io_uring: buffer registration infrastructure

This just prepares the ring for having lists of buffers associated with
it, that the application can provide for SQEs to consume instead of
providing their own.

The buffers are organized by group ID.
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -195,6 +195,13 @@ struct fixed_file_data {
 	struct completion		done;
 };
 
+struct io_buffer {
+	struct list_head list;
+	__u64 addr;
+	__s32 len;
+	__u16 bid;
+};
+
 struct io_ring_ctx {
 	struct {
 		struct percpu_ref	refs;
@@ -272,6 +279,8 @@ struct io_ring_ctx {
 	struct socket		*ring_sock;
 #endif
 
+	struct idr		io_buffer_idr;
+
 	struct idr		personality_idr;
 
 	struct {
@@ -875,6 +884,7 @@ static struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
 	INIT_LIST_HEAD(&ctx->cq_overflow_list);
 	init_completion(&ctx->completions[0]);
 	init_completion(&ctx->completions[1]);
+	idr_init(&ctx->io_buffer_idr);
 	idr_init(&ctx->personality_idr);
 	mutex_init(&ctx->uring_lock);
 	init_waitqueue_head(&ctx->wait);
@@ -6524,6 +6534,30 @@ static int io_eventfd_unregister(struct io_ring_ctx *ctx)
 	return -ENXIO;
 }
 
+static int __io_destroy_buffers(int id, void *p, void *data)
+{
+	struct io_ring_ctx *ctx = data;
+	struct io_buffer *buf = p;
+
+	/* the head kbuf is the list itself */
+	while (!list_empty(&buf->list)) {
+		struct io_buffer *nxt;
+
+		nxt = list_first_entry(&buf->list, struct io_buffer, list);
+		list_del(&nxt->list);
+		kfree(nxt);
+	}
+	kfree(buf);
+	idr_remove(&ctx->io_buffer_idr, id);
+	return 0;
+}
+
+static void io_destroy_buffers(struct io_ring_ctx *ctx)
+{
+	idr_for_each(&ctx->io_buffer_idr, __io_destroy_buffers, ctx);
+	idr_destroy(&ctx->io_buffer_idr);
+}
+
 static void io_ring_ctx_free(struct io_ring_ctx *ctx)
 {
 	io_finish_async(ctx);
@@ -6534,6 +6568,7 @@ static void io_ring_ctx_free(struct io_ring_ctx *ctx)
 	io_sqe_buffer_unregister(ctx);
 	io_sqe_files_unregister(ctx);
 	io_eventfd_unregister(ctx);
+	io_destroy_buffers(ctx);
 	idr_destroy(&ctx->personality_idr);
 
 #if defined(CONFIG_UNIX)