[PATCH bpf-next 3/3] bpf: introduce bpf_relay_output helper

[Philo Lu <lulie@linux.alibaba.com>]

Like perfbuf/ringbuf, a helper is needed to write into the buffer, named
bpf_relay_output, whose usage is same as ringbuf. Note that it works only
after relay files are set, i.e., after calling map_update_elem for the
created relay map.

Signed-off-by: Philo Lu <lulie@linux.alibaba.com>
---
 include/linux/bpf.h      |  1 +
 include/uapi/linux/bpf.h | 10 ++++++++++
 kernel/bpf/helpers.c     |  4 ++++
 kernel/bpf/relaymap.c    | 26 ++++++++++++++++++++++++++
 kernel/bpf/verifier.c    |  8 ++++++++
 kernel/trace/bpf_trace.c |  4 ++++
 6 files changed, 53 insertions(+)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 7671530d6e4e..b177122369e6 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -3095,6 +3095,7 @@ extern const struct bpf_func_proto bpf_get_retval_proto;
 extern const struct bpf_func_proto bpf_user_ringbuf_drain_proto;
 extern const struct bpf_func_proto bpf_cgrp_storage_get_proto;
 extern const struct bpf_func_proto bpf_cgrp_storage_delete_proto;
+extern const struct bpf_func_proto bpf_relay_output_proto;
 
 const struct bpf_func_proto *tracing_prog_func_proto(
   enum bpf_func_id func_id, const struct bpf_prog *prog);
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 143b75676bd3..03c0c1953ba1 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -5686,6 +5686,15 @@ union bpf_attr {
  *		0 on success.
  *
  *		**-ENOENT** if the bpf_local_storage cannot be found.
+ *
+ * long bpf_relay_output(void *map, void *data, u64 size, u64 flags)
+ * 	Description
+ * 		Copy *size* bytes from *data* into *map* of type BPF_MAP_TYPE_RELAY.
+ * 		Currently, the *flags* must be 0.
+ * 	Return
+ * 		0 on success.
+ *
+ *		**-ENOENT** if the relay base_file in debugfs cannot be found.
  */
 #define ___BPF_FUNC_MAPPER(FN, ctx...)			\
 	FN(unspec, 0, ##ctx)				\
@@ -5900,6 +5909,7 @@ union bpf_attr {
 	FN(user_ringbuf_drain, 209, ##ctx)		\
 	FN(cgrp_storage_get, 210, ##ctx)		\
 	FN(cgrp_storage_delete, 211, ##ctx)		\
+	FN(relay_output, 212, ##ctx)		\
 	/* */
 
 /* backwards-compatibility macros for users of __BPF_FUNC_MAPPER that don't
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index be72824f32b2..0c26e87ce729 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -1720,6 +1720,10 @@ bpf_base_func_proto(enum bpf_func_id func_id)
 		return &bpf_ringbuf_discard_proto;
 	case BPF_FUNC_ringbuf_query:
 		return &bpf_ringbuf_query_proto;
+#ifdef CONFIG_RELAY
+	case BPF_FUNC_relay_output:
+		return &bpf_relay_output_proto;
+#endif
 	case BPF_FUNC_strncmp:
 		return &bpf_strncmp_proto;
 	case BPF_FUNC_strtol:
diff --git a/kernel/bpf/relaymap.c b/kernel/bpf/relaymap.c
index 588c8de0a4bd..f9e2e4a780df 100644
--- a/kernel/bpf/relaymap.c
+++ b/kernel/bpf/relaymap.c
@@ -173,6 +173,32 @@ static u64 relay_map_mem_usage(const struct bpf_map *map)
 	return usage;
 }
 
+BPF_CALL_4(bpf_relay_output, struct bpf_map *, map, void *, data, u64, size,
+	   u64, flags)
+{
+	struct bpf_relay_map *rmap;
+
+	/* not support any flag now */
+	if (unlikely(flags))
+		return -EINVAL;
+
+	rmap = container_of(map, struct bpf_relay_map, map);
+	if (!rmap->relay_chan->has_base_filename)
+		return -ENOENT;
+
+	relay_write(rmap->relay_chan, data, size);
+	return 0;
+}
+
+const struct bpf_func_proto bpf_relay_output_proto = {
+	.func		= bpf_relay_output,
+	.ret_type	= RET_INTEGER,
+	.arg1_type	= ARG_CONST_MAP_PTR,
+	.arg2_type	= ARG_PTR_TO_MEM | MEM_RDONLY,
+	.arg3_type	= ARG_CONST_SIZE_OR_ZERO,
+	.arg4_type	= ARG_ANYTHING,
+};
+
 BTF_ID_LIST_SINGLE(relay_map_btf_ids, struct, bpf_relay_map)
 const struct bpf_map_ops relay_map_ops = {
 	.map_meta_equal = bpf_map_meta_equal,
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index f13008d27f35..8c8287d6ae18 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -8800,6 +8800,10 @@ static int check_map_func_compatibility(struct bpf_verifier_env *env,
 		if (func_id != BPF_FUNC_user_ringbuf_drain)
 			goto error;
 		break;
+	case BPF_MAP_TYPE_RELAY:
+		if (func_id != BPF_FUNC_relay_output)
+			goto error;
+		break;
 	case BPF_MAP_TYPE_STACK_TRACE:
 		if (func_id != BPF_FUNC_get_stackid)
 			goto error;
@@ -8932,6 +8936,10 @@ static int check_map_func_compatibility(struct bpf_verifier_env *env,
 		if (map->map_type != BPF_MAP_TYPE_USER_RINGBUF)
 			goto error;
 		break;
+	case BPF_FUNC_relay_output:
+		if (map->map_type != BPF_MAP_TYPE_RELAY)
+			goto error;
+		break;
 	case BPF_FUNC_get_stackid:
 		if (map->map_type != BPF_MAP_TYPE_STACK_TRACE)
 			goto error;
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 7ac6c52b25eb..5b13553c6232 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -1594,6 +1594,10 @@ bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 		return &bpf_ringbuf_discard_proto;
 	case BPF_FUNC_ringbuf_query:
 		return &bpf_ringbuf_query_proto;
+#ifdef CONFIG_RELAY
+	case BPF_FUNC_relay_output:
+		return &bpf_relay_output_proto;
+#endif
 	case BPF_FUNC_jiffies64:
 		return &bpf_jiffies64_proto;
 	case BPF_FUNC_get_task_stack:
-- 
2.32.0.3.g01195cf9f