io_uring/zcrx: allow synchronous buffer return

Returning buffers via a ring is performant and convenient, but it
becomes a problem when/if the user misconfigured the ring size and it
becomes full. Add a synchronous way to return buffers back to the page
pool via a new register opcode. It's supposed to be a reliable slow
path for refilling.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 7 insertions, 0 deletions

diff --git a/io_uring/zcrx.h b/io_uring/zcrx.h
index a48871b5adad..33ef61503092 100644
--- a/io_uring/zcrx.h
+++ b/io_uring/zcrx.h
@@ -63,6 +63,8 @@ struct io_zcrx_ifq {
 };
 
 #if defined(CONFIG_IO_URING_ZCRX)
+int io_zcrx_return_bufs(struct io_ring_ctx *ctx,
+			void __user *arg, unsigned nr_arg);
 int io_register_zcrx_ifq(struct io_ring_ctx *ctx,
 			 struct io_uring_zcrx_ifq_reg __user *arg);
 void io_unregister_zcrx_ifqs(struct io_ring_ctx *ctx);
@@ -95,6 +97,11 @@ static inline struct io_mapped_region *io_zcrx_get_region(struct io_ring_ctx *ct
 {
 	return NULL;
 }
+static inline int io_zcrx_return_bufs(struct io_ring_ctx *ctx,
+				      void __user *arg, unsigned nr_arg)
+{
+	return -EOPNOTSUPP;
+}
 #endif
 
 int io_recvzc(struct io_kiocb *req, unsigned int issue_flags);