io_uring task work dispatch makes an indirect call to struct io_kiocb's
io_task_work.func field to allow running arbitrary task work functions.
In the uring_cmd case, this calls io_uring_cmd_work(), which immediately
makes another indirect call to struct io_uring_cmd's task_work_cb field.
Change the uring_cmd task work callbacks to functions whose signatures
match io_req_tw_func_t. Add a function io_uring_cmd_from_tw() to convert
from the task work's struct io_tw_req argument to struct io_uring_cmd *.
Define a constant IO_URING_CMD_TASK_WORK_ISSUE_FLAGS to avoid
manufacturing issue_flags in the uring_cmd task work callbacks. Now
uring_cmd task work dispatch makes a single indirect call to the
uring_cmd implementation's callback. This also allows removing the
task_work_cb field from struct io_uring_cmd, freeing up 8 bytes for
future storage.

Signed-off-by: Caleb Sander Mateos <csander@purestorage.com>
---
 block/ioctl.c                |  4 +++-
 drivers/block/ublk_drv.c     | 15 +++++++++------
 drivers/nvme/host/ioctl.c    |  5 +++--
 fs/btrfs/ioctl.c             |  4 +++-
 fs/fuse/dev_uring.c          |  5 +++--
 include/linux/io_uring/cmd.h | 22 +++++++++++++---------
 io_uring/uring_cmd.c         | 14 ++------------
 7 files changed, 36 insertions(+), 33 deletions(-)

diff --git a/block/ioctl.c b/block/ioctl.c
index d7489a56b33c..44de038660e7 100644
--- a/block/ioctl.c
+++ b/block/ioctl.c
@@ -767,12 +767,14 @@ long compat_blkdev_ioctl(struct file *file, unsigned cmd, unsigned long arg)
 struct blk_iou_cmd {
 	int res;
 	bool nowait;
 };
 
-static void blk_cmd_complete(struct io_uring_cmd *cmd, unsigned int issue_flags)
+static void blk_cmd_complete(struct io_tw_req tw_req, io_tw_token_t tw)
 {
+	unsigned int issue_flags = IO_URING_CMD_TASK_WORK_ISSUE_FLAGS;
+	struct io_uring_cmd *cmd = io_uring_cmd_from_tw(tw_req);
 	struct blk_iou_cmd *bic = io_uring_cmd_to_pdu(cmd, struct blk_iou_cmd);
 
 	if (bic->res == -EAGAIN && bic->nowait)
 		io_uring_cmd_issue_blocking(cmd);
 	else
diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
index 0c74a41a6753..bdccd15ba577 100644
--- a/drivers/block/ublk_drv.c
+++ b/drivers/block/ublk_drv.c
@@ -1346,13 +1346,14 @@ static void ublk_dispatch_req(struct ublk_queue *ubq,
 
 	if (ublk_prep_auto_buf_reg(ubq, req, io, issue_flags))
 		ublk_complete_io_cmd(io, req, UBLK_IO_RES_OK, issue_flags);
 }
 
-static void ublk_cmd_tw_cb(struct io_uring_cmd *cmd,
-			   unsigned int issue_flags)
+static void ublk_cmd_tw_cb(struct io_tw_req tw_req, io_tw_token_t tw)
 {
+	unsigned int issue_flags = IO_URING_CMD_TASK_WORK_ISSUE_FLAGS;
+	struct io_uring_cmd *cmd = io_uring_cmd_from_tw(tw_req);
 	struct ublk_uring_cmd_pdu *pdu = ublk_get_uring_cmd_pdu(cmd);
 	struct ublk_queue *ubq = pdu->ubq;
 
 	ublk_dispatch_req(ubq, pdu->req, issue_flags);
 }
@@ -1364,13 +1365,14 @@ static void ublk_queue_cmd(struct ublk_queue *ubq, struct request *rq)
 
 	pdu->req = rq;
 	io_uring_cmd_complete_in_task(cmd, ublk_cmd_tw_cb);
 }
 
-static void ublk_cmd_list_tw_cb(struct io_uring_cmd *cmd,
-		unsigned int issue_flags)
+static void ublk_cmd_list_tw_cb(struct io_tw_req tw_req, io_tw_token_t tw)
 {
+	unsigned int issue_flags = IO_URING_CMD_TASK_WORK_ISSUE_FLAGS;
+	struct io_uring_cmd *cmd = io_uring_cmd_from_tw(tw_req);
 	struct ublk_uring_cmd_pdu *pdu = ublk_get_uring_cmd_pdu(cmd);
 	struct request *rq = pdu->req_list;
 	struct request *next;
 
 	do {
@@ -2521,13 +2523,14 @@ static inline struct request *__ublk_check_and_get_req(struct ublk_device *ub,
 fail_put:
 	ublk_put_req_ref(io, req);
 	return NULL;
 }
 
