ovl: generalize the lower_layers[] array

Rename lower_layers[] array to layers[], extend its size by one and
initialize layers[0] with upper layer values.  Lower layers are now
addressed with index 1..numlower.  layers[0] is reserved even with lower
only overlay.

[SzM: replace ofs->numlower with ofs->numlayer, the latter's value is
incremented by one]
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/overlayfs/export.c

@@ -424,7 +424,6 @@ static struct dentry *ovl_lookup_real_inode(struct super_block *sb,
 					    struct ovl_layer *layer)
 {
 	struct ovl_fs *ofs = sb->s_fs_info;
-	struct ovl_layer upper_layer = { .mnt = ofs->upper_mnt };
 	struct dentry *index = NULL;
 	struct dentry *this = NULL;
 	struct inode *inode;
@@ -466,7 +465,7 @@ static struct dentry *ovl_lookup_real_inode(struct super_block *sb,
 		 * recursive call walks back from indexed upper to the topmost
 		 * connected/hashed upper parent (or up to root).
 		 */
-		this = ovl_lookup_real(sb, upper, &upper_layer);
+		this = ovl_lookup_real(sb, upper, &ofs->layers[0]);
 		dput(upper);
 	}
 
@@ -646,8 +645,7 @@ static struct dentry *ovl_get_dentry(struct super_block *sb,
 				     struct dentry *index)
 {
 	struct ovl_fs *ofs = sb->s_fs_info;
-	struct ovl_layer upper_layer = { .mnt = ofs->upper_mnt };
-	struct ovl_layer *layer = upper ? &upper_layer : lowerpath->layer;
+	struct ovl_layer *layer = upper ? &ofs->layers[0] : lowerpath->layer;
 	struct dentry *real = upper ?: (index ?: lowerpath->dentry);
 
 	/*

fs/overlayfs/namei.c

@@ -322,16 +322,16 @@ int ovl_check_origin_fh(struct ovl_fs *ofs, struct ovl_fh *fh, bool connected,
 	struct dentry *origin = NULL;
 	int i;
 
-	for (i = 0; i < ofs->numlower; i++) {
+	for (i = 1; i < ofs->numlayer; i++) {
 		/*
 		 * If lower fs uuid is not unique among lower fs we cannot match
 		 * fh->uuid to layer.
 		 */
-		if (ofs->lower_layers[i].fsid &&
-		    ofs->lower_layers[i].fs->bad_uuid)
+		if (ofs->layers[i].fsid &&
+		    ofs->layers[i].fs->bad_uuid)
 			continue;
 
-		origin = ovl_decode_real_fh(fh, ofs->lower_layers[i].mnt,
+		origin = ovl_decode_real_fh(fh, ofs->layers[i].mnt,
 					    connected);
 		if (origin)
 			break;
@@ -354,7 +354,7 @@ int ovl_check_origin_fh(struct ovl_fs *ofs, struct ovl_fh *fh, bool connected,
 	}
 	**stackp = (struct ovl_path){
 		.dentry = origin,
-		.layer = &ofs->lower_layers[i]
+		.layer = &ofs->layers[i]
 	};
 
 	return 0;
@@ -885,7 +885,7 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 
 	if (!d.stop && poe->numlower) {
 		err = -ENOMEM;
-		stack = kcalloc(ofs->numlower, sizeof(struct ovl_path),
+		stack = kcalloc(ofs->numlayer - 1, sizeof(struct ovl_path),
 				GFP_KERNEL);
 		if (!stack)
 			goto out_put_upper;

fs/overlayfs/ovl_entry.h

@@ -45,10 +45,10 @@ struct ovl_path {
 /* private information held for overlayfs's superblock */
 struct ovl_fs {
 	struct vfsmount *upper_mnt;
-	unsigned int numlower;
+	unsigned int numlayer;
 	/* Number of unique lower sb that differ from upper sb */
 	unsigned int numlowerfs;
-	struct ovl_layer *lower_layers;
+	struct ovl_layer *layers;
 	struct ovl_sb *lower_fs;
 	/* workbasedir is the path at workdir= mount option */
 	struct dentry *workbasedir;

fs/overlayfs/super.c

@@ -224,13 +224,13 @@ 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++) {
-		iput(ofs->lower_layers[i].trap);
-		mntput(ofs->lower_layers[i].mnt);
+	for (i = 1; i < ofs->numlayer; i++) {
+		iput(ofs->layers[i].trap);
+		mntput(ofs->layers[i].mnt);
 	}
 	for (i = 0; i < ofs->numlowerfs; i++)
 		free_anon_bdev(ofs->lower_fs[i].pseudo_dev);
-	kfree(ofs->lower_layers);
+	kfree(ofs->layers);
 	kfree(ofs->lower_fs);
 
 	kfree(ofs->config.lowerdir);
@@ -1319,16 +1319,16 @@ static int ovl_get_fsid(struct ovl_fs *ofs, const struct path *path)
 	return ofs->numlowerfs;
 }
 
