On Thu, Jul 30, 2020 at 02:59:20PM +0300, Kirill Tkhai wrote: > Currently, there is no a way to list or iterate all or subset of namespaces > in the system. Some namespaces are exposed in /proc/[pid]/ns/ directories, > but some also may be as open files, which are not attached to a process. > When a namespace open fd is sent over unix socket and then closed, it is > impossible to know whether the namespace exists or not. > > Also, even if namespace is exposed as attached to a process or as open file, > iteration over /proc/*/ns/* or /proc/*/fd/* namespaces is not fast, because > this multiplies at tasks and fds number. > > This patchset introduces a new /proc/namespaces/ directory, which exposes > subset of permitted namespaces in linear view: > > # ls /proc/namespaces/ -l > lrwxrwxrwx 1 root root 0 Jul 29 16:50 'cgroup:[4026531835]' -> 'cgroup:[4026531835]' > lrwxrwxrwx 1 root root 0 Jul 29 16:50 'ipc:[4026531839]' -> 'ipc:[4026531839]' > lrwxrwxrwx 1 root root 0 Jul 29 16:50 'mnt:[4026531840]' -> 'mnt:[4026531840]' > lrwxrwxrwx 1 root root 0 Jul 29 16:50 'mnt:[4026531861]' -> 'mnt:[4026531861]' > lrwxrwxrwx 1 root root 0 Jul 29 16:50 'mnt:[4026532133]' -> 'mnt:[4026532133]' > lrwxrwxrwx 1 root root 0 Jul 29 16:50 'mnt:[4026532134]' -> 'mnt:[4026532134]' > lrwxrwxrwx 1 root root 0 Jul 29 16:50 'mnt:[4026532135]' -> 'mnt:[4026532135]' > lrwxrwxrwx 1 root root 0 Jul 29 16:50 'mnt:[4026532136]' -> 'mnt:[4026532136]' > lrwxrwxrwx 1 root root 0 Jul 29 16:50 'net:[4026531993]' -> 'net:[4026531993]' > lrwxrwxrwx 1 root root 0 Jul 29 16:50 'pid:[4026531836]' -> 'pid:[4026531836]' > lrwxrwxrwx 1 root root 0 Jul 29 16:50 'time:[4026531834]' -> 'time:[4026531834]' > lrwxrwxrwx 1 root root 0 Jul 29 16:50 'user:[4026531837]' -> 'user:[4026531837]' > lrwxrwxrwx 1 root root 0 Jul 29 16:50 'uts:[4026531838]' -> 'uts:[4026531838]' > > Namespace ns is exposed, in case of its user_ns is permitted from /proc's pid_ns. > I.e., /proc is related to pid_ns, so in /proc/namespace we show only a ns, which is > > in_userns(pid_ns->user_ns, ns->user_ns). > > In case of ns is a user_ns: > > in_userns(pid_ns->user_ns, ns). > > The patchset follows this steps: > > 1)A generic counter in ns_common is introduced instead of separate > counters for every ns type (net::count, uts_namespace::kref, > user_namespace::count, etc). Patches [1-8]; > 2)Patch [9] introduces IDR to link and iterate alive namespaces; > 3)Patch [10] is refactoring; > 4)Patch [11] actually adds /proc/namespace directory and fs methods; > 5)Patches [12-23] make every namespace to use the added methods > and to appear in /proc/namespace directory. > > This may be usefull to write effective debug utils (say, fast build > of networks topology) and checkpoint/restore software. Kirill, Thanks for working on this! We have a need for this functionality too for namespace introspection. I actually had a prototype of this as well but mine was based on debugfs but /proc/namespaces seems like a good place. Christian
