[PATCH] add receive_room flow control to flush_to_ldisc

Flush data serially to line discipline in blocks no larger than
tty->receive_room to avoid losing data if line discipline is busy (such as
N_TTY operating at high speed on heavily loaded system) or does not accept
data in large blocks (such as N_MOUSE).

Signed-off-by: Paul Fulghum <paulkf@microgate.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 24 insertions, 13 deletions

diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index b846d87f2b56..1f03ebf165d9 100644
--- a/drivers/char/tty_io.c
+++ b/drivers/char/tty_io.c
@@ -2771,8 +2771,7 @@ static void flush_to_ldisc(void *private_)
         struct tty_struct *tty = (struct tty_struct *) private_;
         unsigned long   flags;
         struct tty_ldisc *disc;
-        struct tty_buffer *tbuf;
-        int count;
+        struct tty_buffer *tbuf, *head;
         char *char_buf;
         unsigned char *flag_buf;
 
@@ -2781,21 +2780,33 @@ static void flush_to_ldisc(void *private_)
                 return;
 
         spin_lock_irqsave(&tty->buf.lock, flags);
-        while((tbuf = tty->buf.head) != NULL) {
-                while ((count = tbuf->commit - tbuf->read) != 0) {
-                        char_buf = tbuf->char_buf_ptr + tbuf->read;
-                        flag_buf = tbuf->flag_buf_ptr + tbuf->read;
-                        tbuf->read += count;
+        head = tty->buf.head;
+        if (head != NULL) {
+                tty->buf.head = NULL;
+                for (;;) {
+                        int count = head->commit - head->read;
+                        if (!count) {
+                                if (head->next == NULL)
+                                        break;
+                                tbuf = head;
+                                head = head->next;
+                                tty_buffer_free(tty, tbuf);
+                                continue;
+                        }
+                        if (!tty->receive_room) {
+                                schedule_delayed_work(&tty->buf.work, 1);
+                                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->receive_buf(tty, char_buf, flag_buf, count);
                         spin_lock_irqsave(&tty->buf.lock, flags);
                 }
-                if (tbuf->active)
-                        break;
-                tty->buf.head = tbuf->next;
-                if (tty->buf.head == NULL)
-                        tty->buf.tail = NULL;
-                tty_buffer_free(tty, tbuf);
+                tty->buf.head = head;
         }
         spin_unlock_irqrestore(&tty->buf.lock, flags);