Re: [PATCHv7 1/6] io_uring/rw: move fixed buffer import to issue path

[Jens Axboe <axboe@kernel.dk>]

On 2/26/25 11:20 AM, Keith Busch wrote:
> From: Keith Busch <kbusch@kernel.org>
> 
> Registered buffers may depend on a linked command, which makes the prep
> path too early to import. Move to the issue path when the node is
> actually needed like all the other users of fixed buffers.

Conceptually I think this patch is fine, but it does bother me with
random bool arguments. We could fold in something like the (totally
tested) below diff to get rid of that. What do you think?

diff --git a/io_uring/rw.c b/io_uring/rw.c
index 728d695d2552..a8a46a32f20d 100644
--- a/io_uring/rw.c
+++ b/io_uring/rw.c
@@ -248,8 +248,8 @@ static int io_prep_rw_pi(struct io_kiocb *req, struct io_rw *rw, int ddir,
 	return ret;
 }
 
-static int io_prep_rw(struct io_kiocb *req, const struct io_uring_sqe *sqe,
-		      int ddir, bool do_import)
+static int __io_prep_rw(struct io_kiocb *req, const struct io_uring_sqe *sqe,
+			int ddir)
 {
 	struct io_rw *rw = io_kiocb_to_cmd(req, struct io_rw);
 	unsigned ioprio;
@@ -285,14 +285,6 @@ static int io_prep_rw(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 	rw->len = READ_ONCE(sqe->len);
 	rw->flags = READ_ONCE(sqe->rw_flags);
 
-	if (do_import && !io_do_buffer_select(req)) {
-		struct io_async_rw *io = req->async_data;
-
-		ret = io_import_rw_buffer(ddir, req, io, 0);
-		if (unlikely(ret))
-			return ret;
-	}
-
 	attr_type_mask = READ_ONCE(sqe->attr_type_mask);
 	if (attr_type_mask) {
 		u64 attr_ptr;
@@ -307,27 +299,52 @@ static int io_prep_rw(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 	return ret;
 }
 
+static int io_rw_do_import(struct io_kiocb *req, int ddir)
+{
+	if (!io_do_buffer_select(req)) {
+		struct io_async_rw *io = req->async_data;
+		int ret;
+
+		ret = io_import_rw_buffer(ddir, req, io, 0);
+		if (unlikely(ret))
+			return ret;
+	}
+
+	return 0;
+}
+
+static int io_prep_rw(struct io_kiocb *req, const struct io_uring_sqe *sqe,
+		      int ddir)
+{
+	int ret;
+
+	ret = __io_prep_rw(req, sqe, ddir);
+	if (unlikely(ret))
+		return ret;
+
+	return io_rw_do_import(req, ITER_DEST);
+}
+
 int io_prep_read(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 {
-	return io_prep_rw(req, sqe, ITER_DEST, true);
+	return io_prep_rw(req, sqe, ITER_DEST);
 }
 
 int io_prep_write(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 {
-	return io_prep_rw(req, sqe, ITER_SOURCE, true);
+	return io_prep_rw(req, sqe, ITER_SOURCE);
 }
 
 static int io_prep_rwv(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 		       int ddir)
 {
-	const bool do_import = !(req->flags & REQ_F_BUFFER_SELECT);
 	int ret;
 
-	ret = io_prep_rw(req, sqe, ddir, do_import);
+	ret = io_prep_rw(req, sqe, ddir);
 	if (unlikely(ret))
 		return ret;
-	if (do_import)
-		return 0;
+	if (!(req->flags & REQ_F_BUFFER_SELECT))
+		return io_rw_do_import(req, ddir);
 
 	/*
 	 * Have to do this validation here, as this is in io_read() rw->len
@@ -364,12 +381,12 @@ static int io_init_rw_fixed(struct io_kiocb *req, unsigned int issue_flags,
 
 int io_prep_read_fixed(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 {
-	return io_prep_rw(req, sqe, ITER_DEST, false);
+	return io_prep_rw(req, sqe, ITER_DEST);
 }
 
 int io_prep_write_fixed(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 {
-	return io_prep_rw(req, sqe, ITER_SOURCE, false);
+	return io_prep_rw(req, sqe, ITER_SOURCE);
 }
 
 /*
@@ -385,7 +402,7 @@ int io_read_mshot_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 	if (!(req->flags & REQ_F_BUFFER_SELECT))
 		return -EINVAL;
 
-	ret = io_prep_rw(req, sqe, ITER_DEST, false);
+	ret = io_prep_rw(req, sqe, ITER_DEST);
 	if (unlikely(ret))
 		return ret;
 

-- 
Jens Axboe