On Thu, 2016-07-07 at 19:16 -0700, Andrew Vagin wrote: > On Thu, Jul 07, 2016 at 12:17:35PM -0700, James Bottomley wrote: > > 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, I am not sure that I understood you correctly. We have one > file system for all namespace files, how we can show per-file > properties in mount options. We have two ways of getting information. For a namespace that only exists as a bind mount we only have what the mount/mountinfo shows, so you see something like this: jejb@jarvis:~> mount|grep nsfs nsfs on /run/build-container/userns type nsfs (rw) nsfs on /run/build-container/ppc64 type nsfs (rw) the (rw) are the mount options. We could add the ability to add other mount options to this via the superblock .show_options callback. We could make it show the type and parent user namespace. > I think we can show all required information in fdinfo. We open a > namespaces file (/proc/pid/ns/N) and then read /proc/pid/fdinfo/X for > it. Not if we don't have an extant process in the namespace, we can't use these files because they don't exist, plus fdinfo on the /proc/<pid>/ns/X doesn't tell you what the parent user_ns of X is (again, we could add this information somewhere ... not sure where yet). 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
