tty: make receive_buf() return the amout of bytes received

it makes it simpler to keep track of the amount of
bytes received and simplifies how flush_to_ldisc counts
the remaining bytes. It also fixes a bug of lost bytes
on n_tty when flushing too many bytes via the USB
serial gadget driver.

Tested-by: Stefan Bigler <stefan.bigler@keymile.com>
Tested-by: Toby Gray <toby.gray@realvnc.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

20 files changed, 125 insertions, 113 deletions

diff --git a/drivers/bluetooth/hci_ldisc.c b/drivers/bluetooth/hci_ldisc.c
index 48ad2a7ab080..0d4da5e14ba0 100644
--- a/drivers/bluetooth/hci_ldisc.c
+++ b/drivers/bluetooth/hci_ldisc.c
@@ -357,22 +357,26 @@ static void hci_uart_tty_wakeup(struct tty_struct *tty)
  *     
  * Return Value:    None
  */
-static void hci_uart_tty_receive(struct tty_struct *tty, const u8 *data, char *flags, int count)
+static unsigned int hci_uart_tty_receive(struct tty_struct *tty,
+                const u8 *data, char *flags, int count)
 {
         struct hci_uart *hu = (void *)tty->disc_data;
+        int received;
 
         if (!hu || tty != hu->tty)
-                return;
+                return -ENODEV;
 
         if (!test_bit(HCI_UART_PROTO_SET, &hu->flags))
-                return;
+                return -EINVAL;
 
         spin_lock(&hu->rx_lock);
-        hu->proto->recv(hu, (void *) data, count);
+        received = hu->proto->recv(hu, (void *) data, count);
         hu->hdev->stat.byte_rx += count;
         spin_unlock(&hu->rx_lock);
 
         tty_unthrottle(tty);
+
+        return received;
 }
 
 static int hci_uart_register_dev(struct hci_uart *hu)
diff --git a/drivers/input/serio/serport.c b/drivers/input/serio/serport.c
index 8755f5f3ad37..f3698967edf6 100644
--- a/drivers/input/serio/serport.c
+++ b/drivers/input/serio/serport.c
@@ -120,17 +120,21 @@ static void serport_ldisc_close(struct tty_struct *tty)
  * 'interrupt' routine.
  */
 
-static void serport_ldisc_receive(struct tty_struct *tty, const unsigned char *cp, char *fp, int count)
+static unsigned int serport_ldisc_receive(struct tty_struct *tty,
+                const unsigned char *cp, char *fp, int count)
 {
         struct serport *serport = (struct serport*) tty->disc_data;
         unsigned long flags;
         unsigned int ch_flags;
+        int ret = 0;
         int i;
 
         spin_lock_irqsave(&serport->lock, flags);
 
-        if (!test_bit(SERPORT_ACTIVE, &serport->flags))
+        if (!test_bit(SERPORT_ACTIVE, &serport->flags)) {
+                ret = -EINVAL;
                 goto out;
+        }
 
         for (i = 0; i < count; i++) {
                 switch (fp[i]) {
@@ -152,6 +156,8 @@ static void serport_ldisc_receive(struct tty_struct *tty, const unsigned char *c
 
 out:
         spin_unlock_irqrestore(&serport->lock, flags);
+
+        return ret == 0 ? count : ret;
 }
 
 /*
diff --git a/drivers/isdn/gigaset/ser-gigaset.c b/drivers/isdn/gigaset/ser-gigaset.c
index 86a5c4f7775e..1d44d470897c 100644
--- a/drivers/isdn/gigaset/ser-gigaset.c
+++ b/drivers/isdn/gigaset/ser-gigaset.c
@@ -674,7 +674,7 @@ gigaset_tty_ioctl(struct tty_struct *tty, struct file *file,
  *      cflags  buffer containing error flags for received characters (ignored)
  *      count   number of received characters
  */
-static void
+static unsigned int
 gigaset_tty_receive(struct tty_struct *tty, const unsigned char *buf,
                     char *cflags, int count)
 {
@@ -683,12 +683,12 @@ gigaset_tty_receive(struct tty_struct *tty, const unsigned char *buf,
         struct inbuf_t *inbuf;
 
         if (!cs)
-                return;
+                return -ENODEV;
         inbuf = cs->inbuf;
         if (!inbuf) {
                 dev_err(cs->dev, "%s: no inbuf\n", __func__);
                 cs_put(cs);
-                return;
+                return -EINVAL;
         }
 
         tail = inbuf->tail;
@@ -725,6 +725,8 @@ gigaset_tty_receive(struct tty_struct *tty, const unsigned char *buf,
         gig_dbg(DEBUG_INTR, "%s-->BH", __func__);
         gigaset_schedule_event(cs);
         cs_put(cs);
+
+        return count;
 }
 