-static void ublk_ch_uring_cmd_cb(struct io_uring_cmd *cmd,
-		unsigned int issue_flags)
+static void ublk_ch_uring_cmd_cb(struct io_tw_req tw_req, io_tw_token_t tw)
 {
+	unsigned int issue_flags = IO_URING_CMD_TASK_WORK_ISSUE_FLAGS;
+	struct io_uring_cmd *cmd = io_uring_cmd_from_tw(tw_req);
 	int ret = ublk_ch_uring_cmd_local(cmd, issue_flags);
 
 	if (ret != -EIOCBQUEUED)
 		io_uring_cmd_done(cmd, ret, issue_flags);
 }
diff --git a/drivers/nvme/host/ioctl.c b/drivers/nvme/host/ioctl.c
index c212fa952c0f..6a2a0ef29674 100644
--- a/drivers/nvme/host/ioctl.c
+++ b/drivers/nvme/host/ioctl.c
@@ -396,13 +396,14 @@ static inline struct nvme_uring_cmd_pdu *nvme_uring_cmd_pdu(
 		struct io_uring_cmd *ioucmd)
 {
 	return io_uring_cmd_to_pdu(ioucmd, struct nvme_uring_cmd_pdu);
 }
 
-static void nvme_uring_task_cb(struct io_uring_cmd *ioucmd,
-			       unsigned issue_flags)
+static void nvme_uring_task_cb(struct io_tw_req tw_req, io_tw_token_t tw)
 {
+	unsigned int issue_flags = IO_URING_CMD_TASK_WORK_ISSUE_FLAGS;
+	struct io_uring_cmd *ioucmd = io_uring_cmd_from_tw(tw_req);
 	struct nvme_uring_cmd_pdu *pdu = nvme_uring_cmd_pdu(ioucmd);
 
 	if (pdu->bio)
 		blk_rq_unmap_user(pdu->bio);
 	io_uring_cmd_done32(ioucmd, pdu->status, pdu->result, issue_flags);
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 185bef0df1c2..1936927ee6a4 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -4647,12 +4647,14 @@ struct btrfs_uring_priv {
 struct io_btrfs_cmd {
 	struct btrfs_uring_encoded_data *data;
 	struct btrfs_uring_priv *priv;
 };
 
-static void btrfs_uring_read_finished(struct io_uring_cmd *cmd, unsigned int issue_flags)
+static void btrfs_uring_read_finished(struct io_tw_req tw_req, io_tw_token_t tw)
 {
+	unsigned int issue_flags = IO_URING_CMD_TASK_WORK_ISSUE_FLAGS;
+	struct io_uring_cmd *cmd = io_uring_cmd_from_tw(tw_req);
 	struct io_btrfs_cmd *bc = io_uring_cmd_to_pdu(cmd, struct io_btrfs_cmd);
 	struct btrfs_uring_priv *priv = bc->priv;
 	struct btrfs_inode *inode = BTRFS_I(file_inode(priv->iocb.ki_filp));
 	struct extent_io_tree *io_tree = &inode->io_tree;
 	pgoff_t index;
diff --git a/fs/fuse/dev_uring.c b/fs/fuse/dev_uring.c
index 71b0c9662716..30923495e80f 100644
--- a/fs/fuse/dev_uring.c
+++ b/fs/fuse/dev_uring.c
@@ -1207,13 +1207,14 @@ static void fuse_uring_send(struct fuse_ring_ent *ent, struct io_uring_cmd *cmd,
 /*
  * This prepares and sends the ring request in fuse-uring task context.
  * User buffers are not mapped yet - the application does not have permission
  * to write to it - this has to be executed in ring task context.
  */
-static void fuse_uring_send_in_task(struct io_uring_cmd *cmd,
-				    unsigned int issue_flags)
+static void fuse_uring_send_in_task(struct io_tw_req tw_req, io_tw_token_t tw)
 {
+	unsigned int issue_flags = IO_URING_CMD_TASK_WORK_ISSUE_FLAGS;
+	struct io_uring_cmd *cmd = io_uring_cmd_from_tw(tw_req);
 	struct fuse_ring_ent *ent = uring_cmd_to_ring_ent(cmd);
 	struct fuse_ring_queue *queue = ent->queue;
 	int err;
 
 	if (!io_uring_cmd_should_terminate_tw(cmd)) {
diff --git a/include/linux/io_uring/cmd.h b/include/linux/io_uring/cmd.h
index b84b97c21b43..8e3322fb6fa5 100644
--- a/include/linux/io_uring/cmd.h
+++ b/include/linux/io_uring/cmd.h
@@ -9,21 +9,17 @@
 /* only top 8 bits of sqe->uring_cmd_flags for kernel internal use */
 #define IORING_URING_CMD_CANCELABLE	(1U << 30)
 /* io_uring_cmd is being issued again */
 #define IORING_URING_CMD_REISSUE	(1U << 31)
 
