ovl: allocate anon bdev per unique lower fs

Instead of allocating an anonymous bdev per lower layer, allocate
one anonymous bdev per every unique lower fs that is different than
upper fs.

Every unique lower fs is assigned an fsid > 0 and the number of
unique lower fs are stored in ofs->numlowerfs.

The assigned fsid is stored in the lower layer struct and will be
used also for inode number multiplexing.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

1 files changed, 48 insertions, 18 deletions

diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index 7c24619ae7fc..7d97d30cad39 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -236,11 +236,12 @@ static void ovl_free_fs(struct ovl_fs *ofs)
 	if (ofs->upperdir_locked)
 		ovl_inuse_unlock(ofs->upper_mnt->mnt_root);
 	mntput(ofs->upper_mnt);
-	for (i = 0; i < ofs->numlower; i++) {
+	for (i = 0; i < ofs->numlower; i++)
 		mntput(ofs->lower_layers[i].mnt);
-		free_anon_bdev(ofs->lower_layers[i].pseudo_dev);
-	}
+	for (i = 0; i < ofs->numlowerfs; i++)
+		free_anon_bdev(ofs->lower_fs[i].pseudo_dev);
 	kfree(ofs->lower_layers);
+	kfree(ofs->lower_fs);
 
 	kfree(ofs->config.lowerdir);
 	kfree(ofs->config.upperdir);
@@ -1108,6 +1109,35 @@ out:
 	return err;
 }
 
+/* Get a unique fsid for the layer */
+static int ovl_get_fsid(struct ovl_fs *ofs, struct super_block *sb)
+{
+	unsigned int i;
+	dev_t dev;
+	int err;
+
+	/* fsid 0 is reserved for upper fs even with non upper overlay */
+	if (ofs->upper_mnt && ofs->upper_mnt->mnt_sb == sb)
+		return 0;
+
+	for (i = 0; i < ofs->numlowerfs; i++) {
+		if (ofs->lower_fs[i].sb == sb)
+			return i + 1;
+	}
+
+	err = get_anon_bdev(&dev);
+	if (err) {
+		pr_err("overlayfs: failed to get anonymous bdev for lowerpath\n");
+		return err;
+	}
+
+	ofs->lower_fs[ofs->numlowerfs].sb = sb;
+	ofs->lower_fs[ofs->numlowerfs].pseudo_dev = dev;
+	ofs->numlowerfs++;
+
+	return ofs->numlowerfs;
+}
+
 static int ovl_get_lower_layers(struct ovl_fs *ofs, struct path *stack,
 				unsigned int numlower)
 {
@@ -1119,23 +1149,27 @@ static int ovl_get_lower_layers(struct ovl_fs *ofs, struct path *stack,
 				    GFP_KERNEL);
 	if (ofs->lower_layers == NULL)
 		goto out;
+
+	ofs->lower_fs = kcalloc(numlower, sizeof(struct ovl_sb),
+				GFP_KERNEL);
+	if (ofs->lower_fs == NULL)
+		goto out;
+
 	for (i = 0; i < numlower; i++) {
 		struct vfsmount *mnt;
-		dev_t dev;
+		int fsid;
 
-		err = get_anon_bdev(&dev);
-		if (err) {
-			pr_err("overlayfs: failed to get anonymous bdev for lowerpath\n");
+		err = fsid = ovl_get_fsid(ofs, stack[i].mnt->mnt_sb);
+		if (err < 0)
 			goto out;
-		}
 
 		mnt = clone_private_mount(&stack[i]);
 		err = PTR_ERR(mnt);
 		if (IS_ERR(mnt)) {
 			pr_err("overlayfs: failed to clone lowerpath\n");
-			free_anon_bdev(dev);
 			goto out;
 		}
+
 		/*
 		 * Make lower layers R/O.  That way fchmod/fchown on lower file
 		 * will fail instead of modifying lower fs.
@@ -1143,15 +1177,13 @@ static int ovl_get_lower_layers(struct ovl_fs *ofs, struct path *stack,
 		mnt->mnt_flags |= MNT_READONLY | MNT_NOATIME;
 
 		ofs->lower_layers[ofs->numlower].mnt = mnt;
-		ofs->lower_layers[ofs->numlower].pseudo_dev = dev;
 		ofs->lower_layers[ofs->numlower].idx = i + 1;
+		ofs->lower_layers[ofs->numlower].fsid = fsid;
+		if (fsid) {
+			ofs->lower_layers[ofs->numlower].fs =
+				&ofs->lower_fs[fsid - 1];
+		}
 		ofs->numlower++;
-
-		/* Check if all lower layers are on same sb */
-		if (i == 0)
-			ofs->same_sb = mnt->mnt_sb;
-		else if (ofs->same_sb != mnt->mnt_sb)
-			ofs->same_sb = NULL;
 	}
 	err = 0;
 out:
@@ -1305,8 +1337,6 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 	/* If the upper fs is nonexistent, we mark overlayfs r/o too */
 	if (!ofs->upper_mnt)
 		sb->s_flags |= SB_RDONLY;
-	else if (ofs->upper_mnt->mnt_sb != ofs->same_sb)
-		ofs->same_sb = NULL;
 
 	if (!(ovl_force_readonly(ofs)) && ofs->config.index) {
 		err = ovl_get_indexdir(ofs, oe, &upperpath);