Merge branch 'overlayfs-next' of git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/vfs into for-next

7 files changed, 517 insertions, 319 deletions

diff --git a/Documentation/filesystems/overlayfs.txt b/Documentation/filesystems/overlayfs.txt
index a27c950ece61..6db0e5d1da07 100644
--- a/Documentation/filesystems/overlayfs.txt
+++ b/Documentation/filesystems/overlayfs.txt
@@ -159,6 +159,22 @@ overlay filesystem (though an operation on the name of the file such as
 rename or unlink will of course be noticed and handled).
 
 
+Multiple lower layers
+---------------------
+
+Multiple lower layers can now be given using the the colon (":") as a
+separator character between the directory names.  For example:
+
+  mount -t overlay overlay -olowerdir=/lower1:/lower2:/lower3 /merged
+
+As the example shows, "upperdir=" and "workdir=" may be omitted.  In
+that case the overlay will be read-only.
+
+The specified lower directories will be stacked beginning from the
+rightmost one and going left.  In the above example lower1 will be the
+top, lower2 the middle and lower3 the bottom layer.
+
+
 Non-standard behavior
 ---------------------
 
@@ -196,3 +212,15 @@ Changes to the underlying filesystems while part of a mounted overlay
 filesystem are not allowed.  If the underlying filesystem is changed,
 the behavior of the overlay is undefined, though it will not result in
 a crash or deadlock.
+
+Testsuite
+---------
+
+There's testsuite developed by David Howells at:
+
+  git://git.infradead.org/users/dhowells/unionmount-testsuite.git
+
+Run as root:
+
+  # cd unionmount-testsuite
+  # ./run --ov
diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c
index ea10a8719107..24f640441bd9 100644
--- a/fs/overlayfs/copy_up.c
+++ b/fs/overlayfs/copy_up.c
@@ -191,7 +191,6 @@ int ovl_set_attr(struct dentry *upperdentry, struct kstat *stat)
                 ovl_set_timestamps(upperdentry, stat);
 
         return err;
-
 }
 
 static int ovl_copy_up_locked(struct dentry *workdir, struct dentry *upperdir,
@@ -385,7 +384,7 @@ int ovl_copy_up(struct dentry *dentry)
                 struct kstat stat;
                 enum ovl_path_type type = ovl_path_type(dentry);
 
-                if (type != OVL_PATH_LOWER)
+                if (OVL_TYPE_UPPER(type))
                         break;
 
                 next = dget(dentry);
@@ -394,7 +393,7 @@ int ovl_copy_up(struct dentry *dentry)
                         parent = dget_parent(next);
 
                         type = ovl_path_type(parent);
-                        if (type != OVL_PATH_LOWER)
+                        if (OVL_TYPE_UPPER(type))
                                 break;
 
                         dput(next);
diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
index 8ffc4b980f1b..0dc4c33a0a1b 100644
--- a/fs/overlayfs/dir.c
+++ b/fs/overlayfs/dir.c
@@ -118,14 +118,14 @@ int ovl_create_real(struct inode *dir, struct dentry *newdentry,
 
 static int ovl_set_opaque(struct dentry *upperdentry)
 {
-        return ovl_do_setxattr(upperdentry, ovl_opaque_xattr, "y", 1, 0);
+        return ovl_do_setxattr(upperdentry, OVL_XATTR_OPAQUE, "y", 1, 0);
 }
 
 static void ovl_remove_opaque(struct dentry *upperdentry)
 {
         int err;
 
-        err = ovl_do_removexattr(upperdentry, ovl_opaque_xattr);
+        err = ovl_do_removexattr(upperdentry, OVL_XATTR_OPAQUE);
         if (err) {
                 pr_warn("overlayfs: failed to remove opaque from '%s' (%i)\n",
                         upperdentry->d_name.name, err);
@@ -152,7 +152,7 @@ static int ovl_dir_getattr(struct vfsmount *mnt, struct dentry *dentry,
          * correct link count.  nlink=1 seems to pacify 'find' and
          * other utilities.
          */
-        if (type == OVL_PATH_MERGE)
+        if (OVL_TYPE_MERGE(type))
                 stat->nlink = 1;
 
         return 0;
@@ -506,7 +506,7 @@ static int ovl_remove_and_whiteout(struct dentry *dentry, bool is_dir)
         struct dentry *opaquedir = NULL;
         int err;
 
-        if (is_dir) {
+        if (is_dir && OVL_TYPE_MERGE_OR_LOWER(ovl_path_type(dentry))) {
                 opaquedir = ovl_check_empty_and_clear(dentry);
                 err = PTR_ERR(opaquedir);
                 if (IS_ERR(opaquedir))
@@ -630,7 +630,7 @@ static int ovl_do_remove(struct dentry *dentry, bool is_dir)
                 goto out_drop_write;
 
         type = ovl_path_type(dentry);
-        if (type == OVL_PATH_PURE_UPPER) {
+        if (OVL_TYPE_PURE_UPPER(type)) {
                 err = ovl_remove_upper(dentry, is_dir);
         } else {
                 const struct cred *old_cred;
@@ -712,7 +712,7 @@ static int ovl_rename2(struct inode *olddir, struct dentry *old,
         /* Don't copy up directory trees */
         old_type = ovl_path_type(old);
         err = -EXDEV;
-        if ((old_type == OVL_PATH_LOWER || old_type == OVL_PATH_MERGE) && is_dir)
+        if (OVL_TYPE_MERGE_OR_LOWER(old_type) && is_dir)
                 goto out;
 
         if (new->d_inode) {
@@ -725,25 +725,25 @@ static int ovl_rename2(struct inode *olddir, struct dentry *old,
 
                 new_type = ovl_path_type(new);
                 err = -EXDEV;
-                if (!overwrite && (new_type == OVL_PATH_LOWER || new_type == OVL_PATH_MERGE) && new_is_dir)
+                if (!overwrite && OVL_TYPE_MERGE_OR_LOWER(new_type) && new_is_dir)
                         goto out;
 
                 err = 0;
-                if (new_type == OVL_PATH_LOWER && old_type == OVL_PATH_LOWER) {
+                if (!OVL_TYPE_UPPER(new_type) && !OVL_TYPE_UPPER(old_type)) {
                         if (ovl_dentry_lower(old)->d_inode ==
                             ovl_dentry_lower(new)->d_inode)
                                 goto out;
                 }
-                if (new_type != OVL_PATH_LOWER && old_type != OVL_PATH_LOWER) {
+                if (OVL_TYPE_UPPER(new_type) && OVL_TYPE_UPPER(old_type)) {
                         if (ovl_dentry_upper(old)->d_inode ==
                             ovl_dentry_upper(new)->d_inode)
                                 goto out;
                 }
         } else {
                 if (ovl_dentry_is_opaque(new))
-                        new_type = OVL_PATH_UPPER;
+                        new_type = __OVL_PATH_UPPER;
                 else
-                        new_type = OVL_PATH_PURE_UPPER;
+                        new_type = __OVL_PATH_UPPER | __OVL_PATH_PURE;
         }
 
         err = ovl_want_write(old);
@@ -763,8 +763,8 @@ static int ovl_rename2(struct inode *olddir, struct dentry *old,
                         goto out_drop_write;
         }
 
-        old_opaque = old_type != OVL_PATH_PURE_UPPER;
-        new_opaque = new_type != OVL_PATH_PURE_UPPER;
+        old_opaque = !OVL_TYPE_PURE_UPPER(old_type);
+        new_opaque = !OVL_TYPE_PURE_UPPER(new_type);
 
         if (old_opaque || new_opaque) {
                 err = -ENOMEM;
@@ -787,7 +787,7 @@ static int ovl_rename2(struct inode *olddir, struct dentry *old,
                 old_cred = override_creds(override_cred);
         }
 
-        if (overwrite && (new_type == OVL_PATH_LOWER || new_type == OVL_PATH_MERGE) && new_is_dir) {
+        if (overwrite && OVL_TYPE_MERGE_OR_LOWER(new_type) && new_is_dir) {
                 opaquedir = ovl_check_empty_and_clear(new);
                 err = PTR_ERR(opaquedir);
                 if (IS_ERR(opaquedir)) {
diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index 07d74b24913b..04f124884687 100644
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -205,7 +205,7 @@ static int ovl_readlink(struct dentry *dentry, char __user *buf, int bufsiz)
 
 static bool ovl_is_private_xattr(const char *name)
 {
-        return strncmp(name, "trusted.overlay.", 14) == 0;
+        return strncmp(name, OVL_XATTR_PRE_NAME, OVL_XATTR_PRE_LEN) == 0;
 }
 
 int ovl_setxattr(struct dentry *dentry, const char *name,
@@ -238,7 +238,10 @@ out:
 static bool ovl_need_xattr_filter(struct dentry *dentry,
                                   enum ovl_path_type type)
 {
-        return type == OVL_PATH_UPPER && S_ISDIR(dentry->d_inode->i_mode);
+        if ((type & (__OVL_PATH_PURE | __OVL_PATH_UPPER)) == __OVL_PATH_UPPER)
+                return S_ISDIR(dentry->d_inode->i_mode);
+        else
+                return false;
 }
 
 ssize_t ovl_getxattr(struct dentry *dentry, const char *name,
@@ -299,7 +302,7 @@ int ovl_removexattr(struct dentry *dentry, const char *name)
         if (ovl_need_xattr_filter(dentry, type) && ovl_is_private_xattr(name))
                 goto out_drop_write;
 
-        if (type == OVL_PATH_LOWER) {
+        if (!OVL_TYPE_UPPER(type)) {
                 err = vfs_getxattr(realpath.dentry, name, NULL, 0);
                 if (err < 0)
                         goto out_drop_write;
@@ -321,7 +324,7 @@ out:
 static bool ovl_open_need_copy_up(int flags, enum ovl_path_type type,
                                   struct dentry *realdentry)
 {
-        if (type != OVL_PATH_LOWER)
+        if (OVL_TYPE_UPPER(type))
                 return false;
 
         if (special_file(realdentry->d_inode->i_mode))
@@ -430,5 +433,4 @@ struct inode *ovl_new_inode(struct super_block *sb, umode_t mode,
         }
 
         return inode;
-
 }
diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index 814bed33dd07..17ac5afc9ffb 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -12,13 +12,20 @@
 struct ovl_entry;
 
 enum ovl_path_type {
-        OVL_PATH_PURE_UPPER,
-        OVL_PATH_UPPER,
-        OVL_PATH_MERGE,
-        OVL_PATH_LOWER,
+        __OVL_PATH_PURE         = (1 << 0),
+        __OVL_PATH_UPPER        = (1 << 1),
+        __OVL_PATH_MERGE        = (1 << 2),
 };
 
-extern const char *ovl_opaque_xattr;
+#define OVL_TYPE_UPPER(type)    ((type) & __OVL_PATH_UPPER)
+#define OVL_TYPE_MERGE(type)    ((type) & __OVL_PATH_MERGE)
+#define OVL_TYPE_PURE_UPPER(type) ((type) & __OVL_PATH_PURE)
+#define OVL_TYPE_MERGE_OR_LOWER(type) \
+        (OVL_TYPE_MERGE(type) || !OVL_TYPE_UPPER(type))
+
+#define OVL_XATTR_PRE_NAME "trusted.overlay."
+#define OVL_XATTR_PRE_LEN  16
+#define OVL_XATTR_OPAQUE   OVL_XATTR_PRE_NAME"opaque"
 
 static inline int ovl_do_rmdir(struct inode *dir, struct dentry *dentry)
 {
@@ -130,6 +137,7 @@ void ovl_dentry_version_inc(struct dentry *dentry);
 void ovl_path_upper(struct dentry *dentry, struct path *path);
 void ovl_path_lower(struct dentry *dentry, struct path *path);
 enum ovl_path_type ovl_path_real(struct dentry *dentry, struct path *path);
+int ovl_path_next(int idx, struct dentry *dentry, struct path *path);
 struct dentry *ovl_dentry_upper(struct dentry *dentry);
 struct dentry *ovl_dentry_lower(struct dentry *dentry);
 struct dentry *ovl_dentry_real(struct dentry *dentry);
diff --git a/fs/overlayfs/readdir.c b/fs/overlayfs/readdir.c
index c0205990a9f5..907870e81a72 100644
--- a/fs/overlayfs/readdir.c
+++ b/fs/overlayfs/readdir.c
@@ -24,7 +24,6 @@ struct ovl_cache_entry {
         struct list_head l_node;
         struct rb_node node;
         bool is_whiteout;
-        bool is_cursor;
         char name[];
 };
 
@@ -40,6 +39,7 @@ struct ovl_readdir_data {
         struct rb_root root;
         struct list_head *list;
         struct list_head middle;
+        struct dentry *dir;
         int count;
         int err;
 };
@@ -48,7 +48,7 @@ struct ovl_dir_file {
         bool is_real;
         bool is_upper;
         struct ovl_dir_cache *cache;
-        struct ovl_cache_entry cursor;
+        struct list_head *cursor;
         struct file *realfile;
         struct file *upperfile;
 };
@@ -79,23 +79,49 @@ static struct ovl_cache_entry *ovl_cache_entry_find(struct rb_root *root,
         return NULL;
 }
 
-static struct ovl_cache_entry *ovl_cache_entry_new(const char *name, int len,
+static struct ovl_cache_entry *ovl_cache_entry_new(struct dentry *dir,
+                                                   const char *name, int len,
                                                    u64 ino, unsigned int d_type)
 {
         struct ovl_cache_entry *p;
         size_t size = offsetof(struct ovl_cache_entry, name[len + 1]);
 
         p = kmalloc(size, GFP_KERNEL);
-        if (p) {
-                memcpy(p->name, name, len);
-                p->name[len] = '\0';
-                p->len = len;
-                p->type = d_type;
-                p->ino = ino;
-                p->is_whiteout = false;
-                p->is_cursor = false;
-        }
+        if (!p)
+                return NULL;
+
+        memcpy(p->name, name, len);
+        p->name[len] = '\0';
+        p->len = len;
+        p->type = d_type;
+        p->ino = ino;
+        p->is_whiteout = false;
+
+        if (d_type == DT_CHR) {
+                struct dentry *dentry;
+                const struct cred *old_cred;
+                struct cred *override_cred;
+
+                override_cred = prepare_creds();
+                if (!override_cred) {
+                        kfree(p);
+                        return NULL;
+                }
+
+                /*
+                 * CAP_DAC_OVERRIDE for lookup
+                 */
+                cap_raise(override_cred->cap_effective, CAP_DAC_OVERRIDE);
+                old_cred = override_creds(override_cred);
 
+                dentry = lookup_one_len(name, dir, len);
+                if (!IS_ERR(dentry)) {
+                        p->is_whiteout = ovl_is_whiteout(dentry);
+                        dput(dentry);
+                }
+                revert_creds(old_cred);
+                put_cred(override_cred);
+        }
         return p;
 }
 
@@ -122,7 +148,7 @@ static int ovl_cache_entry_add_rb(struct ovl_readdir_data *rdd,
                         return 0;
         }
 
-        p = ovl_cache_entry_new(name, len, ino, d_type);
+        p = ovl_cache_entry_new(rdd->dir, name, len, ino, d_type);
         if (p == NULL)
                 return -ENOMEM;
 
@@ -143,7 +169,7 @@ static int ovl_fill_lower(struct ovl_readdir_data *rdd,
         if (p) {
                 list_move_tail(&p->l_node, &rdd->middle);
         } else {
-                p = ovl_cache_entry_new(name, namelen, ino, d_type);
+                p = ovl_cache_entry_new(rdd->dir, name, namelen, ino, d_type);
                 if (p == NULL)
                         rdd->err = -ENOMEM;
                 else
@@ -168,7 +194,6 @@ static void ovl_cache_put(struct ovl_dir_file *od, struct dentry *dentry)
 {
         struct ovl_dir_cache *cache = od->cache;
 
-        list_del_init(&od->cursor.l_node);
         WARN_ON(cache->refcount <= 0);
         cache->refcount--;
         if (!cache->refcount) {
@@ -204,6 +229,7 @@ static inline int ovl_dir_read(struct path *realpath,
         if (IS_ERR(realfile))
                 return PTR_ERR(realfile);
 
+        rdd->dir = realpath->dentry;
         rdd->ctx.pos = 0;
         do {
                 rdd->count = 0;
@@ -227,108 +253,58 @@ static void ovl_dir_reset(struct file *file)
         if (cache && ovl_dentry_version_get(dentry) != cache->version) {
                 ovl_cache_put(od, dentry);
                 od->cache = NULL;
+                od->cursor = NULL;
         }
-        WARN_ON(!od->is_real && type != OVL_PATH_MERGE);
-        if (od->is_real && type == OVL_PATH_MERGE)
+        WARN_ON(!od->is_real && !OVL_TYPE_MERGE(type));
+        if (od->is_real && OVL_TYPE_MERGE(type))
                 od->is_real = false;
 }
 
-static int ovl_dir_mark_whiteouts(struct dentry *dir,
-                                  struct ovl_readdir_data *rdd)
-{
-        struct ovl_cache_entry *p;
-        struct dentry *dentry;
-        const struct cred *old_cred;
-        struct cred *override_cred;
-
-        override_cred = prepare_creds();
-        if (!override_cred) {
-                ovl_cache_free(rdd->list);
-                return -ENOMEM;
-        }
-
-        /*
-         * CAP_DAC_OVERRIDE for lookup
-         */
-        cap_raise(override_cred->cap_effective, CAP_DAC_OVERRIDE);
-        old_cred = override_creds(override_cred);
-
-        mutex_lock(&dir->d_inode->i_mutex);
-        list_for_each_entry(p, rdd->list, l_node) {
-                if (p->is_cursor)
-                        continue;
-
-                if (p->type != DT_CHR)
-                        continue;
-
-                dentry = lookup_one_len(p->name, dir, p->len);
-                if (IS_ERR(dentry))
-                        continue;
-
-                p->is_whiteout = ovl_is_whiteout(dentry);
-                dput(dentry);
-        }
-        mutex_unlock(&dir->d_inode->i_mutex);
-
-        revert_creds(old_cred);
-        put_cred(override_cred);
-
-        return 0;
-}
-
 static int ovl_dir_read_merged(struct dentry *dentry, struct list_head *list)
 {
         int err;
-        struct path lowerpath;
-        struct path upperpath;
+        struct path realpath;
         struct ovl_readdir_data rdd = {
                 .ctx.actor = ovl_fill_merge,
                 .list = list,
                 .root = RB_ROOT,
                 .is_merge = false,
         };
+        int idx, next;
 
-        ovl_path_lower(dentry, &lowerpath);
-        ovl_path_upper(dentry, &upperpath);
+        for (idx = 0; idx != -1; idx = next) {
+                next = ovl_path_next(idx, dentry, &realpath);
 
-        if (upperpath.dentry) {
-                err = ovl_dir_read(&upperpath, &rdd);
-                if (err)
-                        goto out;
-
-                if (lowerpath.dentry) {
-                        err = ovl_dir_mark_whiteouts(upperpath.dentry, &rdd);
+                if (next != -1) {
+                        err = ovl_dir_read(&realpath, &rdd);
                         if (err)
-                                goto out;
+                                break;
+                } else {
+                        /*
+                         * Insert lowest layer entries before upper ones, this
+                         * allows offsets to be reasonably constant
+                         */
+                        list_add(&rdd.middle, rdd.list);
+                        rdd.is_merge = true;
+                        err = ovl_dir_read(&realpath, &rdd);
+                        list_del(&rdd.middle);
                 }
         }
-        if (lowerpath.dentry) {
-                /*
-                 * Insert lowerpath entries before upperpath ones, this allows
-                 * offsets to be reasonably constant
-                 */
-                list_add(&rdd.middle, rdd.list);
-                rdd.is_merge = true;
-                err = ovl_dir_read(&lowerpath, &rdd);
-                list_del(&rdd.middle);
-        }
-out:
         return err;
 }
 
 static void ovl_seek_cursor(struct ovl_dir_file *od, loff_t pos)
 {
-        struct ovl_cache_entry *p;
+        struct list_head *p;
         loff_t off = 0;
 
-        list_for_each_entry(p, &od->cache->entries, l_node) {
-                if (p->is_cursor)
-                        continue;
+        list_for_each(p, &od->cache->entries) {
                 if (off >= pos)
                         break;
                 off++;
         }
-        list_move_tail(&od->cursor.l_node, &p->l_node);
+        /* Cursor is safe since the cache is stable */
+        od->cursor = p;
 }
 
 static struct ovl_dir_cache *ovl_cache_get(struct dentry *dentry)
@@ -367,6 +343,7 @@ static int ovl_iterate(struct file *file, struct dir_context *ctx)
 {
         struct ovl_dir_file *od = file->private_data;
         struct dentry *dentry = file->f_path.dentry;
+        struct ovl_cache_entry *p;
 
         if (!ctx->pos)
                 ovl_dir_reset(file);
@@ -385,19 +362,13 @@ static int ovl_iterate(struct file *file, struct dir_context *ctx)
                 ovl_seek_cursor(od, ctx->pos);
         }
 
-        while (od->cursor.l_node.next != &od->cache->entries) {
-                struct ovl_cache_entry *p;
-
-                p = list_entry(od->cursor.l_node.next, struct ovl_cache_entry, l_node);
-                /* Skip cursors */
-                if (!p->is_cursor) {
-                        if (!p->is_whiteout) {
-                                if (!dir_emit(ctx, p->name, p->len, p->ino, p->type))
-                                        break;
-                        }
-                        ctx->pos++;
-                }
-                list_move(&od->cursor.l_node, &p->l_node);
+        while (od->cursor != &od->cache->entries) {
+                p = list_entry(od->cursor, struct ovl_cache_entry, l_node);
+                if (!p->is_whiteout)
+                        if (!dir_emit(ctx, p->name, p->len, p->ino, p->type))
+                                break;
+                od->cursor = p->l_node.next;
+                ctx->pos++;
         }
         return 0;
 }
@@ -452,7 +423,7 @@ static int ovl_dir_fsync(struct file *file, loff_t start, loff_t end,
         /*
          * Need to check if we started out being a lower dir, but got copied up
          */
-        if (!od->is_upper && ovl_path_type(dentry) != OVL_PATH_LOWER) {
+        if (!od->is_upper && OVL_TYPE_UPPER(ovl_path_type(dentry))) {
                 struct inode *inode = file_inode(file);
 
                 realfile = lockless_dereference(od->upperfile);
@@ -516,11 +487,9 @@ static int ovl_dir_open(struct inode *inode, struct file *file)
                 kfree(od);
                 return PTR_ERR(realfile);
         }
-        INIT_LIST_HEAD(&od->cursor.l_node);
         od->realfile = realfile;
-        od->is_real = (type != OVL_PATH_MERGE);
-        od->is_upper = (type != OVL_PATH_LOWER);
-        od->cursor.is_cursor = true;
+        od->is_real = !OVL_TYPE_MERGE(type);
+        od->is_upper = OVL_TYPE_UPPER(type);
         file->private_data = od;
 
         return 0;
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index f16d318b71f8..b90952f528b1 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -35,7 +35,8 @@ struct ovl_config {
 /* private information held for overlayfs's superblock */
 struct ovl_fs {
         struct vfsmount *upper_mnt;
-        struct vfsmount *lower_mnt;
+        unsigned numlower;
+        struct vfsmount **lower_mnt;
         struct dentry *workdir;
         long lower_namelen;
         /* pathnames of lower and upper dirs, for show_options */
@@ -47,7 +48,6 @@ struct ovl_dir_cache;
 /* private information held for every overlayfs dentry */
 struct ovl_entry {
         struct dentry *__upperdentry;
-        struct dentry *lowerdentry;
         struct ovl_dir_cache *cache;
         union {
                 struct {
@@ -56,30 +56,36 @@ struct ovl_entry {
                 };
                 struct rcu_head rcu;
         };
+        unsigned numlower;
+        struct path lowerstack[];
 };
 
-const char *ovl_opaque_xattr = "trusted.overlay.opaque";
+#define OVL_MAX_STACK 500
 
+static struct dentry *__ovl_dentry_lower(struct ovl_entry *oe)
+{
+        return oe->numlower ? oe->lowerstack[0].dentry : NULL;
+}
 
 enum ovl_path_type ovl_path_type(struct dentry *dentry)
 {
         struct ovl_entry *oe = dentry->d_fsdata;
+        enum ovl_path_type type = 0;
 
         if (oe->__upperdentry) {
-                if (oe->lowerdentry) {
+                type = __OVL_PATH_UPPER;
+
+                if (oe->numlower) {
                         if (S_ISDIR(dentry->d_inode->i_mode))
-                                return OVL_PATH_MERGE;
-                        else
-                                return OVL_PATH_UPPER;
-                } else {
-                        if (oe->opaque)
-                                return OVL_PATH_UPPER;
-                        else
-                                return OVL_PATH_PURE_UPPER;
+                                type |= __OVL_PATH_MERGE;
+                } else if (!oe->opaque) {
+                        type |= __OVL_PATH_PURE;
                 }
         } else {
-                return OVL_PATH_LOWER;
+                if (oe->numlower > 1)
+                        type |= __OVL_PATH_MERGE;
         }
+        return type;
 }
 
 static struct dentry *ovl_upperdentry_dereference(struct ovl_entry *oe)
@@ -98,10 +104,9 @@ void ovl_path_upper(struct dentry *dentry, struct path *path)
 
 enum ovl_path_type ovl_path_real(struct dentry *dentry, struct path *path)
 {
-
         enum ovl_path_type type = ovl_path_type(dentry);
 
-        if (type == OVL_PATH_LOWER)
+        if (!OVL_TYPE_UPPER(type))
                 ovl_path_lower(dentry, path);
         else
                 ovl_path_upper(dentry, path);
@@ -120,7 +125,7 @@ struct dentry *ovl_dentry_lower(struct dentry *dentry)
 {
         struct ovl_entry *oe = dentry->d_fsdata;
 
