net: x25_asy: Delete the x25_asy driver

This driver transports LAPB (X.25 link layer) frames over TTY links.

I can safely say that this driver has no actual user because it was
not working at all until:
commit 8fdcabea ("drivers/net/wan/x25_asy: Fix to make it work")

The code in its current state still has problems:

1.
The uses of "struct x25_asy" in x25_asy_unesc (when receiving) and in
x25_asy_write_wakeup (when sending) are not protected by locks against
x25_asy_change_mtu's changing of the transmitting/receiving buffers.
Also, all "netif_running" checks in this driver are not protected by
locks against the ndo_stop function.

2.
The driver stops all TTY read/write when the netif is down.
I think this is not right because this may cause the last outgoing frame
before the netif goes down to be incompletely transmitted, and the first
incoming frame after the netif goes up to be incompletely received.

And there may also be other problems.

I was planning to fix these problems but after recent discussions about
deleting other old networking code, I think we may just delete this
driver, too.
Signed-off-by: Xie He <xie.he.0141@gmail.com>
Acked-by: Martin Schiller <ms@dev.tdt.de>
Link: https://lore.kernel.org/r/20201105073434.429307-1-xie.he.0141@gmail.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

Documentation/process/magic-number.rst

@@ -84,7 +84,6 @@ PPP_MAGIC             0x5002           ppp                      ``include/linux/
 SSTATE_MAGIC          0x5302           serial_state             ``include/linux/serial.h``
 SLIP_MAGIC            0x5302           slip                     ``drivers/net/slip.h``
 STRIP_MAGIC           0x5303           strip                    ``drivers/net/strip.c``
-X25_ASY_MAGIC         0x5303           x25_asy                  ``drivers/net/x25_asy.h``
 SIXPACK_MAGIC         0x5304           sixpack                  ``drivers/net/hamradio/6pack.h``
 AX25_MAGIC            0x5316           ax_disp                  ``drivers/net/mkiss.h``
 TTY_MAGIC             0x5401           tty_struct               ``include/linux/tty.h``

Documentation/translations/it_IT/process/magic-number.rst

@@ -90,7 +90,6 @@ PPP_MAGIC             0x5002           ppp                      ``include/linux/
 SSTATE_MAGIC          0x5302           serial_state             ``include/linux/serial.h``
 SLIP_MAGIC            0x5302           slip                     ``drivers/net/slip.h``
 STRIP_MAGIC           0x5303           strip                    ``drivers/net/strip.c``
-X25_ASY_MAGIC         0x5303           x25_asy                  ``drivers/net/x25_asy.h``
 SIXPACK_MAGIC         0x5304           sixpack                  ``drivers/net/hamradio/6pack.h``
 AX25_MAGIC            0x5316           ax_disp                  ``drivers/net/mkiss.h``
 TTY_MAGIC             0x5401           tty_struct               ``include/linux/tty.h``

Documentation/translations/zh_CN/process/magic-number.rst

@@ -73,7 +73,6 @@ PPP_MAGIC             0x5002           ppp                      ``include/linux/
 SSTATE_MAGIC          0x5302           serial_state             ``include/linux/serial.h``
 SLIP_MAGIC            0x5302           slip                     ``drivers/net/slip.h``
 STRIP_MAGIC           0x5303           strip                    ``drivers/net/strip.c``
-X25_ASY_MAGIC         0x5303           x25_asy                  ``drivers/net/x25_asy.h``
 SIXPACK_MAGIC         0x5304           sixpack                  ``drivers/net/hamradio/6pack.h``
 AX25_MAGIC            0x5316           ax_disp                  ``drivers/net/mkiss.h``
 TTY_MAGIC             0x5401           tty_struct               ``include/linux/tty.h``

arch/mips/configs/gpr_defconfig

@@ -230,7 +230,6 @@ CONFIG_DSCC4_PCISYNC=y
 CONFIG_DSCC4_PCI_RST=y
 CONFIG_DLCI=m
 CONFIG_LAPBETHER=m
-CONFIG_X25_ASY=m
 # CONFIG_INPUT_KEYBOARD is not set
 # CONFIG_INPUT_MOUSE is not set
 # CONFIG_SERIO is not set

