diff --git a/src/kernel/core/fs/bootfs.c b/src/kernel/core/fs/bootfs.c
index 9d210132bb..d2280448cf 100755
--- a/src/kernel/core/fs/bootfs.c
+++ b/src/kernel/core/fs/bootfs.c
@@ -1006,7 +1006,7 @@ bootfs_write_stat(fs_volume _fs, fs_vnode _v, const struct stat *stat, int stat_
 //	#pragma mark -
 
 
-static struct fs_calls bootfs_calls = {
+static struct fs_ops bootfs_ops = {
 	&bootfs_mount,
 	&bootfs_unmount,
 	NULL,
@@ -1082,6 +1082,6 @@ bootstrap_bootfs(void)
 
 	dprintf("bootstrap_bootfs: found bootdir at %p\n", bootdir);
 
-	return vfs_register_filesystem("bootfs", &bootfs_calls);
+	return vfs_register_filesystem("bootfs", &bootfs_ops);
 }
 
diff --git a/src/kernel/core/fs/devfs.c b/src/kernel/core/fs/devfs.c
index 8e5996303f..ad4e69b16c 100755
--- a/src/kernel/core/fs/devfs.c
+++ b/src/kernel/core/fs/devfs.c
@@ -60,7 +60,7 @@ struct devfs_stream {
 		} dir;
 		struct stream_dev {
 			void *ident;
-			device_hooks *calls;
+			device_hooks *ops;
 			struct devfs_part_map *part_map;
 		} dev;
 		struct stream_symlink {
@@ -368,13 +368,13 @@ devfs_set_partition( struct devfs *fs, struct devfs_vnode *v,
 	part_node = devfs_create_vnode(fs, part_name);
 	
 	if (part_node == NULL) {
-		res = ENOMEM;
+		res = B_NO_MEMORY;
 		goto err2;
 	}
 
 	part_node->stream.type = STREAM_TYPE_DEVICE;
 	part_node->stream.u.dev.ident = v->stream.u.dev.ident;
-	part_node->stream.u.dev.calls = v->stream.u.dev.calls;
+	part_node->stream.u.dev.ops = v->stream.u.dev.ops;
 	part_node->stream.u.dev.part_map = part_map;
 
 	hash_insert(fs->vnode_list_hash, part_node);
@@ -645,7 +645,7 @@ devfs_open(fs_volume _fs, fs_vnode _v, int oflags, fs_cookie *_cookie)
 	if (vnode->stream.type != STREAM_TYPE_DEVICE)
 		return EINVAL;
 
-	status = vnode->stream.u.dev.calls->open(vnode->name, oflags, &cookie->u.dev.dcookie);
+	status = vnode->stream.u.dev.ops->open(vnode->name, oflags, &cookie->u.dev.dcookie);
 	*_cookie = cookie;
 
 	return status;
@@ -662,7 +662,7 @@ devfs_close(fs_volume _fs, fs_vnode _v, fs_cookie _cookie)
 
 	if (vnode->stream.type == STREAM_TYPE_DEVICE) {
 		// pass the call through to the underlying device
-		return vnode->stream.u.dev.calls->close(cookie->u.dev.dcookie);
+		return vnode->stream.u.dev.ops->close(cookie->u.dev.dcookie);
 	}
 
 	return B_OK;
@@ -679,7 +679,7 @@ devfs_free_cookie(fs_volume _fs, fs_vnode _v, fs_cookie _cookie)
 
 	if (vnode->stream.type == STREAM_TYPE_DEVICE) {
 		// pass the call through to the underlying device
-		vnode->stream.u.dev.calls->free(cookie->u.dev.dcookie);
+		vnode->stream.u.dev.ops->free(cookie->u.dev.dcookie);
 	}
 
 	if (cookie)
@@ -725,7 +725,7 @@ devfs_read(fs_volume _fs, fs_vnode _v, fs_cookie _cookie, off_t pos, void *buffe
 	}
 
 	// pass the call through to the device
-	return vnode->stream.u.dev.calls->read(cookie->u.dev.dcookie, pos, buffer, length);
+	return vnode->stream.u.dev.ops->read(cookie->u.dev.dcookie, pos, buffer, length);
 }
 
 
@@ -752,7 +752,7 @@ devfs_write(fs_volume _fs, fs_vnode _v, fs_cookie _cookie, off_t pos, const void
 			pos += part_map->offset;
 		}
 