-        return oe->lowerdentry;
+        return __ovl_dentry_lower(oe);
 }
 
 struct dentry *ovl_dentry_real(struct dentry *dentry)
@@ -130,7 +135,7 @@ struct dentry *ovl_dentry_real(struct dentry *dentry)
 
         realdentry = ovl_upperdentry_dereference(oe);
         if (!realdentry)
-                realdentry = oe->lowerdentry;
+                realdentry = __ovl_dentry_lower(oe);
 
         return realdentry;
 }
@@ -143,7 +148,7 @@ struct dentry *ovl_entry_real(struct ovl_entry *oe, bool *is_upper)
         if (realdentry) {
                 *is_upper = true;
         } else {
-                realdentry = oe->lowerdentry;
+                realdentry = __ovl_dentry_lower(oe);
                 *is_upper = false;
         }
         return realdentry;
@@ -165,11 +170,9 @@ void ovl_set_dir_cache(struct dentry *dentry, struct ovl_dir_cache *cache)
 
 void ovl_path_lower(struct dentry *dentry, struct path *path)
 {
-        struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
         struct ovl_entry *oe = dentry->d_fsdata;
 
-        path->mnt = ofs->lower_mnt;
-        path->dentry = oe->lowerdentry;
+        *path = oe->numlower ? oe->lowerstack[0] : (struct path) { NULL, NULL };
 }
 
 int ovl_want_write(struct dentry *dentry)
@@ -249,7 +252,7 @@ static bool ovl_is_opaquedir(struct dentry *dentry)
         if (!S_ISDIR(inode->i_mode) || !inode->i_op->getxattr)
                 return false;
 
-        res = inode->i_op->getxattr(dentry, ovl_opaque_xattr, &val, 1);
+        res = inode->i_op->getxattr(dentry, OVL_XATTR_OPAQUE, &val, 1);
         if (res == 1 && val == 'y')
                 return true;
 
@@ -261,8 +264,11 @@ static void ovl_dentry_release(struct dentry *dentry)
         struct ovl_entry *oe = dentry->d_fsdata;
 
         if (oe) {
+                unsigned int i;
+
                 dput(oe->__upperdentry);
-                dput(oe->lowerdentry);
+                for (i = 0; i < oe->numlower; i++)
+                        dput(oe->lowerstack[i].dentry);
                 kfree_rcu(oe, rcu);
         }
 }
@@ -271,9 +277,15 @@ static const struct dentry_operations ovl_dentry_operations = {
         .d_release = ovl_dentry_release,
 };
 
-static struct ovl_entry *ovl_alloc_entry(void)
+static struct ovl_entry *ovl_alloc_entry(unsigned int numlower)
 {
-        return kzalloc(sizeof(struct ovl_entry), GFP_KERNEL);
+        size_t size = offsetof(struct ovl_entry, lowerstack[numlower]);
+        struct ovl_entry *oe = kzalloc(size, GFP_KERNEL);
+
+        if (oe)
+                oe->numlower = numlower;
+
+        return oe;
 }
 
 static inline struct dentry *ovl_lookup_real(struct dentry *dir,
@@ -295,82 +307,154 @@ static inline struct dentry *ovl_lookup_real(struct dentry *dir,
         return dentry;
 }
 
+/*
+ * Returns next layer in stack starting from top.
+ * Returns -1 if this is the last layer.
+ */
+int ovl_path_next(int idx, struct dentry *dentry, struct path *path)
+{
+        struct ovl_entry *oe = dentry->d_fsdata;
+
+        BUG_ON(idx < 0);
+        if (idx == 0) {
+                ovl_path_upper(dentry, path);
+                if (path->dentry)
+                        return oe->numlower ? 1 : -1;
+                idx++;
+        }
+        BUG_ON(idx > oe->numlower);
+        *path = oe->lowerstack[idx - 1];
+
+        return (idx < oe->numlower) ? idx + 1 : -1;
+}
+
 struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
                           unsigned int flags)
 {
         struct ovl_entry *oe;
-        struct dentry *upperdir;
-        struct dentry *lowerdir;
-        struct dentry *upperdentry = NULL;
-        struct dentry *lowerdentry = NULL;
+        struct ovl_entry *poe = dentry->d_parent->d_fsdata;
+        struct path *stack = NULL;
+        struct dentry *upperdir, *upperdentry = NULL;
+        unsigned int ctr = 0;
         struct inode *inode = NULL;
+        bool upperopaque = false;
+        struct dentry *this, *prev = NULL;
+        unsigned int i;
         int err;
 
-        err = -ENOMEM;
-        oe = ovl_alloc_entry();
-        if (!oe)
-                goto out;
-
-        upperdir = ovl_dentry_upper(dentry->d_parent);
-        lowerdir = ovl_dentry_lower(dentry->d_parent);
-
+        upperdir = ovl_upperdentry_dereference(poe);
         if (upperdir) {
-                upperdentry = ovl_lookup_real(upperdir, &dentry->d_name);
-                err = PTR_ERR(upperdentry);
-                if (IS_ERR(upperdentry))
-                        goto out_put_dir;
-
-                if (lowerdir && upperdentry) {
-                        if (ovl_is_whiteout(upperdentry)) {
-                                dput(upperdentry);
-                                upperdentry = NULL;
-                                oe->opaque = true;
-                        } else if (ovl_is_opaquedir(upperdentry)) {
-                                oe->opaque = true;
+                this = ovl_lookup_real(upperdir, &dentry->d_name);
+                err = PTR_ERR(this);
+                if (IS_ERR(this))
+                        goto out;
+
+                if (this) {
+                        if (ovl_is_whiteout(this)) {
+                                dput(this);
+                                this = NULL;
+                                upperopaque = true;
+                        } else if (poe->numlower && ovl_is_opaquedir(this)) {
+                                upperopaque = true;
                         }
                 }
+                upperdentry = prev = this;
         }
-        if (lowerdir && !oe->opaque) {
-                lowerdentry = ovl_lookup_real(lowerdir, &dentry->d_name);
-                err = PTR_ERR(lowerdentry);
-                if (IS_ERR(lowerdentry))
-                        goto out_dput_upper;
+
+        if (!upperopaque && poe->numlower) {
+                err = -ENOMEM;
+                stack = kcalloc(poe->numlower, sizeof(struct path), GFP_KERNEL);
+                if (!stack)
+                        goto out_put_upper;
         }
 
