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Subject[PATCH 74/80] tty: Minor tidyups and document fixes for n_tty
Date
From: Alan Cox <alan@redhat.com>

Remove/fix some bogus NULL checks, comment some locking etc

Signed-off-by: Alan Cox <alan@redhat.com>
---
drivers/char/n_tty.c | 48 +++++++++++++++++++++++++++++++++++++-----------
1 files changed, 37 insertions(+), 11 deletions(-)

diff --git a/drivers/char/n_tty.c b/drivers/char/n_tty.c
index b4f5dcc..c0285b9 100644
--- a/drivers/char/n_tty.c
+++ b/drivers/char/n_tty.c
@@ -99,6 +99,7 @@ static inline int tty_put_user(struct tty_struct *tty, unsigned char x,

static void n_tty_set_room(struct tty_struct *tty)
{
+ /* tty->read_cnt is not read locked ? */
int left = N_TTY_BUF_SIZE - tty->read_cnt - 1;

/*
@@ -121,6 +122,16 @@ static void put_tty_queue_nolock(unsigned char c, struct tty_struct *tty)
}
}

+/**
+ * put_tty_queue - add character to tty
+ * @c: character
+ * @tty: tty device
+ *
+ * Add a character to the tty read_buf queue. This is done under the
+ * read_lock to serialize character addition and also to protect us
+ * against parallel reads or flushes
+ */
+
static void put_tty_queue(unsigned char c, struct tty_struct *tty)
{
unsigned long flags;
@@ -137,14 +148,11 @@ static void put_tty_queue(unsigned char c, struct tty_struct *tty)
* check_unthrottle - allow new receive data
* @tty; tty device
*
- * Check whether to call the driver.unthrottle function.
- * We test the TTY_THROTTLED bit first so that it always
- * indicates the current state. The decision about whether
- * it is worth allowing more input has been taken by the caller.
+ * Check whether to call the driver unthrottle functions
+ *
* Can sleep, may be called under the atomic_read_lock mutex but
* this is not guaranteed.
*/
-
static void check_unthrottle(struct tty_struct *tty)
{
if (tty->count)
@@ -158,6 +166,8 @@ static void check_unthrottle(struct tty_struct *tty)
* Reset the read buffer counters, clear the flags,
* and make sure the driver is unthrottled. Called
* from n_tty_open() and n_tty_flush_buffer().
+ *
+ * Locking: tty_read_lock for read fields.
*/
static void reset_buffer_flags(struct tty_struct *tty)
{
@@ -181,7 +191,7 @@ static void reset_buffer_flags(struct tty_struct *tty)
* at hangup) or when the N_TTY line discipline internally has to
* clean the pending queue (for example some signals).
*
- * Locking: ctrl_lock
+ * Locking: ctrl_lock, read_lock.
*/

static void n_tty_flush_buffer(struct tty_struct *tty)
@@ -207,6 +217,8 @@ static void n_tty_flush_buffer(struct tty_struct *tty)
*
* Report the number of characters buffered to be delivered to user
* at this instant in time.
+ *
+ * Locking: read_lock
*/

static ssize_t n_tty_chars_in_buffer(struct tty_struct *tty)
@@ -410,6 +422,8 @@ break_out:
*
* Echo user input back onto the screen. This must be called only when
* L_ECHO(tty) is true. Called from the driver receive_buf path.
+ *
+ * Relies on BKL for tty column locking
*/

static void echo_char(unsigned char c, struct tty_struct *tty)
@@ -422,6 +436,12 @@ static void echo_char(unsigned char c, struct tty_struct *tty)
opost(c, tty);
}

+/**
+ * finsh_erasing - complete erase
+ * @tty: tty doing the erase
+ *
+ * Relies on BKL for tty column locking
+ */
static inline void finish_erasing(struct tty_struct *tty)
{
if (tty->erasing) {
@@ -439,6 +459,8 @@ static inline void finish_erasing(struct tty_struct *tty)
* Perform erase and necessary output when an erase character is
* present in the stream from the driver layer. Handles the complexities
* of UTF-8 multibyte symbols.
+ *
+ * Locking: read_lock for tty buffers, BKL for column/erasing state
*/

static void eraser(unsigned char c, struct tty_struct *tty)
@@ -447,6 +469,7 @@ static void eraser(unsigned char c, struct tty_struct *tty)
int head, seen_alnums, cnt;
unsigned long flags;

+ /* FIXME: locking needed ? */
if (tty->read_head == tty->canon_head) {
/* opost('\a', tty); */ /* what do you think? */
return;
@@ -481,6 +504,7 @@ static void eraser(unsigned char c, struct tty_struct *tty)
}

seen_alnums = 0;
+ /* FIXME: Locking ?? */
while (tty->read_head != tty->canon_head) {
head = tty->read_head;

@@ -583,6 +607,8 @@ static void eraser(unsigned char c, struct tty_struct *tty)
* may caus terminal flushing to take place according to the termios
* settings and character used. Called from the driver receive_buf
* path so serialized.
+ *
+ * Locking: ctrl_lock, read_lock (both via flush buffer)
*/

static inline void isig(int sig, struct tty_struct *tty, int flush)
@@ -1007,6 +1033,8 @@ int is_ignored(int sig)
* and is protected from re-entry by the tty layer. The user is
* guaranteed that this function will not be re-entered or in progress
* when the ldisc is closed.
+ *
+ * Locking: Caller holds tty->termios_mutex
*/

static void n_tty_set_termios(struct tty_struct *tty, struct ktermios *old)
@@ -1266,10 +1294,7 @@ static ssize_t read_chan(struct tty_struct *tty, struct file *file,

do_it_again:

- if (!tty->read_buf) {
- printk(KERN_ERR "n_tty_read_chan: read_buf == NULL?!?\n");
- return -EIO;
- }
+ BUG_ON(!tty->read_buf);

c = job_control(tty, file);
if (c < 0)
@@ -1589,7 +1614,7 @@ static unsigned long inq_canon(struct tty_struct *tty)
{
int nr, head, tail;

- if (!tty->canon_data || !tty->read_buf)
+ if (!tty->canon_data)
return 0;
head = tty->canon_head;
tail = tty->read_tail;
@@ -1613,6 +1638,7 @@ static int n_tty_ioctl(struct tty_struct *tty, struct file *file,
case TIOCOUTQ:
return put_user(tty_chars_in_buffer(tty), (int __user *) arg);
case TIOCINQ:
+ /* FIXME: Locking */
retval = tty->read_cnt;
if (L_ICANON(tty))
retval = inq_canon(tty);


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