The long and short of it is:

DO NOT compile ftape/zftape as a module.  The entry in
/proc/devices (27 zft) is never created.

Here are the results of doing it as a module:

Attempt to dump stuff to tape via several devices:

tar -cvf /dev/ftape *
tar: Cannot open /dev/ftape: No such device
tar: Error is not recoverable: exiting now

tar -cvf /dev/rft0 *
tar: Cannot open /dev/rft0: No such device
tar: Error is not recoverable: exiting now

tar -cvf /dev/qft0 *
tar: Cannot open /dev/qft0: No such device
tar: Error is not recoverable: exiting now

tar -cvf /dev/zqft0 *
tar: Cannot open /dev/zqft0: No such device
tar: Error is not recoverable: exiting now


Look at the /dev directory to see that devices do exist:

ls -la ftape
lrwxrwxrwx   1 root     root            4 Mar 29 09:33 ftape
-> rft0
ls -la rft0
crw-rw----   1 root     disk      27,   0 May  5  1998 rft0
ls -la qft0
crw-rw----   1 root     disk      27,   0 Apr 17 11:53 qft0
ls -la zqft0
crw-rw----   1 root     disk      27,  16 Apr 17 11:53 zqft0

Look into /var/log/messages file to see what it has to say:

Jul  8 10:26:17 kernel: ftape v3.04d 25/11/97
Jul  8 10:26:17 kernel: =A9 1993-1996 Bas Laarhoven
(bas <bas> )
Jul  8 10:26:17 kernel: =A9 1995-1996 Kai
Harrekilde-Petersen (khp
<khp> )
Jul  8 10:26:17 kernel: =A9 1996-1997 Claus-Justus Heine
(claus.rwth-aachen.de
<claus.rwth-aachen.de> )
Jul  8 10:26:17 kernel: QIC-117 driver for
QIC-40/80/3010/3020 floppy tape drives
Jul  8 10:26:17 kernel: Compiled for Linux version 2.2.5-22
with versioned symbols
Jul  8 10:26:17 kernel: [000] ftape-init.c (ftape_init) -
installing QIC-117 floppy tape hardware drive ... .
Jul  8 10:26:17 kernel: [001] ftape-init.c (ftape_init) -
ftape_init @ 0xc4823050.
Jul  8 10:26:17 kernel: [002]   ftape-buffer.c
(add_one_buffer) - buffer nr #1 @ c3177410, dma area @
c0fa8000.
Jul  8 10:26:17 kernel: [003]   ftape-buffer.c
(add_one_buffer) - buffer nr #2 @ c1219630, dma area @
c0fa0000.
Jul  8 10:26:17 kernel: [004]   ftape-buffer.c
(add_one_buffer) - buffer nr #3 @ c10a6490, dma area @
c0f78000.
Jul  8 10:26:17 kernel: [005]   ftape-calibr.c (time_inb) -
inb() duration: 651 nsec.
Jul  8 10:26:17 kernel: [006]  ftape-calibr.c
(ftape_calibrate) - TC for 'ftape_udelay()' =3D 2619 nsec
(at 2559 counts).
Jul  8 10:26:17 kernel: [007]  ftape-calibr.c
(ftape_calibrate) - TC for 'fdc_wait()' =3D 2080 nsec (at
2559 counts).

Unload module via rmmod command:

Jul  8 10:47:26 kernel: [008]   ftape-buffer.c
(del_one_buffer) - releasing buffer nr #3 @ c10a6490, dma
area @ c0f78000.
Jul  8 10:47:26 kernel: [009]   ftape-buffer.c
(del_one_buffer) - releasing buffer nr #2 @ c1219630, dma
area @ c0fa0000.
Jul  8 10:47:26 kernel: [010]   ftape-buffer.c
(del_one_buffer) - releasing buffer nr #1 @ c3177410, dma
area @ c0fa8000.
Jul  8 10:47:26 kernel: ftape: unloaded.