[RFC PATCH v4 1/2] io_uring: add helpers for io_uring_cmd completion in submitter-task.

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

Completion of io_uring_cmd ioctl may involve referencing certain
ioctl-specefic fields, requiring original submitter-context.
Introduce two APIs for that purpose:
a. io_uring_cmd_complete_in_task
b. io_uring_cbh_to_io_uring_cmd

The APIs facilitate reusing task-work infra, while driver gets to
implement ioctl-specific handling in a callback.

Signed-off-by: Kanchan Joshi  <joshi.k@samsung.com>
Signed-off-by: Anuj Gupta <anuj20.g@samsung.com>
---
 fs/io_uring.c            | 23 +++++++++++++++++++++++
 include/linux/io_uring.h | 12 ++++++++++++
 2 files changed, 35 insertions(+)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index b6e1b6b51c5f..a8629c460bdd 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -2079,6 +2079,29 @@ static void io_req_task_submit(struct callback_head *cb)
 	__io_req_task_submit(req);
 }
 
+struct io_uring_cmd *io_uring_cbh_to_io_uring_cmd(struct callback_head *cb)
+{
+	return &container_of(cb, struct io_kiocb, task_work)->uring_cmd;
+}
+EXPORT_SYMBOL_GPL(io_uring_cbh_to_io_uring_cmd);
+
+int io_uring_cmd_complete_in_task(struct io_uring_cmd *ioucmd,
+			void (*driver_cb)(struct callback_head *))
+{
+	int ret;
+	struct io_kiocb *req = container_of(ioucmd, struct io_kiocb, uring_cmd);
+
+	req->task_work.func = driver_cb;
+	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(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 9956c0f5f9d0..526bc58dea25 100644
--- a/include/linux/io_uring.h
+++ b/include/linux/io_uring.h
@@ -19,6 +19,9 @@ struct io_uring_cmd {
 
 #if defined(CONFIG_IO_URING)
 void io_uring_cmd_done(struct io_uring_cmd *cmd, ssize_t ret);
+int io_uring_cmd_complete_in_task(struct io_uring_cmd *ioucmd,
+			void (*driver_cb)(struct callback_head *));
+struct io_uring_cmd *io_uring_cbh_to_io_uring_cmd(struct callback_head *cbh);
 struct sock *io_uring_get_socket(struct file *file);
 void __io_uring_task_cancel(void);
 void __io_uring_files_cancel(struct files_struct *files);
@@ -43,6 +46,15 @@ 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 io_uring_cmd_complete_in_task(struct io_uring_cmd *ioucmd,
+			void (*driver_cb)(struct callback_head *))
+{
+	return -1;
+}
+struct io_uring_cmd *io_uring_cbh_to_io_uring_cmd(struct callback_head *)
+{
+	return NULL;
+}
 static inline struct sock *io_uring_get_socket(struct file *file)
 {
 	return NULL;
-- 
2.25.1