On Thu, 2016-07-07 at 20:21 +0200, Michael Kerrisk (man-pages) wrote: > On 7 July 2016 at 17:01, James Bottomley > <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx> wrote: [Serge already answered the parenting issue] > > On Thu, 2016-07-07 at 08:36 -0500, Serge E. Hallyn wrote: > > > Hm. Probably best-effort based on the process hierarchy. So > > > yeah you could probably get a tree into a state that would be > > > wrongly recreated. Create a new netns, bind mount it, exit; Have > > > another task create a new user_ns, bind mount it, exit; Third > > > task setns()s first to the new netns then to the new user_ns. I > > > suspect criu will recreate that wrongly. > > > > This is a bit pathological, and you have to be root to do it: so > > root can set up a nesting hierarchy, bind it and destroy the pids > > but I know of no current orchestration system which does this. > > > > Actually, I have to back pedal a bit: the way I currently set up > > architecture emulation containers does precisely this: I set up the > > namespaces unprivileged with child mount namespaces, but then I ask > > root to bind the userns and kill the process that created it so I > > have a permanent handle to enter the namespace by, so I suspect > > that when our current orchestration systems get more sophisticated, > > they might eventually want to do something like this as well. > > > > In theory, we could get nsfs to show this information as an option > > (just add a show_options entry to the superblock ops), but the > > problem is that although each namespace has a parent user_ns, > > there's no way to get it without digging in the namespace specific > > structure. Probably we should restructure to move it into > > ns_common, then we could display it (and enforce all namespaces > > having owning user_ns) but it would be a > > I'm missing something here. Is it not already the case that all > namespaces have an owning user_ns? Um, yes, I don't believe I said they don't. The problem I thought you were having is that there's no way of seeing what it is. nsfs is the Namespace fileystem where bound namespaces appear to a cat of /proc/self/mounts. It can display any information that's in ns_common (the common core of namespaces) but the owning user_ns pointer currently isn't in this structure. Every user namespace has a pointer to it, but they're all privately embedded in the individual namespace specific structures. What I was proposing was that since every current namespace has a pointer somewhere to the owning user namespace, we could abstract this out into ns_common so it's now accessible to be displayed by nsfs, probably as a mount option. James -- 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
