[RFC][PATCH 0/6] Enable multiple mounts of devpts

[Kyle Moffett]

On Tue, Aug 5, 2008 at 2:15 AM, Eric W. Biederman <ebiederm at xmission.com> wrote:
>
>> There definitely needs to be a mount option (and possibly a config
>> option to forcibly enable the mount option).  I personally have 5 or 6
>> different custom scripts that depend on being able to unmount and
>> remount devpts without losing access to the TTYs therein.  Eventually
>> I will need to port those over to use "mount --move", but it would be
>> bad to have a random kernel upgrade just break my imaging/cloning
>> system.
>
> An interesting point.  What should the semantics be.  If we unmount /dev/pts
> and people still have ptys open.  -EBUSY?  Except for lazy unmounts?

Well, even if it's unmounted you can still access your pty with
/dev/tty.  As it stands right now it's possible to "umount /dev/pts"
from an SSH login and still have a mostly-functional system.  The only
failure will be when somebody needs a pseudo-TTY and you have devpts
unmounted and UNIX98 ptys turned off.

So for the legacy case, the behavior should be exactly as it is now.
In the CONFIG_DEVPTY_FORCE_PERMOUNT/"permount"-option case, I agree
that you could easily go either way.

Cheers,
Kyle Moffett