UBUNTU: SAUCE: overlay: add backwards compatible overlayfs format support V4

Adds a nearly completely compatible overlayfs filesystem type to overlay
fs, allowing it to mount those filesystems.  It does still require the
new workdir= arguement to allow them to be writable.  This is aimed to
be paired with an overlayfs userspace mount helper.

V2: Fix up rename handling, which was leaving chardev-0 style whiteouts
    lying about.
V3: pull up to mainline v4.0.
V4: pull up to mainline v4.2.

BugLink: http://bugs.launchpad.net/bugs/1395877
BugLink: http://bugs.launchpad.net/bugs/1410480
BugLink: http://bugs.launchpad.net/bugs/1478609Signed-off-by: Andy Whitcroft <apw@canonical.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

fs/overlayfs/Kconfig

@@ -8,3 +8,10 @@ config OVERLAY_FS
 	  merged with the 'upper' object.
 
 	  For more information see Documentation/filesystems/overlayfs.txt
+
+config OVERLAY_FS_V1
+	bool "Overlayfs filesystem (V1) format support"
+	help
+	  Support the older whiteout format overlayfs filesystems via
+	  the overlay module.  This is needed to support legacy kernels
+	  built using the original overlayfs patch set.

fs/overlayfs/dir.c

@@ -48,6 +48,34 @@ struct dentry *ovl_lookup_temp(struct dentry *workdir, struct dentry *dentry)
 	return temp;
 }
 
+#ifdef CONFIG_OVERLAY_FS_V1
+static const char *ovl_whiteout_symlink = "(overlay-whiteout)";
+int ovl_do_whiteout_v1(struct inode *workdir,
+			      struct dentry *dentry)
+{
+	int err;
+
+	err = vfs_symlink(workdir, dentry, ovl_whiteout_symlink);
+	if (err)
+		return err;
+
+	err = vfs_setxattr(dentry, ovl_whiteout_xattr, "y", 1, 0);
+	if (err)
+		vfs_unlink(workdir, dentry, NULL);
+
+	if (err) {
+		/*
+		 * There's no way to recover from failure to whiteout.
+		 * What should we do?  Log a big fat error and... ?
+		 */
+		pr_err("overlayfs: ERROR - failed to whiteout '%s'\n",
+		       dentry->d_name.name);
+	}
+
+	return err;
+}
+#endif
+
 /* caller holds i_mutex on workdir */
 static struct dentry *ovl_whiteout(struct dentry *workdir,
 				   struct dentry *dentry)
@@ -60,7 +88,7 @@ static struct dentry *ovl_whiteout(struct dentry *workdir,
 	if (IS_ERR(whiteout))
 		return whiteout;
 
-	err = ovl_do_whiteout(wdir, whiteout);
+	err = ovl_do_whiteout(wdir, whiteout, dentry);
 	if (err) {
 		dput(whiteout);
 		whiteout = ERR_PTR(err);
@@ -699,6 +727,51 @@ static int ovl_rmdir(struct inode *dir, struct dentry *dentry)
 	return ovl_do_remove(dentry, true);
 }
 
+/*
+ * ovl_downgrade_whiteout -- build a symlink whiteout and install it
+ * over the existing chardev whiteout.
+ */
+static void ovl_downgrade_whiteout(struct dentry *old_upperdir,
+				   struct dentry *old)
+{
+	struct dentry *workdir = ovl_workdir(old);
+	struct dentry *legacy_whiteout = NULL;
+	struct dentry *whtdentry;
+	int err;
+
+	err = ovl_lock_rename_workdir(workdir, old_upperdir);
+	if (err)
+		goto out;
+
+	whtdentry = lookup_one_len(old->d_name.name, old_upperdir,
+				   old->d_name.len);
+	if (IS_ERR(whtdentry)) {
+		err = PTR_ERR(whtdentry);
+		goto out_unlock_workdir;
+	}
+
+	legacy_whiteout = ovl_whiteout(workdir, old);
+	if (IS_ERR(legacy_whiteout)) {
+		err = PTR_ERR(legacy_whiteout);
+		goto out_dput;
+	}
+
+	err = ovl_do_rename(workdir->d_inode, legacy_whiteout,
+			    old_upperdir->d_inode, whtdentry, 0);
+	if (err)
+		ovl_cleanup(workdir->d_inode, legacy_whiteout);
+
+out_dput:
+	dput(whtdentry);
+	dput(legacy_whiteout);
+out_unlock_workdir:
+	unlock_rename(workdir, old_upperdir);
+out:
+	if (err)
+		pr_err("overlayfs: dowgrade of '%pd2' whiteout failed (%i)\n",
+		       old, err);
+}
+
 static int ovl_rename2(struct inode *olddir, struct dentry *old,
 		       struct inode *newdir, struct dentry *new,
 		       unsigned int flags)
@@ -919,6 +992,9 @@ static int ovl_rename2(struct inode *olddir, struct dentry *old,
 	dput(newdentry);
 out_unlock:
 	unlock_rename(new_upperdir, old_upperdir);
+
+	if (!err && ovl_config_legacy(old) && flags & RENAME_WHITEOUT)
+		ovl_downgrade_whiteout(old_upperdir, old);
 out_revert_creds:
 	if (old_opaque || new_opaque) {
 		revert_creds(old_cred);

