From: John Johansen <jjohansen@suse.de>
Subject: Fix __d_path to allow for old and new behavior bnc#380763

Fix __d_path so that it can be told whether or not to connect
disconnect path to the root.  This is easier and more efficient
than trying to reconnect these paths for d_path and get_cwd
after the fact.

Signed-off-by: John Johansen <jjohansen@suse.de>

---
 fs/dcache.c            |   56 ++++++++++++++++++-------------------------------
 fs/namespace.c         |    2 -
 include/linux/dcache.h |    2 -
 3 files changed, 23 insertions(+), 37 deletions(-)

--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1755,6 +1755,7 @@ shouldnt_be_hashed:
  * @buffer: buffer to return value in
  * @buflen: buffer length
  * @fail_deleted: what to return for deleted files
+ * @disconnect: don't return a path starting with / when disconnected
  *
  * Convert a dentry into an ASCII path name. If the entry has been deleted,
  * then if @fail_deleted is true, ERR_PTR(-ENOENT) is returned. Otherwise,
@@ -1768,9 +1769,10 @@ shouldnt_be_hashed:
  */
 char *__d_path(struct dentry *dentry, struct vfsmount *vfsmnt,
 	       struct path *root, char *buffer, int buflen,
-	       int fail_deleted)
+	       int fail_deleted, int disconnect)
 {
-	int namelen, is_slash, vfsmount_locked = 0;
+	int namelen, vfsmount_locked = 0;
+	const unsigned char *name;
 
 	if (buflen < 2)
 		return ERR_PTR(-ENAMETOOLONG);
@@ -1832,22 +1834,21 @@ global_root:
 	 * unconnected dentry, or the file is on a pseudo filesystem.
 	 */
 	namelen = dentry->d_name.len;
-	is_slash = (namelen == 1 && *dentry->d_name.name == '/');
-	if (is_slash || (dentry->d_sb->s_flags & MS_NOUSER)) {
-		/*
-		 * Make sure we won't return a pathname starting with '/'.
-		 *
-		 * Historically, we also glue together the root dentry and
-		 * remaining name for pseudo filesystems like pipefs, which
-		 * have the MS_NOUSER flag set. This results in pathnames
-		 * like "pipe:[439336]".
-		 */
-		if (*buffer == '/') {
-			buffer++;
-			buflen++;
-		}
-		if (is_slash)
-			goto out;
+	name = dentry->d_name.name;
+
+	/*
+	 * If this is a root dentry, then overwrite the slash.  This
+	 * will also DTRT with pseudo filesystems which have root
+	 * dentries named "foo:".
+	 */
+	if (IS_ROOT(dentry)) {
+		buffer++;
+		buflen++;
+	}
+	if (disconnect && *name == '/') {
+	    /* Make sure we won't return a pathname starting with '/' */
+		name++;
+		namelen--;
 	}
 	if (buflen < namelen)
 		goto Elong;
@@ -1860,19 +1861,6 @@ Elong:
 	goto out;
 }
 
-static char *__connect_d_path(char *path, char *buffer, struct dentry *dentry)
-{
-	if (!IS_ERR(path) && *path != '/' &&
-	    !(dentry->d_sb->s_flags & MS_NOUSER)) {
-		/* Pretend that disconnected paths are hanging off the root. */
-		if (path == buffer)
-			path = ERR_PTR(-ENAMETOOLONG);
-		else
-			*--path = '/';
-	}
-	return path;
-}
-
 /**
  * d_path - return the path of a dentry
  * @path: path to report
@@ -1905,8 +1893,7 @@ char *d_path(struct path *path, char *bu
 	root = current->fs->root;
 	path_get(&current->fs->root);
 	read_unlock(&current->fs->lock);
-	res = __d_path(path->dentry, path->mnt, &root, buf, buflen, 0);
-	res = __connect_d_path(res, buf, path->dentry);
+	res = __d_path(path->dentry, path->mnt, &root, buf, buflen, 0, 0);
 	path_put(&root);
 	return res;
 }
@@ -1966,8 +1953,7 @@ asmlinkage long sys_getcwd(char __user *
 	path_get(&current->fs->root);
 	read_unlock(&current->fs->lock);
 
-	cwd = __d_path(pwd.dentry, pwd.mnt, &root, page, PAGE_SIZE, 1);
-	cwd = __connect_d_path(cwd, page, pwd.dentry);
+	cwd = __d_path(pwd.dentry, pwd.mnt, &root, page, PAGE_SIZE, 1, 0);
 	error = PTR_ERR(cwd);
 	if (IS_ERR(cwd))
 		goto out;
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1869,7 +1869,7 @@ char *d_namespace_path(struct dentry *de
 	if (ns_root.mnt)
 		ns_root.dentry = dget(ns_root.mnt->mnt_root);
 	spin_unlock(&vfsmount_lock);
-	res = __d_path(dentry, vfsmnt, &ns_root, buf, buflen, 1);
+	res = __d_path(dentry, vfsmnt, &ns_root, buf, buflen, 1, 1);
 	path_put(&root);
 	path_put(&ns_root);
 
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -301,7 +301,7 @@ extern int d_validate(struct dentry *, s
  */
 extern char *dynamic_dname(struct dentry *, char *, int, const char *, ...);
 extern char *__d_path(struct dentry *, struct vfsmount *, struct path *,
-		      char *, int, int);
+		      char *, int, int, int);
 extern char *d_path(struct path *, char *, int);
 
 /* Allocation counts.. */