 /*
diff --git a/drivers/misc/ti-st/st_core.c b/drivers/misc/ti-st/st_core.c
index 486117f72c9f..cb98a7da98ef 100644
--- a/drivers/misc/ti-st/st_core.c
+++ b/drivers/misc/ti-st/st_core.c
@@ -744,8 +744,8 @@ static void st_tty_close(struct tty_struct *tty)
         pr_debug("%s: done ", __func__);
 }
 
-static void st_tty_receive(struct tty_struct *tty, const unsigned char *data,
-                           char *tty_flags, int count)
+static unsigned int st_tty_receive(struct tty_struct *tty,
+                const unsigned char *data, char *tty_flags, int count)
 {
 #ifdef VERBOSE
         print_hex_dump(KERN_DEBUG, ">in>", DUMP_PREFIX_NONE,
@@ -758,6 +758,8 @@ static void st_tty_receive(struct tty_struct *tty, const unsigned char *data,
          */
         st_recv(tty->disc_data, data, count);
         pr_debug("done %s", __func__);
+
+        return count;
 }
 
 /* wake-up function called in from the TTY layer
diff --git a/drivers/net/caif/caif_serial.c b/drivers/net/caif/caif_serial.c
index 3df0c0f8b8bf..73c7e03617ec 100644
--- a/drivers/net/caif/caif_serial.c
+++ b/drivers/net/caif/caif_serial.c
@@ -167,8 +167,8 @@ static inline void debugfs_tx(struct ser_device *ser, const u8 *data, int size)
 
 #endif
 
-static void ldisc_receive(struct tty_struct *tty, const u8 *data,
-                        char *flags, int count)
+static unsigned int ldisc_receive(struct tty_struct *tty,
+                const u8 *data, char *flags, int count)
 {
         struct sk_buff *skb = NULL;
         struct ser_device *ser;
@@ -215,6 +215,8 @@ static void ldisc_receive(struct tty_struct *tty, const u8 *data,
         } else
                 ++ser->dev->stats.rx_dropped;
         update_tty_status(ser);
+
+        return count;
 }
 
 static int handle_tx(struct ser_device *ser)
diff --git a/drivers/net/can/slcan.c b/drivers/net/can/slcan.c
index b423965a78d1..c600954998d5 100644
--- a/drivers/net/can/slcan.c
+++ b/drivers/net/can/slcan.c
@@ -425,16 +425,17 @@ static void slc_setup(struct net_device *dev)
  * in parallel
  */
 
-static void slcan_receive_buf(struct tty_struct *tty,
+static unsigned int slcan_receive_buf(struct tty_struct *tty,
                               const unsigned char *cp, char *fp, int count)
 {
         struct slcan *sl = (struct slcan *) tty->disc_data;
+        int bytes = count;
 
         if (!sl || sl->magic != SLCAN_MAGIC || !netif_running(sl->dev))
-                return;
+                return -ENODEV;
 
         /* Read the characters out of the buffer */
-        while (count--) {
+        while (bytes--) {
                 if (fp && *fp++) {
                         if (!test_and_set_bit(SLF_ERROR, &sl->flags))
                                 sl->dev->stats.rx_errors++;
@@ -443,6 +444,8 @@ static void slcan_receive_buf(struct tty_struct *tty,
                 }
                 slcan_unesc(sl, *cp++);
         }
+
+        return count;
 }
 
