[RFC v2 10/19] io_uring: add send notifiers registration

[Pavel Begunkov <asml.silence@gmail.com>]

Add IORING_REGISTER_TX_CTX and IORING_UNREGISTER_TX_CTX. Transmission
(i.e. send) context will serve be used to notify the userspace when
fixed buffers used for zerocopy sends are released by the kernel.

Notification of a single tx context lives in generations, where each
generation posts one CQE with ->user_data equal to the specified tag and
->res is a generation number starting from 0. All requests issued
against a ctx will get attached to the current generation of
notifications. Then, the userspace will be able to request to flush the
notification allowing it to post a CQE when all buffers of all requests
attached to it are released by the kernel. It'll also switch the
generation to a new one with a sequence number incremented by one.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 fs/io_uring.c                 | 72 +++++++++++++++++++++++++++++++++++
 include/uapi/linux/io_uring.h |  7 ++++
 2 files changed, 79 insertions(+)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 59380e3454ad..a01f91e70fa5 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -94,6 +94,8 @@
 #define IORING_MAX_CQ_ENTRIES	(2 * IORING_MAX_ENTRIES)
 #define IORING_SQPOLL_CAP_ENTRIES_VALUE 8
 
+#define IORING_MAX_TX_NOTIFIERS	(1U << 10)
+
 /* only define max */
 #define IORING_MAX_FIXED_FILES	(1U << 15)
 #define IORING_MAX_RESTRICTIONS	(IORING_RESTRICTION_LAST + \
@@ -326,6 +328,15 @@ struct io_submit_state {
 	struct blk_plug		plug;
 };
 
+struct io_tx_notifier {
+};
+
+struct io_tx_ctx {
+	struct io_tx_notifier	*notifier;
+	u64			tag;
+	u32			seq;
+};
+
 struct io_ring_ctx {
 	/* const or read-mostly hot data */
 	struct {
@@ -373,6 +384,8 @@ struct io_ring_ctx {
 		unsigned		nr_user_files;
 		unsigned		nr_user_bufs;
 		struct io_mapped_ubuf	**user_bufs;
+		struct io_tx_ctx	*tx_ctxs;
+		unsigned		nr_tx_ctxs;
 
 		struct io_submit_state	submit_state;
 		struct list_head	timeout_list;
@@ -9199,6 +9212,55 @@ static int io_buffer_validate(struct iovec *iov)
 	return 0;
 }
 
+static int io_sqe_tx_ctx_unregister(struct io_ring_ctx *ctx)
+{
+	if (!ctx->nr_tx_ctxs)
+		return -ENXIO;
+
+	kvfree(ctx->tx_ctxs);
+	ctx->tx_ctxs = NULL;
+	ctx->nr_tx_ctxs = 0;
+	return 0;
+}
+
+static int io_sqe_tx_ctx_register(struct io_ring_ctx *ctx,
+				  void __user *arg, unsigned int nr_args)
+{
+	struct io_uring_tx_ctx_register __user *tx_args = arg;
+	struct io_uring_tx_ctx_register tx_arg;
+	unsigned i;
+	int ret;
+
+	if (ctx->nr_tx_ctxs)
+		return -EBUSY;
+	if (!nr_args)
+		return -EINVAL;
+	if (nr_args > IORING_MAX_TX_NOTIFIERS)
+		return -EMFILE;
+
+	ctx->tx_ctxs = kvcalloc(nr_args, sizeof(ctx->tx_ctxs[0]),
+				GFP_KERNEL_ACCOUNT);
+	if (!ctx->tx_ctxs)
+		return -ENOMEM;
+
+	for (i = 0; i < nr_args; i++, ctx->nr_tx_ctxs++) {
+		struct io_tx_ctx *tx_ctx = &ctx->tx_ctxs[i];
+
+		if (copy_from_user(&tx_arg, &tx_args[i], sizeof(tx_arg))) {
+			ret = -EFAULT;
+			goto out_fput;
+		}
+		tx_ctx->tag = tx_arg.tag;
+	}
+	return 0;
+
+out_fput:
+	kvfree(ctx->tx_ctxs);
+	ctx->tx_ctxs = NULL;
+	ctx->nr_tx_ctxs = 0;
+	return ret;
+}
+
 static int io_sqe_buffers_register(struct io_ring_ctx *ctx, void __user *arg,
 				   unsigned int nr_args, u64 __user *tags)
 {
@@ -9429,6 +9491,7 @@ static __cold void io_ring_ctx_free(struct io_ring_ctx *ctx)
 #endif
 	WARN_ON_ONCE(!list_empty(&ctx->ltimeout_list));
 
+	io_sqe_tx_ctx_unregister(ctx);
 	io_mem_free(ctx->rings);
 	io_mem_free(ctx->sq_sqes);
 
@@ -11104,6 +11167,15 @@ static int __io_uring_register(struct io_ring_ctx *ctx, unsigned opcode,
 			break;
 		ret = io_register_iowq_max_workers(ctx, arg);
 		break;
+	case IORING_REGISTER_TX_CTX:
+		ret = io_sqe_tx_ctx_register(ctx, arg, nr_args);
+		break;
+	case IORING_UNREGISTER_TX_CTX:
+		ret = -EINVAL;
+		if (arg || nr_args)
+			break;
+		ret = io_sqe_tx_ctx_unregister(ctx);
+		break;
 	default:
 		ret = -EINVAL;
 		break;
diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 787f491f0d2a..f2e8d18e40e0 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -325,6 +325,9 @@ enum {
 	/* set/get max number of io-wq workers */
 	IORING_REGISTER_IOWQ_MAX_WORKERS	= 19,
 
+	IORING_REGISTER_TX_CTX			= 20,
+	IORING_UNREGISTER_TX_CTX		= 21,
+
 	/* this goes last */
 	IORING_REGISTER_LAST
 };
@@ -365,6 +368,10 @@ struct io_uring_rsrc_update2 {
 	__u32 resv2;
 };
 
+struct io_uring_tx_ctx_register {
+	__u64 tag;
+};
+
 /* Skip updating fd indexes set to this value in the fd table */
 #define IORING_REGISTER_FILES_SKIP	(-2)
 
-- 
2.34.1