MFC r311954, r311996, r312077, r312080:

  Rework tty_drain() to poll the hardware for completion, and restore
  drain timeout handling to historical freebsd behavior.

  The primary reason for these changes is the need to have tty_drain() call
  ttydevsw_busy() at some reasonable sub-second rate, to poll hardware that
  doesn't signal an interrupt when the transmit shift register becomes empty
  (which includes virtually all USB serial hardware).  Such hardware hangs
  in a ttyout wait, because it never gets an opportunity to trigger a wakeup
  from the sleep in tty_drain() by calling ttydisc_getc() again, after
  handing the last of the buffered data to the hardware.

  Restructure the tty_drain loop so that device-busy is checked one more time
  after tty_timedwait() returns an error only if the error is EWOULDBLOCK;
  other errors cause an immediate return.  This fixes the case of the tty
  disappearing while in tty_drain().

  Check tty_gone() after allocating IO buffers.  The tty lock has to be
  dropped then reacquired due to using M_WAITOK, which opens a window in
  which the tty device can disappear.  Check for this and return ENXIO
  back up the call chain so that callers can cope.

  Correct the comments about how much buffer is allocated.

1 files changed, 2 insertions, 2 deletions

diff --git a/sys/sys/ttyqueue.h b/sys/sys/ttyqueue.h
index 2d1a565..c8d85d6 100644
--- a/sys/sys/ttyqueue.h
+++ b/sys/sys/ttyqueue.h
@@ -69,7 +69,7 @@ struct ttyoutq {
 
 #ifdef _KERNEL
 /* Input queue handling routines. */
-void	ttyinq_setsize(struct ttyinq *ti, struct tty *tp, size_t len);
+int	ttyinq_setsize(struct ttyinq *ti, struct tty *tp, size_t len);
 void	ttyinq_free(struct ttyinq *ti);
 int	ttyinq_read_uio(struct ttyinq *ti, struct tty *tp, struct uio *uio,
     size_t readlen, size_t flushlen);
@@ -136,7 +136,7 @@ void	ttyinq_line_iterate_from_reprintpos(struct ttyinq *ti,
 
 /* Output queue handling routines. */
 void	ttyoutq_flush(struct ttyoutq *to);
-void	ttyoutq_setsize(struct ttyoutq *to, struct tty *tp, size_t len);
+int	ttyoutq_setsize(struct ttyoutq *to, struct tty *tp, size_t len);
 void	ttyoutq_free(struct ttyoutq *to);
 size_t	ttyoutq_read(struct ttyoutq *to, void *buf, size_t len);
 int	ttyoutq_read_uio(struct ttyoutq *to, struct tty *tp, struct uio *uio);