vfs: new internal helper: mnt_has_parent(mnt)

vfsmounts have ->mnt_parent pointing either to a different vfsmount
or to itself; it's never NULL and termination condition in loops
traversing the tree towards root is mnt == mnt->mnt_parent.  At least
one place (see the next patch) is confused about what's going on;
let's add an explicit helper checking it right way and use it in
all places where we need it.  Not that there had been too many,
but...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 3 insertions, 3 deletions

diff --git a/fs/dcache.c b/fs/dcache.c
index 89509b5a090e..8a75e3b0f49d 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -38,6 +38,7 @@
 #include <linux/prefetch.h>
 #include <linux/ratelimit.h>
 #include "internal.h"
+#include "mount.h"
 
 /*
  * Usage:
@@ -2460,9 +2461,8 @@ static int prepend_path(const struct path *path,
 
                 if (dentry == vfsmnt->mnt_root || IS_ROOT(dentry)) {
                         /* Global root? */
-                        if (vfsmnt->mnt_parent == vfsmnt) {
+                        if (!mnt_has_parent(vfsmnt))
                                 goto global_root;
-                        }
                         dentry = vfsmnt->mnt_mountpoint;
                         vfsmnt = vfsmnt->mnt_parent;
                         continue;
@@ -2862,7 +2862,7 @@ int path_is_under(struct path *path1, struct path *path2)
         br_read_lock(vfsmount_lock);
         if (mnt != path2->mnt) {
                 for (;;) {
-                        if (mnt->mnt_parent == mnt) {
+                        if (!mnt_has_parent(mnt)) {
                                 br_read_unlock(vfsmount_lock);
                                 return 0;
                         }