[RFC 1/3] io_uring: add helper for uring_cmd completion in submitter-task

[Kanchan Joshi <joshi.k@samsung.com>]

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

Signed-off-by: Kanchan Joshi <joshi.k@samsung.com>
---
 fs/io_uring.c            | 37 +++++++++++++++++++++++++++++++++----
 include/linux/io_uring.h |  8 ++++++++
 2 files changed, 41 insertions(+), 4 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 116ac0f179e0..d4ed1326b9f1 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -775,9 +775,12 @@ struct io_kiocb {
 		/* use only after cleaning per-op data, see io_clean_op() */
 		struct io_completion	compl;
 	};
-
-	/* opcode allocated if it needs to store data for async defer */
-	void				*async_data;
+	union {
+		/* opcode allocated if it needs to store data for async defer */
+		void				*async_data;
+		/* used for uring-cmd, when driver needs to update in task */
+		void (*driver_cb)(struct io_uring_cmd *cmd);
+	};
 	u8				opcode;
 	/* polled IO has completed */
 	u8				iopoll_completed;
@@ -1719,7 +1722,7 @@ static void io_dismantle_req(struct io_kiocb *req)
 {
 	io_clean_op(req);
 
-	if (req->async_data)
+	if (io_op_defs[req->opcode].async_size && req->async_data)
 		kfree(req->async_data);
 	if (req->file)
 		io_put_file(req, req->file, (req->flags & REQ_F_FIXED_FILE));
@@ -2035,6 +2038,31 @@ static void io_req_task_submit(struct callback_head *cb)
 	__io_req_task_submit(req);
 }
 
+static void uring_cmd_work(struct callback_head *cb)
+{
+	struct io_kiocb *req = container_of(cb, struct io_kiocb, task_work);
+	struct io_uring_cmd *cmd = &req->uring_cmd;
+
+	req->driver_cb(cmd);
+}
+int uring_cmd_complete_in_task(struct io_uring_cmd *ioucmd,
+			void (*driver_cb)(struct io_uring_cmd *))
+{
+	int ret;
+	struct io_kiocb *req = container_of(ioucmd, struct io_kiocb, uring_cmd);
+
+	req->driver_cb = driver_cb;
+	req->task_work.func = uring_cmd_work;
+	ret = io_req_task_work_add(req);
+	if (unlikely(ret)) {
+		req->result = -ECANCELED;
+		percpu_ref_get(&req->ctx->refs);
+		io_req_task_work_add_fallback(req, io_req_task_cancel);
+	}
+	return ret;
+}
+EXPORT_SYMBOL_GPL(uring_cmd_complete_in_task);
+
 static void io_req_task_queue(struct io_kiocb *req)
 {
 	int ret;
@@ -3537,6 +3565,7 @@ void io_uring_cmd_done(struct io_uring_cmd *cmd, ssize_t ret)
 		req_set_fail_links(req);
 	io_req_complete(req, ret);
 }
+EXPORT_SYMBOL_GPL(io_uring_cmd_done);
 
 static int io_uring_cmd_prep(struct io_kiocb *req,
 			     const struct io_uring_sqe *sqe)
diff --git a/include/linux/io_uring.h b/include/linux/io_uring.h
index 5849b15334b8..dba8f0b3da9f 100644
--- a/include/linux/io_uring.h
+++ b/include/linux/io_uring.h
@@ -41,6 +41,8 @@ struct io_uring_cmd {
 
 #if defined(CONFIG_IO_URING)
 void io_uring_cmd_done(struct io_uring_cmd *cmd, ssize_t ret);
+int 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_task_cancel(void);
 void __io_uring_files_cancel(struct files_struct *files);
@@ -65,6 +67,12 @@ 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)
 {
 }
+
+int uring_cmd_complete_in_task(struct io_uring_cmd *ioucmd,
+			void (*driver_cb)(struct io_uring_cmd *))
+{
+	return -1;
+}
 static inline struct sock *io_uring_get_socket(struct file *file)
 {
 	return NULL;
-- 
2.25.1