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SubjectRe: [RFC]Pid conversion between pid namespace
Quoting chenhanxiao@cn.fujitsu.com (chenhanxiao@cn.fujitsu.com):
> Hi,
>
> Let me summarize our discussions of ID conversion by pros/cons:
>
> A) make new system call for translation
> A-1) systemcall(ID, NS1, NS2) into (ID).
> pros:
> - has a reference ns(NS2)
> We could get any lower level ID directly.
>
> cons:
> - lack of hierarchy information.
> CRIU need hierarchy info for checkpoint/restore in nested containers.
> - not easy for debug.
> And a lot of tools/libs need be modified.
>
> A-2) syscall pid_t getnspid(pid_t query_pid, pid_t observer_pid)
> pros:
> - ns procfs free, easy to use.
> We could get rid of mounted ns procfs.
>
> cons:
> - may find multiple results in nested ns.
> We wished the new API could tell us the exact answer.
> But if getnspid return more than one results will bring trouble to admins,

(See below for more, but) the question being posed to getnspid has precisely
one answer.

> they had to make another decision.
> Or we marked the deepest level for translation as prerequisite.
>
> -based on current pidns, no reference ns.

Hm, no. The intent here was that

observer_pid would be in current ns
query_pid would be in observer_pid's ns.

So this would be ideal for "I got a pid in a logfile created by rsyslog in
a nested contaner, what is the logged pid in my pidns."

Taking a set of tasks (like a container with nesting) and bulding a tree
of all pids shouldn't be too difficult either. Start with the init pid,
call getnspid($pid, $init_pid) for every $pid in the container; to figure
out whether any $pid is itself a nested init_pid, we can compare the
/proc/$$/ns/pid, as well as look at getnspid($pid, $pid).

> B) make/change proc file/directories
> B-1) expand /proc/pid/status
> pros:
> - easy to use and to debug
> - already had existed interface in kernel
>
> cons:
> - based on current ns
> for middle level, we had to make another decision.
> - do not have hierarchy info.
>
> B-2) /proc/<pidX>/ns/proc/ which would contain everything
> pros:
> - have enough info from /proc in container
>
> cons:
> - Requirements unclear.
> We need more discussion to decide which items should not be exposed.
> - do not have hierarchy info.
>
>
> How about do these things in two steps:
>
> C) 1. expose all sets of pid, pgid, sid and tgid
> via expanded /proc/PID/status
> We could get translated IDs from container like:
> NStgid: 16465 5 1
> NSpid: 16465 5 1
> NSpgid: 16465 5 1
> NSsid: 16423 1 0
> (a set of IDs with 3 level of ns)
>
> 2. add hierarchy info under /proc
> We lacked of method of getting hierarchy info, which is useful.
> Then we could know the relationship of ns.
> How about adding a new proc file just under /proc
> to show the hierarchy like readlink did:
> pid:[4026531836]-> [4026532390] -> [4026532484]
> pid:[4026531836]-> [4026532491]
> (A 3 level pid and 2 level pid_
>
> Any comments would be appreciated.
>
> Thanks,
> - Chen
>
> > -----Original Message-----
> > Subject: [RFC]Pid conversion between pid namespace
> >
> > Hi,
> >
> > We had some discussions on how to carry out
> > pid conversion between pid namespace via:
> > syscall[1] and procfs[2].
> >
> > Pavel suggested that a syscall like
> > (ID, NS1, NS2) into (ID).
> >
> > Serge suggested that a syscall
> > pid_t getnspid(pid_t query_pid, pid_t observer_pid).
> >
> >
> > Eric and Richard suggested a procfs solution is
> > more appropriate.
> >
> > Oleg suggested that we should expand /proc/pid/status
> > to report this kind of information.
> >
> > And Richard suggested adding a directory like
> > /proc/<pidX>/ns/proc/ which would contain everything
> > from /proc/<pidX inside the namespace>/.
> >
> > As procfs provided a more user friendly interface,
> > how about expose all sets of tgid, pid, pgid, sid
> > by expanding /proc/PID/status in procfs?
> > And we could also expose ns hierarchy under /proc,
> > which could be another reference.
> >
> > Ex:
> > init_pid_ns ns1 ns2
> > t1 2
> > t2 `- 3 1
> > t3 `- 4 `- 5 1
> >
> > We could get in /proc/t3/status:
> > NSpid: 4 5 1
> > We knew that pid 1 in container is pid 4 in init ns.
> >
> > And we could get ns hierarchy under /proc/ns_hierarchy like:
> > init_ns->ns1->ns2 (as the result of readlink)
> > ->ns3
> > We knew that t3 in ns2, and its hierarchy.
> >
> > How these ideas looks like?
> > Any comments would be appreciated.
> >
> > Thanks,
> > - Chen
> >
> >
> > a) syscall
> > http://lwn.net/Articles/602987/
> >
> > b) procfs
> > http://www.spinics.net/lists/kernel/msg1751688.html
> >
> > _______________________________________________
> > Containers mailing list
> > Containers@lists.linux-foundation.org
> > https://lists.linuxfoundation.org/mailman/listinfo/containers
> _______________________________________________
> Containers mailing list
> Containers@lists.linux-foundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/containers


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