io_uring/net: remove dependency on REQ_F_PARTIAL_IO for sr->done_io

Ensure that prep handlers always initialize sr->done_io before any
potential failure conditions, and with that, we now it's always been
set even for the failure case.

With that, we don't need to use the REQ_F_PARTIAL_IO flag to gate on that.
Additionally, we should not overwrite req->cqe.res unless sr->done_io is
actually positive.
Signed-off-by: Jens Axboe <axboe@kernel.dk>

io_uring/net.c

@@ -387,6 +387,8 @@ int io_sendmsg_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 {
 	struct io_sr_msg *sr = io_kiocb_to_cmd(req, struct io_sr_msg);
 
+	sr->done_io = 0;
+
 	if (req->opcode == IORING_OP_SEND) {
 		if (READ_ONCE(sqe->__pad3[0]))
 			return -EINVAL;
@@ -409,7 +411,6 @@ int io_sendmsg_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 	if (req->ctx->compat)
 		sr->msg_flags |= MSG_CMSG_COMPAT;
 #endif
-	sr->done_io = 0;
 	return 0;
 }
 
@@ -631,6 +632,8 @@ int io_recvmsg_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 {
 	struct io_sr_msg *sr = io_kiocb_to_cmd(req, struct io_sr_msg);
 
+	sr->done_io = 0;
+
 	if (unlikely(sqe->file_index || sqe->addr2))
 		return -EINVAL;
 
@@ -667,7 +670,6 @@ int io_recvmsg_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 	if (req->ctx->compat)
 		sr->msg_flags |= MSG_CMSG_COMPAT;
 #endif
-	sr->done_io = 0;
 	sr->nr_multishot_loops = 0;
 	return 0;
 }
@@ -1055,6 +1057,8 @@ int io_send_zc_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 	struct io_ring_ctx *ctx = req->ctx;
 	struct io_kiocb *notif;
 
+	zc->done_io = 0;
+
 	if (unlikely(READ_ONCE(sqe->__pad2[0]) || READ_ONCE(sqe->addr3)))
 		return -EINVAL;
 	/* we don't support IOSQE_CQE_SKIP_SUCCESS just yet */
@@ -1107,8 +1111,6 @@ int io_send_zc_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 	if (zc->msg_flags & MSG_DONTWAIT)
 		req->flags |= REQ_F_NOWAIT;
 
-	zc->done_io = 0;
-
 #ifdef CONFIG_COMPAT
 	if (req->ctx->compat)
 		zc->msg_flags |= MSG_CMSG_COMPAT;
@@ -1353,7 +1355,7 @@ void io_sendrecv_fail(struct io_kiocb *req)
 {
 	struct io_sr_msg *sr = io_kiocb_to_cmd(req, struct io_sr_msg);
 
-	if (req->flags & REQ_F_PARTIAL_IO)
+	if (sr->done_io)
 		req->cqe.res = sr->done_io;
 
 	if ((req->flags & REQ_F_NEED_CLEANUP) &&