Cedric Le Goater <clg@xxxxxxxxxx> writes: > On 06/16/2011 03:06 PM, Oleg Nesterov wrote: >> On 06/16, Cedric Le Goater wrote: >>> >>> We have a case where a task in a parent pid namespace needs to kill >>> another task in a sub pid namespace only knowing its internal pid. >>> the latter has been communicated to the parent task through a file or >>> a unix socket. >> >> OK, thanks, this partly answers my question... But if they communicate >> anyway, it is not clear why the signal is needed. > > Well, user space always finds ways to challenge the kernel. > > Our case is related to HPC. The batch manager runs jobs inside lxc > containers (using namespaces) and signals are sent to the application > for different reasons. First, to cleanly exit but also for other more > specific actions related to the cluster interconnects. In that case I really recommend unix domain sockets. You likely won't need a kernel upgrade to make use of those and their pid translation ability. >>> a new kill syscall could be the solution: >>> >>> int pidns_kill(pid_t init_pid, pid_t some_pid); >>> >>> where 'init_pid' identifies the namespace and 'some_pid' identifies >>> a task in this namespace. this is very specific but why not. >> >> Yes, I also thought about this. Should be trivial. >> >> Or int sys_tell_me_its_pid(pid_t init_pid, pid_t some_pid). > > why not. it's even better because more general. If we get as far as a new system call (and I don't think any of this needs a new system call) we really should use a namespace file descriptor to identify the pid namespace not a pid. >> Just in case.... This is hack, yes, but in fact you do not need the >> kernel changes to send a signal inside the namespace. You could >> ptrace sub_init, and execute the necessary code "inside" the namespace. > > hmm, I look at that. Looking at the ptrace interactions are definitely worthwhile. I remember there were a few very weird things with pids when ptracing a process in another pid namespace. It may be that ActivePid is enough to allow the tracer to figure out the confusing information it is getting. I would be surprised if using ptrace to send signals is how you want to do things. It works, and it is a great argument from a security perspective on allowing things that we already allow. Using ptrace to run system calls was cumbersome and not easily portable across architectures last time I looked. Eric _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers
