diff --git a/tasks/fs0/include/fs.h b/tasks/fs0/include/fs.h
index 0081912..e256b7d 100644
--- a/tasks/fs0/include/fs.h
+++ b/tasks/fs0/include/fs.h
@@ -53,7 +53,8 @@ struct vnode_ops {
 	vnode_op_t link;
 	vnode_op_t unlink;
 	int (*mkdir)(struct vnode *parent, const char *name);
-	int (*mknod)(struct vnode *parent, const char *name, unsigned int mode);
+	struct vnode *(*mknod)(struct vnode *parent, const char *name,
+			       unsigned int mode);
 	vnode_op_t rmdir;
 	vnode_op_t rename;
 	vnode_op_t getattr;
diff --git a/tasks/fs0/src/memfs/vnode.c b/tasks/fs0/src/memfs/vnode.c
index c1d1ef8..1eef0b4 100644
--- a/tasks/fs0/src/memfs/vnode.c
+++ b/tasks/fs0/src/memfs/vnode.c
@@ -208,9 +208,10 @@ int memfs_write_vnode(struct superblock *sb, struct vnode *v)
 
 /*
  * Creates ordinary files and directories at the moment. In the future,
- * other file types will be added.
+ * other file types will be added. Returns the created node.
  */
-int memfs_vnode_mknod(struct vnode *v, const char *dirname, unsigned int mode)
+struct vnode *memfs_vnode_mknod(struct vnode *v, const char *dirname,
+				unsigned int mode)
 {
 	struct dentry *d, *parent = list_entry(v->dentries.next,
 					       struct dentry, vref);
@@ -230,25 +231,25 @@ int memfs_vnode_mknod(struct vnode *v, const char *dirname, unsigned int mode)
 
 	/* Populate the children */
 	if ((err = v->ops.readdir(v)) < 0)
-		return err;
+		return PTR_ERR(err);
 
 	/* Check there's no existing child with same name */
 	list_for_each_entry(d, &parent->children, child) {
 		/* Does the name exist as a child? */
 		if(d->ops.compare(d, dirname))
-			return -EEXIST;
+			return PTR_ERR(-EEXIST);
 	}
 
 	/* Allocate a new vnode for the new directory */
 	if (IS_ERR(newv = v->sb->ops->alloc_vnode(v->sb)))
-		return (int)newv;
+		return newv;
 
 	/* Initialise the vnode */
 	vfs_set_type(newv, S_IFDIR);
 
 	/* Get the next directory entry available on the parent vnode */
 	if (v->dirbuf.npages * PAGE_SIZE <= v->size)
-		return -ENOSPC;
+		return PTR_ERR(-ENOSPC);
 
 	/* Fill in the new entry to parent directory entry */
 	memfsd = (struct memfs_dentry *)&v->dirbuf.buffer[v->size];
@@ -267,7 +268,7 @@ int memfs_vnode_mknod(struct vnode *v, const char *dirname, unsigned int mode)
 
 	/* Allocate a new vfs dentry */
 	if (!(newd = vfs_alloc_dentry()))
-		return -ENOMEM;
+		return PTR_ERR(-ENOMEM);
 
 	/* Initialise it */
 	newd->ops = generic_dentry_operations;
@@ -285,7 +286,7 @@ int memfs_vnode_mknod(struct vnode *v, const char *dirname, unsigned int mode)
 	list_add(&newd->cache_list, &dentry_cache);
 	list_add(&newv->cache_list, &vnode_cache);
 
-	return 0;
+	return newv;
 }
 
 /*
diff --git a/tasks/fs0/src/syscalls.c b/tasks/fs0/src/syscalls.c
index e6e50b1..c829720 100644
--- a/tasks/fs0/src/syscalls.c
+++ b/tasks/fs0/src/syscalls.c
@@ -58,35 +58,41 @@ void print_vnode(struct vnode *v)
 }
 
 /* Creates a node under a directory, e.g. a file, directory. */
-int vfs_create(struct tcb *task, struct pathdata *pdata, unsigned int mode)
+struct vnode *vfs_create(struct tcb *task, struct pathdata *pdata,
+			 unsigned int mode)
 {
-	struct vnode *vparent;
+	struct vnode *vparent, *newnode;
 	const char *nodename;
-	int err;
 
 	/* The last component is to be created */
 	nodename = pathdata_last_component(pdata);
 
 	/* Check that the parent directory exists. */
 	if (IS_ERR(vparent = vfs_lookup_bypath(pdata)))
-		return (int)vparent;
+		return vparent;
 
 	/* The parent vnode must be a directory. */
 	if (!vfs_isdir(vparent))
-		return -ENOENT;
+		return PTR_ERR(-ENOENT);
 
 	/* Create new directory under the parent */
-	if ((err = vparent->ops.mknod(vparent, nodename, mode)) < 0)
-		return err;
+	if (IS_ERR(newnode = vparent->ops.mknod(vparent, nodename, mode)))
+		return newnode;
 
