Import some improvements to the TTY code from the MPSAFE TTY branch.

- Change the ddb(4) commands to be more useful (by thompsa@):
  - `show ttys' is now called `show all ttys'. This command will now
    also display the address where the TTY data structure resides.
  - Add `show tty <addr>', which dumps the TTY in a readable form.

- Place an upper bound on the TTY buffer sizes. Some drivers do not want
  to care about baud rates. Protect these drivers by preventing the TTY
  buffers from getting enormous. Right now we'll just clamp it to 64K,
  which is pretty high, taking into account that these buffers are only
  used by the built-in discipline.

- Only call ttydev_leave() when needed. Back in April/May the TTY
  reference counting mechanism was a little different, which required us
  to call ttydev_leave() each time we finished a cdev operation.
  Nowadays we only need to call ttydev_leave() when we really mark it as
  being closed.

- Improve return codes of read() and write() on TTY device nodes.

- Make sure we really wake up all blocked threads when the driver calls
  tty_rel_gone(). There were some possible code paths where we didn't
  properly wake up any readers/writers.

- Add extra assertions to prevent sleeping on a TTY that has been
  abandoned by the driver.

- Use ttydev_cdevsw as a more reliable method to figure out whether a
  device node is a real TTY device node.

Obtained from:	//depot/projects/mpsafetty/...
Reviewed by:	thompsa

1 files changed, 9 insertions, 4 deletions

diff --git a/share/man/man4/ddb.4 b/share/man/man4/ddb.4
index 07505cd..a08dc49 100644
--- a/share/man/man4/ddb.4
+++ b/share/man/man4/ddb.4
@@ -540,6 +540,13 @@ modifier will alter the display to show VM map
 addresses for the process and not show other information.
 .\"
 .Pp
+.It Ic show Cm all ttys
+Show all TTY's within the system.
+Output is similar to
+.Xr pstat 8 ,
+but also includes the address of the TTY structure.
+.\"
+.Pp
 .It Ic show Cm allchains
 Show the same information like "show lockchain" does, but
 for every thread in the system.
@@ -963,10 +970,8 @@ Backtrace.
 .El
 .\"
 .Pp
-.It Ic show Cm ttys
-Show all TTY's within the system.
-Output is similar to
-.Xr pstat 8 .
+.It Ic show Cm tty Ar addr
+Display the contents of a TTY structure in a readable form.
 .\"
 .Pp
 .It Ic show Cm turnstile Ar addr