new predicate: anon_ns_root(mount)

checks if mount is the root of an anonymouns namespace.
Switch open-coded equivalents to using it.

For mounts that belong to anon namespace !mnt_has_parent(mount)
is the same as mount == ns->root, and intent is more obvious in
the latter form.

Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 7 insertions, 0 deletions

diff --git a/fs/mount.h b/fs/mount.h
index f10776003643..f20e6ed845fe 100644
--- a/fs/mount.h
+++ b/fs/mount.h
@@ -161,6 +161,13 @@ static inline bool is_anon_ns(struct mnt_namespace *ns)
 	return ns->seq == 0;
 }
 
+static inline bool anon_ns_root(const struct mount *m)
+{
+	struct mnt_namespace *ns = READ_ONCE(m->mnt_ns);
+
+	return !IS_ERR_OR_NULL(ns) && is_anon_ns(ns) && m == ns->root;
+}
+
 static inline bool mnt_ns_attached(const struct mount *mnt)
 {
 	return !RB_EMPTY_NODE(&mnt->mnt_node);