diff --git a/fs/incfs/format.c b/fs/incfs/format.c
index c56e559b6893..3261d5d4b8f6 100644
--- a/fs/incfs/format.c
+++ b/fs/incfs/format.c
@@ -89,11 +89,42 @@ static int truncate_backing_file(struct backing_file_context *bfc,
 	return result;
 }
 
+static int write_to_bf(struct backing_file_context *bfc, const void *buf,
+			size_t count, loff_t pos)
+{
+	ssize_t res = incfs_kwrite(bfc->bc_file, buf, count, pos);
+
+	if (res < 0)
+		return res;
+	if (res != count)
+		return -EIO;
+	return 0;
+}
+
+static int append_zeros_no_fallocate(struct backing_file_context *bfc,
+				     size_t file_size, size_t len)
+{
+	u8 buffer[256] = {};
+	size_t i;
+
+	for (i = 0; i < len; i += sizeof(buffer)) {
+		int to_write = len - i > sizeof(buffer)
+			? sizeof(buffer) : len - i;
+		int err = write_to_bf(bfc, buffer, to_write, file_size + i);
+
+		if (err)
+			return err;
+	}
+
+	return 0;
+}
+
 /* Append a given number of zero bytes to the end of the backing file. */
 static int append_zeros(struct backing_file_context *bfc, size_t len)
 {
 	loff_t file_size = 0;
 	loff_t new_last_byte_offset = 0;
+	int result;
 
 	if (!bfc)
 		return -EFAULT;
@@ -110,19 +141,11 @@ static int append_zeros(struct backing_file_context *bfc, size_t len)
 	 */
 	file_size = incfs_get_end_offset(bfc->bc_file);
 	new_last_byte_offset = file_size + len - 1;
-	return vfs_fallocate(bfc->bc_file, 0, new_last_byte_offset, 1);
-}
+	result = vfs_fallocate(bfc->bc_file, 0, new_last_byte_offset, 1);
+	if (result != -EOPNOTSUPP)
+		return result;
 
-static int write_to_bf(struct backing_file_context *bfc, const void *buf,
-			size_t count, loff_t pos)
-{
-	ssize_t res = incfs_kwrite(bfc->bc_file, buf, count, pos);
-
-	if (res < 0)
-		return res;
-	if (res != count)
-		return -EIO;
-	return 0;
+	return append_zeros_no_fallocate(bfc, file_size, len);
 }
 
 static u32 calc_md_crc(struct incfs_md_header *record)
diff --git a/fs/incfs/vfs.c b/fs/incfs/vfs.c
index 58acbbd5dcdb..0b8051d88c74 100644
--- a/fs/incfs/vfs.c
+++ b/fs/incfs/vfs.c
@@ -1931,17 +1931,17 @@ static int file_open(struct inode *inode, struct file *file)
 	struct file *backing_file = NULL;
 	struct path backing_path = {};
 	int err = 0;
+	int flags = O_NOATIME | O_LARGEFILE |
+		(S_ISDIR(inode->i_mode) ? O_RDONLY : O_RDWR);
 
 	if (!mi)
 		return -EBADF;
 
 	get_incfs_backing_path(file->f_path.dentry, &backing_path);
-
 	if (!backing_path.dentry)
 		return -EBADF;
 
-	backing_file = dentry_open(
-		&backing_path, O_RDWR | O_NOATIME | O_LARGEFILE, mi->mi_owner);
+	backing_file = dentry_open(&backing_path, flags, mi->mi_owner);
 	path_put(&backing_path);
 
 	if (IS_ERR(backing_file)) {