-static int ovl_get_lower_layers(struct super_block *sb, struct ovl_fs *ofs,
-				struct path *stack, unsigned int numlower)
+static int ovl_get_layers(struct super_block *sb, struct ovl_fs *ofs,
+			  struct path *stack, unsigned int numlower)
 {
 	int err;
 	unsigned int i;
 
 	err = -ENOMEM;
-	ofs->lower_layers = kcalloc(numlower, sizeof(struct ovl_layer),
-				    GFP_KERNEL);
-	if (ofs->lower_layers == NULL)
+	ofs->layers = kcalloc(numlower + 1, sizeof(struct ovl_layer),
+			      GFP_KERNEL);
+	if (ofs->layers == NULL)
 		goto out;
 
 	ofs->lower_fs = kcalloc(numlower, sizeof(struct ovl_sb),
@@ -1336,6 +1336,12 @@ static int ovl_get_lower_layers(struct super_block *sb, struct ovl_fs *ofs,
 	if (ofs->lower_fs == NULL)
 		goto out;
 
+	/* idx 0 is reserved for upper fs even with lower only overlay */
+	ofs->layers[0].mnt = ofs->upper_mnt;
+	ofs->layers[0].idx = 0;
+	ofs->layers[0].fsid = 0;
+	ofs->numlayer = 1;
+
 	for (i = 0; i < numlower; i++) {
 		struct vfsmount *mnt;
 		struct inode *trap;
@@ -1369,15 +1375,15 @@ static int ovl_get_lower_layers(struct super_block *sb, struct ovl_fs *ofs,
 		 */
 		mnt->mnt_flags |= MNT_READONLY | MNT_NOATIME;
 
-		ofs->lower_layers[ofs->numlower].trap = trap;
-		ofs->lower_layers[ofs->numlower].mnt = mnt;
-		ofs->lower_layers[ofs->numlower].idx = i + 1;
-		ofs->lower_layers[ofs->numlower].fsid = fsid;
+		ofs->layers[ofs->numlayer].trap = trap;
+		ofs->layers[ofs->numlayer].mnt = mnt;
+		ofs->layers[ofs->numlayer].idx = ofs->numlayer;
+		ofs->layers[ofs->numlayer].fsid = fsid;
 		if (fsid) {
-			ofs->lower_layers[ofs->numlower].fs =
+			ofs->layers[ofs->numlayer].fs =
 				&ofs->lower_fs[fsid - 1];
 		}
-		ofs->numlower++;
+		ofs->numlayer++;
 	}
 
 	/*
@@ -1464,7 +1470,7 @@ static struct ovl_entry *ovl_get_lowerstack(struct super_block *sb,
 		goto out_err;
 	}
 
-	err = ovl_get_lower_layers(sb, ofs, stack, numlower);
+	err = ovl_get_layers(sb, ofs, stack, numlower);
 	if (err)
 		goto out_err;
 
@@ -1475,7 +1481,7 @@ static struct ovl_entry *ovl_get_lowerstack(struct super_block *sb,
 
 	for (i = 0; i < numlower; i++) {
 		oe->lowerstack[i].dentry = dget(stack[i].dentry);
-		oe->lowerstack[i].layer = &ofs->lower_layers[i];
+		oe->lowerstack[i].layer = &ofs->layers[i+1];
 	}
 
 	if (remote)
@@ -1556,9 +1562,9 @@ static int ovl_check_overlapping_layers(struct super_block *sb,
 			return err;
 	}
 
-	for (i = 0; i < ofs->numlower; i++) {
+	for (i = 1; i < ofs->numlayer; i++) {
 		err = ovl_check_layer(sb, ofs,
-				      ofs->lower_layers[i].mnt->mnt_root,
+				      ofs->layers[i].mnt->mnt_root,
 				      "lowerdir");
 		if (err)
 			return err;