-		written = vnode->stream.u.dev.calls->write(cookie->u.dev.dcookie, pos, buf, len);
+		written = vnode->stream.u.dev.ops->write(cookie->u.dev.dcookie, pos, buf, len);
 		return written;
 	}
 	return EINVAL;
@@ -888,7 +888,7 @@ devfs_ioctl(fs_volume _fs, fs_vnode _v, fs_cookie _cookie, ulong op, void *buf,
 				return devfs_set_partition(fs, v, cookie, buf, len);
 		}
 
-		return v->stream.u.dev.calls->control(cookie->u.dev.dcookie, op, buf, len);
+		return v->stream.u.dev.ops->control(cookie->u.dev.dcookie, op, buf, len);
 	}
 	return EINVAL;
 }
@@ -902,9 +902,9 @@ static int devfs_canpage(fs_volume _fs, fs_vnode _v)
 	TRACE(("devfs_canpage: vnode 0x%x\n", v));
 
 	if(v->stream.type == STREAM_TYPE_DEVICE) {
-		if(!v->stream.u.dev.calls->dev_canpage)
+		if(!v->stream.u.dev.ops->dev_canpage)
 			return 0;
-		return v->stream.u.dev.calls->dev_canpage(v->stream.u.dev.ident);
+		return v->stream.u.dev.ops->dev_canpage(v->stream.u.dev.ident);
 	} else {
 		return 0;
 	}
@@ -919,7 +919,7 @@ static ssize_t devfs_readpage(fs_volume _fs, fs_vnode _v, iovecs *vecs, off_t po
 	if(v->stream.type == STREAM_TYPE_DEVICE) {
 		struct devfs_part_map *part_map = v->stream.u.dev.part_map;
 			
-		if(!v->stream.u.dev.calls->dev_readpage)
+		if(!v->stream.u.dev.ops->dev_readpage)
 			return ERR_NOT_ALLOWED;
 			
 		if( part_map ) {
@@ -934,7 +934,7 @@ static ssize_t devfs_readpage(fs_volume _fs, fs_vnode _v, iovecs *vecs, off_t po
 			pos += part_map->offset;
 		}
 
-		return v->stream.u.dev.calls->dev_readpage(v->stream.u.dev.ident, vecs, pos);
+		return v->stream.u.dev.ops->dev_readpage(v->stream.u.dev.ident, vecs, pos);
 	} else {
 		return ERR_NOT_ALLOWED;
 	}
@@ -949,7 +949,7 @@ static ssize_t devfs_writepage(fs_volume _fs, fs_vnode _v, iovecs *vecs, off_t p
 	if(v->stream.type == STREAM_TYPE_DEVICE) {
 		struct devfs_part_map *part_map = v->stream.u.dev.part_map;
 
-		if(!v->stream.u.dev.calls->dev_writepage)
+		if(!v->stream.u.dev.ops->dev_writepage)
 			return ERR_NOT_ALLOWED;
 
 		if( part_map ) {
@@ -964,7 +964,7 @@ static ssize_t devfs_writepage(fs_volume _fs, fs_vnode _v, iovecs *vecs, off_t p
 			pos += part_map->offset;
 		}
 
-		return v->stream.u.dev.calls->dev_writepage(v->stream.u.dev.ident, vecs, pos);
+		return v->stream.u.dev.ops->dev_writepage(v->stream.u.dev.ident, vecs, pos);
 	} else {
 		return ERR_NOT_ALLOWED;
 	}
@@ -1045,7 +1045,7 @@ devfs_write_stat(fs_volume _fs, fs_vnode _v, const struct stat *stat, int stat_m
 //	#pragma mark -
 
 
-static struct fs_calls devfs_calls = {
+static struct fs_ops devfs_ops = {
 	&devfs_mount,
 	&devfs_unmount,
 	NULL,
@@ -1107,12 +1107,12 @@ bootstrap_devfs(void)
 
 	TRACE(("bootstrap_devfs: entry\n"));
 
