pty: Rework the pty layer to use the normal buffering logic
This fixes the ppp problems and various other issues with call locking
caused by one side of a pty called in one locking context trying to match
another with differing rules on the other side. We also get a big slack
space to work with that means we can bury the flow control deadlock case
for any conceivable real world situation.
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/drivers/char/pty.c b/drivers/char/pty.c
index daebe1b..9d1b4f5 100644
--- a/drivers/char/pty.c
+++ b/drivers/char/pty.c
@@ -75,114 +75,88 @@
*/
static void pty_unthrottle(struct tty_struct *tty)
{
- struct tty_struct *o_tty = tty->link;
-
- if (!o_tty)
- return;
-
- tty_wakeup(o_tty);
+ tty_wakeup(tty->link);
set_bit(TTY_THROTTLED, &tty->flags);
}
-/*
- * WSH 05/24/97: modified to
- * (1) use space in tty->flip instead of a shared temp buffer
- * The flip buffers aren't being used for a pty, so there's lots
- * of space available. The buffer is protected by a per-pty
- * semaphore that should almost never come under contention.
- * (2) avoid redundant copying for cases where count >> receive_room
- * N.B. Calls from user space may now return an error code instead of
- * a count.
+/**
+ * pty_space - report space left for writing
+ * @to: tty we are writing into
*
- * FIXME: Our pty_write method is called with our ldisc lock held but
- * not our partners. We can't just wait on the other one blindly without
- * risking deadlocks. At some point when everything has settled down we need
- * to look into making pty_write at least able to sleep over an ldisc change.
- *
- * The return on no ldisc is a bit counter intuitive but the logic works
- * like this. During an ldisc change the other end will flush its buffers. We
- * thus return the full length which is identical to the case where we had
- * proper locking and happened to queue the bytes just before the flush during
- * the ldisc change.
+ * The tty buffers allow 64K but we sneak a peak and clip at 8K this
+ * allows a lot of overspill room for echo and other fun messes to
+ * be handled properly
*/
+
+static int pty_space(struct tty_struct *to)
+{
+ int n = 8192 - to->buf.memory_used;
+ if (n < 0)
+ return 0;
+ return n;
+}
+
+/**
+ * pty_write - write to a pty
+ * @tty: the tty we write from
+ * @buf: kernel buffer of data
+ * @count: bytes to write
+ *
+ * Our "hardware" write method. Data is coming from the ldisc which
+ * may be in a non sleeping state. We simply throw this at the other
+ * end of the link as if we were an IRQ handler receiving stuff for
+ * the other side of the pty/tty pair.
+ */
+
static int pty_write(struct tty_struct *tty, const unsigned char *buf,
int count)
{
struct tty_struct *to = tty->link;
- struct tty_ldisc *ld;
- int c = count;
+ int c;
- if (!to || tty->stopped)
+ if (tty->stopped)
return 0;
- ld = tty_ldisc_ref(to);
- if (ld) {
- c = to->receive_room;
- if (c > count)
- c = count;
- ld->ops->receive_buf(to, buf, NULL, c);
- tty_ldisc_deref(ld);
+ /* This isn't locked but our 8K is quite sloppy so no
+ big deal */
+
+ c = pty_space(to);
+ if (c > count)
+ c = count;
+ if (c > 0) {
+ /* Stuff the data into the input queue of the other end */
+ c = tty_insert_flip_string(to, buf, c);
+ /* And shovel */
+ tty_flip_buffer_push(to);
+ tty_wakeup(tty);
}
return c;
}
+/**
+ * pty_write_room - write space
+ * @tty: tty we are writing from
+ *
+ * Report how many bytes the ldisc can send into the queue for
+ * the other device.
+ */
+
static int pty_write_room(struct tty_struct *tty)
{
- struct tty_struct *to = tty->link;
-
- if (!to || tty->stopped)
- return 0;
-
- return to->receive_room;
+ return pty_space(tty->link);
}
-/*
- * WSH 05/24/97: Modified for asymmetric MASTER/SLAVE behavior
- * The chars_in_buffer() value is used by the ldisc select() function
- * to hold off writing when chars_in_buffer > WAKEUP_CHARS (== 256).
- * The pty driver chars_in_buffer() Master/Slave must behave differently:
+/**
+ * pty_chars_in_buffer - characters currently in our tx queue
+ * @tty: our tty
*
- * The Master side needs to allow typed-ahead commands to accumulate
- * while being canonicalized, so we report "our buffer" as empty until
- * some threshold is reached, and then report the count. (Any count >
- * WAKEUP_CHARS is regarded by select() as "full".) To avoid deadlock
- * the count returned must be 0 if no canonical data is available to be
- * read. (The N_TTY ldisc.chars_in_buffer now knows this.)
- *
- * The Slave side passes all characters in raw mode to the Master side's
- * buffer where they can be read immediately, so in this case we can
- * return the true count in the buffer.
+ * Report how much we have in the transmit queue. As everything is
+ * instantly at the other end this is easy to implement.
*/
+
static int pty_chars_in_buffer(struct tty_struct *tty)
{
- struct tty_struct *to = tty->link;
- struct tty_ldisc *ld;
- int count = 0;
-
- /* We should get the line discipline lock for "tty->link" */
- if (!to)
- return 0;
- /* We cannot take a sleeping reference here without deadlocking with
- an ldisc change - but it doesn't really matter */
- ld = tty_ldisc_ref(to);
- if (ld == NULL)
- return 0;
-
- /* The ldisc must report 0 if no characters available to be read */
- if (ld->ops->chars_in_buffer)
- count = ld->ops->chars_in_buffer(to);
-
- tty_ldisc_deref(ld);
-
- if (tty->driver->subtype == PTY_TYPE_SLAVE)
- return count;
-
- /* Master side driver ... if the other side's read buffer is less than
- * half full, return 0 to allow writers to proceed; otherwise return
- * the count. This leaves a comfortable margin to avoid overflow,
- * and still allows half a buffer's worth of typed-ahead commands.
- */
- return (count < N_TTY_BUF_SIZE/2) ? 0 : count;
+ return 0;
}
/* Set the lock flag on a pty */
@@ -202,20 +176,10 @@
{
struct tty_struct *to = tty->link;
unsigned long flags;
- struct tty_ldisc *ld;
if (!to)
return;
- ld = tty_ldisc_ref(to);
-
- /* The other end is changing discipline */
- if (!ld)
- return;
-
- if (ld->ops->flush_buffer)
- to->ldisc->ops->flush_buffer(to);
- tty_ldisc_deref(ld);
-
+ /* tty_buffer_flush(to); FIXME */
if (to->packet) {
spin_lock_irqsave(&tty->ctrl_lock, flags);
tty->ctrl_status |= TIOCPKT_FLUSHWRITE;