 /************************************
diff --git a/drivers/net/hamradio/6pack.c b/drivers/net/hamradio/6pack.c
index 3e5d0b6b6516..992089639ea4 100644
--- a/drivers/net/hamradio/6pack.c
+++ b/drivers/net/hamradio/6pack.c
@@ -456,7 +456,7 @@ out:
  * a block of 6pack data has been received, which can now be decapsulated
  * and sent on to some IP layer for further processing.
  */
-static void sixpack_receive_buf(struct tty_struct *tty,
+static unsigned int sixpack_receive_buf(struct tty_struct *tty,
         const unsigned char *cp, char *fp, int count)
 {
         struct sixpack *sp;
@@ -464,11 +464,11 @@ static void sixpack_receive_buf(struct tty_struct *tty,
         int count1;
 
         if (!count)
-                return;
+                return 0;
 
         sp = sp_get(tty);
         if (!sp)
-                return;
+                return -ENODEV;
 
         memcpy(buf, cp, count < sizeof(buf) ? count : sizeof(buf));
 
@@ -487,6 +487,8 @@ static void sixpack_receive_buf(struct tty_struct *tty,
 
         sp_put(sp);
         tty_unthrottle(tty);
+
+        return count1;
 }
 
 /*
diff --git a/drivers/net/hamradio/mkiss.c b/drivers/net/hamradio/mkiss.c
index 4c628393c8b1..0e4f23531140 100644
--- a/drivers/net/hamradio/mkiss.c
+++ b/drivers/net/hamradio/mkiss.c
@@ -923,13 +923,14 @@ static long mkiss_compat_ioctl(struct tty_struct *tty, struct file *file,
  * a block of data has been received, which can now be decapsulated
  * and sent on to the AX.25 layer for further processing.
  */
-static void mkiss_receive_buf(struct tty_struct *tty, const unsigned char *cp,
-        char *fp, int count)
+static unsigned int mkiss_receive_buf(struct tty_struct *tty,
+                const unsigned char *cp, char *fp, int count)
 {
         struct mkiss *ax = mkiss_get(tty);
+        int bytes = count;
 
         if (!ax)
-                return;
+                return -ENODEV;
 
         /*
          * Argh! mtu change time! - costs us the packet part received
@@ -939,7 +940,7 @@ static void mkiss_receive_buf(struct tty_struct *tty, const unsigned char *cp,
                 ax_changedmtu(ax);
 
         /* Read the characters out of the buffer */
-        while (count--) {
+        while (bytes--) {
                 if (fp != NULL && *fp++) {
                         if (!test_and_set_bit(AXF_ERROR, &ax->flags))
                                 ax->dev->stats.rx_errors++;
@@ -952,6 +953,8 @@ static void mkiss_receive_buf(struct tty_struct *tty, const unsigned char *cp,
 
         mkiss_put(ax);
         tty_unthrottle(tty);
+
+        return count;
 }
 
 /*
diff --git a/drivers/net/irda/irtty-sir.c b/drivers/net/irda/irtty-sir.c
index 3352b2443e58..035861d8acb1 100644
--- a/drivers/net/irda/irtty-sir.c
+++ b/drivers/net/irda/irtty-sir.c
@@ -216,23 +216,23 @@ static int irtty_do_write(struct sir_dev *dev, const unsigned char *ptr, size_t
  * usbserial:   urb-complete-interrupt / softint
  */
 
-static void irtty_receive_buf(struct tty_struct *tty, const unsigned char *cp,
-                              char *fp, int count) 
+static unsigned int irtty_receive_buf(struct tty_struct *tty,
+                const unsigned char *cp, char *fp, int count)
 {
         struct sir_dev *dev;
         struct sirtty_cb *priv = tty->disc_data;
         int     i;
 
-        IRDA_ASSERT(priv != NULL, return;);
-        IRDA_ASSERT(priv->magic == IRTTY_MAGIC, return;);
+        IRDA_ASSERT(priv != NULL, return -ENODEV;);
+        IRDA_ASSERT(priv->magic == IRTTY_MAGIC, return -EINVAL;);
 
         if (unlikely(count==0))         /* yes, this happens */
-                return;
+                return 0;
 
         dev = priv->dev;
         if (!dev) {
                 IRDA_WARNING("%s(), not ready yet!\n", __func__);
-                return;
+                return -ENODEV;
         }
 
         for (i = 0; i < count; i++) {
@@ -242,11 +242,13 @@ static void irtty_receive_buf(struct tty_struct *tty, const unsigned char *cp,
                 if (fp && *fp++) { 
                         IRDA_DEBUG(0, "Framing or parity error!\n");
                         sirdev_receive(dev, NULL, 0);   /* notify sir_dev (updating stats) */
-                        return;
+                        return -EINVAL;
                 }
         }
 
