Fix some edge cases in the TTY queues:

- In the current design, when a TTY decreases its baud rate, it tries to
  shrink the queues. This may not always be possible, because it will
  not free any blocks that are still filled with data.

  Change the TTY queues to store a `quota' value as well, which means it
  will not free any blocks when changing the baud rate, but when placing
  blocks back into the queue. When the amount of blocks exceeds the
  quota, they get freed.

  It also fixes some edge cases, where TIOCSETA during read()/
  write()-calls could actually make the queue a tiny bit bigger than in
  normal cases.

- Don't leak blocks of memory when calling TIOCSETA when the device
  driver abandons the TTY while allocating memory.

- Create ttyoutq_init() and ttyinq_init() to initialize the queues,
  instead of initializing them by hand. The new TTY snoop driver also
  creates an outq, so it's good to have a proper interface to do this.

Obtained from:	//depot/projects/mpsafetty/...

1 files changed, 18 insertions, 0 deletions

diff --git a/sys/sys/ttyqueue.h b/sys/sys/ttyqueue.h
index 3e72fef..24e1187 100644
--- a/sys/sys/ttyqueue.h
+++ b/sys/sys/ttyqueue.h
@@ -52,6 +52,7 @@ struct ttyinq {
 	unsigned int			ti_reprint;
 	unsigned int			ti_end;
 	unsigned int			ti_nblocks;
+	unsigned int			ti_quota;
 };
 #define TTYINQ_DATASIZE 128
 
@@ -62,12 +63,14 @@ struct ttyoutq {
 	unsigned int			to_begin;
 	unsigned int			to_end;
 	unsigned int			to_nblocks;
+	unsigned int			to_quota;
 };
 #define TTYOUTQ_DATASIZE (256 - sizeof(STAILQ_ENTRY(ttyoutq_block)))
 
 #ifdef _KERNEL
 /* Input queue handling routines. */
 void	ttyinq_setsize(struct ttyinq *, struct tty *, size_t);
+void	ttyinq_free(struct ttyinq *);
 int	ttyinq_read_uio(struct ttyinq *, struct tty *, struct uio *,
     size_t, size_t);
 size_t	ttyinq_write(struct ttyinq *, const void *, size_t, int);
@@ -80,6 +83,13 @@ void	ttyinq_unputchar(struct ttyinq *);
 void	ttyinq_reprintpos_set(struct ttyinq *);
 void	ttyinq_reprintpos_reset(struct ttyinq *);
 
+static __inline void
+ttyinq_init(struct ttyinq *ti)
+{
+
+	TAILQ_INIT(&ti->ti_list);
+}
+
 static __inline size_t
 ttyinq_getsize(struct ttyinq *ti)
 {
@@ -124,11 +134,19 @@ void	ttyinq_line_iterate_from_reprintpos(struct ttyinq *,
 /* Output queue handling routines. */
 void	ttyoutq_flush(struct ttyoutq *);
 void	ttyoutq_setsize(struct ttyoutq *, struct tty *, size_t);
+void	ttyoutq_free(struct ttyoutq *);
 size_t	ttyoutq_read(struct ttyoutq *, void *, size_t);
 int	ttyoutq_read_uio(struct ttyoutq *, struct tty *, struct uio *);
 size_t	ttyoutq_write(struct ttyoutq *, const void *, size_t);
 int	ttyoutq_write_nofrag(struct ttyoutq *, const void *, size_t);
 
+static __inline void
+ttyoutq_init(struct ttyoutq *to)
+{
+
+	STAILQ_INIT(&to->to_list);
+}
+
 static __inline size_t
 ttyoutq_getsize(struct ttyoutq *to)
 {