Messages in this thread | | | Subject | Re: [PATCH v4] pidns: introduce syscall translate_pid | From | Nagarathnam Muthusamy <> | Date | Mon, 16 Oct 2017 15:07:52 -0700 |
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On 10/16/2017 02:36 PM, Andrew Morton wrote: > On Sat, 14 Oct 2017 11:17:47 +0300 Konstantin Khlebnikov <khlebnikov@yandex-team.ru> wrote: > >>>>> pid_t translate_pid(pid_t pid, int source, int target); >>>>> >>>>> This syscall converts pid from source pid-ns into pid in target pid-ns. >>>>> If pid is unreachable from target pid-ns it returns zero. >>>>> >>>>> Pid-namespaces are referred file descriptors opened to proc files >>>>> /proc/[pid]/ns/pid or /proc/[pid]/ns/pid_for_children. Negative argument >>>>> refers to current pid namespace, same as file /proc/self/ns/pid. >>>>> >>>>> Kernel expose virtual pids in /proc/[pid]/status:NSpid, but backward >>>>> translation requires scanning all tasks. Also pids could be translated >>>>> by sending them through unix socket between namespaces, this method is >>>>> slow and insecure because other side is exposed inside pid namespace. >> Andrew asked why we might need this. >> >> Such conversion is required for interaction between processes across pid-namespaces. >> For example to identify process in container by pid file looking from outside. >> >> Two years ago I've solved this in project of mine with monstrous code which >> forks couple times just to convert pid, lucky for me performance wasn't important. > That's a single user who needed this a single time, and found a > userspace-based solution anyway. This is not exactly compelling! > > Is there a stronger case to be made? How does this change benefit our > users? Sell it to us! Oracle database is planning to use pid namespace for sandboxing database instances and they need an API similar to translate_pid to effectively translate process IDs from other pid namespaces. Prakash (cced in mail) can provide more details on this usecase.
Thanks, Nagarathnam.
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