[RFC PATCH v4 1/5] io_uring/cmd: introduce io_async_cmd for hide io_uring_cmd_data

[Sidong Yang <sidong.yang@furiosa.ai>]

io_uring_cmd_data should not be exposed for drivers to avoid to be
abused its private fields. io_async_cmd is new struct that has
io_uring_cmd_data for offset 0. So driver could be use async_data as
io_uring_cmd_data as used before. And private fields would be added in
io_async_cmd.

Signed-off-by: Sidong Yang <sidong.yang@furiosa.ai>
---
 io_uring/io_uring.c  |  2 +-
 io_uring/opdef.c     |  2 +-
 io_uring/uring_cmd.c | 21 ++++++++++++++-------
 io_uring/uring_cmd.h |  6 ++++++
 4 files changed, 22 insertions(+), 9 deletions(-)

diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 5ff30a7092ed..513f036bccbb 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -335,7 +335,7 @@ static __cold struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
 			    sizeof(struct io_async_rw),
 			    offsetof(struct io_async_rw, clear));
 	ret |= io_alloc_cache_init(&ctx->uring_cache, IO_ALLOC_CACHE_MAX,
-			    sizeof(struct io_uring_cmd_data), 0);
+			    sizeof(struct io_async_cmd), 0);
 	spin_lock_init(&ctx->msg_lock);
 	ret |= io_alloc_cache_init(&ctx->msg_cache, IO_ALLOC_CACHE_MAX,
 			    sizeof(struct io_kiocb), 0);
diff --git a/io_uring/opdef.c b/io_uring/opdef.c
index 7fd173197b1e..e4aa61a414fb 100644
--- a/io_uring/opdef.c
+++ b/io_uring/opdef.c
@@ -416,7 +416,7 @@ const struct io_issue_def io_issue_defs[] = {
 		.plug			= 1,
 		.iopoll			= 1,
 		.iopoll_queue		= 1,
-		.async_size		= sizeof(struct io_uring_cmd_data),
+		.async_size		= sizeof(struct io_async_cmd),
 		.prep			= io_uring_cmd_prep,
 		.issue			= io_uring_cmd,
 	},
diff --git a/io_uring/uring_cmd.c b/io_uring/uring_cmd.c
index de39b602aa82..e4cd6fe9fd47 100644
--- a/io_uring/uring_cmd.c
+++ b/io_uring/uring_cmd.c
@@ -19,7 +19,8 @@
 static void io_req_uring_cleanup(struct io_kiocb *req, unsigned int issue_flags)
 {
 	struct io_uring_cmd *ioucmd = io_kiocb_to_cmd(req, struct io_uring_cmd);
-	struct io_uring_cmd_data *cache = req->async_data;
+	struct io_async_cmd *ac = req->async_data;
+	struct io_uring_cmd_data *cache = &ac->data;
 
 	if (cache->op_data) {
 		kfree(cache->op_data);
@@ -169,12 +170,18 @@ static int io_uring_cmd_prep_setup(struct io_kiocb *req,
 				   const struct io_uring_sqe *sqe)
 {
 	struct io_uring_cmd *ioucmd = io_kiocb_to_cmd(req, struct io_uring_cmd);
-	struct io_uring_cmd_data *cache;
+	struct io_async_cmd *ac;
 
-	cache = io_uring_alloc_async_data(&req->ctx->uring_cache, req);
-	if (!cache)
+	/*
+	 * 'data' must be at offset 0 to allow casting io_async_cmd to
+	 * io_uring_cmd_data in io_uring_cmd_get_async_data().
+	 */
+	BUILD_BUG_ON(offsetof(struct io_async_cmd, data) != 0);
+
+	ac = io_uring_alloc_async_data(&req->ctx->uring_cache, req);
+	if (!ac)
 		return -ENOMEM;
-	cache->op_data = NULL;
+	ac->data.op_data = NULL;
 
 	/*
 	 * Unconditionally cache the SQE for now - this is only needed for
@@ -183,8 +190,8 @@ static int io_uring_cmd_prep_setup(struct io_kiocb *req,
 	 * that it doesn't read in per-op data, play it safe and ensure that
 	 * any SQE data is stable beyond prep. This can later get relaxed.
 	 */
-	memcpy(cache->sqes, sqe, uring_sqe_size(req->ctx));
-	ioucmd->sqe = cache->sqes;
+	memcpy(ac->data.sqes, sqe, uring_sqe_size(req->ctx));
+	ioucmd->sqe = ac->data.sqes;
 	return 0;
 }
 
diff --git a/io_uring/uring_cmd.h b/io_uring/uring_cmd.h
index f6837ee0955b..f3593012658c 100644
--- a/io_uring/uring_cmd.h
+++ b/io_uring/uring_cmd.h
@@ -1,5 +1,11 @@
 // SPDX-License-Identifier: GPL-2.0
 
+#include <linux/io_uring/cmd.h>
+
+struct io_async_cmd {
+	struct io_uring_cmd_data data;
+};
+
 int io_uring_cmd(struct io_kiocb *req, unsigned int issue_flags);
 int io_uring_cmd_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe);
 
-- 
2.43.0