         sirdev_receive(dev, cp, count);
+
+        return count;
 }
 
 /*
diff --git a/drivers/net/ppp_async.c b/drivers/net/ppp_async.c
index a1b82c9c67d2..53872d7d7382 100644
--- a/drivers/net/ppp_async.c
+++ b/drivers/net/ppp_async.c
@@ -340,7 +340,7 @@ ppp_asynctty_poll(struct tty_struct *tty, struct file *file, poll_table *wait)
 }
 
 /* May sleep, don't call from interrupt level or with interrupts disabled */
-static void
+static unsigned int
 ppp_asynctty_receive(struct tty_struct *tty, const unsigned char *buf,
                   char *cflags, int count)
 {
@@ -348,7 +348,7 @@ ppp_asynctty_receive(struct tty_struct *tty, const unsigned char *buf,
         unsigned long flags;
 
         if (!ap)
-                return;
+                return -ENODEV;
         spin_lock_irqsave(&ap->recv_lock, flags);
         ppp_async_input(ap, buf, cflags, count);
         spin_unlock_irqrestore(&ap->recv_lock, flags);
@@ -356,6 +356,8 @@ ppp_asynctty_receive(struct tty_struct *tty, const unsigned char *buf,
                 tasklet_schedule(&ap->tsk);
         ap_put(ap);
         tty_unthrottle(tty);
+
+        return count;
 }
 
 static void
diff --git a/drivers/net/ppp_synctty.c b/drivers/net/ppp_synctty.c
index 2573f525f11c..0815790a5cf9 100644
--- a/drivers/net/ppp_synctty.c
+++ b/drivers/net/ppp_synctty.c
@@ -381,7 +381,7 @@ ppp_sync_poll(struct tty_struct *tty, struct file *file, poll_table *wait)
 }
 
 /* May sleep, don't call from interrupt level or with interrupts disabled */
-static void
+static unsigned int
 ppp_sync_receive(struct tty_struct *tty, const unsigned char *buf,
                   char *cflags, int count)
 {
@@ -389,7 +389,7 @@ ppp_sync_receive(struct tty_struct *tty, const unsigned char *buf,
         unsigned long flags;
 
         if (!ap)
-                return;
+                return -ENODEV;
         spin_lock_irqsave(&ap->recv_lock, flags);
         ppp_sync_input(ap, buf, cflags, count);
         spin_unlock_irqrestore(&ap->recv_lock, flags);
@@ -397,6 +397,8 @@ ppp_sync_receive(struct tty_struct *tty, const unsigned char *buf,
                 tasklet_schedule(&ap->tsk);
         sp_put(ap);
         tty_unthrottle(tty);
+
+        return count;
 }
 
 static void
diff --git a/drivers/net/slip.c b/drivers/net/slip.c
index 86cbb9ea2f26..86718d358395 100644
--- a/drivers/net/slip.c
+++ b/drivers/net/slip.c
@@ -670,16 +670,17 @@ static void sl_setup(struct net_device *dev)
  * in parallel
  */
 
-static void slip_receive_buf(struct tty_struct *tty, const unsigned char *cp,
-                                                        char *fp, int count)
+static unsigned int slip_receive_buf(struct tty_struct *tty,
+                const unsigned char *cp, char *fp, int count)
 {
         struct slip *sl = tty->disc_data;
+        int bytes = count;
 
         if (!sl || sl->magic != SLIP_MAGIC || !netif_running(sl->dev))
-                return;
+                return -ENODEV;
 
         /* Read the characters out of the buffer */
-        while (count--) {
+        while (bytes--) {
                 if (fp && *fp++) {
                         if (!test_and_set_bit(SLF_ERROR, &sl->flags))
                                 sl->dev->stats.rx_errors++;
@@ -693,6 +694,8 @@ static void slip_receive_buf(struct tty_struct *tty, const unsigned char *cp,
 #endif
                         slip_unesc(sl, *cp++);
         }
+
+        return count;
 }
 
