNAME defined on line 7
	(eth0 by default).  First freeze TCP is enabled for IFNAME,
	which should put TCP peers into persist mode.  Then IFNAME is
	disabled so all packets going through it are dropped,
	simulating a network disconnection.  After waiting a while
	freeze TCP is disabled for IFNAME, the interface is enabled,
	and three duplicate ACKs are sent to bring TCP peers out of
	persists mode.