fs/overlayfs/overlayfs.h

@@ -27,6 +27,8 @@ enum ovl_path_type {
 #define OVL_XATTR_PRE_LEN  16
 #define OVL_XATTR_OPAQUE   OVL_XATTR_PRE_NAME"opaque"
 
+extern const char *ovl_whiteout_xattr; /* XXX: should be ^^ */
+
 static inline int ovl_do_rmdir(struct inode *dir, struct dentry *dentry)
 {
 	int err = vfs_rmdir(dir, dentry);
@@ -124,12 +126,28 @@ static inline int ovl_do_rename(struct inode *olddir, struct dentry *olddentry,
 	return err;
 }
 
-static inline int ovl_do_whiteout(struct inode *dir, struct dentry *dentry)
+#ifdef CONFIG_OVERLAY_FS_V1
+extern int ovl_config_legacy(struct dentry *dentry);
+#else
+#define ovl_config_legacy(x) (0)
+#endif
+
+int ovl_do_whiteout_v1(struct inode *dir, struct dentry *dentry);
+
+static inline int ovl_do_whiteout_v2(struct inode *dir, struct dentry *dentry)
 {
 	int err = vfs_whiteout(dir, dentry);
 	pr_debug("whiteout(%pd2) = %i\n", dentry, err);
 	return err;
 }
+static inline int ovl_do_whiteout(struct inode *dir, struct dentry *dentry,
+				  struct dentry *ovlentry)
+{
+	if (ovl_config_legacy(ovlentry))
+		return ovl_do_whiteout_v1(dir, dentry);
+
+	return ovl_do_whiteout_v2(dir, dentry);
+}
 
 enum ovl_path_type ovl_path_type(struct dentry *dentry);
 u64 ovl_dentry_version_get(struct dentry *dentry);
@@ -149,7 +167,7 @@ int ovl_want_write(struct dentry *dentry);
 void ovl_drop_write(struct dentry *dentry);
 bool ovl_dentry_is_opaque(struct dentry *dentry);
 void ovl_dentry_set_opaque(struct dentry *dentry, bool opaque);
-bool ovl_is_whiteout(struct dentry *dentry);
+bool ovl_is_whiteout(struct dentry *dentry, int is_legacy);
 void ovl_dentry_update(struct dentry *dentry, struct dentry *upperdentry);
 struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 			  unsigned int flags);

fs/overlayfs/readdir.c

@@ -43,6 +43,7 @@ struct ovl_readdir_data {
 	struct ovl_cache_entry *first_maybe_whiteout;
 	int count;
 	int err;
+	int is_legacy;
 };
 
 struct ovl_dir_file {
@@ -98,7 +99,7 @@ static struct ovl_cache_entry *ovl_cache_entry_new(struct ovl_readdir_data *rdd,
 	p->ino = ino;
 	p->is_whiteout = false;
 
-	if (d_type == DT_CHR) {
+	if ((d_type == DT_CHR && !rdd->is_legacy) || (d_type == DT_LNK && rdd->is_legacy)) {
 		p->next_maybe_whiteout = rdd->first_maybe_whiteout;
 		rdd->first_maybe_whiteout = p;
 	}
@@ -224,7 +225,7 @@ static int ovl_check_whiteouts(struct dentry *dir, struct ovl_readdir_data *rdd)
 			rdd->first_maybe_whiteout = p->next_maybe_whiteout;
 			dentry = lookup_one_len(p->name, dir, p->len);
 			if (!IS_ERR(dentry)) {
-				p->is_whiteout = ovl_is_whiteout(dentry);
+				p->is_whiteout = ovl_is_whiteout(dentry, rdd->is_legacy);
 				dput(dentry);
 			}
 		}
@@ -290,6 +291,7 @@ static int ovl_dir_read_merged(struct dentry *dentry, struct list_head *list)
 		.list = list,
 		.root = RB_ROOT,
 		.is_merge = false,
+		.is_legacy = ovl_config_legacy(dentry),
 	};
 	int idx, next;
 

fs/overlayfs/super.c

@@ -40,6 +40,7 @@ struct ovl_fs {
 	struct vfsmount **lower_mnt;
 	struct dentry *workdir;
 	long lower_namelen;
+	int legacy;
 	/* pathnames of lower and upper dirs, for show_options */
 	struct ovl_config config;
 };
@@ -237,13 +238,56 @@ u64 ovl_dentry_version_get(struct dentry *dentry)
 	return oe->version;
 }
 