 /************************************
diff --git a/drivers/net/wan/x25_asy.c b/drivers/net/wan/x25_asy.c
index 24297b274cd4..40398bf7d036 100644
--- a/drivers/net/wan/x25_asy.c
+++ b/drivers/net/wan/x25_asy.c
@@ -517,17 +517,18 @@ static int x25_asy_close(struct net_device *dev)
  * and sent on to some IP layer for further processing.
  */
 
-static void x25_asy_receive_buf(struct tty_struct *tty,
+static unsigned int x25_asy_receive_buf(struct tty_struct *tty,
                                 const unsigned char *cp, char *fp, int count)
 {
         struct x25_asy *sl = tty->disc_data;
+        int bytes = count;
 
         if (!sl || sl->magic != X25_ASY_MAGIC || !netif_running(sl->dev))
                 return;
 
 
         /* Read the characters out of the buffer */
-        while (count--) {
+        while (bytes--) {
                 if (fp && *fp++) {
                         if (!test_and_set_bit(SLF_ERROR, &sl->flags))
                                 sl->dev->stats.rx_errors++;
@@ -536,6 +537,8 @@ static void x25_asy_receive_buf(struct tty_struct *tty,
                 }
                 x25_asy_unesc(sl, *cp++);
         }
+
+        return count;
 }
 
 /*
diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index 47f8cdb207f1..6abc73598847 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -2138,8 +2138,8 @@ static void gsmld_detach_gsm(struct tty_struct *tty, struct gsm_mux *gsm)
         gsm->tty = NULL;
 }
 
-static void gsmld_receive_buf(struct tty_struct *tty, const unsigned char *cp,
-                              char *fp, int count)
+static unsigned int gsmld_receive_buf(struct tty_struct *tty,
+                const unsigned char *cp, char *fp, int count)
 {
         struct gsm_mux *gsm = tty->disc_data;
         const unsigned char *dp;
@@ -2173,6 +2173,8 @@ static void gsmld_receive_buf(struct tty_struct *tty, const unsigned char *cp,
         }
         /* FASYNC if needed ? */
         /* If clogged call tty_throttle(tty); */
+
+        return count;
 }
 
 /**
diff --git a/drivers/tty/n_hdlc.c b/drivers/tty/n_hdlc.c
index cea56033b34c..cac666314aef 100644
--- a/drivers/tty/n_hdlc.c
+++ b/drivers/tty/n_hdlc.c
@@ -188,8 +188,8 @@ static unsigned int n_hdlc_tty_poll(struct tty_struct *tty, struct file *filp,
                                     poll_table *wait);
 static int n_hdlc_tty_open(struct tty_struct *tty);
 static void n_hdlc_tty_close(struct tty_struct *tty);
-static void n_hdlc_tty_receive(struct tty_struct *tty, const __u8 *cp,
-                               char *fp, int count);
+static unsigned int n_hdlc_tty_receive(struct tty_struct *tty,
+                const __u8 *cp, char *fp, int count);
 static void n_hdlc_tty_wakeup(struct tty_struct *tty);
 
 #define bset(p,b)       ((p)[(b) >> 5] |= (1 << ((b) & 0x1f)))
@@ -509,8 +509,8 @@ static void n_hdlc_tty_wakeup(struct tty_struct *tty)
  * Called by tty low level driver when receive data is available. Data is
  * interpreted as one HDLC frame.
  */
-static void n_hdlc_tty_receive(struct tty_struct *tty, const __u8 *data,
-                               char *flags, int count)
+static unsigned int n_hdlc_tty_receive(struct tty_struct *tty,
+                const __u8 *data, char *flags, int count)
 {
         register struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
         register struct n_hdlc_buf *buf;
@@ -521,20 +521,20 @@ static void n_hdlc_tty_receive(struct tty_struct *tty, const __u8 *data,
                 
         /* This can happen if stuff comes in on the backup tty */
         if (!n_hdlc || tty != n_hdlc->tty)
-                return;
+                return -ENODEV;
                 
         /* verify line is using HDLC discipline */
         if (n_hdlc->magic != HDLC_MAGIC) {
                 printk("%s(%d) line not using HDLC discipline\n",
                         __FILE__,__LINE__);
-                return;
+                return -EINVAL;
         }
         
         if ( count>maxframe ) {
                 if (debuglevel >= DEBUG_LEVEL_INFO)     
                         printk("%s(%d) rx count>maxframesize, data discarded\n",
                                __FILE__,__LINE__);
-                return;
+                return -EINVAL;
         }
 