-	return vfs_register_filesystem("devfs", &devfs_calls);
+	return vfs_register_filesystem("devfs", &devfs_ops);
 }
 
 
 status_t
-devfs_publish_device(const char *path, void *ident, device_hooks *calls)
+devfs_publish_device(const char *path, void *ident, device_hooks *ops)
 {
 	int err = 0;
 	int i, last;
@@ -1121,9 +1121,9 @@ devfs_publish_device(const char *path, void *ident, device_hooks *calls)
 	struct devfs_vnode *v;
 	bool at_leaf;
 
-	TRACE(("devfs_publish_device: entry path '%s', ident %p, hooks %p\n", path, ident, calls));
+	TRACE(("devfs_publish_device: entry path '%s', ident %p, hooks %p\n", path, ident, ops));
 
-	if (calls == NULL || path == NULL) {
+	if (ops == NULL || path == NULL) {
 		panic("devfs_publish_device called with NULL pointer!\n");
 		return EINVAL;
 	}
@@ -1189,7 +1189,7 @@ devfs_publish_device(const char *path, void *ident, device_hooks *calls)
 			// this is the last component
 			v->stream.type = STREAM_TYPE_DEVICE;
 			v->stream.u.dev.ident = ident;
-			v->stream.u.dev.calls = calls;
+			v->stream.u.dev.ops = ops;
 		} else {
 			// this is a dir
 			v->stream.type = STREAM_TYPE_DIR;
diff --git a/src/kernel/core/fs/rootfs.c b/src/kernel/core/fs/rootfs.c
index f9aab43537..27c68bc4c2 100755
--- a/src/kernel/core/fs/rootfs.c
+++ b/src/kernel/core/fs/rootfs.c
@@ -922,7 +922,7 @@ rootfs_write_stat(fs_volume _fs, fs_vnode _v, const struct stat *stat, int stat_
 //	#pragma mark -
 
 
-static struct fs_calls rootfs_calls = {
+static struct fs_ops rootfs_ops = {
 	&rootfs_mount,
 	&rootfs_unmount,
 	NULL,
@@ -983,5 +983,5 @@ bootstrap_rootfs(void)
 {
 	dprintf("bootstrap_rootfs: entry\n");
 
-	return vfs_register_filesystem("rootfs", &rootfs_calls);
+	return vfs_register_filesystem("rootfs", &rootfs_ops);
 }
diff --git a/src/kernel/core/fs/vfs.c b/src/kernel/core/fs/vfs.c
index c2566b244c..909a6a4d6e 100755
--- a/src/kernel/core/fs/vfs.c
+++ b/src/kernel/core/fs/vfs.c
@@ -85,18 +85,18 @@ struct vnode_hash_key {
 
 typedef struct file_system {
 	struct file_system	*next;
-	struct fs_calls		*calls;
+	struct fs_ops		*ops;
 	const char			*name;
 	image_id			image;
 	int32				ref_count;
 } file_system;
 
-#define FS_CALL(vnode,call) (vnode->mount->fs->calls->call)
+#define FS_CALL(vnode, op) (vnode->mount->fs->ops->op)
 
 struct fs_mount {
 	struct fs_mount	*next;
 	file_system		*fs;
-	mount_id			id;
+	mount_id		id;
 	void			*cookie;
 	char			*mount_point;
 	recursive_lock	rlock;
@@ -233,7 +233,7 @@ mount_hash(void *_m, const void *_key, unsigned int range)
  */
 
 static file_system *
-new_file_system(const char *name, struct fs_calls *calls)
+new_file_system(const char *name, struct fs_ops *ops)
 {
 	file_system *fs;
 
@@ -244,7 +244,7 @@ new_file_system(const char *name, struct fs_calls *calls)
 		return NULL;
 
 	fs->name = name;
-	fs->calls = calls;
+	fs->ops = ops;
 	fs->image = -1;
 	fs->ref_count = 0;
 
@@ -281,8 +281,9 @@ static file_system *
 load_file_system(const char *name)
 {
 	char path[SYS_MAX_PATH_LEN];
-	struct fs_calls **calls;
-	uint32 *version;
+	file_system *fs;
+	struct fs_ops **ops;
+	int32 *version;
 	void (*init)();
 	image_id image;
 
