On Tue, Oct 17, 2017 at 8:38 AM, Prakash Sangappa <prakash.sangappa@xxxxxxxxxx> wrote: > > > On 10/16/17 5:52 PM, Andy Lutomirski wrote: >> >> On Mon, Oct 16, 2017 at 3:54 PM, prakash.sangappa >> <prakash.sangappa@xxxxxxxxxx> wrote: >>> >>> >>> On 10/16/2017 03:07 PM, Nagarathnam Muthusamy wrote: >>>> >>>> >>>> >>>> On 10/16/2017 02:36 PM, Andrew Morton wrote: >>>>> >>>>> On Sat, 14 Oct 2017 11:17:47 +0300 Konstantin Khlebnikov >>>>> <khlebnikov@xxxxxxxxxxxxxx> 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. >>> >>> >>> As Nagarathnam indicated, Oracle Database will be using pid namespaces >>> and >>> needs a direct method of converting pids of processes in the pid >>> namespace >>> hierarchy. In this use case multiple >>> nested PID namespaces will be used. The currently available mechanism >>> are >>> not very efficient for this use case. For ex. as Konstantin described, >>> using >>> /proc/<pid>/status would require the application to scan all the pid's >>> status files to determine the pid of given process in a child namespace. >>> >>> Use of SCM_CREDENTIALS's socket message is another way, which would >>> require >>> every process starting inside a pid namespace to send this message and >>> the >>> receiving process in the target namespace would have to save the >>> converted >>> pid and reference it. This mechanism becomes cumbersome especially if the >>> application has to deal with multiple nested pid namespaces. Also, the >>> Database needs to be able to convert a thread's global pid(gettid()). >>> Passing the thread's pid(gettid()) in SCM_CREDENTIALS message requires >>> CAP_SYS_ADMIN, which is an issue. >>> >>> So having a direct method, like the API that Konstantin is proposing, >>> will >>> work best for the Database >>> since pid of a process in any of the nested pid namespaces can be >>> converted >>> as and when required. I think with the proposed API, the application >>> should >>> be able to convert pid of a process or tid(gettid()) of a thread as well. >>> >> >> Can you explain what Oracle's database is planning to do with this >> information? > > > Database uses the PID to programmatically find out if the process/thread is > alive(kill 0) also send signals to the processes requesting it to dump > status/debug information and kill the processes in case of a shutdown abort > of the instance. What I'm wondering is: how does the caller of kill() end up controlling a task whose pid it doesn't know in its own namespace? > > -Prakash. > > -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