         /* get a free HDLC buffer */    
@@ -550,7 +550,7 @@ static void n_hdlc_tty_receive(struct tty_struct *tty, const __u8 *data,
                 if (debuglevel >= DEBUG_LEVEL_INFO)     
                         printk("%s(%d) no more rx buffers, data discarded\n",
                                __FILE__,__LINE__);
-                return;
+                return -EINVAL;
         }
                 
         /* copy received data to HDLC buffer */
@@ -565,6 +565,8 @@ static void n_hdlc_tty_receive(struct tty_struct *tty, const __u8 *data,
         if (n_hdlc->tty->fasync != NULL)
                 kill_fasync (&n_hdlc->tty->fasync, SIGIO, POLL_IN);
 
+        return count;
+
 }       /* end of n_hdlc_tty_receive() */
 
 /**
diff --git a/drivers/tty/n_r3964.c b/drivers/tty/n_r3964.c
index 5c6c31459a2f..a4bc39c21a43 100644
--- a/drivers/tty/n_r3964.c
+++ b/drivers/tty/n_r3964.c
@@ -139,8 +139,8 @@ static int r3964_ioctl(struct tty_struct *tty, struct file *file,
 static void r3964_set_termios(struct tty_struct *tty, struct ktermios *old);
 static unsigned int r3964_poll(struct tty_struct *tty, struct file *file,
                 struct poll_table_struct *wait);
-static void r3964_receive_buf(struct tty_struct *tty, const unsigned char *cp,
-                char *fp, int count);
+static unsigned int r3964_receive_buf(struct tty_struct *tty,
+                const unsigned char *cp, char *fp, int count);
 
 static struct tty_ldisc_ops tty_ldisc_N_R3964 = {
         .owner = THIS_MODULE,
@@ -1239,8 +1239,8 @@ static unsigned int r3964_poll(struct tty_struct *tty, struct file *file,
         return result;
 }
 
-static void r3964_receive_buf(struct tty_struct *tty, const unsigned char *cp,
-                        char *fp, int count)
+static unsigned int r3964_receive_buf(struct tty_struct *tty,
+                const unsigned char *cp, char *fp, int count)
 {
         struct r3964_info *pInfo = tty->disc_data;
         const unsigned char *p;
@@ -1257,6 +1257,8 @@ static void r3964_receive_buf(struct tty_struct *tty, const unsigned char *cp,
                 }
 
         }
+
+        return count;
 }
 
 MODULE_LICENSE("GPL");
diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index 0ad32888091c..95d0a9c2dd13 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -81,38 +81,6 @@ static inline int tty_put_user(struct tty_struct *tty, unsigned char x,
         return put_user(x, ptr);
 }
 
-/**
- *      n_tty_set__room -       receive space
- *      @tty: terminal
- *
- *      Called by the driver to find out how much data it is
- *      permitted to feed to the line discipline without any being lost
- *      and thus to manage flow control. Not serialized. Answers for the
- *      "instant".
- */
-
-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;
-        int old_left;
-
-        /*
-         * If we are doing input canonicalization, and there are no
-         * pending newlines, let characters through without limit, so
-         * that erase characters will be handled.  Other excess
-         * characters will be beeped.
-         */
-        if (left <= 0)
-                left = tty->icanon && !tty->canon_data;
-        old_left = tty->receive_room;
-        tty->receive_room = left;
-
-        /* Did this open up the receive buffer? We may need to flip */
-        if (left && !old_left)
-                schedule_work(&tty->buf.work);
-}
-
 static void put_tty_queue_nolock(unsigned char c, struct tty_struct *tty)
 {
         if (tty->read_cnt < N_TTY_BUF_SIZE) {
@@ -184,7 +152,6 @@ static void reset_buffer_flags(struct tty_struct *tty)
 
         tty->canon_head = tty->canon_data = tty->erasing = 0;
         memset(&tty->read_flags, 0, sizeof tty->read_flags);
-        n_tty_set_room(tty);
         check_unthrottle(tty);
 }
 
@@ -1360,17 +1327,19 @@ static void n_tty_write_wakeup(struct tty_struct *tty)
  *      calls one at a time and in order (or using flush_to_ldisc)
  */
 
