[PATCH] TTY layer buffering revamp

The API and code have been through various bits of initial review by
serial driver people but they definitely need to live somewhere for a
while so the unconverted drivers can get knocked into shape, existing
drivers that have been updated can be better tuned and bugs whacked out.

This replaces the tty flip buffers with kmalloc objects in rings. In the
normal situation for an IRQ driven serial port at typical speeds the
behaviour is pretty much the same, two buffers end up allocated and the
kernel cycles between them as before.

When there are delays or at high speed we now behave far better as the
buffer pool can grow a bit rather than lose characters. This also means
that we can operate at higher speeds reliably.

For drivers that receive characters in blocks (DMA based, USB and
especially virtualisation) the layer allows a lot of driver specific
code that works around the tty layer with private secondary queues to be
removed. The IBM folks need this sort of layer, the smart serial port
people do, the virtualisers do (because a virtualised tty typically
operates at infinite speed rather than emulating 9600 baud).

Finally many drivers had invalid and unsafe attempts to avoid buffer
overflows by directly invoking tty methods extracted out of the innards
of work queue structs. These are no longer needed and all go away. That
fixes various random hangs with serial ports on overflow.

The other change in here is to optimise the receive_room path that is
used by some callers. It turns out that only one ldisc uses receive room
except asa constant and it updates it far far less than the value is
read. We thus make it a variable not a function call.

I expect the code to contain bugs due to the size alone but I'll be
watching and squashing them and feeding out new patches as it goes.

Because the buffers now dynamically expand you should only run out of
buffering when the kernel runs out of memory for real.  That means a lot of
the horrible hacks high performance drivers used to do just aren't needed any
more.

Description:

tty_insert_flip_char is an old API and continues to work as before, as does
tty_flip_buffer_push() [this is why many drivers dont need modification].  It
does now also return the number of chars inserted

There are also

tty_buffer_request_room(tty, len)

which asks for a buffer block of the length requested and returns the space
found.  This improves efficiency with hardware that knows how much to
transfer.

and tty_insert_flip_string_flags(tty, str, flags, len)

to insert a string of characters and flags

For a smart interface the usual code is

    len = tty_request_buffer_room(tty, amount_hardware_says);
    tty_insert_flip_string(tty, buffer_from_card, len);

More description!

At the moment tty buffers are attached directly to the tty.  This is causing a
lot of the problems related to tty layer locking, also problems at high speed
and also with bursty data (such as occurs in virtualised environments)

I'm working on ripping out the flip buffers and replacing them with a pool of
dynamically allocated buffers.  This allows both for old style "byte I/O"
devices and also helps virtualisation and smart devices where large blocks of
data suddenely materialise and need storing.

So far so good.  Lots of drivers reference tty->flip.*.  Several of them also
call directly and unsafely into function pointers it provides.  This will all
break.  Most drivers can use tty_insert_flip_char which can be kept as an API
but others need more.

At the moment I've added the following interfaces, if people think more will
be needed now is a good time to say

 int tty_buffer_request_room(tty, size)

Try and ensure at least size bytes are available, returns actual room (may be
zero).  At the moment it just uses the flipbuf space but that will change.
Repeated calls without characters being added are not cumulative.  (ie if you
call it with 1, 1, 1, and then 4 you'll have four characters of space.  The
other functions will also try and grow buffers in future but this will be a
more efficient way when you know block sizes.

 int tty_insert_flip_char(tty, ch, flag)

As before insert a character if there is room.  Now returns 1 for success, 0
for failure.

 int tty_insert_flip_string(tty, str, len)

Insert a block of non error characters.  Returns the number inserted.

 int tty_prepare_flip_string(tty, strptr, len)

Adjust the buffer to allow len characters to be added.  Returns a buffer
pointer in strptr and the length available.  This allows for hardware that
needs to use functions like insl or mencpy_fromio.

