io_uring: introduce io_prep_reg_iovec()

iovecs that are turned into registered buffers are imported in a special
way with an offset, so that later we can do an in place translation. Add
a helper function taking care of it.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/7de2ecb9ed5efc3c5cf320232236966da5ad4ccc.1741457480.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: isilence

io_uring/net.c

@@ -403,9 +403,7 @@ static int io_sendmsg_zc_setup(struct io_kiocb *req, const struct io_uring_sqe *
 	struct io_sr_msg *sr = io_kiocb_to_cmd(req, struct io_sr_msg);
 	struct io_async_msghdr *kmsg = req->async_data;
 	struct user_msghdr msg;
-	int ret, iovec_off;
-	struct iovec *iov;
-	void *res;
+	int ret;
 
 	if (!(sr->flags & IORING_RECVSEND_FIXED_BUF))
 		return io_sendmsg_setup(req, sqe);
@@ -416,24 +414,9 @@ static int io_sendmsg_zc_setup(struct io_kiocb *req, const struct io_uring_sqe *
 	if (unlikely(ret))
 		return ret;
 	sr->msg_control = kmsg->msg.msg_control_user;
-
-	if (msg.msg_iovlen > kmsg->vec.nr || WARN_ON_ONCE(!kmsg->vec.iovec)) {
-		ret = io_vec_realloc(&kmsg->vec, msg.msg_iovlen);
-		if (ret)
-			return ret;
-		req->flags |= REQ_F_NEED_CLEANUP;
-	}
-	iovec_off = kmsg->vec.nr - msg.msg_iovlen;
-	iov = kmsg->vec.iovec + iovec_off;
-
-	res = iovec_from_user(msg.msg_iov, msg.msg_iovlen, kmsg->vec.nr, iov,
-			      io_is_compat(req->ctx));
-	if (IS_ERR(res))
-		return PTR_ERR(res);
-
 	kmsg->msg.msg_iter.nr_segs = msg.msg_iovlen;
-	req->flags |= REQ_F_IMPORT_BUFFER;
-	return ret;
+
+	return io_prep_reg_iovec(req, &kmsg->vec, msg.msg_iov, msg.msg_iovlen);
 }
 
 #define SENDMSG_FLAGS (IORING_RECVSEND_POLL_FIRST | IORING_RECVSEND_BUNDLE)

io_uring/rsrc.c

@@ -1397,3 +1397,29 @@ int io_import_reg_vec(int ddir, struct iov_iter *iter,
 
 	return io_vec_fill_bvec(ddir, iter, imu, iov, nr_iovs, vec);
 }
+
+int io_prep_reg_iovec(struct io_kiocb *req, struct iou_vec *iv,
+		      const struct iovec __user *uvec, size_t uvec_segs)
+{
+	struct iovec *iov;
+	int iovec_off, ret;
+	void *res;
+
+	if (uvec_segs > iv->nr) {
+		ret = io_vec_realloc(iv, uvec_segs);
+		if (ret)
+			return ret;
+		req->flags |= REQ_F_NEED_CLEANUP;
+	}
+
+	/* pad iovec to the right */
+	iovec_off = iv->nr - uvec_segs;
+	iov = iv->iovec + iovec_off;
+	res = iovec_from_user(uvec, uvec_segs, uvec_segs, iov,
+			      io_is_compat(req->ctx));
+	if (IS_ERR(res))
+		return PTR_ERR(res);
+
+	req->flags |= REQ_F_IMPORT_BUFFER;
+	return 0;
+}

io_uring/rsrc.h

@@ -67,6 +67,8 @@ int io_import_reg_vec(int ddir, struct iov_iter *iter,
 			struct io_kiocb *req, struct iou_vec *vec,
 			unsigned nr_iovs, unsigned iovec_off,
 			unsigned issue_flags);
+int io_prep_reg_iovec(struct io_kiocb *req, struct iou_vec *iv,
+			const struct iovec __user *uvec, size_t uvec_segs);
 
 int io_register_clone_buffers(struct io_ring_ctx *ctx, void __user *arg);
 int io_sqe_buffers_unregister(struct io_ring_ctx *ctx);

io_uring/rw.c

@@ -407,28 +407,9 @@ static int io_rw_prep_reg_vec(struct io_kiocb *req)
 	struct io_rw *rw = io_kiocb_to_cmd(req, struct io_rw);
 	struct io_async_rw *io = req->async_data;
 	const struct iovec __user *uvec;
-	size_t uvec_segs = rw->len;
-	struct iovec *iov;
-	int iovec_off, ret;
-	void *res;
 
-	if (uvec_segs > io->vec.nr) {
-		ret = io_vec_realloc(&io->vec, uvec_segs);
-		if (ret)
-			return ret;
-		req->flags |= REQ_F_NEED_CLEANUP;
-	}
-	/* pad iovec to the right */
-	iovec_off = io->vec.nr - uvec_segs;
-	iov = io->vec.iovec + iovec_off;
 	uvec = u64_to_user_ptr(rw->addr);
-	res = iovec_from_user(uvec, uvec_segs, uvec_segs, iov,
-			      io_is_compat(req->ctx));
-	if (IS_ERR(res))
-		return PTR_ERR(res);
-
-	req->flags |= REQ_F_IMPORT_BUFFER;
-	return 0;
+	return io_prep_reg_iovec(req, &io->vec, uvec, rw->len);
 }
 
 int io_prep_readv_fixed(struct io_kiocb *req, const struct io_uring_sqe *sqe)