-bool ovl_is_whiteout(struct dentry *dentry)
+#ifdef CONFIG_OVERLAY_FS_V1
+int ovl_config_legacy(struct dentry *dentry)
+{
+	struct super_block *sb = dentry->d_sb;
+	struct ovl_fs *ufs = sb->s_fs_info;
+
+	return ufs->legacy;
+}
+
+const char *ovl_whiteout_xattr = "trusted.overlay.whiteout";
+
+bool ovl_is_whiteout_v1(struct dentry *dentry)
+{
+	int res;
+	char val;
+
+	if (!dentry)
+		return false;
+	if (!dentry->d_inode)
+		return false;
+	if (!S_ISLNK(dentry->d_inode->i_mode))
+		return false;
+	if (!dentry->d_inode->i_op->getxattr)
+		return false;
+
+	res = dentry->d_inode->i_op->getxattr(dentry, ovl_whiteout_xattr, &val, 1);
+	if (res == 1 && val == 'y')
+		return true;
+
+	return false;
+}
+#else
+#define ovl_is_whiteout_v1(x) (0)
+#endif
+
+bool ovl_is_whiteout_v2(struct dentry *dentry)
 {
 	struct inode *inode = dentry->d_inode;
 
 	return inode && IS_WHITEOUT(inode);
 }
 
+bool ovl_is_whiteout(struct dentry *dentry, int is_legacy)
+{
+	if (is_legacy)
+		return ovl_is_whiteout_v2(dentry) || ovl_is_whiteout_v1(dentry);
+
+	return ovl_is_whiteout_v2(dentry);
+}
+
 static bool ovl_is_opaquedir(struct dentry *dentry)
 {
 	int res;
@@ -408,6 +452,7 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 	struct dentry *this, *prev = NULL;
 	unsigned int i;
 	int err;
+	int is_legacy = ovl_config_legacy(dentry);
 
 	upperdir = ovl_upperdentry_dereference(poe);
 	if (upperdir) {
@@ -422,7 +467,7 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 				err = -EREMOTE;
 				goto out;
 			}
-			if (ovl_is_whiteout(this)) {
+			if (ovl_is_whiteout(this, is_legacy)) {
 				dput(this);
 				this = NULL;
 				upperopaque = true;
@@ -456,7 +501,7 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 		}
 		if (!this)
 			continue;
-		if (ovl_is_whiteout(this)) {
+		if (ovl_is_whiteout(this, is_legacy)) {
 			dput(this);
 			break;
 		}
@@ -1107,14 +1152,59 @@ static struct file_system_type ovl_fs_type = {
 };
 MODULE_ALIAS_FS("overlay");
 
+#ifdef CONFIG_OVERLAY_FS_V1
+static int ovl_v1_fill_super(struct super_block *sb, void *data, int silent)
+{
+	int ret;
+	struct ovl_fs *ufs;
+
+	ret = ovl_fill_super(sb, data, silent);
+	if (ret)
+		return ret;
+
+	/* Mark this as a overlayfs format. */
+	ufs = sb->s_fs_info;
+	ufs->legacy = 1;
+
+	return ret;
+}
+
+static struct dentry *ovl_mount_v1(struct file_system_type *fs_type, int flags,
+				const char *dev_name, void *raw_data)
+{
+	return mount_nodev(fs_type, flags, raw_data, ovl_v1_fill_super);
+}
+
+static struct file_system_type ovl_v1_fs_type = {
+	.owner		= THIS_MODULE,
+	.name		= "overlayfs",
+	.mount		= ovl_mount_v1,
+	.kill_sb	= kill_anon_super,
+	.fs_flags	= FS_USERNS_MOUNT,  /* XXX */
+};
+MODULE_ALIAS_FS("overlayfs");
+MODULE_ALIAS("overlayfs");
+#endif
+
 static int __init ovl_init(void)
 {
+	int ret;
+
+	if (IS_ENABLED(CONFIG_OVERLAY_FS_V1)) {
+		ret = register_filesystem(&ovl_v1_fs_type);
+		if (ret)
+			return ret;
+	}
+
 	return register_filesystem(&ovl_fs_type);
 }
 
 static void __exit ovl_exit(void)
 {
 	unregister_filesystem(&ovl_fs_type);
+
+	if (IS_ENABLED(CONFIG_OVERLAY_FS_V1))
+		unregister_filesystem(&ovl_v1_fs_type);
 }
 
 module_init(ovl_init);