io_uring/net: simplify zerocopy send user API

Following user feedback, this patch simplifies zerocopy send API. One of
the main complaints is that the current API is difficult with the
userspace managing notification slots, and then send retries with error
handling make it even worse.

Instead of keeping notification slots change it to the per-request
notifications model, which posts both completion and notification CQEs
for each request when any data has been sent, and only one CQE if it
fails. All notification CQEs will have IORING_CQE_F_NOTIF set and
IORING_CQE_F_MORE in completion CQEs indicates whether to wait a
notification or not.

IOSQE_CQE_SKIP_SUCCESS is disallowed with zerocopy sends for now.

This is less flexible, but greatly simplifies the user API and also the
kernel implementation. We reuse notif helpers in this patch, but in the
future there won't be need for keeping two requests.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/95287640ab98fc9417370afb16e310677c63e6ce.1662027856.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 2 insertions, 10 deletions

diff --git a/io_uring/notif.c b/io_uring/notif.c
index 11f45640684a..38d77165edc3 100644
--- a/io_uring/notif.c
+++ b/io_uring/notif.c
@@ -42,8 +42,7 @@ static void io_uring_tx_zerocopy_callback(struct sk_buff *skb,
 	}
 }
 
-struct io_kiocb *io_alloc_notif(struct io_ring_ctx *ctx,
-				struct io_notif_slot *slot)
+struct io_kiocb *io_alloc_notif(struct io_ring_ctx *ctx)
 	__must_hold(&ctx->uring_lock)
 {
 	struct io_kiocb *notif;
@@ -59,27 +58,20 @@ struct io_kiocb *io_alloc_notif(struct io_ring_ctx *ctx,
 	io_get_task_refs(1);
 	notif->rsrc_node = NULL;
 	io_req_set_rsrc_node(notif, ctx, 0);
-	notif->cqe.user_data = slot->tag;
-	notif->cqe.flags = slot->seq++;
-	notif->cqe.res = 0;
 
 	nd = io_notif_to_data(notif);
 	nd->account_pages = 0;
 	nd->uarg.flags = SKBFL_ZEROCOPY_FRAG | SKBFL_DONT_ORPHAN;
 	nd->uarg.callback = io_uring_tx_zerocopy_callback;
-	/* master ref owned by io_notif_slot, will be dropped on flush */
 	refcount_set(&nd->uarg.refcnt, 1);
 	return notif;
 }
 
-void io_notif_slot_flush(struct io_notif_slot *slot)
+void io_notif_flush(struct io_kiocb *notif)
 	__must_hold(&slot->notif->ctx->uring_lock)
 {
-	struct io_kiocb *notif = slot->notif;
 	struct io_notif_data *nd = io_notif_to_data(notif);
 
-	slot->notif = NULL;
-
 	/* drop slot's master ref */
 	if (refcount_dec_and_test(&nd->uarg.refcnt)) {
 		notif->io_task_work.func = __io_notif_complete_tw;