fsopen(vun.i2.r, filename.i1a.r, access.i2.r, status.i2.r
	       [,ext_status.i4.r] [,dispose.i2.r] [,readonly.i2.r]
	       [,event_flag.i2.r] [,timeout.i2.r] [,astfunc.f.v] [,shared.i2.r]

	File Sharing service routine called to open an existing file (fspec)
	on the central disk for subsequent I/O operations. The file must
	reside in an RSXFSHARE directory or related subdirectory. Various file
	attributes may be specified or defaulted with this call.  A
	relationship is established linking the virtual unit number (vun)
	with the file for subsequent file references.

	vun		virtual unit number on which the file is to be opened
	filename	null terminated file name
	access		type of record access
			(FSHR_DIRECT -> direct (random by record number),
			 FSHR_SEQUENTIAL -> sequential,
			 FSHR_APPEND -> append (sequential),
			 FSHR_KEYED -> keyed or indexed access)
	status		returned ACNET status code
	[ext_status]	returned extended status from VMS/RMS
	[dispose]	specifies the dispositon of the file after closing
			(FSHR_SAVE -> save file (default),
			 FSHR_SUBMIT -> submit to batch queue)
	[readonly]	specifies the read/write access of the file
			(FSHR_READ_ACCESS -> readonly (default),
			 FSHR_WRITE_ACCESS -> read/write access)
	[event_flag]	specifies an I/O completion event flag
			(open is asynchronous if this is specified and
			 non-zero) (default is NULL)
	[timeout]	user-specified network timeout interval in units
			of seconds (default is 10 seconds)
	[astfunc]	specifies the address of a routine to be executed
			at AST level on I/O completion (read is asynchronous
			if this is specified and non-zero) (default is NULL)
			(This argument is no longer used.  Only synchronous
			 calls can be made.)
	[shared]	specifies scope of access to the file (default is NULL)
			(FSHR_EXCLUSIVE -> exclusive access,
			 FSHR_SHARED -> shared (default))
	[max_record]	maximum record to be written to the file

	This function requires the following include files:

	cnsparam_h, clib_h

	Related functions:

	fsclos, fsread, fswrit, fsunlk, fsrdm, fsrew, fsweof, fsdel