-        if (lowerdentry && upperdentry &&
-            (!S_ISDIR(upperdentry->d_inode->i_mode) ||
-             !S_ISDIR(lowerdentry->d_inode->i_mode))) {
-                dput(lowerdentry);
-                lowerdentry = NULL;
-                oe->opaque = true;
+        for (i = 0; !upperopaque && i < poe->numlower; i++) {
+                bool opaque = false;
+                struct path lowerpath = poe->lowerstack[i];
+
+                this = ovl_lookup_real(lowerpath.dentry, &dentry->d_name);
+                err = PTR_ERR(this);
+                if (IS_ERR(this)) {
+                        /*
+                         * If it's positive, then treat ENAMETOOLONG as ENOENT.
+                         */
+                        if (err == -ENAMETOOLONG && (upperdentry || ctr))
+                                continue;
+                        goto out_put;
+                }
+                if (!this)
+                        continue;
+                if (ovl_is_whiteout(this)) {
+                        dput(this);
+                        break;
+                }
+                /*
+                 * Only makes sense to check opaque dir if this is not the
+                 * lowermost layer.
+                 */
+                if (i < poe->numlower - 1 && ovl_is_opaquedir(this))
+                        opaque = true;
+
+                if (prev && (!S_ISDIR(prev->d_inode->i_mode) ||
+                             !S_ISDIR(this->d_inode->i_mode))) {
+                        /*
+                         * FIXME: check for upper-opaqueness maybe better done
+                         * in remove code.
+                         */
+                        if (prev == upperdentry)
+                                upperopaque = true;
+                        dput(this);
+                        break;
+                }
+                /*
+                 * If this is a non-directory then stop here.
+                 */
+                if (!S_ISDIR(this->d_inode->i_mode))
+                        opaque = true;
+
+                stack[ctr].dentry = this;
+                stack[ctr].mnt = lowerpath.mnt;
+                ctr++;
+                prev = this;
+                if (opaque)
+                        break;
         }
 
-        if (lowerdentry || upperdentry) {
+        oe = ovl_alloc_entry(ctr);
+        err = -ENOMEM;
+        if (!oe)
+                goto out_put;
+
+        if (upperdentry || ctr) {
                 struct dentry *realdentry;
 
-                realdentry = upperdentry ? upperdentry : lowerdentry;
+                realdentry = upperdentry ? upperdentry : stack[0].dentry;
+
                 err = -ENOMEM;
                 inode = ovl_new_inode(dentry->d_sb, realdentry->d_inode->i_mode,
                                       oe);
                 if (!inode)
-                        goto out_dput;
+                        goto out_free_oe;
                 ovl_copyattr(realdentry->d_inode, inode);
         }
 
+        oe->opaque = upperopaque;
         oe->__upperdentry = upperdentry;
-        oe->lowerdentry = lowerdentry;
-
+        memcpy(oe->lowerstack, stack, sizeof(struct path) * ctr);
+        kfree(stack);
         dentry->d_fsdata = oe;
         d_add(dentry, inode);
 
         return NULL;
 
-out_dput:
-        dput(lowerdentry);
-out_dput_upper:
-        dput(upperdentry);
-out_put_dir:
+out_free_oe:
         kfree(oe);
+out_put:
+        for (i = 0; i < ctr; i++)
+                dput(stack[i].dentry);
+        kfree(stack);
+out_put_upper:
+        dput(upperdentry);
 out:
         return ERR_PTR(err);
 }
@@ -383,10 +467,12 @@ struct file *ovl_path_open(struct path *path, int flags)
 static void ovl_put_super(struct super_block *sb)
 {
         struct ovl_fs *ufs = sb->s_fs_info;
+        unsigned i;
 
         dput(ufs->workdir);
         mntput(ufs->upper_mnt);
-        mntput(ufs->lower_mnt);
+        for (i = 0; i < ufs->numlower; i++)
+                mntput(ufs->lower_mnt[i]);
 
         kfree(ufs->config.lowerdir);
         kfree(ufs->config.upperdir);
@@ -400,7 +486,7 @@ static void ovl_put_super(struct super_block *sb)
  * @buf: The struct kstatfs to fill in with stats
  *
  * Get the filesystem statistics.  As writes always target the upper layer
- * filesystem pass the statfs to the same filesystem.
+ * filesystem pass the statfs to the upper filesystem (if it exists)
  */
 static int ovl_statfs(struct dentry *dentry, struct kstatfs *buf)
 {
@@ -409,7 +495,7 @@ static int ovl_statfs(struct dentry *dentry, struct kstatfs *buf)
         struct path path;
         int err;
 
-        ovl_path_upper(root_dentry, &path);
+        ovl_path_real(root_dentry, &path);
 
         err = vfs_statfs(&path, buf);
         if (!err) {
@@ -432,8 +518,21 @@ static int ovl_show_options(struct seq_file *m, struct dentry *dentry)
         struct ovl_fs *ufs = sb->s_fs_info;
 
         seq_printf(m, ",lowerdir=%s", ufs->config.lowerdir);
-        seq_printf(m, ",upperdir=%s", ufs->config.upperdir);
-        seq_printf(m, ",workdir=%s", ufs->config.workdir);
+        if (ufs->config.upperdir) {
+                seq_printf(m, ",upperdir=%s", ufs->config.upperdir);
+                seq_printf(m, ",workdir=%s", ufs->config.workdir);
+        }
+        return 0;
+}
+
+static int ovl_remount(struct super_block *sb, int *flags, char *data)
+{
+        struct ovl_fs *ufs = sb->s_fs_info;
+
+        if (!(*flags & MS_RDONLY) &&
+            (!ufs->upper_mnt || (ufs->upper_mnt->mnt_sb->s_flags & MS_RDONLY)))
+                return -EROFS;
+
         return 0;
 }
 
@@ -441,6 +540,7 @@ static const struct super_operations ovl_super_operations = {
         .put_super      = ovl_put_super,
         .statfs         = ovl_statfs,
         .show_options   = ovl_show_options,
+        .remount_fs     = ovl_remount,
 };
 
 enum {
@@ -585,24 +685,6 @@ static void ovl_unescape(char *s)
         }
 }
 
-static int ovl_mount_dir(const char *name, struct path *path)
-{
-        int err;
-        char *tmp = kstrdup(name, GFP_KERNEL);
-
-        if (!tmp)
-                return -ENOMEM;
-
-        ovl_unescape(tmp);
-        err = kern_path(tmp, LOOKUP_FOLLOW, path);
-        if (err) {
-                pr_err("overlayfs: failed to resolve '%s': %i\n", tmp, err);
-                err = -EINVAL;
-        }
-        kfree(tmp);
-        return err;
-}
-
 static bool ovl_is_allowed_fs_type(struct dentry *root)
 {
         const struct dentry_operations *dop = root->d_op;
@@ -622,6 +704,75 @@ static bool ovl_is_allowed_fs_type(struct dentry *root)
         return true;
 }
 
