Messages in this thread | | | Subject | Re: [PATCH RFC] pidns: introduce syscall getvpid | From | Konstantin Khlebnikov <> | Date | Wed, 16 Sep 2015 10:37:33 +0300 |
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On 15.09.2015 20:41, Serge Hallyn wrote: > Quoting Stéphane Graber (stgraber@ubuntu.com): >> On Tue, Sep 15, 2015 at 06:01:38PM +0300, Konstantin Khlebnikov wrote: >>> On 15.09.2015 17:27, Eric W. Biederman wrote: >>>> Konstantin Khlebnikov <khlebnikov@yandex-team.ru> writes: >>>> >>>>> pid_t getvpid(pid_t pid, pid_t source, pid_t target); >>>>> >>>>> This syscall converts pid from one pid-ns into pid in another pid-ns: >>>>> it takes @pid in namespace of @source task (zero for current) and >>>>> returns related pid in namespace of @target task (zero for current too). >>>>> If pid is unreachable from target pid-ns then it returns zero. >>>> >>>> This interface as presented is inherently racy. It would be better >>>> if source and target were file descriptors referring to the namespaces >>>> you wish to translate between. >>> >>> Yep, it's racy. As well as any operation with non-child pids. >>> With file descriptors for source/target result will be racy anyway. >>> >>>> >>>>> Such conversion is required for interaction between processes from >>>>> different pid-namespaces. For example when system service talks with >>>>> client from isolated container via socket about task in container: >>>> >>>> Sockets are already supported. At least the metadata of sockets is. >>>> >>>> Maybe we need this but I am not convinced of it's utility. >>>> >>>> What are you trying to do that motivates this? >>> >>> I'm working on hierarchical container management system which >>> allows to create and control nested sub-containers from containers >>> ( https://github.com/yandex/porto ). Main server works in host and >>> have to interact with all levels of nested namespaces. This syscall >>> makes some operations much easier: server must remember only pid in >>> host pid namespace and convert it into right vpid on demand. >> >> Note that as Eric said earlier, sending a PID inside a ucred through a >> unix socket will have the pid translated. >> >> So while your solution certainly should be faster, you can already achieve >> what you want today by doing: >> >> == Translate PID in container to PID in host >> - open a socket >> - setns to container's pidns >> - send ucred from that container containing the requested container PID >> - host sees the host PID >> >> == Translate PID on host to PID in container >> - open a socket >> - setns to container's pidns >> - send ucred from the host containing the request host PID >> (send will fail if the host PID isn't part of that container) >> - container sees the container PID > > In addition, since commit e4bc332451 : /proc/PID/status: show all sets of pid according to ns > we now also have 'NSpid' etc in /proc/$$/status. >
As I see this works perfectly only for converting host pid into virtual.
Backward conversion is troublesome: we have to scan all pids in host procfs and somehow filter tasks from container and its sub-pid-ns. Or I am missing something trivial?
-- Konstantin
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