vfs: add path_is_mountpoint() helper
d_mountpoint() can only be used reliably to establish if a dentry is
not mounted in any namespace. It isn't aware of the possibility there
may be multiple mounts using a given dentry that may be in a different
namespace.
Add helper functions, path_is_mountpoint(), that checks if a struct path
is a mountpoint for this case.
Link: http://lkml.kernel.org/r/20161011053358.27645.9729.stgit@pluto.themaw.net
Signed-off-by: Ian Kent <raven@themaw.net>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Omar Sandoval <osandov@osandov.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/mount.h b/fs/mount.h
index d2e25d7..2c856fc 100644
--- a/fs/mount.h
+++ b/fs/mount.h
@@ -94,6 +94,12 @@ extern struct mount *__lookup_mnt_last(struct vfsmount *, struct dentry *);
extern int __legitimize_mnt(struct vfsmount *, unsigned);
extern bool legitimize_mnt(struct vfsmount *, unsigned);
+static inline bool __path_is_mountpoint(const struct path *path)
+{
+ struct mount *m = __lookup_mnt(path->mnt, path->dentry);
+ return m && likely(!(m->mnt.mnt_flags & MNT_SYNC_UMOUNT));
+}
+
extern void __detach_mounts(struct dentry *dentry);
static inline void detach_mounts(struct dentry *dentry)