Re: [PATCH 14/16] vfs: Implement mount_super_once

[Linus Torvalds]

On Tue, Apr 19, 2016 at 11:22 AM, Eric W. Biederman
<ebiederm@xxxxxxxxxxxx> wrote:
> Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> writes:
>>
>> No.
>>
>> We want to get *rid* of the idiotic "primary instance" crap.
>
> That is actually pretty much the opposite of what you said last time,
> but having looked at the cost to maintian a "primary instance" notion
> and what will break if we don't I am happy to remove such a notion
> from devpts.

No, it's what I said last time too, but there may have been an misunderstanding.

I _violently_ oppose the stupid DEVPTS_MULTIPLE_INSTANCES config option.

But I do _not_ oppose it because I want to have that "primary
instance" cap. Quite the reverse. I oppose it because the *option* is
stupid, and we should not have such an option.

The kernel should always do multiple instances. There should never
_ever_ be a "single instance" option, although obviously if you were
to do a bind-mount of devpts, the bound mount would be the same
instance.

But if you do two separate mounts, they should alwats be separate insnaces.

So what I want to fix is the crazy "that doesn't work" problem with
Ubuntu or CentOS (or whatever distro it was) breaking, because
/dev/ptmx ends up pointing to the *wrong* instance.

This is literally why I think /dev/ptmx should just look up /dev/pts -
simply to get rid of that idiotic special instance. It should not
exist. It should not exist in the kernel, and it shouldn't exist in
user space.

                 Linus