Introduces the basic structure for a batched I/O feature in the ublk driver.
It adds placeholder functions and a new file operations structure,
ublk_ch_batch_io_fops, which will be used for fetching and committing I/O
commands in batches. Currently, the feature is disabled.

Reviewed-by: Caleb Sander Mateos <csander@purestorage.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 drivers/block/ublk_drv.c | 26 +++++++++++++++++++++++++-
 1 file changed, 25 insertions(+), 1 deletion(-)

diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
index dd9c35758a46..1fcca52591c3 100644
--- a/drivers/block/ublk_drv.c
+++ b/drivers/block/ublk_drv.c
@@ -254,6 +254,11 @@ static inline struct request *__ublk_check_and_get_req(struct ublk_device *ub,
 		u16 q_id, u16 tag, struct ublk_io *io, size_t offset);
 static inline unsigned int ublk_req_build_flags(struct request *req);
 
+static inline bool ublk_dev_support_batch_io(const struct ublk_device *ub)
+{
+	return false;
+}
+
 static inline struct ublksrv_io_desc *
 ublk_get_iod(const struct ublk_queue *ubq, unsigned tag)
 {
@@ -2512,6 +2517,12 @@ static int ublk_ch_uring_cmd(struct io_uring_cmd *cmd, unsigned int issue_flags)
 	return ublk_ch_uring_cmd_local(cmd, issue_flags);
 }
 
+static int ublk_ch_batch_io_uring_cmd(struct io_uring_cmd *cmd,
+				       unsigned int issue_flags)
+{
+	return -EOPNOTSUPP;
+}
+
 static inline bool ublk_check_ubuf_dir(const struct request *req,
 		int ubuf_dir)
 {
@@ -2618,6 +2629,16 @@ static const struct file_operations ublk_ch_fops = {
 	.mmap = ublk_ch_mmap,
 };
 
+static const struct file_operations ublk_ch_batch_io_fops = {
+	.owner = THIS_MODULE,
+	.open = ublk_ch_open,
+	.release = ublk_ch_release,
+	.read_iter = ublk_ch_read_iter,
+	.write_iter = ublk_ch_write_iter,
+	.uring_cmd = ublk_ch_batch_io_uring_cmd,
+	.mmap = ublk_ch_mmap,
+};
+
 static void ublk_deinit_queue(struct ublk_device *ub, int q_id)
 {
 	struct ublk_queue *ubq = ub->queues[q_id];
@@ -2778,7 +2799,10 @@ static int ublk_add_chdev(struct ublk_device *ub)
 	if (ret)
 		goto fail;
 
-	cdev_init(&ub->cdev, &ublk_ch_fops);
+	if (ublk_dev_support_batch_io(ub))
+		cdev_init(&ub->cdev, &ublk_ch_batch_io_fops);
+	else
+		cdev_init(&ub->cdev, &ublk_ch_fops);
 	ret = cdev_device_add(&ub->cdev, dev);
 	if (ret)
 		goto fail;
-- 
2.47.0