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

["H. Peter Anvin" <hpa-YMNOUZJC4hwAvxtiuMwx3w@public.gmane.org>]

sukadev-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org wrote:
> 
> Ok. But was wondering if we can pass the ptmx symlink burden to the
> 'container-startup sripts' since they are the ones that need the second
> or subsequent mount of devpts.
> 
> So, initially and for systems that don't need multiple mounts of devpts,
> existing behavior can continue (/dev/ptmx is a node).
> 
> Container startup scripts have to anyway remount /dev/pts and mknod
> /dev/pts/ptmx. These scripts could additionally check if /dev/ptmx is
> a node and make it a symlink. The container script would have to do
> this check while it still has access to the first mount of devpts
> and mknod in the first devpts mnt.
> 
> But then again, the first mount is still special in the kernel.
> 

You're right, I think we can do this and still retain most of the 
advantages, at least for a transition period.

The idea would be that you'd have a mount option, that if you do not 
specify it, you get a bind to the in-kernel mount; otherwise you get a 
new instance.  ptmx, if not invoked from inside a devpts filesystem, 
would default to the kernel-mounted instance.

Unfortunately I believe that means parsing the command options in 
getpts_get_sb() to know if we do have the "multi" option, but that isn't 
really all that difficult; it just means breaking the parser out as a 
separate subroutine.

	-hpa