[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>

diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index b846d87f2b56ad80a89145c443d5ea48cda89f96..1f03ebf165d90fa353e7f7a081015d18f453382b 100644 (file)
--- 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);