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SubjectRe: (pspace,pid) vs true pid virtualization
>> However, if we're going to get anywhere, the first decision which we
>> need to make is whether to go with a (container,pid), (pspace,pid) or
>> equivalent pair like approach, or a virtualized pid approach. Linus had
>> previously said that he prefers the former. Since there has been much
>> discussion since then, I thought I'd try to recap the pros and cons of
>> each approach, with the hope that the head Penguins will chime in one
>> more time, after which we can hopefully focus our efforts.
I think the first thing we have to do, is not to decide which pids we
want to see, but what and how we want to virtualize.

> I am thinking that you can have both. Not in the sense of
> overcomplicating, but in the sense of having your cake and eating it
> too.
BTW, really, why not both?
Eric, can we do something universal which will suite all the parties?

> The only thing which is a unique, system wide identifier for the process
> is the &task_struct. So we are already virtualising this pointer into a
> PID for userland. The only difference is that we cache it (nay, keep
> the authorative version of it) in the task_struct.
>
> The (XID, PID) approach internally is also fine. This says that there
> is a container XID, and within it, the PID refers to a particular
> task_struct. A given task_struct will likely exist in more than one
> place in the (XID, PID) space. Perhaps the values of PID for XID = 0
> and XID = task.xid can be cached in the task_struct, but that is a
> detail.
>
> Depending on the flags on the XID, we can incorporate all the approaches
> being tabled. You want virtualised pids? Well, that'll hurt a little,
> but suit yourself - set a flag on your container and inside the
> container you get virtualised PIDs. You want a flat view for all your
> vservers? Fine, just use an XID without the virtualisation flag and
> with the "all seeing eye" property set. Or you use an XID _with_ the
> virtualisation flag set, and then call a tuple-endowed API to find the
> information you're after.
This sounds good. But pspaces are also used for access controls. So this
should be incorparated there as well.

Kirill


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