2 files changed, 46 insertions, 8 deletions

diff --git a/fs/dcache.c b/fs/dcache.c
index 635c2aa427ed..3ee588d5f585 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1759,10 +1759,8 @@ static int prepend(char **buffer, int *buflen, const char *str,
 
 /**
  * d_path - return the path of a dentry
- * @dentry: dentry to report
- * @vfsmnt: vfsmnt to which the dentry belongs
- * @root: root dentry
- * @rootmnt: vfsmnt to which the root dentry belongs
+ * @path: the dentry/vfsmount to report
+ * @root: root vfsmnt/dentry (may be modified by this function)
  * @buffer: buffer to return value in
  * @buflen: buffer length
  *
@@ -1772,10 +1770,15 @@ static int prepend(char **buffer, int *buflen, const char *str,
  * Returns the buffer or an error code if the path was too long.
  *
  * "buflen" should be positive. Caller holds the dcache_lock.
+ *
+ * If path is not reachable from the supplied root, then the value of
+ * root is changed (without modifying refcounts).
  */
-static char *__d_path(struct dentry *dentry, struct vfsmount *vfsmnt,
-                       struct path *root, char *buffer, int buflen)
+char *__d_path(const struct path *path, struct path *root,
+               char *buffer, int buflen)
 {
+        struct dentry *dentry = path->dentry;
+        struct vfsmount *vfsmnt = path->mnt;
         char * end = buffer+buflen;
         char * retval;
 
@@ -1824,6 +1827,8 @@ global_root:
         if (prepend(&retval, &buflen, dentry->d_name.name,
                     dentry->d_name.len) != 0)
                 goto Elong;
+        root->mnt = vfsmnt;
+        root->dentry = dentry;
         return retval;
 Elong:
         return ERR_PTR(-ENAMETOOLONG);
@@ -1846,6 +1851,7 @@ char *d_path(struct path *path, char *buf, int buflen)
 {
         char *res;
         struct path root;
+        struct path tmp;
 
         /*
          * We have various synthetic filesystems that never get mounted.  On
@@ -1862,7 +1868,8 @@ char *d_path(struct path *path, char *buf, int buflen)
         path_get(&root);
         read_unlock(&current->fs->lock);
         spin_lock(&dcache_lock);
-        res = __d_path(path->dentry, path->mnt, &root, buf, buflen);
+        tmp = root;
+        res = __d_path(path, &tmp, buf, buflen);
         spin_unlock(&dcache_lock);
         path_put(&root);
         return res;
@@ -1970,9 +1977,10 @@ asmlinkage long sys_getcwd(char __user *buf, unsigned long size)
         spin_lock(&dcache_lock);
         if (pwd.dentry->d_parent == pwd.dentry || !d_unhashed(pwd.dentry)) {
                 unsigned long len;
+                struct path tmp = root;
                 char * cwd;
 
-                cwd = __d_path(pwd.dentry, pwd.mnt, &root, page, PAGE_SIZE);
+                cwd = __d_path(&pwd, &tmp, page, PAGE_SIZE);
                 spin_unlock(&dcache_lock);
 
                 error = PTR_ERR(cwd);
diff --git a/fs/seq_file.c b/fs/seq_file.c
index ae59f5a6c5c1..3f54dbd6c49b 100644
--- a/fs/seq_file.c
+++ b/fs/seq_file.c
@@ -393,6 +393,36 @@ int seq_path(struct seq_file *m, struct path *path, char *esc)
 EXPORT_SYMBOL(seq_path);
 
 /*
+ * Same as seq_path, but relative to supplied root.
+ *
+ * root may be changed, see __d_path().
+ */
+int seq_path_root(struct seq_file *m, struct path *path, struct path *root,
+                  char *esc)
+{
+        int err = -ENAMETOOLONG;
+        if (m->count < m->size) {
+                char *s = m->buf + m->count;
+                char *p;
+
+                spin_lock(&dcache_lock);
+                p = __d_path(path, root, s, m->size - m->count);
+                spin_unlock(&dcache_lock);
+                err = PTR_ERR(p);
+                if (!IS_ERR(p)) {
+                        s = mangle_path(s, p, esc);
+                        if (s) {
+                                p = m->buf + m->count;
+                                m->count = s - m->buf;
+                                return 0;
+                        }
+                }
+        }
+        m->count = m->size;
+        return err;
+}
+
+/*
  * returns the path of the 'dentry' from the root of its filesystem.
  */
 int seq_dentry(struct seq_file *m, struct dentry *dentry, char *esc)