On Sat, Jul 23, 2016 at 04:56:44PM -0500, Eric W. Biederman wrote: > "W. Trevor King" <wking@xxxxxxxxxx> writes: > > On Sat, Jul 23, 2016 at 02:38:56PM -0700, James Bottomley wrote: > >> On Sat, 2016-07-23 at 14:14 -0700, W. Trevor King wrote: > >> > namespaces(7) and clone(2) both have: > >> > > >> > When a network namespace is freed (i.e., when the last > >> > process in the namespace terminates), its physical network > >> > devices are moved back to the initial network namespace (not > >> > to the parent of the process). > >> > > >> > So the initial network namespace (the head of > >> > net_namespace_list?) is special [1]. To understand how > >> > physical network devices will be handled, it seems like we want > >> > to treat network devices as a depth-1 tree, with all > >> > non-initial net namespaces as children of the initial net > >> > namespace. Can we extend this series' NS_GET_PARENT to return: > >> > > >> > * EPERM for an unprivileged caller (like this series currently > >> > does for PID namespaces), > >> > * ENOENT when called on net_namespace_list, and > >> > * net_namespace_list when called on any other net namespace. > >> > >> What's the practical application of this? independent net > >> namespaces are managed by the ip netns command. It pins them by > >> a bind mount in a flat fashion; if we make them hierarchical the > >> tool would probably need updating to reflect this, so we're going > >> to need a reason to give the network people. Just having the > >> interfaces not go back to root when you do an ip netns delete > >> doesn't seem very compelling. > > > > I'm not suggesting we add support for deeper nesting, I'm suggesting > > we use NS_GET_PARENT to allow sufficiently privileged users to > > determine if a given net namespace is the initial net namespace. You > > could do this already with something like: > > > > 1. Create a new net namespace. > > 2. Add a physical network device to that namespace. > > 3. Delete that namespace. > > 4. See if the physical network device shows up in your > > initial-net-namespace candidate. > > 5. Delete the physical network device (hopefully it ended up > > somewhere you can find it ;). > > > > But using an NS_GET_PARENT call seems much safer and easier. > > Have you had the problem in practice where you can't tell which > network namespace is the initial network namespace. This all seems > like a theoretical problem rather than a real one. I haven't had any practical problems here, I'm just trying to wrap my head around namespace-relationship discovery. The special physical network device handling seems a lot like init re-parenting (with no PR_SET_CHILD_SUBREAPER analog in a 1-deep namespace tree), so calling the initial network namespace a parent (and all the other namespaces its direct children) seems natural enough. If that doesn't sound convincing, I'm happy to punt this idea until someone runs into a practical problem ;). Cheers, Trevor -- This email may be signed or encrypted with GnuPG (http://www.gnupg.org). For more information, see http://en.wikipedia.org/wiki/Pretty_Good_Privacy
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