kern/141150: TIOCDRAIN ioctl on pts/pty master hangs

john hood jh at
Thu Dec 3 22:50:01 UTC 2009

>Number:         141150
>Category:       kern
>Synopsis:       TIOCDRAIN ioctl on pts/pty master hangs
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    freebsd-bugs
>State:          open
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Thu Dec 03 22:50:01 UTC 2009
>Originator:     john hood
>Release:        8.0-RELEASE
Sandstorm Enterprises
FreeBSD 8.0-RELEASE FreeBSD 8.0-RELEASE #0: Tue Dec  1 20:49:34 EST 2009     jh at  amd64

our ancient 'gksu' port is broken-- it hangs after running the su/sudo command, and so output from the command never appears and gksu never exits.

the problem is twofold-- a bug in libgksu, which calls tcdrain() on the master side of a pty; and a bug in kernel, which hangs rather than returning an error on the tty ioctl.

see ports/141149 for a report + patch on libgksu.

I observe this on both 7.1 and 8.0.

8.0 kernel sleeps on ttyout when this happens.

In 8.0, ptsdev_ioctl() already seems to have some code to handle just this case, but it's only applied to the TIOCSETA[FW] ioctls used by tcsetattr().  So maybe it just needs to do this for TIOCFLUSH/TIOCDRAIN too.

In 7.1, something different happens, of course-- it looks like all these cases go through to the slave pty, and just TIOCSETA[FW] get a flush beforehand.

sudo pkg_add -r gksu
gdb gksu id



More information about the freebsd-bugs mailing list