[RFC v2 2/5] io_uring/bpf: add stubs for bpf struct_ops

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

Add some basic helpers and definitions for implementing bpf struct_ops.
There are no callbaack yet, and registration will always fail.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 include/linux/io_uring_types.h |  4 ++
 io_uring/Kconfig               |  5 ++
 io_uring/Makefile              |  1 +
 io_uring/bpf.c                 | 93 ++++++++++++++++++++++++++++++++++
 io_uring/bpf.h                 | 26 ++++++++++
 io_uring/io_uring.c            |  3 ++
 6 files changed, 132 insertions(+)
 create mode 100644 io_uring/bpf.c
 create mode 100644 io_uring/bpf.h

diff --git a/include/linux/io_uring_types.h b/include/linux/io_uring_types.h
index 2922635986f5..26ee1a6f52e7 100644
--- a/include/linux/io_uring_types.h
+++ b/include/linux/io_uring_types.h
@@ -8,6 +8,8 @@
 #include <linux/llist.h>
 #include <uapi/linux/io_uring.h>
 
+struct io_uring_ops;
+
 enum {
 	/*
 	 * A hint to not wake right away but delay until there are enough of
@@ -344,6 +346,8 @@ struct io_ring_ctx {
 
 		void			*cq_wait_arg;
 		size_t			cq_wait_size;
+
+		struct io_uring_ops	*bpf_ops;
 	} ____cacheline_aligned_in_smp;
 
 	/*
diff --git a/io_uring/Kconfig b/io_uring/Kconfig
index 4b949c42c0bf..b4dad9b74544 100644
--- a/io_uring/Kconfig
+++ b/io_uring/Kconfig
@@ -9,3 +9,8 @@ config IO_URING_ZCRX
 	depends on PAGE_POOL
 	depends on INET
 	depends on NET_RX_BUSY_POLL
+
+config IO_URING_BPF
+	def_bool y
+	depends on IO_URING
+	depends on BPF_SYSCALL && BPF_JIT && DEBUG_INFO_BTF
diff --git a/io_uring/Makefile b/io_uring/Makefile
index d97c6b51d584..58f46c0f9895 100644
--- a/io_uring/Makefile
+++ b/io_uring/Makefile
@@ -21,3 +21,4 @@ obj-$(CONFIG_EPOLL)		+= epoll.o
 obj-$(CONFIG_NET_RX_BUSY_POLL)	+= napi.o
 obj-$(CONFIG_NET) += net.o cmd_net.o
 obj-$(CONFIG_PROC_FS) += fdinfo.o
+obj-$(CONFIG_IO_URING_BPF)	+= bpf.o
diff --git a/io_uring/bpf.c b/io_uring/bpf.c
new file mode 100644
index 000000000000..3096c54e4fb3
--- /dev/null
+++ b/io_uring/bpf.c
@@ -0,0 +1,93 @@
+#include <linux/mutex.h>
+
+#include "bpf.h"
+#include "register.h"
+
+static struct io_uring_ops io_bpf_ops_stubs = {
+};
+
+static bool bpf_io_is_valid_access(int off, int size,
+				    enum bpf_access_type type,
+				    const struct bpf_prog *prog,
+				    struct bpf_insn_access_aux *info)
+{
+	if (type != BPF_READ)
+		return false;
+	if (off < 0 || off >= sizeof(__u64) * MAX_BPF_FUNC_ARGS)
+		return false;
+	if (off % size != 0)
+		return false;
+
+	return btf_ctx_access(off, size, type, prog, info);
+}
+
+static int bpf_io_btf_struct_access(struct bpf_verifier_log *log,
+				    const struct bpf_reg_state *reg, int off,
+				    int size)
+{
+	return -EACCES;
+}
+
+static const struct bpf_verifier_ops bpf_io_verifier_ops = {
+	.get_func_proto = bpf_base_func_proto,
+	.is_valid_access = bpf_io_is_valid_access,
+	.btf_struct_access = bpf_io_btf_struct_access,
+};
+
+static int bpf_io_init(struct btf *btf)
+{
+	return 0;
+}
+
+static int bpf_io_check_member(const struct btf_type *t,
+				const struct btf_member *member,
+				const struct bpf_prog *prog)
+{
+	return 0;
+}
+
+static int bpf_io_init_member(const struct btf_type *t,
+			       const struct btf_member *member,
+			       void *kdata, const void *udata)
+{
+	return 0;
+}
+
+static int bpf_io_reg(void *kdata, struct bpf_link *link)
+{
+	return -EOPNOTSUPP;
+}
+
+static void bpf_io_unreg(void *kdata, struct bpf_link *link)
+{
+}
+
+void io_unregister_bpf_ops(struct io_ring_ctx *ctx)
+{
+}
+
+static struct bpf_struct_ops bpf_io_uring_ops = {
+	.verifier_ops = &bpf_io_verifier_ops,
+	.reg = bpf_io_reg,
+	.unreg = bpf_io_unreg,
+	.check_member = bpf_io_check_member,
+	.init_member = bpf_io_init_member,
+	.init = bpf_io_init,
+	.cfi_stubs = &io_bpf_ops_stubs,
+	.name = "io_uring_ops",
+	.owner = THIS_MODULE,
+};
+
+static int __init io_uring_bpf_init(void)
+{
+	int ret;
+
+	ret = register_bpf_struct_ops(&bpf_io_uring_ops, io_uring_ops);
+	if (ret) {
+		pr_err("io_uring: Failed to register struct_ops (%d)\n", ret);
+		return ret;
+	}
+
+	return 0;
+}
+__initcall(io_uring_bpf_init);
diff --git a/io_uring/bpf.h b/io_uring/bpf.h
new file mode 100644
index 000000000000..a61c489d306b
--- /dev/null
+++ b/io_uring/bpf.h
@@ -0,0 +1,26 @@
+// SPDX-License-Identifier: GPL-2.0
+#ifndef IOU_BPF_H
+#define IOU_BPF_H
+
+#include <linux/io_uring_types.h>
+#include <linux/bpf.h>
+
+#include "io_uring.h"
+
+struct io_uring_ops {
+};
+
+static inline bool io_bpf_attached(struct io_ring_ctx *ctx)
+{
+	return IS_ENABLED(CONFIG_BPF) && ctx->bpf_ops != NULL;
+}
+
+#ifdef CONFIG_BPF
+void io_unregister_bpf_ops(struct io_ring_ctx *ctx);
+#else
+static inline void io_unregister_bpf_ops(struct io_ring_ctx *ctx)
+{
+}
+#endif
+
+#endif
\ No newline at end of file
diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 9cc4d8f335a1..8f68e898d60c 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -98,6 +98,7 @@
 #include "msg_ring.h"
 #include "memmap.h"
 #include "zcrx.h"
+#include "bpf.h"
 
 #include "timeout.h"
 #include "poll.h"
@@ -2870,6 +2871,8 @@ static __cold void io_ring_exit_work(struct work_struct *work)
 	struct io_tctx_node *node;
 	int ret;
 
+	io_unregister_bpf_ops(ctx);
+
 	/*
 	 * If we're doing polled IO and end up having requests being
 	 * submitted async (out-of-line), then completions can come in while
-- 
2.49.0