Signed-off-by: Alan Cox <alan@redhat.com>
Cc: Paul Fulghum <paulkf@microgate.com>
Signed-off-by: Hirokazu Takata <takata@linux-m32r.org>
Signed-off-by: Serge Hallyn <serue@us.ibm.com>
Signed-off-by: Jeff Dike <jdike@addtoit.com>
Signed-off-by: John Hawkes <hawkes@sgi.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

9 files changed, 11 insertions, 69 deletions

diff --git a/drivers/net/hamradio/6pack.c b/drivers/net/hamradio/6pack.c
index 9099986..102c1f0 100644
--- a/drivers/net/hamradio/6pack.c
+++ b/drivers/net/hamradio/6pack.c
@@ -456,11 +456,6 @@ out:
 
 /* ----------------------------------------------------------------------- */
 
-static int sixpack_receive_room(struct tty_struct *tty)
-{
-	return 65536;  /* We can handle an infinite amount of data. :-) */
-}
-
 /*
  * Handle the 'receiver data ready' interrupt.
  * This function is called by the 'tty_io' module in the kernel when
@@ -671,6 +666,7 @@ static int sixpack_open(struct tty_struct *tty)
 
 	/* Done.  We have linked the TTY line to a channel. */
 	tty->disc_data = sp;
+	tty->receive_room = 65536;
 
 	/* Now we're ready to register. */
 	if (register_netdev(dev))
@@ -802,7 +798,6 @@ static struct tty_ldisc sp_ldisc = {
 	.close		= sixpack_close,
 	.ioctl		= sixpack_ioctl,
 	.receive_buf	= sixpack_receive_buf,
-	.receive_room	= sixpack_receive_room,
 	.write_wakeup	= sixpack_write_wakeup,
 };
 
diff --git a/drivers/net/hamradio/mkiss.c b/drivers/net/hamradio/mkiss.c
index f4424cf..dc5e9d5 100644
--- a/drivers/net/hamradio/mkiss.c
+++ b/drivers/net/hamradio/mkiss.c
@@ -753,6 +753,7 @@ static int mkiss_open(struct tty_struct *tty)
 
 	ax->tty = tty;
 	tty->disc_data = ax;
+	tty->receive_room = 65535;
 
 	if (tty->driver->flush_buffer)
 		tty->driver->flush_buffer(tty);
@@ -940,11 +941,6 @@ static void mkiss_receive_buf(struct tty_struct *tty, const unsigned char *cp,
 		tty->driver->unthrottle(tty);
 }
 
-static int mkiss_receive_room(struct tty_struct *tty)
-{
-	return 65536;  /* We can handle an infinite amount of data. :-) */
-}
-
 /*
  * Called by the driver when there's room for more data.  If we have
  * more packets to send, we send them here.
@@ -983,7 +979,6 @@ static struct tty_ldisc ax_ldisc = {
 	.close		= mkiss_close,
 	.ioctl		= mkiss_ioctl,
 	.receive_buf	= mkiss_receive_buf,
-	.receive_room	= mkiss_receive_room,
 	.write_wakeup	= mkiss_write_wakeup
 };
 
diff --git a/drivers/net/irda/irtty-sir.c b/drivers/net/irda/irtty-sir.c
index b8d1123..101750b 100644
--- a/drivers/net/irda/irtty-sir.c
+++ b/drivers/net/irda/irtty-sir.c
@@ -289,22 +289,6 @@ static void irtty_receive_buf(struct tty_struct *tty, const unsigned char *cp,
 }
 
 /*
- * Function irtty_receive_room (tty)
- *
- *    Used by the TTY to find out how much data we can receive at a time
- * 
-*/
-static int irtty_receive_room(struct tty_struct *tty) 
-{
-	struct sirtty_cb *priv = tty->disc_data;
-
-	IRDA_ASSERT(priv != NULL, return 0;);
-	IRDA_ASSERT(priv->magic == IRTTY_MAGIC, return 0;);
-
-	return 65536;  /* We can handle an infinite amount of data. :-) */
-}
-
-/*
  * Function irtty_write_wakeup (tty)
  *
  *    Called by the driver when there's room for more data.  If we have
@@ -534,6 +518,7 @@ static int irtty_open(struct tty_struct *tty)
 
 	dev->priv = priv;
 	tty->disc_data = priv;
+	tty->receive_room = 65536;
 
 	up(&irtty_sem);
 