+static int ovl_mount_dir_noesc(const char *name, struct path *path)
+{
+        int err = -EINVAL;
+
+        if (!*name) {
+                pr_err("overlayfs: empty lowerdir\n");
+                goto out;
+        }
+        err = kern_path(name, LOOKUP_FOLLOW, path);
+        if (err) {
+                pr_err("overlayfs: failed to resolve '%s': %i\n", name, err);
+                goto out;
+        }
+        err = -EINVAL;
+        if (!ovl_is_allowed_fs_type(path->dentry)) {
+                pr_err("overlayfs: filesystem on '%s' not supported\n", name);
+                goto out_put;
+        }
+        if (!S_ISDIR(path->dentry->d_inode->i_mode)) {
+                pr_err("overlayfs: '%s' not a directory\n", name);
+                goto out_put;
+        }
+        return 0;
+
+out_put:
+        path_put(path);
+out:
+        return err;
+}
+
+static int ovl_mount_dir(const char *name, struct path *path)
+{
+        int err = -ENOMEM;
+        char *tmp = kstrdup(name, GFP_KERNEL);
+
+        if (tmp) {
+                ovl_unescape(tmp);
+                err = ovl_mount_dir_noesc(tmp, path);
+                kfree(tmp);
+        }
+        return err;
+}
+
+static int ovl_lower_dir(const char *name, struct path *path, long *namelen,
+                         int *stack_depth)
+{
+        int err;
+        struct kstatfs statfs;
+
+        err = ovl_mount_dir_noesc(name, path);
+        if (err)
+                goto out;
+
+        err = vfs_statfs(path, &statfs);
+        if (err) {
+                pr_err("overlayfs: statfs failed on '%s'\n", name);
+                goto out_put;
+        }
+        *namelen = max(*namelen, statfs.f_namelen);
+        *stack_depth = max(*stack_depth, path->mnt->mnt_sb->s_stack_depth);
+
+        return 0;
+
+out_put:
+        path_put(path);
+out:
+        return err;
+}
+
 /* Workdir should not be subdir of upperdir and vice versa */
 static bool ovl_workdir_ok(struct dentry *workdir, struct dentry *upperdir)
 {
@@ -634,16 +785,39 @@ static bool ovl_workdir_ok(struct dentry *workdir, struct dentry *upperdir)
         return ok;
 }
 
+static unsigned int ovl_split_lowerdirs(char *str)
+{
+        unsigned int ctr = 1;
+        char *s, *d;
+
+        for (s = d = str;; s++, d++) {
+                if (*s == '\\') {
+                        s++;
+                } else if (*s == ':') {
+                        *d = '\0';
+                        ctr++;
+                        continue;
+                }
+                *d = *s;
+                if (!*s)
+                        break;
+        }
+        return ctr;
+}
+
 static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 {
-        struct path lowerpath;
-        struct path upperpath;
-        struct path workpath;
-        struct inode *root_inode;
+        struct path upperpath = { NULL, NULL };
+        struct path workpath = { NULL, NULL };
         struct dentry *root_dentry;
         struct ovl_entry *oe;
         struct ovl_fs *ufs;
-        struct kstatfs statfs;
+        struct path *stack = NULL;
+        char *lowertmp;
+        char *lower;
+        unsigned int numlower;
+        unsigned int stacklen = 0;
+        unsigned int i;
         int err;
 
         err = -ENOMEM;
@@ -655,123 +829,135 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
         if (err)
                 goto out_free_config;
 
-        /* FIXME: workdir is not needed for a R/O mount */
         err = -EINVAL;
-        if (!ufs->config.upperdir || !ufs->config.lowerdir ||
-            !ufs->config.workdir) {
-                pr_err("overlayfs: missing upperdir or lowerdir or workdir\n");
+        if (!ufs->config.lowerdir) {
+                pr_err("overlayfs: missing 'lowerdir'\n");
                 goto out_free_config;
         }
 
-        err = -ENOMEM;
-        oe = ovl_alloc_entry();
-        if (oe == NULL)
-                goto out_free_config;
-
-        err = ovl_mount_dir(ufs->config.upperdir, &upperpath);
-        if (err)
-                goto out_free_oe;
-
-        err = ovl_mount_dir(ufs->config.lowerdir, &lowerpath);
-        if (err)
-                goto out_put_upperpath;
+        sb->s_stack_depth = 0;
+        if (ufs->config.upperdir) {
+                /* FIXME: workdir is not needed for a R/O mount */
+                if (!ufs->config.workdir) {
+                        pr_err("overlayfs: missing 'workdir'\n");
+                        goto out_free_config;
+                }
 
-        err = ovl_mount_dir(ufs->config.workdir, &workpath);
-        if (err)
-                goto out_put_lowerpath;
+                err = ovl_mount_dir(ufs->config.upperdir, &upperpath);
+                if (err)
+                        goto out_free_config;
 
-        err = -EINVAL;
-        if (!S_ISDIR(upperpath.dentry->d_inode->i_mode) ||
-            !S_ISDIR(lowerpath.dentry->d_inode->i_mode) ||
-            !S_ISDIR(workpath.dentry->d_inode->i_mode)) {
-                pr_err("overlayfs: upperdir or lowerdir or workdir not a directory\n");
-                goto out_put_workpath;
-        }
+                err = ovl_mount_dir(ufs->config.workdir, &workpath);
+                if (err)
+                        goto out_put_upperpath;
 
-        if (upperpath.mnt != workpath.mnt) {
-                pr_err("overlayfs: workdir and upperdir must reside under the same mount\n");
-                goto out_put_workpath;
-        }
-        if (!ovl_workdir_ok(workpath.dentry, upperpath.dentry)) {
-                pr_err("overlayfs: workdir and upperdir must be separate subtrees\n");
-                goto out_put_workpath;
+                err = -EINVAL;
+                if (upperpath.mnt != workpath.mnt) {
+                        pr_err("overlayfs: workdir and upperdir must reside under the same mount\n");
+                        goto out_put_workpath;
+                }
+                if (!ovl_workdir_ok(workpath.dentry, upperpath.dentry)) {
+                        pr_err("overlayfs: workdir and upperdir must be separate subtrees\n");
+                        goto out_put_workpath;
+                }
+                sb->s_stack_depth = upperpath.mnt->mnt_sb->s_stack_depth;
         }
-
-        if (!ovl_is_allowed_fs_type(upperpath.dentry)) {
-                pr_err("overlayfs: filesystem of upperdir is not supported\n");
+        err = -ENOMEM;
+        lowertmp = kstrdup(ufs->config.lowerdir, GFP_KERNEL);
+        if (!lowertmp)
                 goto out_put_workpath;
-        }
 
-        if (!ovl_is_allowed_fs_type(lowerpath.dentry)) {
-                pr_err("overlayfs: filesystem of lowerdir is not supported\n");
-                goto out_put_workpath;
-        }
+        err = -EINVAL;
+        stacklen = ovl_split_lowerdirs(lowertmp);
+        if (stacklen > OVL_MAX_STACK)
+                goto out_free_lowertmp;
+
+        stack = kcalloc(stacklen, sizeof(struct path), GFP_KERNEL);
+        if (!stack)
+                goto out_free_lowertmp;
+
+        lower = lowertmp;
+        for (numlower = 0; numlower < stacklen; numlower++) {
+                err = ovl_lower_dir(lower, &stack[numlower],
+                                    &ufs->lower_namelen, &sb->s_stack_depth);
+                if (err)
+                        goto out_put_lowerpath;
 