arch/mips/configs/mtx1_defconfig

@@ -380,7 +380,6 @@ CONFIG_DSCC4_PCISYNC=y
 CONFIG_DSCC4_PCI_RST=y
 CONFIG_DLCI=m
 CONFIG_LAPBETHER=m
-CONFIG_X25_ASY=m
 # CONFIG_KEYBOARD_ATKBD is not set
 CONFIG_KEYBOARD_GPIO=y
 # CONFIG_INPUT_MOUSE is not set

drivers/net/wan/Kconfig

@@ -383,21 +383,6 @@ config LAPBETHER
 
 	  If unsure, say N.
 
-config X25_ASY
-	tristate "X.25 async driver"
-	depends on LAPB && X25 && TTY
-	help
-	  Send and receive X.25 frames over regular asynchronous serial
-	  lines such as telephone lines equipped with ordinary modems.
-
-	  Experts should note that this driver doesn't currently comply with
-	  the asynchronous HDLS framing protocols in CCITT recommendation X.25.
-
-	  To compile this driver as a module, choose M here: the
-	  module will be called x25_asy.
-
-	  If unsure, say N.
-
 config SBNI
 	tristate "Granch SBNI12 Leased Line adapter support"
 	depends on X86

drivers/net/wan/Makefile

@@ -18,7 +18,6 @@ obj-$(CONFIG_HOSTESS_SV11)	+= z85230.o	hostess_sv11.o
 obj-$(CONFIG_SEALEVEL_4021)	+= z85230.o	sealevel.o
 obj-$(CONFIG_COSA)		+= cosa.o
 obj-$(CONFIG_FARSYNC)		+= farsync.o
-obj-$(CONFIG_X25_ASY)		+= x25_asy.o
 
 obj-$(CONFIG_LANMEDIA)		+= lmc/
 

drivers/net/wan/x25_asy.h

-/* SPDX-License-Identifier: GPL-2.0 */
-#ifndef _LINUX_X25_ASY_H
-#define _LINUX_X25_ASY_H
-
-/* X.25 asy configuration. */
-#define SL_NRUNIT	256		/* MAX number of X.25 channels;
-					   This can be overridden with
-					   insmod -ox25_asy_maxdev=nnn	*/
-#define SL_MTU		256	
-
-/* X25 async protocol characters. */
-#define X25_END         0x7E		/* indicates end of frame	*/
-#define X25_ESC         0x7D		/* indicates byte stuffing	*/
-#define X25_ESCAPE(x)	((x)^0x20)
-#define X25_UNESCAPE(x)	((x)^0x20)
-
-
-struct x25_asy {
-  int			magic;
-
-  /* Various fields. */
-  spinlock_t		lock;
-  struct tty_struct	*tty;		/* ptr to TTY structure		*/
-  struct net_device	*dev;		/* easy for intr handling	*/
-
-  /* These are pointers to the malloc()ed frame buffers. */
-  unsigned char		*rbuff;		/* receiver buffer		*/
-  int                   rcount;         /* received chars counter       */
-  unsigned char		*xbuff;		/* transmitter buffer		*/
-  unsigned char         *xhead;         /* pointer to next byte to XMIT */
-  int                   xleft;          /* bytes left in XMIT queue     */
-  int                   buffsize;       /* Max buffers sizes            */
-
-  unsigned long		flags;		/* Flag values/ mode etc	*/
-#define SLF_INUSE	0		/* Channel in use               */
-#define SLF_ESCAPE	1               /* ESC received                 */
-#define SLF_ERROR	2               /* Parity, etc. error           */
-};
-
-
-
-#define X25_ASY_MAGIC 0x5303
-
-int x25_asy_init(struct net_device *dev);
-
-#endif	/* _LINUX_X25_ASY.H */