@@ -299,11 +300,29 @@ load_file_system(const char *name)
 		return NULL;
 
 	init = (void *)elf_lookup_symbol(image, "init_file_system");
-	if (!init)
+	version = (int32 *)elf_lookup_symbol(image, "api_version");
+	ops = (fs_ops **)elf_lookup_symbol(image, "fs_entry");
+	if (init == NULL || version == NULL || ops == NULL) {
+		dprintf("vfs: add-on \"%s\" doesn't export all necessary symbols.\n", name);
+		goto err;
+	}
+
+	if (*version != B_CURRENT_FS_API_VERSION) {
+		dprintf("vfs: add-on \"%s\" supports unknown API version %ld\n", name, *version);
+		goto err;
+	}
+
+	fs = new_file_system(name, *ops);
+	if (fs == NULL)
 		goto err;
 
+	fs->image = image;
+
+	// initialize file system add-on
 	init();
 
+	return fs;
+
 err:
 	elf_unload_kspace(path);
 	return NULL;
@@ -1625,17 +1644,17 @@ vfs_bootstrap_all_filesystems(void)
 
 
 int
-vfs_register_filesystem(const char *name, struct fs_calls *calls)
+vfs_register_filesystem(const char *name, struct fs_ops *ops)
 {
 	status_t status = B_OK;
 	file_system *fs;
 
-	if (name == NULL || *name == '\0' || calls == NULL)
+	if (name == NULL || *name == '\0' || ops == NULL)
 		return B_BAD_VALUE;
 
 	mutex_lock(&gFileSystemsMutex);
 
-	fs = new_file_system(name, calls);
+	fs = new_file_system(name, ops);
 	if (fs == NULL)
 		status = B_NO_MEMORY;
 
@@ -2660,7 +2679,7 @@ fs_mount(char *path, const char *device, const char *fsName, void *args, bool ke
 			goto err3;
 		}
 
-		err = mount->fs->calls->mount(mount->id, device, NULL, &mount->cookie, &root_id);
+		err = mount->fs->ops->mount(mount->id, device, NULL, &mount->cookie, &root_id);
 		if (err < 0) {
 			err = ERR_VFS_GENERAL;
 			goto err3;
@@ -2688,7 +2707,7 @@ fs_mount(char *path, const char *device, const char *fsName, void *args, bool ke
 		mount->covers_vnode = covered_vnode;
 
 		// mount it
-		err = mount->fs->calls->mount(mount->id, device, NULL, &mount->cookie, &root_id);
+		err = mount->fs->ops->mount(mount->id, device, NULL, &mount->cookie, &root_id);
 		if (err < 0)
 			goto err4;
 	}
@@ -2716,7 +2735,7 @@ fs_mount(char *path, const char *device, const char *fsName, void *args, bool ke
 	return 0;
 
 err5:
-	mount->fs->calls->unmount(mount->cookie);
+	mount->fs->ops->unmount(mount->cookie);
 err4:
 	if (mount->covers_vnode)
 		put_vnode(mount->covers_vnode);
@@ -2807,7 +2826,7 @@ fs_unmount(char *path, bool kernel)
 
 	mutex_unlock(&gMountOpMutex);
 
-	mount->fs->calls->unmount(mount->cookie);
+	mount->fs->ops->unmount(mount->cookie);
 
 	// release the file system
 	put_file_system(mount->fs);
@@ -2837,7 +2856,7 @@ fs_sync(void)
 
 	hash_open(gMountsTable, &iter);
 	while ((mount = hash_next(gMountsTable, &iter))) {
-		mount->fs->calls->sync(mount->cookie);
+		mount->fs->ops->sync(mount->cookie);
 	}
 	hash_close(gMountsTable, &iter, false);
 
@@ -2862,8 +2881,8 @@ fs_read_info(dev_t device, struct fs_info *info)
 		goto error;
 	}
 
-	if (mount->fs->calls->read_fs_info)
-		status = mount->fs->calls->read_fs_info(mount->cookie, info);
+	if (mount->fs->ops->read_fs_info)
+		status = mount->fs->ops->read_fs_info(mount->cookie, info);
 	else
 		status = EOPNOTSUPP;
 
@@ -2891,8 +2910,8 @@ fs_write_info(dev_t device, const struct fs_info *info, int mask)
 		goto error;
 	}
 
-	if (mount->fs->calls->write_fs_info)
-		status = mount->fs->calls->write_fs_info(mount->cookie, info, mask);
+	if (mount->fs->ops->write_fs_info)
+		status = mount->fs->ops->write_fs_info(mount->cookie, info, mask);
 	else
 		status = EROFS;