tty: The big operations rework

- Operations are now a shared const function block as with most other Linux
  objects

- Introduce wrappers for some optional functions to get consistent behaviour

- Wrap put_char which used to be patched by the tty layer

- Document which functions are needed/optional

- Make put_char report success/fail

- Cache the driver->ops pointer in the tty as tty->ops

- Remove various surplus lock calls we no longer need

- Remove proc_write method as noted by Alexey Dobriyan

- Introduce some missing sanity checks where certain driver/ldisc
  combinations would oops as they didn't check needed methods were present

[akpm@linux-foundation.org: fix fs/compat_ioctl.c build]
[akpm@linux-foundation.org: fix isicom]
[akpm@linux-foundation.org: fix arch/ia64/hp/sim/simserial.c build]
[akpm@linux-foundation.org: fix kgdb]
Signed-off-by: Alan Cox <alan@redhat.com>
Acked-by: Greg Kroah-Hartman <gregkh@suse.de>
Cc: Jason Wessel <jason.wessel@windriver.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 62 insertions, 48 deletions

diff --git a/include/linux/tty.h b/include/linux/tty.h
index 2699298b00ef..c36a76da2ae2 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -177,9 +177,13 @@ struct signal_struct;
  * size each time the window is created or resized anyway.
  *                                              - TYT, 9/14/92
  */
+
+struct tty_operations;
+
 struct tty_struct {
         int     magic;
         struct tty_driver *driver;
+        const struct tty_operations *ops;
         int index;
         struct tty_ldisc ldisc;
         struct mutex termios_mutex;
@@ -295,6 +299,10 @@ extern void tty_unregister_device(struct tty_driver *driver, unsigned index);
 extern int tty_read_raw_data(struct tty_struct *tty, unsigned char *bufp,
                              int buflen);
 extern void tty_write_message(struct tty_struct *tty, char *msg);
+extern int tty_put_char(struct tty_struct *tty, unsigned char c);
+extern int tty_chars_in_buffer(struct tty_struct *tty);
+extern int tty_write_room(struct tty_struct *tty);
+extern void tty_driver_flush_buffer(struct tty_struct *tty);
 
 extern int is_current_pgrp_orphaned(void);
 extern struct pid *tty_get_pgrp(struct tty_struct *tty);
diff --git a/include/linux/tty_driver.h b/include/linux/tty_driver.h
index 21f69aca4505..f80d73b690f6 100644
--- a/include/linux/tty_driver.h
+++ b/include/linux/tty_driver.h
@@ -12,11 +12,15 @@
  *      This routine is called when a particular tty device is opened.
  *      This routine is mandatory; if this routine is not filled in,
  *      the attempted open will fail with ENODEV.
+ *
+ *      Required method.
  *     
  * void (*close)(struct tty_struct * tty, struct file * filp);
  *
  *      This routine is called when a particular tty device is closed.
  *
+ *      Required method.
+ *
  * int (*write)(struct tty_struct * tty,
  *               const unsigned char *buf, int count);
  *
@@ -26,7 +30,9 @@
  *      number of characters actually accepted for writing.  This
  *      routine is mandatory.
  *
- * void (*put_char)(struct tty_struct *tty, unsigned char ch);
+ *      Optional: Required for writable devices.
+ *
+ * int (*put_char)(struct tty_struct *tty, unsigned char ch);
  *
  *      This routine is called by the kernel to write a single
  *      character to the tty device.  If the kernel uses this routine,
@@ -34,10 +40,18 @@
  *      done stuffing characters into the driver.  If there is no room
  *      in the queue, the character is ignored.
  *
+ *      Optional: Kernel will use the write method if not provided.
+ *
+ *      Note: Do not call this function directly, call tty_put_char
+ *
  * void (*flush_chars)(struct tty_struct *tty);
  *
  *      This routine is called by the kernel after it has written a
  *      series of characters to the tty device using put_char().  
+ *
+ *      Optional:
+ *
+ *      Note: Do not call this function directly, call tty_driver_flush_chars
  * 
  * int  (*write_room)(struct tty_struct *tty);
  *
@@ -45,6 +59,10 @@
  *      will accept for queuing to be written.  This number is subject
  *      to change as output buffers get emptied, or if the output flow
  *      control is acted.
+ *
+ *      Required if write method is provided else not needed.
+ *
+ *      Note: Do not call this function directly, call tty_write_room
  * 
  * int  (*ioctl)(struct tty_struct *tty, struct file * file,
  *          unsigned int cmd, unsigned long arg);
@@ -53,22 +71,29 @@
  *      device-specific ioctl's.  If the ioctl number passed in cmd
  *      is not recognized by the driver, it should return ENOIOCTLCMD.
  *
+ *      Optional
+ *
  * long (*compat_ioctl)(struct tty_struct *tty, struct file * file,
  *                      unsigned int cmd, unsigned long arg);
  *
  *      implement ioctl processing for 32 bit process on 64 bit system
+ *
+ *      Optional
  * 
  * void (*set_termios)(struct tty_struct *tty, struct ktermios * old);
  *
  *      This routine allows the tty driver to be notified when
- *      device's termios settings have changed.  Note that a
- *      well-designed tty driver should be prepared to accept the case
- *      where old == NULL, and try to do something rational.
+ *      device's termios settings have changed.
+ *
+ *      Optional: Called under the termios lock
+ *
  *
  * void (*set_ldisc)(struct tty_struct *tty);
  *
  *      This routine allows the tty driver to be notified when the
  *      device's termios settings have changed.
+ *
+ *      Optional: Called under BKL (currently)
  * 
  * void (*throttle)(struct tty_struct * tty);
  *
@@ -86,17 +111,27 @@
  *
  *      This routine notifies the tty driver that it should stop
  *      outputting characters to the tty device.  
+ *
+ *      Optional:
+ *
+ *      Note: Call stop_tty not this method.
  * 
  * void (*start)(struct tty_struct *tty);
  *
  *      This routine notifies the tty driver that it resume sending
  *      characters to the tty device.
+ *
+ *      Optional:
+ *
+ *      Note: Call start_tty not this method.
  * 
  * void (*hangup)(struct tty_struct *tty);
  *
  *      This routine notifies the tty driver that it should hangup the
  *      tty device.
  *
+ *      Required:
+ *
  * void (*break_ctl)(struct tty_stuct *tty, int state);
  *
  *      This optional routine requests the tty driver to turn on or
@@ -106,18 +141,26 @@
  *
  *      If this routine is implemented, the high-level tty driver will
  *      handle the following ioctls: TCSBRK, TCSBRKP, TIOCSBRK,
- *      TIOCCBRK.  Otherwise, these ioctls will be passed down to the
- *      driver to handle.
+ *      TIOCCBRK.
+ *
+ *      Optional: Required for TCSBRK/BRKP/etc handling.
  *
  * void (*wait_until_sent)(struct tty_struct *tty, int timeout);
  * 
  *      This routine waits until the device has written out all of the
  *      characters in its transmitter FIFO.
  *
+ *      Optional: If not provided the device is assumed to have no FIFO
+ *
+ *      Note: Usually correct to call tty_wait_until_sent
+ *
  * void (*send_xchar)(struct tty_struct *tty, char ch);
  *
  *      This routine is used to send a high-priority XON/XOFF
  *      character to the device.
+ *
+ *      Optional: If not provided then the write method is called under
+ *      the atomic write lock to keep it serialized with the ldisc.
  */
 
