[PATCH] io_uring/uring_cmd: ensure that device supports IOPOLL

[Jens Axboe <axboe@kernel.dk>]

It's possible for a file type to support uring commands, but not
pollable ones. Hence before issuing one of those, we should check
that it is supported and error out upfront if it isn't.

Cc: stable@vger.kernel.org
Fixes: 5756a3a7e713 ("io_uring: add iopoll infrastructure for io_uring_cmd")
Link: https://github.com/axboe/liburing/issues/816
Signed-off-by: Jens Axboe <axboe@kernel.dk>

---

diff --git a/io_uring/uring_cmd.c b/io_uring/uring_cmd.c
index 446a189b78b0..e3413f131887 100644
--- a/io_uring/uring_cmd.c
+++ b/io_uring/uring_cmd.c
@@ -101,6 +101,18 @@ int io_uring_cmd_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 	return 0;
 }
 
+static bool io_uring_cmd_supported(struct io_ring_ctx *ctx, struct file *file)
+{
+	/* no issue method, fail */
+	if (!file->f_op->uring_cmd)
+		return false;
+	/* IOPOLL enabled and no poll method, fail */
+	if (ctx->flags & IORING_SETUP_IOPOLL && !file->f_op->uring_cmd_iopoll)
+		return false;
+
+	return true;
+}
+
 int io_uring_cmd(struct io_kiocb *req, unsigned int issue_flags)
 {
 	struct io_uring_cmd *ioucmd = io_kiocb_to_cmd(req, struct io_uring_cmd);
@@ -108,7 +120,7 @@ int io_uring_cmd(struct io_kiocb *req, unsigned int issue_flags)
 	struct file *file = req->file;
 	int ret;
 
-	if (!req->file->f_op->uring_cmd)
+	if (!io_uring_cmd_supported(ctx, file))
 		return -EOPNOTSUPP;
 
 	ret = security_uring_cmd(ioucmd);

-- 
Jens Axboe