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authorMichael Kerrisk (man-pages) <mtk.manpages@gmail.com>2017-01-25 14:03:36 +1300
committerEric W. Biederman <ebiederm@xmission.com>2017-01-25 14:43:09 +1300
commite5ff5ce6e20ee22511398bb31fb912466cf82a36 (patch)
tree0d6212638e32f9aa7462bf9d3ea64add6562495a
parent68eb94f16227336a5773b83ecfa8290f1d6b78ce (diff)
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nsfs: Add an ioctl() to return the namespace type
Linux 4.9 added two ioctl() operations that can be used to discover: * the parental relationships for hierarchical namespaces (user and PID) [NS_GET_PARENT] * the user namespaces that owns a specified non-user-namespace [NS_GET_USERNS] For no good reason that I can glean, NS_GET_USERNS was made synonymous with NS_GET_PARENT for user namespaces. It might have been better if NS_GET_USERNS had returned an error if the supplied file descriptor referred to a user namespace, since it suggests that the caller may be confused. More particularly, if it had generated an error, then I wouldn't need the new ioctl() operation proposed here. (On the other hand, what I propose here may be more generally useful.) I would like to write code that discovers namespace relationships for the purpose of understanding the namespace setup on a running system. In particular, given a file descriptor (or pathname) for a namespace, N, I'd like to obtain the corresponding user namespace. Namespace N might be a user namespace (in which case my code would just use N) or a non-user namespace (in which case my code will use NS_GET_USERNS to get the user namespace associated with N). The problem is that there is no way to tell the difference by looking at the file descriptor (and if I try to use NS_GET_USERNS on an N that is a user namespace, I get the parent user namespace of N, which is not what I want). This patch therefore adds a new ioctl(), NS_GET_NSTYPE, which, given a file descriptor that refers to a user namespace, returns the namespace type (one of the CLONE_NEW* constants). Signed-off-by: Michael Kerrisk <mtk-manpages@gmail.com> Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
-rw-r--r--fs/nsfs.c2
-rw-r--r--include/uapi/linux/nsfs.h3
2 files changed, 5 insertions, 0 deletions
diff --git a/fs/nsfs.c b/fs/nsfs.c
index 8c9fb29c6673..5d534763c662 100644
--- a/fs/nsfs.c
+++ b/fs/nsfs.c
@@ -172,6 +172,8 @@ static long ns_ioctl(struct file *filp, unsigned int ioctl,
if (!ns->ops->get_parent)
return -EINVAL;
return open_related_ns(ns, ns->ops->get_parent);
+ case NS_GET_NSTYPE:
+ return ns->ops->type;
default:
return -ENOTTY;
}
diff --git a/include/uapi/linux/nsfs.h b/include/uapi/linux/nsfs.h
index 3af617230d1b..2b48df11056a 100644
--- a/include/uapi/linux/nsfs.h
+++ b/include/uapi/linux/nsfs.h
@@ -9,5 +9,8 @@
#define NS_GET_USERNS _IO(NSIO, 0x1)
/* Returns a file descriptor that refers to a parent namespace */
#define NS_GET_PARENT _IO(NSIO, 0x2)
+/* Returns the type of namespace (CLONE_NEW* value) referred to by
+ file descriptor */
+#define NS_GET_NSTYPE _IO(NSIO, 0x3)
#endif /* __LINUX_NSFS_H */