@@ -605,7 +590,6 @@ static struct tty_ldisc irda_ldisc = {
 	.ioctl		= irtty_ioctl,
  	.poll		= NULL,
 	.receive_buf	= irtty_receive_buf,
-	.receive_room	= irtty_receive_room,
 	.write_wakeup	= irtty_write_wakeup,
 	.owner		= THIS_MODULE,
 };
diff --git a/drivers/net/ppp_async.c b/drivers/net/ppp_async.c
index 400f652..aa6540b 100644
--- a/drivers/net/ppp_async.c
+++ b/drivers/net/ppp_async.c
@@ -189,7 +189,7 @@ ppp_asynctty_open(struct tty_struct *tty)
 		goto out_free;
 
 	tty->disc_data = ap;
-
+	tty->receive_room = 65536;
 	return 0;
 
  out_free:
@@ -343,12 +343,6 @@ ppp_asynctty_poll(struct tty_struct *tty, struct file *file, poll_table *wait)
 	return 0;
 }
 
-static int
-ppp_asynctty_room(struct tty_struct *tty)
-{
-	return 65535;
-}
-
 /*
  * This can now be called from hard interrupt level as well
  * as soft interrupt level or mainline.
@@ -398,7 +392,6 @@ static struct tty_ldisc ppp_ldisc = {
 	.write	= ppp_asynctty_write,
 	.ioctl	= ppp_asynctty_ioctl,
 	.poll	= ppp_asynctty_poll,
-	.receive_room = ppp_asynctty_room,
 	.receive_buf = ppp_asynctty_receive,
 	.write_wakeup = ppp_asynctty_wakeup,
 };
diff --git a/drivers/net/ppp_synctty.c b/drivers/net/ppp_synctty.c
index 4d51c0c..33cb825 100644
--- a/drivers/net/ppp_synctty.c
+++ b/drivers/net/ppp_synctty.c
@@ -237,7 +237,7 @@ ppp_sync_open(struct tty_struct *tty)
 		goto out_free;
 
 	tty->disc_data = ap;
-
+	tty->receive_room = 65536;
 	return 0;
 
  out_free:
@@ -384,12 +384,6 @@ ppp_sync_poll(struct tty_struct *tty, struct file *file, poll_table *wait)
 	return 0;
 }
 
-static int
-ppp_sync_room(struct tty_struct *tty)
-{
-	return 65535;
-}
-
 /*
  * This can now be called from hard interrupt level as well
  * as soft interrupt level or mainline.
@@ -439,7 +433,6 @@ static struct tty_ldisc ppp_sync_ldisc = {
 	.write	= ppp_sync_write,
 	.ioctl	= ppp_synctty_ioctl,
 	.poll	= ppp_sync_poll,
-	.receive_room = ppp_sync_room,
 	.receive_buf = ppp_sync_receive,
 	.write_wakeup = ppp_sync_wakeup,
 };
diff --git a/drivers/net/slip.c b/drivers/net/slip.c
index 404ea42..b2e18d2 100644
--- a/drivers/net/slip.c
+++ b/drivers/net/slip.c
@@ -651,11 +651,6 @@ static void sl_setup(struct net_device *dev)
  ******************************************/
 
 
-static int slip_receive_room(struct tty_struct *tty)
-{
-	return 65536;  /* We can handle an infinite amount of data. :-) */
-}
-
 /*
  * Handle the 'receiver data ready' interrupt.
  * This function is called by the 'tty_io' module in the kernel when
@@ -869,10 +864,6 @@ static int slip_open(struct tty_struct *tty)
 	sl->line = tty_devnum(tty);
 	sl->pid = current->pid;
 	
-	/* FIXME: already done before we were called - seems this can go */
-	if (tty->driver->flush_buffer)
-		tty->driver->flush_buffer(tty);
-		
 	if (!test_bit(SLF_INUSE, &sl->flags)) {
 		/* Perform the low-level SLIP initialization. */
 		if ((err = sl_alloc_bufs(sl, SL_MTU)) != 0)
@@ -897,6 +888,7 @@ static int slip_open(struct tty_struct *tty)
 