-typedef void (*io_uring_cmd_tw_t)(struct io_uring_cmd *cmd,
-				  unsigned issue_flags);
-
 struct io_uring_cmd {
 	struct file	*file;
 	const struct io_uring_sqe *sqe;
-	/* callback to defer completions to task context */
-	io_uring_cmd_tw_t task_work_cb;
 	u32		cmd_op;
 	u32		flags;
 	u8		pdu[32]; /* available inline for free use */
+	u8		unused[8];
 };
 
 static inline const void *io_uring_sqe_cmd(const struct io_uring_sqe *sqe)
 {
 	return sqe->cmd;
@@ -58,11 +54,11 @@ int io_uring_cmd_import_fixed_vec(struct io_uring_cmd *ioucmd,
  */
 void __io_uring_cmd_done(struct io_uring_cmd *cmd, s32 ret, u64 res2,
 			 unsigned issue_flags, bool is_cqe32);
 
 void __io_uring_cmd_do_in_task(struct io_uring_cmd *ioucmd,
-			    io_uring_cmd_tw_t task_work_cb,
+			    io_req_tw_func_t task_work_cb,
 			    unsigned flags);
 
 /*
  * Note: the caller should never hard code @issue_flags and only use the
  * mask provided by the core io_uring code.
@@ -107,11 +103,11 @@ static inline int io_uring_cmd_import_fixed_vec(struct io_uring_cmd *ioucmd,
 static inline void __io_uring_cmd_done(struct io_uring_cmd *cmd, s32 ret,
 		u64 ret2, unsigned issue_flags, bool is_cqe32)
 {
 }
 static inline void __io_uring_cmd_do_in_task(struct io_uring_cmd *ioucmd,
-			    io_uring_cmd_tw_t task_work_cb, unsigned flags)
+			    io_req_tw_func_t task_work_cb, unsigned flags)
 {
 }
 static inline void io_uring_cmd_mark_cancelable(struct io_uring_cmd *cmd,
 		unsigned int issue_flags)
 {
@@ -130,19 +126,27 @@ static inline bool io_uring_mshot_cmd_post_cqe(struct io_uring_cmd *ioucmd,
 {
 	return true;
 }
 #endif
 
+static inline struct io_uring_cmd *io_uring_cmd_from_tw(struct io_tw_req tw_req)
+{
+	return io_kiocb_to_cmd(tw_req.req, struct io_uring_cmd);
+}
+
+/* task_work executor checks the deferred list completion */
+#define IO_URING_CMD_TASK_WORK_ISSUE_FLAGS IO_URING_F_COMPLETE_DEFER
+
 /* users must follow the IOU_F_TWQ_LAZY_WAKE semantics */
 static inline void io_uring_cmd_do_in_task_lazy(struct io_uring_cmd *ioucmd,
-			io_uring_cmd_tw_t task_work_cb)
+			io_req_tw_func_t task_work_cb)
 {
 	__io_uring_cmd_do_in_task(ioucmd, task_work_cb, IOU_F_TWQ_LAZY_WAKE);
 }
 
 static inline void io_uring_cmd_complete_in_task(struct io_uring_cmd *ioucmd,
-			io_uring_cmd_tw_t task_work_cb)
+			io_req_tw_func_t task_work_cb)
 {
 	__io_uring_cmd_do_in_task(ioucmd, task_work_cb, 0);
 }
 
 static inline bool io_uring_cmd_should_terminate_tw(struct io_uring_cmd *cmd)
diff --git a/io_uring/uring_cmd.c b/io_uring/uring_cmd.c
index fc2955e8caaf..5a80d35658dc 100644
--- a/io_uring/uring_cmd.c
+++ b/io_uring/uring_cmd.c
@@ -111,30 +111,20 @@ void io_uring_cmd_mark_cancelable(struct io_uring_cmd *cmd,
 		io_ring_submit_unlock(ctx, issue_flags);
 	}
 }
 EXPORT_SYMBOL_GPL(io_uring_cmd_mark_cancelable);
 
-static void io_uring_cmd_work(struct io_tw_req tw_req, io_tw_token_t tw)
-{
-	struct io_kiocb *req = tw_req.req;
-	struct io_uring_cmd *ioucmd = io_kiocb_to_cmd(req, struct io_uring_cmd);
-
-	/* task_work executor checks the deffered list completion */
-	ioucmd->task_work_cb(ioucmd, IO_URING_F_COMPLETE_DEFER);
-}
-
 void __io_uring_cmd_do_in_task(struct io_uring_cmd *ioucmd,
-			io_uring_cmd_tw_t task_work_cb,
+			io_req_tw_func_t task_work_cb,
 			unsigned flags)
 {
 	struct io_kiocb *req = cmd_to_io_kiocb(ioucmd);
 
 	if (WARN_ON_ONCE(req->flags & REQ_F_APOLL_MULTISHOT))
 		return;
 
-	ioucmd->task_work_cb = task_work_cb;
-	req->io_task_work.func = io_uring_cmd_work;
+	req->io_task_work.func = task_work_cb;
 	__io_req_task_work_add(req, flags);
 }
 EXPORT_SYMBOL_GPL(__io_uring_cmd_do_in_task);
 
 static inline void io_req_set_cqe32_extra(struct io_kiocb *req,
-- 
2.45.2