[PATCH RFC 03/41] target: fileio: check that the backing file supports ->{read,write}_iter

[Christian Brauner <brauner@xxxxxxxxxx>]

With fd_async_io=1 the fileio backend calls ->read_iter() and
->write_iter() of the backing file directly. The synchronous path goes
through vfs_iter_read() and vfs_iter_write() which check for them but
the aio path doesn't. So a backing file without them calls a NULL
pointer on its first I/O.

Refuse such files when configuring the device. On the synchronous path
every read or write that needed the missing method failed with EINVAL
anyway.

Fixes: 769031c92c8b ("scsi: target: target/file: Add support of direct and 
async I/O")
Signed-off-by: Christian Brauner (Amutable) <brauner@xxxxxxxxxx>
---
 drivers/target/target_core_file.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/target/target_core_file.c 
b/drivers/target/target_core_file.c
index ab9824a4852f..a5391e57e9aa 100644
--- a/drivers/target/target_core_file.c
+++ b/drivers/target/target_core_file.c
@@ -144,6 +144,14 @@ static int fd_configure_device(struct se_device *dev)
                goto fail;
        }
        fd_dev->fd_file = file;
+
+       if (!file->f_op->read_iter || !file->f_op->write_iter) {
+               pr_err("FILEIO: %s lacks ->read_iter or ->write_iter\n",
+                      fd_dev->fd_dev_name);
+               ret = -EINVAL;
+               goto fail;
+       }
+
        /*
         * If using a block backend with this struct file, we extract
         * fd_dev->fd_[block,dev]_size from struct block_device.

-- 
2.53.0