devpts: Kill the DEVPTS_MULTIPLE_INSTANCE config option

Retain the code that was previously enabled with
DEVPTS_MULTIPLE_INSTANCES and remove the config option, and kill the
little bit of code that existed only when DEVPTS_MULTIPLE_INSTANCES
was not selected.  With the recently updated semantics userspace
actively depends on having multiple instances of devpts for correct

Having each mount of devpts return a distinct instance ensures that
user space will not accidentally stomp gid or mode devpts options, of
the primary system devpts, by mounting devpts in a chroot environment.
A guarantee that userspace will not stomp attributes of system devpts
removes the need for a setuid root pt_chown executable.

Running a userspace without DEVPTS_MULTIPLE_INSTANCES that has depends
on the current behavior and has removed a setuid root pt_chown
exectuable will allow the system devpts gid and mode options to be
stomped breaking userspace.  Which makes the ability to disable the
code previously selected by DEVPTS_MULTIPLE_INSTANCES actively wrong.

The size increase by always using the DEVPTS_MULTIPLE_INSTANCE
path is minimal, and the code is much easier to maintain and
use without having two different code paths to worry about.

The documentation has been updated to relfect this change.

Signed-off-by: "Eric W. Biederman" <>
3 files changed