[PATCH RFC 02/41] nvmet: check that the file backend supports ->{read,write}_iter

[Christian Brauner <brauner@xxxxxxxxxx>]

The file backend calls ->read_iter() and ->write_iter() of the backing
file directly but never checks that they exist. Everything that isn't a
block device ends up in the file backend. So a namespace pointing to a
file without them calls a NULL pointer on its first I/O. Only
buffered_io=1 gets that far as the O_DIRECT open fails for such files.

Refuse them when the namespace is enabled the same way zloop does since
commit 0c10f8a1a7ae ("zloop: check that the zone backing file support
->{read,write}_iter").

Fixes: d5eff33ee6f8 ("nvmet: add simple file backed ns support")
Signed-off-by: Christian Brauner (Amutable) <brauner@xxxxxxxxxx>
---
 drivers/nvme/target/io-cmd-file.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/nvme/target/io-cmd-file.c 
b/drivers/nvme/target/io-cmd-file.c
index 695963dd932e..dfa8aa46188c 100644
--- a/drivers/nvme/target/io-cmd-file.c
+++ b/drivers/nvme/target/io-cmd-file.c
@@ -47,6 +47,11 @@ int nvmet_file_ns_enable(struct nvmet_ns *ns)
                return ret;
        }
 
+       if (!ns->file->f_op->read_iter || !ns->file->f_op->write_iter) {
+               ret = -EINVAL;
+               goto err;
+       }
+
        nvmet_file_ns_revalidate(ns);
 
        /*

-- 
2.53.0