-        err = vfs_statfs(&lowerpath, &statfs);
-        if (err) {
-                pr_err("overlayfs: statfs failed on lowerpath\n");
-                goto out_put_workpath;
+                lower = strchr(lower, '\0') + 1;
         }
-        ufs->lower_namelen = statfs.f_namelen;
-
-        sb->s_stack_depth = max(upperpath.mnt->mnt_sb->s_stack_depth,
-                                lowerpath.mnt->mnt_sb->s_stack_depth) + 1;
 
         err = -EINVAL;
+        sb->s_stack_depth++;
         if (sb->s_stack_depth > FILESYSTEM_MAX_STACK_DEPTH) {
                 pr_err("overlayfs: maximum fs stacking depth exceeded\n");
-                goto out_put_workpath;
+                goto out_put_lowerpath;
         }
 
-        ufs->upper_mnt = clone_private_mount(&upperpath);
-        err = PTR_ERR(ufs->upper_mnt);
-        if (IS_ERR(ufs->upper_mnt)) {
-                pr_err("overlayfs: failed to clone upperpath\n");
-                goto out_put_workpath;
-        }
+        if (ufs->config.upperdir) {
+                ufs->upper_mnt = clone_private_mount(&upperpath);
+                err = PTR_ERR(ufs->upper_mnt);
+                if (IS_ERR(ufs->upper_mnt)) {
+                        pr_err("overlayfs: failed to clone upperpath\n");
+                        goto out_put_lowerpath;
+                }
 
-        ufs->lower_mnt = clone_private_mount(&lowerpath);
-        err = PTR_ERR(ufs->lower_mnt);
-        if (IS_ERR(ufs->lower_mnt)) {
-                pr_err("overlayfs: failed to clone lowerpath\n");
-                goto out_put_upper_mnt;
+                ufs->workdir = ovl_workdir_create(ufs->upper_mnt, workpath.dentry);
+                err = PTR_ERR(ufs->workdir);
+                if (IS_ERR(ufs->workdir)) {
+                        pr_err("overlayfs: failed to create directory %s/%s\n",
+                               ufs->config.workdir, OVL_WORKDIR_NAME);
+                        goto out_put_upper_mnt;
+                }
         }
 
-        ufs->workdir = ovl_workdir_create(ufs->upper_mnt, workpath.dentry);
-        err = PTR_ERR(ufs->workdir);
-        if (IS_ERR(ufs->workdir)) {
-                pr_err("overlayfs: failed to create directory %s/%s\n",
-                       ufs->config.workdir, OVL_WORKDIR_NAME);
-                goto out_put_lower_mnt;
-        }
+        err = -ENOMEM;
+        ufs->lower_mnt = kcalloc(numlower, sizeof(struct vfsmount *), GFP_KERNEL);
+        if (ufs->lower_mnt == NULL)
+                goto out_put_workdir;
+        for (i = 0; i < numlower; i++) {
+                struct vfsmount *mnt = clone_private_mount(&stack[i]);
 
-        /*
-         * Make lower_mnt R/O.  That way fchmod/fchown on lower file
-         * will fail instead of modifying lower fs.
-         */
-        ufs->lower_mnt->mnt_flags |= MNT_READONLY;
+                err = PTR_ERR(mnt);
+                if (IS_ERR(mnt)) {
+                        pr_err("overlayfs: failed to clone lowerpath\n");
+                        goto out_put_lower_mnt;
+                }
+                /*
+                 * Make lower_mnt R/O.  That way fchmod/fchown on lower file
+                 * will fail instead of modifying lower fs.
+                 */
+                mnt->mnt_flags |= MNT_READONLY;
+
+                ufs->lower_mnt[ufs->numlower] = mnt;
+                ufs->numlower++;
+        }
 
-        /* If the upper fs is r/o, we mark overlayfs r/o too */
-        if (ufs->upper_mnt->mnt_sb->s_flags & MS_RDONLY)
+        /* If the upper fs is r/o or nonexistent, we mark overlayfs r/o too */
+        if (!ufs->upper_mnt || (ufs->upper_mnt->mnt_sb->s_flags & MS_RDONLY))
                 sb->s_flags |= MS_RDONLY;
 
         sb->s_d_op = &ovl_dentry_operations;
 
         err = -ENOMEM;
-        root_inode = ovl_new_inode(sb, S_IFDIR, oe);
-        if (!root_inode)
-                goto out_put_workdir;
+        oe = ovl_alloc_entry(numlower);
+        if (!oe)
+                goto out_put_lower_mnt;
 
-        root_dentry = d_make_root(root_inode);
+        root_dentry = d_make_root(ovl_new_inode(sb, S_IFDIR, oe));
         if (!root_dentry)
-                goto out_put_workdir;
+                goto out_free_oe;
 
         mntput(upperpath.mnt);
-        mntput(lowerpath.mnt);
+        for (i = 0; i < numlower; i++)
+                mntput(stack[i].mnt);
         path_put(&workpath);
+        kfree(lowertmp);
 
         oe->__upperdentry = upperpath.dentry;
-        oe->lowerdentry = lowerpath.dentry;
+        for (i = 0; i < numlower; i++) {
+                oe->lowerstack[i].dentry = stack[i].dentry;
+                oe->lowerstack[i].mnt = ufs->lower_mnt[i];
+        }
 
         root_dentry->d_fsdata = oe;
 
@@ -782,20 +968,26 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 
         return 0;
 
+out_free_oe:
+        kfree(oe);
+out_put_lower_mnt:
+        for (i = 0; i < ufs->numlower; i++)
+                mntput(ufs->lower_mnt[i]);
+        kfree(ufs->lower_mnt);
 out_put_workdir:
         dput(ufs->workdir);
-out_put_lower_mnt:
-        mntput(ufs->lower_mnt);
 out_put_upper_mnt:
         mntput(ufs->upper_mnt);
+out_put_lowerpath:
+        for (i = 0; i < numlower; i++)
+                path_put(&stack[i]);
+        kfree(stack);
+out_free_lowertmp:
+        kfree(lowertmp);
 out_put_workpath:
         path_put(&workpath);
-out_put_lowerpath:
-        path_put(&lowerpath);
 out_put_upperpath:
         path_put(&upperpath);
-out_free_oe:
-        kfree(oe);
 out_free_config:
         kfree(ufs->config.lowerdir);
         kfree(ufs->config.upperdir);