io_uring: add zc notification infrastructure

Add internal part of send zerocopy notifications. There are two main
structures, the first one is struct io_notif, which carries inside
struct ubuf_info and maps 1:1 to it. io_uring will be binding a number
of zerocopy send requests to it and ask to complete (aka flush) it. When
flushed and all attached requests and skbs complete, it'll generate one
and only one CQE. There are intended to be passed into the network layer
as struct msghdr::msg_ubuf.

The second concept is notification slots. The userspace will be able to
register an array of slots and subsequently addressing them by the index
in the array. Slots are independent of each other. Each slot can have
only one notifier at a time (called active notifier) but many notifiers
during the lifetime. When active, a notifier not going to post any
completion but the userspace can attach requests to it by specifying
the corresponding slot while issueing send zc requests. Eventually, the
userspace will want to "flush" the notifier losing any way to attach
new requests to it, however it can use the next atomatically added
notifier of this slot or of any other slot.

When the network layer is done with all enqueued skbs attached to a
notifier and doesn't need the specified in them user data, the flushed
notifier will post a CQE.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/3ecf54c31a85762bf679b0a432c9f43ecf7e61cc.1657643355.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 5 insertions, 0 deletions

diff --git a/include/linux/io_uring_types.h b/include/linux/io_uring_types.h
index 368c34d14b13..f7fab3758cb9 100644
--- a/include/linux/io_uring_types.h
+++ b/include/linux/io_uring_types.h
@@ -34,6 +34,9 @@ struct io_file_table {
 	unsigned int alloc_hint;
 };
 
+struct io_notif;
+struct io_notif_slot;
+
 struct io_hash_bucket {
 	spinlock_t		lock;
 	struct hlist_head	list;
@@ -237,6 +240,8 @@ struct io_ring_ctx {
 		unsigned		nr_user_files;
 		unsigned		nr_user_bufs;
 		struct io_mapped_ubuf	**user_bufs;
+		struct io_notif_slot	*notif_slots;
+		unsigned		nr_notif_slots;
 
 		struct io_submit_state	submit_state;