[PATCH vfs-2.6 2/6] vfs: add d_ancestor()

This adds d_ancestor() instead of d_isparent(), then use it.

If new_dentry == old_dentry, is_subdir() returns 1, looks strange.
"new_dentry == old_dentry" is not subdir obviously. But I'm not
checking callers for now, so this keeps current behavior.

Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>

2 files changed, 33 insertions, 34 deletions

diff --git a/fs/dcache.c b/fs/dcache.c
index c6fd1f27da57..64024005da43 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1720,18 +1720,23 @@ void d_move(struct dentry * dentry, struct dentry * target)
         spin_unlock(&dcache_lock);
 }
 
-/*
- * Helper that returns 1 if p1 is a parent of p2, else 0
+/**
+ * d_ancestor - search for an ancestor
+ * @p1: ancestor dentry
+ * @p2: child dentry
+ *
+ * Returns the ancestor dentry of p2 which is a child of p1, if p1 is
+ * an ancestor of p2, else NULL.
  */
-static int d_isparent(struct dentry *p1, struct dentry *p2)
+struct dentry *d_ancestor(struct dentry *p1, struct dentry *p2)
 {
         struct dentry *p;
 
         for (p = p2; !IS_ROOT(p); p = p->d_parent) {
                 if (p->d_parent == p1)
-                        return 1;
+                        return p;
         }
-        return 0;
+        return NULL;
 }
 
 /*
@@ -1755,7 +1760,7 @@ static struct dentry *__d_unalias(struct dentry *dentry, struct dentry *alias)
 
         /* Check for loops */
         ret = ERR_PTR(-ELOOP);
-        if (d_isparent(alias, dentry))
+        if (d_ancestor(alias, dentry))
                 goto out_err;
 
         /* See lock_rename() */
@@ -2155,31 +2160,27 @@ out:
  * Caller must ensure that "new_dentry" is pinned before calling is_subdir()
  */
   
-int is_subdir(struct dentry * new_dentry, struct dentry * old_dentry)
+int is_subdir(struct dentry *new_dentry, struct dentry *old_dentry)
 {
         int result;
-        struct dentry * saved = new_dentry;
         unsigned long seq;
 
-        /* need rcu_readlock to protect against the d_parent trashing due to
-         * d_move
+        /* FIXME: This is old behavior, needed? Please check callers. */
+        if (new_dentry == old_dentry)
+                return 1;
+
+        /*
+         * Need rcu_readlock to protect against the d_parent trashing
+         * due to d_move
          */
         rcu_read_lock();
-        do {
+        do {
                 /* for restarting inner loop in case of seq retry */
-                new_dentry = saved;
-                result = 0;
                 seq = read_seqbegin(&rename_lock);
-                for (;;) {
-                        if (new_dentry != old_dentry) {
-                                if (IS_ROOT(new_dentry))
-                                        break;
-                                new_dentry = new_dentry->d_parent;
-                                continue;
-                        }
+                if (d_ancestor(old_dentry, new_dentry))
                         result = 1;
-                        break;
-                }
+                else
+                        result = 0;
         } while (read_seqretry(&rename_lock, seq));
         rcu_read_unlock();
 
diff --git a/fs/namei.c b/fs/namei.c
index 068a9e50c8c0..b7cd65224d60 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1454,20 +1454,18 @@ struct dentry *lock_rename(struct dentry *p1, struct dentry *p2)
 
         mutex_lock(&p1->d_inode->i_sb->s_vfs_rename_mutex);
 
-        for (p = p1; !IS_ROOT(p); p = p->d_parent) {
-                if (p->d_parent == p2) {
-                        mutex_lock_nested(&p2->d_inode->i_mutex, I_MUTEX_PARENT);
-                        mutex_lock_nested(&p1->d_inode->i_mutex, I_MUTEX_CHILD);
-                        return p;
-                }
+        p = d_ancestor(p2, p1);
+        if (p) {
+                mutex_lock_nested(&p2->d_inode->i_mutex, I_MUTEX_PARENT);
+                mutex_lock_nested(&p1->d_inode->i_mutex, I_MUTEX_CHILD);
+                return p;
         }
 
-        for (p = p2; !IS_ROOT(p); p = p->d_parent) {
-                if (p->d_parent == p1) {
-                        mutex_lock_nested(&p1->d_inode->i_mutex, I_MUTEX_PARENT);
-                        mutex_lock_nested(&p2->d_inode->i_mutex, I_MUTEX_CHILD);
-                        return p;
-                }
+        p = d_ancestor(p1, p2);
+        if (p) {
+                mutex_lock_nested(&p1->d_inode->i_mutex, I_MUTEX_PARENT);
+                mutex_lock_nested(&p2->d_inode->i_mutex, I_MUTEX_CHILD);
+                return p;
         }
 
         mutex_lock_nested(&p1->d_inode->i_mutex, I_MUTEX_PARENT);