-static void n_tty_receive_buf(struct tty_struct *tty, const unsigned char *cp,
-                              char *fp, int count)
+static unsigned int n_tty_receive_buf(struct tty_struct *tty,
+                const unsigned char *cp, char *fp, int count)
 {
         const unsigned char *p;
         char *f, flags = TTY_NORMAL;
         int     i;
         char    buf[64];
         unsigned long cpuflags;
+        int left;
+        int ret = 0;
 
         if (!tty->read_buf)
-                return;
+                return 0;
 
         if (tty->real_raw) {
                 spin_lock_irqsave(&tty->read_lock, cpuflags);
@@ -1380,6 +1349,7 @@ static void n_tty_receive_buf(struct tty_struct *tty, const unsigned char *cp,
                 memcpy(tty->read_buf + tty->read_head, cp, i);
                 tty->read_head = (tty->read_head + i) & (N_TTY_BUF_SIZE-1);
                 tty->read_cnt += i;
+                ret += i;
                 cp += i;
                 count -= i;
 
@@ -1389,8 +1359,10 @@ static void n_tty_receive_buf(struct tty_struct *tty, const unsigned char *cp,
                 memcpy(tty->read_buf + tty->read_head, cp, i);
                 tty->read_head = (tty->read_head + i) & (N_TTY_BUF_SIZE-1);
                 tty->read_cnt += i;
+                ret += i;
                 spin_unlock_irqrestore(&tty->read_lock, cpuflags);
         } else {
+                ret = count;
                 for (i = count, p = cp, f = fp; i; i--, p++) {
                         if (f)
                                 flags = *f++;
@@ -1418,8 +1390,6 @@ static void n_tty_receive_buf(struct tty_struct *tty, const unsigned char *cp,
                         tty->ops->flush_chars(tty);
         }
 
-        n_tty_set_room(tty);
-
         if ((!tty->icanon && (tty->read_cnt >= tty->minimum_to_wake)) ||
                 L_EXTPROC(tty)) {
                 kill_fasync(&tty->fasync, SIGIO, POLL_IN);
@@ -1432,8 +1402,12 @@ static void n_tty_receive_buf(struct tty_struct *tty, const unsigned char *cp,
          * mode.  We don't want to throttle the driver if we're in
          * canonical mode and don't have a newline yet!
          */
-        if (tty->receive_room < TTY_THRESHOLD_THROTTLE)
+        left = N_TTY_BUF_SIZE - tty->read_cnt - 1;
+
+        if (left < TTY_THRESHOLD_THROTTLE)
                 tty_throttle(tty);
+
+        return ret;
 }
 
 int is_ignored(int sig)
@@ -1477,7 +1451,6 @@ static void n_tty_set_termios(struct tty_struct *tty, struct ktermios *old)
         if (test_bit(TTY_HW_COOK_IN, &tty->flags)) {
                 tty->raw = 1;
                 tty->real_raw = 1;
-                n_tty_set_room(tty);
                 return;
         }
         if (I_ISTRIP(tty) || I_IUCLC(tty) || I_IGNCR(tty) ||
@@ -1530,7 +1503,6 @@ static void n_tty_set_termios(struct tty_struct *tty, struct ktermios *old)
                 else
                         tty->real_raw = 0;
         }
-        n_tty_set_room(tty);
         /* The termios change make the tty ready for I/O */
         wake_up_interruptible(&tty->write_wait);
         wake_up_interruptible(&tty->read_wait);
@@ -1812,8 +1784,6 @@ do_it_again:
                                 retval = -ERESTARTSYS;
                                 break;
                         }
-                        /* FIXME: does n_tty_set_room need locking ? */
-                        n_tty_set_room(tty);
                         timeout = schedule_timeout(timeout);
                         continue;
                 }
@@ -1885,10 +1855,8 @@ do_it_again:
                  * longer than TTY_THRESHOLD_UNTHROTTLE in canonical mode,
                  * we won't get any more characters.
                  */
-                if (n_tty_chars_in_buffer(tty) <= TTY_THRESHOLD_UNTHROTTLE) {
-                        n_tty_set_room(tty);
+                if (n_tty_chars_in_buffer(tty) <= TTY_THRESHOLD_UNTHROTTLE)
                         check_unthrottle(tty);
-                }
 
                 if (b - buf >= minimum)
                         break;
@@ -1910,7 +1878,6 @@ do_it_again:
         } else if (test_and_clear_bit(TTY_PUSH, &tty->flags))
                  goto do_it_again;
 
