Messages in this thread | | | Subject | Re: [PATCH v4] pidns: introduce syscall translate_pid | From | Konstantin Khlebnikov <> | Date | Tue, 17 Oct 2017 10:41:08 +0300 |
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On 17.10.2017 00:05, Nagarathnam Muthusamy wrote: > > > On 10/16/2017 09:24 AM, Oleg Nesterov wrote: >> On 10/13, Konstantin Khlebnikov wrote: >>> >>> On 13.10.2017 19:05, Oleg Nesterov wrote: >>>> I won't insist, but this suggests we should add a new helper, >>>> get_ns_by_fd_type(fd, type), and convert get_net_ns_by_fd() to use it >>>> as well. >>> That was in v3. >>> >>> I'll prefer to this later, separately. And replace fget with fdget which >>> allows to do this without atomic operations if task is single-threaded. >> OK, agreed, >> >>>> Stupid question. Can't we make a simpler API which doesn't need /proc/ ? >>>> I mean, >>>> >>>> sys_translate_pid(pid_t pid, pid_t source_pid, pid_t target_pid) >>>> { >>>> struct pid_namespace *source_ns, *target_ns; >>>> >>>> source_ns = task_active_pid_ns(find_task_by_vpid(source_pid)); >>>> target_ns = task_active_pid_ns(find_task_by_vpid(target_pid)); >>>> >>>> ... >>>> } >>>>> Yes, this is more limited... Do you have a use-case when this is not enough? >>> That was in v1 but considered too racy. >> Hmm, I don't understand... >> >> Yes sure, this is racy but open("/proc/$pid/ns/pid") is racy too? >> >> OK, once you do fd=open("/proc/$pid/ns/pid") you can use this fd even after >> its owner exits, while find_task_by_vpid() will fail or find another task if >> this pid was already reused. >> >> But once again, do you have a use-case when this is important? > > I believe that in V1 Eric pointed out that pid in general is not a clean way to represent > namespace. (https://lkml.org/lkml/2015/9/22/1087) Few old interfaces used pid only because at that time there was no better way to represent > namespaces. >
Yeah, that was a reason.
If we think further - all syscalls who operates with non-child tasks racy and must be be replaced with some kind of pidfd or taskfd.
Eric pointed that too: https://lkml.org/lkml/2015/9/28/508
>> >>> But we could merge both ways: >>> >>> source >= 0 - pidns fs >>> source < 0 - task_pid = -source >> But for what? I must have missed something...
I mean we could have both ways to point namespace in one agrument. Some classic syscalls emply similar magic for negative pids.
This is cheap and looks almost sane. =)
>> >> Oleg. >> >
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