task_session() and task->signal->session

[Eric W. Biederman]

Sukadev Bhattiprolu <sukadev at us.ibm.com> writes:

> Thanks. 
>
> Eric W. Biederman [ebiederm at xmission.com] wrote:
> | Sukadev Bhattiprolu <sukadev at us.ibm.com> writes:
> | 
> | > I am trying to understand the diff between task_session() and
> | > task->signal-session and why we have the two notions of session.
> | > Are we just phasing out one of them ?
> | 
> | Yes.
>
> I guess we are phasing out task->signal->session.

Largely.  There are a couple of cases where it makes sense to
optimize queries from the current pid namespace.  Keeping
some of the pid_t values around for that case helps.

> | 
> | > In general each process has a single session id. The only exception
> | > being a process that unshares its pid ns. Such process will have
> | > exactly two session ids, one for each pid ns. No ?
> | 
> | Each process has a single session.
> | 
> | That session can potentially have a different session id in each
> | pid namespace.
>
> both of us used the word "have" above. But do we actually store (in some
> data structure) the multiple session ids ? Or will the following work:
>
> 	Each task refers to another task (possibly itself) as its session
> 	leader (we find this using task_session()).
>
> 	The session leader, like any other task, has multiple process ids,
> 	one in each namespace.
>
> 	So to find the session id of a task, we find its session leader
> 	and find the appropriate process id of the session leader
>
> 	i.e we don't actually store the multiple sids a task

struct pid is that data structure.  It just needs to be extended
a little to handle multiple pid namespaces.

Eric