Fix pts(4) error codes when slave device is closed.

Unlike pre-MPSAFE TTY, the pts(4) driver always returned ENXIO when a
read() or write() was performed on a pseudo-terminal master device when
the slave device was not opened. The old implementation had different
semantics:

- When the slave device had not been opened yet, read() and write() just
  blocked.
- When the slave device had been closed, a read() call would return 0
  bytes length.
- When the slave device had been closed, a write() call would return
  EIO.

Change the new implementation to return 0 and EIO as well. We don't
implement the first rule, but I suspect this is not needed, because
routines like openpty() also open the slave device node. posix_openpt()
users also do similar things.

Reported by:	rink
Tested by:	rink

1 files changed, 2 insertions, 4 deletions

diff --git a/sys/kern/tty_pts.c b/sys/kern/tty_pts.c
index 8a51448..ee2a9fe 100644
--- a/sys/kern/tty_pts.c
+++ b/sys/kern/tty_pts.c
@@ -135,10 +135,8 @@ ptsdev_read(struct file *fp, struct uio *uio, struct ucred *active_cred,
 			break;
 
 		/* Maybe the device isn't used anyway. */
-		if (tty_opened(tp) == 0) {
-			error = ENXIO;
+		if (tty_opened(tp) == 0)
 			break;
-		}
 
 		/* Wait for more data. */
 		if (fp->f_flag & O_NONBLOCK) {
@@ -204,7 +202,7 @@ ptsdev_write(struct file *fp, struct uio *uio, struct ucred *active_cred,
 
 			/* Maybe the device isn't used anyway. */
 			if (tty_opened(tp) == 0) {
-				error = ENXIO;
+				error = EIO;
 				goto done;
 			}