 #include <linux/fs.h>
@@ -132,7 +175,7 @@ struct tty_operations {
         void (*close)(struct tty_struct * tty, struct file * filp);
         int  (*write)(struct tty_struct * tty,
                       const unsigned char *buf, int count);
-        void (*put_char)(struct tty_struct *tty, unsigned char ch);
+        int  (*put_char)(struct tty_struct *tty, unsigned char ch);
         void (*flush_chars)(struct tty_struct *tty);
         int  (*write_room)(struct tty_struct *tty);
         int  (*chars_in_buffer)(struct tty_struct *tty);
@@ -153,8 +196,6 @@ struct tty_operations {
         void (*send_xchar)(struct tty_struct *tty, char ch);
         int (*read_proc)(char *page, char **start, off_t off,
                           int count, int *eof, void *data);
-        int (*write_proc)(struct file *file, const char __user *buffer,
-                          unsigned long count, void *data);
         int (*tiocmget)(struct tty_struct *tty, struct file *file);
         int (*tiocmset)(struct tty_struct *tty, struct file *file,
                         unsigned int set, unsigned int clear);
@@ -190,48 +231,13 @@ struct tty_driver {
         struct tty_struct **ttys;
         struct ktermios **termios;
         struct ktermios **termios_locked;
-        void *driver_state;     /* only used for the PTY driver */
-        
+        void *driver_state;
+
         /*
-         * Interface routines from the upper tty layer to the tty
-         * driver.      Will be replaced with struct tty_operations.
+         * Driver methods
          */
-        int  (*open)(struct tty_struct * tty, struct file * filp);
-        void (*close)(struct tty_struct * tty, struct file * filp);
-        int  (*write)(struct tty_struct * tty,
-                      const unsigned char *buf, int count);
-        void (*put_char)(struct tty_struct *tty, unsigned char ch);
-        void (*flush_chars)(struct tty_struct *tty);
-        int  (*write_room)(struct tty_struct *tty);
-        int  (*chars_in_buffer)(struct tty_struct *tty);
-        int  (*ioctl)(struct tty_struct *tty, struct file * file,
-                    unsigned int cmd, unsigned long arg);
-        long (*compat_ioctl)(struct tty_struct *tty, struct file * file,
-                             unsigned int cmd, unsigned long arg);
-        void (*set_termios)(struct tty_struct *tty, struct ktermios * old);
-        void (*throttle)(struct tty_struct * tty);
-        void (*unthrottle)(struct tty_struct * tty);
-        void (*stop)(struct tty_struct *tty);
-        void (*start)(struct tty_struct *tty);
-        void (*hangup)(struct tty_struct *tty);
-        void (*break_ctl)(struct tty_struct *tty, int state);
-        void (*flush_buffer)(struct tty_struct *tty);
-        void (*set_ldisc)(struct tty_struct *tty);
-        void (*wait_until_sent)(struct tty_struct *tty, int timeout);
-        void (*send_xchar)(struct tty_struct *tty, char ch);
-        int (*read_proc)(char *page, char **start, off_t off,
-                          int count, int *eof, void *data);
-        int (*write_proc)(struct file *file, const char __user *buffer,
-                          unsigned long count, void *data);
-        int (*tiocmget)(struct tty_struct *tty, struct file *file);
-        int (*tiocmset)(struct tty_struct *tty, struct file *file,
-                        unsigned int set, unsigned int clear);
-#ifdef CONFIG_CONSOLE_POLL
-        int (*poll_init)(struct tty_driver *driver, int line, char *options);
-        int (*poll_get_char)(struct tty_driver *driver, int line);
-        void (*poll_put_char)(struct tty_driver *driver, int line, char ch);
-#endif
 
+        const struct tty_operations *ops;
         struct list_head tty_drivers;
 };