-        n_tty_set_room(tty);
         return retval;
 }
 
diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
index f1a7918d71aa..46de2e075dac 100644
--- a/drivers/tty/tty_buffer.c
+++ b/drivers/tty/tty_buffer.c
@@ -416,6 +416,7 @@ static void flush_to_ldisc(struct work_struct *work)
                 struct tty_buffer *head, *tail = tty->buf.tail;
                 int seen_tail = 0;
                 while ((head = tty->buf.head) != NULL) {
+                        int copied;
                         int count;
                         char *char_buf;
                         unsigned char *flag_buf;
@@ -442,17 +443,19 @@ static void flush_to_ldisc(struct work_struct *work)
                            line discipline as we want to empty the queue */
                         if (test_bit(TTY_FLUSHPENDING, &tty->flags))
                                 break;
-                        if (!tty->receive_room || seen_tail)
-                                break;
-                        if (count > tty->receive_room)
-                                count = tty->receive_room;
                         char_buf = head->char_buf_ptr + head->read;
                         flag_buf = head->flag_buf_ptr + head->read;
-                        head->read += count;
                         spin_unlock_irqrestore(&tty->buf.lock, flags);
-                        disc->ops->receive_buf(tty, char_buf,
+                        copied = disc->ops->receive_buf(tty, char_buf,
                                                         flag_buf, count);
                         spin_lock_irqsave(&tty->buf.lock, flags);
+
+                        head->read += copied;
+
+                        if (copied == 0 || seen_tail) {
+                                schedule_work(&tty->buf.work);
+                                break;
+                        }
                 }
                 clear_bit(TTY_FLUSHING, &tty->flags);
         }
diff --git a/drivers/tty/vt/selection.c b/drivers/tty/vt/selection.c
index fb864e7fcd13..67b1d0d7c8ac 100644
--- a/drivers/tty/vt/selection.c
+++ b/drivers/tty/vt/selection.c
@@ -332,8 +332,7 @@ int paste_selection(struct tty_struct *tty)
                         continue;
                 }
                 count = sel_buffer_lth - pasted;
-                count = min(count, tty->receive_room);
-                tty->ldisc->ops->receive_buf(tty, sel_buffer + pasted,
+                count = tty->ldisc->ops->receive_buf(tty, sel_buffer + pasted,
                                                                 NULL, count);
                 pasted += count;
         }
diff --git a/include/linux/tty_ldisc.h b/include/linux/tty_ldisc.h
index ff7dc08696a8..5b07792ccb46 100644
--- a/include/linux/tty_ldisc.h
+++ b/include/linux/tty_ldisc.h
@@ -76,7 +76,7 @@
  *      tty device.  It is solely the responsibility of the line
  *      discipline to handle poll requests.
  *
- * void (*receive_buf)(struct tty_struct *, const unsigned char *cp,
+ * unsigned int (*receive_buf)(struct tty_struct *, const unsigned char *cp,
  *                     char *fp, int count);
  *
  *      This function is called by the low-level tty driver to send
@@ -84,7 +84,8 @@
  *      processing.  <cp> is a pointer to the buffer of input
  *      character received by the device.  <fp> is a pointer to a
  *      pointer of flag bytes which indicate whether a character was
- *      received with a parity error, etc.
+ *      received with a parity error, etc. Returns the amount of bytes
+ *      received.
  * 
  * void (*write_wakeup)(struct tty_struct *);
  *
@@ -140,8 +141,8 @@ struct tty_ldisc_ops {
         /*
          * The following routines are called from below.
          */
-        void    (*receive_buf)(struct tty_struct *, const unsigned char *cp,
-                               char *fp, int count);
+        unsigned int (*receive_buf)(struct tty_struct *,
+                        const unsigned char *cp, char *fp, int count);
         void    (*write_wakeup)(struct tty_struct *);
         void    (*dcd_change)(struct tty_struct *, unsigned int,
                                 struct pps_event_time *);