On Thu, Jul 21, 2016 at 11:48 PM, Michael Kerrisk (man-pages) <mtk.manpages@xxxxxxxxx> wrote: > Hi Andrey, > > > On 07/21/2016 11:06 PM, Andrew Vagin wrote: >> >> On Thu, Jul 21, 2016 at 04:41:12PM +0200, Michael Kerrisk (man-pages) >> wrote: >>> >>> Hi Andrey, >>> >>> On 07/14/2016 08:20 PM, Andrey Vagin wrote: >> >> >> <snip> >> >>> >>> Could you add here an of the API in detail: what do these FDs refer to, >>> and how do you use them to solve the use case? And could you you add >>> that info to the commit messages please. >> >> >> Hi Michael, >> >> A patch for man-pages is attached. It adds the following text to >> namespaces(7). >> >> Since Linux 4.X, the following ioctl(2) calls are supported for names‐ >> pace file descriptors. The correct syntax is: >> >> fd = ioctl(ns_fd, ioctl_type); >> >> where ioctl_type is one of the following: >> >> NS_GET_USERNS >> Returns a file descriptor that refers to an owning user names‐ >> pace. >> >> NS_GET_PARENT >> Returns a file descriptor that refers to a parent namespace. >> This ioctl(2) can be used for pid and user namespaces. For user >> namespaces, NS_GET_PARENT and NS_GET_USERNS have the same mean‐ >> ing. >> >> In addition to generic ioctl(2) errors, the following specific ones can >> occur: >> >> EINVAL NS_GET_PARENT was called for a nonhierarchical namespace. >> >> EPERM The requested namespace is outside of the current namespace >> scope. >> >> ENOENT ns_fd refers to the init namespace. > > > Thanks for this. But still part of the question remains unanswered. > How do we (in user-space) use the file descriptors to answer any of > the questions that this patch series was designed to solve? (This > info should be in the commit message and the man-pages patch.) I'm sorry, but I am not sure that I understand what you ask. Here are the origin questions: Someone else then asked me a question that led me to wonder about generally introspecting on the parental relationships between user namespaces and the association of other namespaces types with user namespaces. One use would be visualization, in order to understand the running system. Another would be to answer the question I already mentioned: what capability does process X have to perform operations on a resource governed by namespace Y? Here is an example which shows how we can get the owning namespace inode number by using these ioctl-s. $ ls -l /proc/13929/ns/pid lrwxrwxrwx 1 root root 0 Jul 22 21:03 /proc/13929/ns/pid -> 'pid:[4026532228]' $ ./nsowner /proc/13929/ns/pid user:[4026532227] The owning user namespace for pid:[4026532228] is user:[4026532227]. The nsowner tool is cimpiled from this code: int main(int argc, char *argv[]) { char buf[128], path[] = "/proc/self/fd/0123456789"; int ns, uns, ret; ns = open(argv[1], O_RDONLY); if (ns < 0) return 1; uns = ioctl(ns, NS_GET_USERNS); if (uns < 0) return 1; snprintf(path, sizeof(path), "/proc/self/fd/%d", uns); ret = readlink(path, buf, sizeof(buf) - 1); if (ret < 0) return 1; buf[ret] = 0; printf("%s\n", buf); return 0; } Does this example answer to the origin question? If it isn't, could you eloborate what you expect to see here. And I wrote one more example which show all relationships between namespaces. It enumirates all processes in a system, collects all namespaces and determins parent and owning namespaces for each of them, then it constructs a namespace tree and shows it. Here is a code: https://gist.github.com/avagin/db805f95e15ffb0af7e559dbb8de4418 Here is an example of output for my test system: [root@fc24 nsfs]# ./nstree user:[4026531837] \__ mnt:[4026532203] \__ ipc:[4026531839] \__ user:[4026532224] \__ user:[4026532226] \__ user:[4026532227] \__ pid:[4026532228] \__ pid:[4026532225] \__ pid:[4026532228] \__ user:[4026532221] \__ pid:[4026532222] \__ user:[4026532223] \__ mnt:[4026532211] \__ uts:[4026531838] \__ cgroup:[4026531835] \__ pid:[4026531836] \__ pid:[4026532225] \__ pid:[4026532228] \__ pid:[4026532222] \__ mnt:[4026531857] \__ mnt:[4026531840] \__ net:[4026531957] Thanks, Andrew > > Thanks, > > Michael > > >>>> [1] https://lkml.org/lkml/2016/7/6/158 >>>> [2] https://lkml.org/lkml/2016/7/9/101 >>>> >>>> Cc: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx> >>>> Cc: James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx> >>>> Cc: "Michael Kerrisk (man-pages)" <mtk.manpages@xxxxxxxxx> >>>> Cc: "W. Trevor King" <wking@xxxxxxxxxx> >>>> Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx> >>>> Cc: Serge Hallyn <serge.hallyn@xxxxxxxxxxxxx> >>>> >>>> -- >>>> 2.5.5 >>>> >>>> >>> >>> >>> -- >>> Michael Kerrisk >>> Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ >>> Linux/UNIX System Programming Training: http://man7.org/training/ > > > > -- > Michael Kerrisk > Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ > Linux/UNIX System Programming Training: http://man7.org/training/ > _______________________________________________ > Containers mailing list > Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx > https://lists.linuxfoundation.org/mailman/listinfo/containers -- 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