ARM: 9480/1: entry: expand comment in __switch_tografted

As per discussion between the developers in the mail thread
linked, expand the comment in __switch_to so that readers
of the code understand what is going on.

Suggested-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Linus Walleij <linusw@kernel.org>>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>

1 files changed, 92 insertions, 0 deletions

diff --git a/io_uring/epoll.c b/io_uring/epoll.c
new file mode 100644
index 000000000..8d4610246
--- /dev/null
+++ b/io_uring/epoll.c
@@ -0,0 +1,92 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/file.h>
+#include <linux/fs.h>
+#include <linux/uaccess.h>
+#include <linux/io_uring.h>
+#include <linux/eventpoll.h>
+
+#include <uapi/linux/io_uring.h>
+
+#include "io_uring.h"
+#include "epoll.h"
+
+struct io_epoll {
+	struct file			*file;
+	int				epfd;
+	int				op;
+	int				fd;
+	struct epoll_event		event;
+};
+
+struct io_epoll_wait {
+	struct file			*file;
+	int				maxevents;
+	struct epoll_event __user	*events;
+};
+
+int io_epoll_ctl_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
+{
+	struct io_epoll *epoll = io_kiocb_to_cmd(req, struct io_epoll);
+
+	if (sqe->buf_index || sqe->splice_fd_in)
+		return -EINVAL;
+
+	epoll->epfd = READ_ONCE(sqe->fd);
+	epoll->op = READ_ONCE(sqe->len);
+	epoll->fd = READ_ONCE(sqe->off);
+
+	if (ep_op_has_event(epoll->op)) {
+		struct epoll_event __user *ev;
+
+		ev = u64_to_user_ptr(READ_ONCE(sqe->addr));
+		if (copy_from_user(&epoll->event, ev, sizeof(*ev)))
+			return -EFAULT;
+	}
+
+	return 0;
+}
+
+int io_epoll_ctl(struct io_kiocb *req, unsigned int issue_flags)
+{
+	struct io_epoll *ie = io_kiocb_to_cmd(req, struct io_epoll);
+	int ret;
+	bool force_nonblock = issue_flags & IO_URING_F_NONBLOCK;
+
+	ret = do_epoll_ctl(ie->epfd, ie->op, ie->fd, &ie->event, force_nonblock);
+	if (force_nonblock && ret == -EAGAIN)
+		return -EAGAIN;
+
+	if (ret < 0)
+		req_set_fail(req);
+	io_req_set_res(req, ret, 0);
+	return IOU_COMPLETE;
+}
+
+int io_epoll_wait_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
+{
+	struct io_epoll_wait *iew = io_kiocb_to_cmd(req, struct io_epoll_wait);
+
+	if (sqe->off || sqe->rw_flags || sqe->buf_index || sqe->splice_fd_in)
+		return -EINVAL;
+
+	iew->maxevents = READ_ONCE(sqe->len);
+	iew->events = u64_to_user_ptr(READ_ONCE(sqe->addr));
+	return 0;
+}
+
+int io_epoll_wait(struct io_kiocb *req, unsigned int issue_flags)
+{
+	struct io_epoll_wait *iew = io_kiocb_to_cmd(req, struct io_epoll_wait);
+	int ret;
+
+	ret = epoll_sendevents(req->file, iew->events, iew->maxevents);
+	if (ret == 0)
+		return -EAGAIN;
+	if (ret < 0)
+		req_set_fail(req);
+
+	io_req_set_res(req, ret, 0);
+	return IOU_COMPLETE;
+}