 	// print_vnode(vparent);
-	return 0;
+	return newnode;
 }
 
 /* FIXME:
  * - Is it already open?
  * - Allocate a copy of path string since lookup destroys it
  * - Check flags and mode.
+ *
+ * TODO:
+ * - All return paths should return by destroying pdata.
+ * - Need another pdata for vfs_create since first lookup destroys it.
+ * - Or perhaps we check O_CREAT first, and do lookup once, without the
+ *   last path component which is to be created.
  */
 int sys_open(l4id_t sender, const char *pathname, int flags, unsigned int mode)
 {
@@ -94,7 +100,7 @@ int sys_open(l4id_t sender, const char *pathname, int flags, unsigned int mode)
 	struct vnode *v;
 	struct tcb *task;
 	int fd;
-	int err;
+	int retval;
 
 	/* Get the task */
 	BUG_ON(!(task = find_task(sender)));
@@ -107,16 +113,17 @@ int sys_open(l4id_t sender, const char *pathname, int flags, unsigned int mode)
 		return 0;
 	}
 
-	/* Get the vnode */
-	if (IS_ERR(v = vfs_lookup_bypath(pdata))) {
-		if (!(flags & O_CREAT)) {
-			l4_ipc_return((int)v);
-			return 0;
-		} else {
-			if ((err = vfs_create(task, pdata, mode)) < 0) {
-				l4_ipc_return(err);
-				return 0;
-			}
+	/* Creating new node, file or directory */
+	if (flags & O_CREAT) {
+		if (IS_ERR(v = vfs_create(task, pdata, mode))) {
+			retval = (int)v;
+			goto out;
+		}
+	} else {
+		/* Not creating, just opening, get the vnode */
+		if (IS_ERR(v = vfs_lookup_bypath(pdata))) {
+			retval = (int)v;
+			goto out;
 		}
 	}
 
@@ -129,8 +136,9 @@ int sys_open(l4id_t sender, const char *pathname, int flags, unsigned int mode)
 	/* Tell the pager about opened vnode information */
 	BUG_ON(pager_sys_open(sender, fd, v->vnum, v->size) < 0);
 
+out:
 	pathdata_destroy(pdata);
-	l4_ipc_return(fd);
+	l4_ipc_return(retval);
 	return 0;
 }
 
@@ -160,6 +168,7 @@ int sys_mkdir(l4id_t sender, const char *pathname, unsigned int mode)
 {
 	struct tcb *task;
 	struct pathdata *pdata;
+	struct vnode *v;
 
 	/* Get the task */
 	BUG_ON(!(task = find_task(sender)));
@@ -173,7 +182,10 @@ int sys_mkdir(l4id_t sender, const char *pathname, unsigned int mode)
 	}
 
 	/* Create the directory or fail */
-	l4_ipc_return(vfs_create(task, pdata, mode));
+	if (IS_ERR(v = vfs_create(task, pdata, mode)))
+		l4_ipc_return((int)v);
+	else
+		l4_ipc_return(0);
 
 	/* Destroy extracted path data */
 	pathdata_destroy(pdata);
diff --git a/tasks/mm0/src/file.c b/tasks/mm0/src/file.c
index ed29d49..61a86da 100644
--- a/tasks/mm0/src/file.c
+++ b/tasks/mm0/src/file.c
@@ -268,6 +268,7 @@ int sys_read(l4id_t sender, int fd, void *buf, int count)
 
 int sys_write(l4id_t sender, int fd, void *buf, int count)
 {
+	BUG();
 	return 0;
 }
 
diff --git a/tasks/test0/src/fileio.c b/tasks/test0/src/fileio.c
index 7054cd3..c5453b6 100644
--- a/tasks/test0/src/fileio.c
+++ b/tasks/test0/src/fileio.c
@@ -12,22 +12,51 @@ int fileio(void)
 	int fd;
 	ssize_t cnt;
 	int err;
+	char buf[128];
+	off_t offset;
 
 	char *str = "I WROTE TO THIS FILE\n";
 
 	if ((fd = open("/home/bahadir/newfile.txt", O_RDWR | O_CREAT | O_TRUNC, S_IRWXU)) < 0) {
 		perror("OPEN");
-		return 0;
+		return -1;
 	}
 
 	if ((int)(cnt = write(fd, str, strlen(str))) < 0) {
 		perror("WRITE");
-		return 0;
+		return -1;
 	}
 
-	if ((err = close(fd)) < 0)
+	if ((int)(offset = lseek(fd, 0, SEEK_SET)) < 0) {
+		perror("LSEEK");
+		return -1;
+	}
+	if ((int)(cnt = read(fd, buf, strlen(str))) < 0) {
+		perror("WRITE");
+		return -1;
+	}
+
+	printf("Read: %d bytes from file.\n", cnt);
+	if (cnt) {
+		printf("Read string: %s\n", buf);
+	}
+
+	if ((err = close(fd)) < 0) {
 		perror("CLOSE");
+		return -1;
+	}
 
 	return 0;
 }
 
+#if defined(HOST_TESTS)
+int main(void)
+{
+	printf("File IO test:\n");
+	if (fileio() == 0)
+		printf("-- PASSED --\n");
+
+	return 0;
+}
+#endif
+