io_uring: add support for IORING_OP_CLOSE

This works just like close(2), unsurprisingly. We remove the file
descriptor and post the completion inline, then offload the actual
(potential) last file put to async context.

Mark the async part of this work as uncancellable, as we really must
guarantee that the latter part of the close is run.
Signed-off-by: NJens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -301,6 +301,12 @@ struct io_poll_iocb {
 	struct wait_queue_entry		wait;
 };
 
+struct io_close {
+	struct file			*file;
+	struct file			*put_file;
+	int				fd;
+};
+
 struct io_timeout_data {
 	struct io_kiocb			*req;
 	struct hrtimer			timer;
@@ -414,6 +420,7 @@ struct io_kiocb {
 		struct io_connect	connect;
 		struct io_sr_msg	sr_msg;
 		struct io_open		open;
+		struct io_close		close;
 	};
 
 	struct io_async_ctx		*io;
@@ -2228,6 +2235,94 @@ static int io_openat(struct io_kiocb *req, struct io_kiocb **nxt,
 	return 0;
 }
 
+static int io_close_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
+{
+	/*
+	 * If we queue this for async, it must not be cancellable. That would
+	 * leave the 'file' in an undeterminate state.
+	 */
+	req->work.flags |= IO_WQ_WORK_NO_CANCEL;
+
+	if (sqe->ioprio || sqe->off || sqe->addr || sqe->len ||
+	    sqe->rw_flags || sqe->buf_index)
+		return -EINVAL;
+	if (sqe->flags & IOSQE_FIXED_FILE)
+		return -EINVAL;
+
+	req->close.fd = READ_ONCE(sqe->fd);
+	if (req->file->f_op == &io_uring_fops ||
+	    req->close.fd == req->ring_fd)
+		return -EBADF;
+
+	return 0;
+}
+
+static void io_close_finish(struct io_wq_work **workptr)
+{
+	struct io_kiocb *req = container_of(*workptr, struct io_kiocb, work);
+	struct io_kiocb *nxt = NULL;
+
+	/* Invoked with files, we need to do the close */
+	if (req->work.files) {
+		int ret;
+
+		ret = filp_close(req->close.put_file, req->work.files);
+		if (ret < 0) {
+			req_set_fail_links(req);
+		}
+		io_cqring_add_event(req, ret);
+	}
+
+	fput(req->close.put_file);
+
+	/* we bypassed the re-issue, drop the submission reference */
+	io_put_req(req);
+	io_put_req_find_next(req, &nxt);
+	if (nxt)
+		io_wq_assign_next(workptr, nxt);
+}
+
+static int io_close(struct io_kiocb *req, struct io_kiocb **nxt,
+		    bool force_nonblock)
+{
+	int ret;
+
+	req->close.put_file = NULL;
+	ret = __close_fd_get_file(req->close.fd, &req->close.put_file);
+	if (ret < 0)
+		return ret;
+
+	/* if the file has a flush method, be safe and punt to async */
+	if (req->close.put_file->f_op->flush && !io_wq_current_is_worker()) {
+		req->work.flags |= IO_WQ_WORK_NEEDS_FILES;
+		goto eagain;
+	}
+
+	/*
+	 * No ->flush(), safely close from here and just punt the
+	 * fput() to async context.
+	 */
+	ret = filp_close(req->close.put_file, current->files);
+
+	if (ret < 0)
+		req_set_fail_links(req);
+	io_cqring_add_event(req, ret);
+
+	if (io_wq_current_is_worker()) {
+		struct io_wq_work *old_work, *work;
+
+		old_work = work = &req->work;
+		io_close_finish(&work);
+		if (work && work != old_work)
+			*nxt = container_of(work, struct io_kiocb, work);
+		return 0;
+	}
+
+eagain:
+	req->work.func = io_close_finish;
+	return -EAGAIN;
+}
+
 static int io_prep_sfr(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 {
 	struct io_ring_ctx *ctx = req->ctx;
@@ -3256,6 +3351,9 @@ static int io_req_defer_prep(struct io_kiocb *req,
 	case IORING_OP_OPENAT:
 		ret = io_openat_prep(req, sqe);
 		break;
+	case IORING_OP_CLOSE:
+		ret = io_close_prep(req, sqe);
+		break;
 	default:
 		printk_once(KERN_WARNING "io_uring: unhandled opcode %d\n",
 				req->opcode);
@@ -3426,6 +3524,14 @@ static int io_issue_sqe(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 		}
 		ret = io_openat(req, nxt, force_nonblock);
 		break;
+	case IORING_OP_CLOSE:
+		if (sqe) {
+			ret = io_close_prep(req, sqe);
+			if (ret)
+				break;
+		}
+		ret = io_close(req, nxt, force_nonblock);
+		break;
 	default:
 		ret = -EINVAL;
 		break;
@@ -3572,6 +3678,9 @@ static int io_grab_files(struct io_kiocb *req)
 	int ret = -EBADF;
 	struct io_ring_ctx *ctx = req->ctx;
 
+	if (!req->ring_file)
+		return -EBADF;
+
 	rcu_read_lock();
 	spin_lock_irq(&ctx->inflight_lock);
 	/*

include/uapi/linux/io_uring.h

@@ -79,6 +79,7 @@ enum {
 	IORING_OP_CONNECT,
 	IORING_OP_FALLOCATE,
 	IORING_OP_OPENAT,
+	IORING_OP_CLOSE,
 
 	/* this goes last, obviously */
 	IORING_OP_LAST,