[RFC 01/13] io_uring: add infra for uring_cmd completion in submitter-task

[Kanchan Joshi]

Completion of a uring_cmd ioctl may involve referencing certain
ioctl-specific fields, requiring original submitter context.
Export an API that driver can use for this purpose.
The API facilitates reusing task-work infra of io_uring, while driver
gets to implement cmd-specific handling in a callback.

Signed-off-by: Kanchan Joshi <joshi.k at samsung.com>
Signed-off-by: Anuj Gupta <anuj20.g at samsung.com>
---
 fs/io_uring.c            | 16 ++++++++++++++++
 include/linux/io_uring.h |  8 ++++++++
 2 files changed, 24 insertions(+)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index e96ed3d0385e..246f1085404d 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -2450,6 +2450,22 @@ static void io_req_task_submit(struct io_kiocb *req, bool *locked)
 		io_req_complete_failed(req, -EFAULT);
 }
 
+static void io_uring_cmd_work(struct io_kiocb *req, bool *locked)
+{
+	req->uring_cmd.driver_cb(&req->uring_cmd);
+}
+
+void io_uring_cmd_complete_in_task(struct io_uring_cmd *ioucmd,
+			void (*driver_cb)(struct io_uring_cmd *))
+{
+	struct io_kiocb *req = container_of(ioucmd, struct io_kiocb, uring_cmd);
+
+	req->uring_cmd.driver_cb = driver_cb;
+	req->io_task_work.func = io_uring_cmd_work;
+	io_req_task_work_add(req, !!(req->ctx->flags & IORING_SETUP_SQPOLL));
+}
+EXPORT_SYMBOL_GPL(io_uring_cmd_complete_in_task);
+
 static void io_req_task_queue_fail(struct io_kiocb *req, int ret)
 {
 	req->result = ret;
diff --git a/include/linux/io_uring.h b/include/linux/io_uring.h
index 64e788b39a86..f4b4990a3b62 100644
--- a/include/linux/io_uring.h
+++ b/include/linux/io_uring.h
@@ -14,11 +14,15 @@ struct io_uring_cmd {
 	__u16		op;
 	__u16		unused;
 	__u32		len;
+	/* used if driver requires update in task context*/
+	void (*driver_cb)(struct io_uring_cmd *cmd);
 	__u64		pdu[5];	/* 40 bytes available inline for free use */
 };
 
 #if defined(CONFIG_IO_URING)
 void io_uring_cmd_done(struct io_uring_cmd *cmd, ssize_t ret);
+void io_uring_cmd_complete_in_task(struct io_uring_cmd *ioucmd,
+			void (*driver_cb)(struct io_uring_cmd *));
 struct sock *io_uring_get_socket(struct file *file);
 void __io_uring_cancel(bool cancel_all);
 void __io_uring_free(struct task_struct *tsk);
@@ -42,6 +46,10 @@ static inline void io_uring_free(struct task_struct *tsk)
 static inline void io_uring_cmd_done(struct io_uring_cmd *cmd, ssize_t ret)
 {
 }
+static inline void io_uring_cmd_complete_in_task(struct io_uring_cmd *ioucmd,
+			void (*driver_cb)(struct io_uring_cmd *))
+{
+}
 static inline struct sock *io_uring_get_socket(struct file *file)
 {
 	return NULL;
-- 
2.25.1