 	/* Done.  We have linked the TTY line to a channel. */
 	rtnl_unlock();
+	tty->receive_room = 65536;	/* We don't flow control */
 	return sl->dev->base_addr;
 
 err_free_bufs:
@@ -1329,7 +1321,6 @@ static struct tty_ldisc	sl_ldisc = {
 	.close	 	= slip_close,
 	.ioctl		= slip_ioctl,
 	.receive_buf	= slip_receive_buf,
-	.receive_room	= slip_receive_room,
 	.write_wakeup	= slip_write_wakeup,
 };
 
diff --git a/drivers/net/wan/pc300_tty.c b/drivers/net/wan/pc300_tty.c
index 52f26b9..931cbdf6 100644
--- a/drivers/net/wan/pc300_tty.c
+++ b/drivers/net/wan/pc300_tty.c
@@ -689,7 +689,7 @@ static void cpc_tty_rx_work(void * data)
 					}
 				}	
 				cpc_tty->buf_rx.first = cpc_tty->buf_rx.first->next;
-				kfree(buf);
+				kfree((void *)buf);
 				buf = cpc_tty->buf_rx.first;
 				flg_rx = 1;
 			}
diff --git a/drivers/net/wan/x25_asy.c b/drivers/net/wan/x25_asy.c
index bdf672c..9c3ccc6 100644
--- a/drivers/net/wan/x25_asy.c
+++ b/drivers/net/wan/x25_asy.c
@@ -515,11 +515,6 @@ static int x25_asy_close(struct net_device *dev)
 	return 0;
 }
 
-static int x25_asy_receive_room(struct tty_struct *tty)
-{
-	return 65536;  /* We can handle an infinite amount of data. :-) */
-}
-
 /*
  * Handle the 'receiver data ready' interrupt.
  * This function is called by the 'tty_io' module in the kernel when
@@ -573,6 +568,7 @@ static int x25_asy_open_tty(struct tty_struct *tty)
 
 	sl->tty = tty;
 	tty->disc_data = sl;
+	tty->receive_room = 65536;
 	if (tty->driver->flush_buffer)  {
 		tty->driver->flush_buffer(tty);
 	}
@@ -779,7 +775,6 @@ static struct tty_ldisc x25_ldisc = {
 	.close		= x25_asy_close_tty,
 	.ioctl		= x25_asy_ioctl,
 	.receive_buf	= x25_asy_receive_buf,
-	.receive_room	= x25_asy_receive_room,
 	.write_wakeup	= x25_asy_write_wakeup,
 };
 
diff --git a/drivers/net/wireless/strip.c b/drivers/net/wireless/strip.c
index d25264b..18baacf 100644
--- a/drivers/net/wireless/strip.c
+++ b/drivers/net/wireless/strip.c
@@ -1675,11 +1675,6 @@ static int strip_rebuild_header(struct sk_buff *skb)
 /************************************************************************/
 /* Receiving routines							*/
 
-static int strip_receive_room(struct tty_struct *tty)
-{
-	return 0x10000;		/* We can handle an infinite amount of data. :-) */
-}
-
 /*
  * This function parses the response to the ATS300? command,
  * extracting the radio version and serial number.
@@ -2424,7 +2419,7 @@ static struct net_device_stats *strip_get_stats(struct net_device *dev)
 /*
  * Here's the order things happen:
  * When the user runs "slattach -p strip ..."
- *  1. The TTY module calls strip_open
+ *  1. The TTY module calls strip_open;;
  *  2. strip_open calls strip_alloc
  *  3.                  strip_alloc calls register_netdev
  *  4.                  register_netdev calls strip_dev_init
@@ -2652,6 +2647,8 @@ static int strip_open(struct tty_struct *tty)
 
 	strip_info->tty = tty;
 	tty->disc_data = strip_info;
+	tty->receive_room = 65536;
+
 	if (tty->driver->flush_buffer)
 		tty->driver->flush_buffer(tty);
 
@@ -2762,7 +2759,6 @@ static struct tty_ldisc strip_ldisc = {
 	.close = strip_close,
 	.ioctl = strip_ioctl,
 	.receive_buf = strip_receive_buf,
-	.receive_room = strip_receive_room,
 	.write_wakeup = strip_write_some_more,
 };