[PATCH bpf-next v1 2/3] bpf: add bpf_relay_output kfunc

[Philo Lu <lulie@xxxxxxxxxxxxxxxxx>]

A kfunc is needed to write into the relay channel, named
bpf_relay_output. The usage is same as bpf_ringbuf_output helper. It
only works after relay files are set, i.e., after calling
map_update_elem for the created relay map.

Signed-off-by: Philo Lu <lulie@xxxxxxxxxxxxxxxxx>
---
 kernel/bpf/helpers.c  |  3 +++
 kernel/bpf/relaymap.c | 22 ++++++++++++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index be72824f32b2..22480b69ff27 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -2617,6 +2617,9 @@ BTF_ID_FLAGS(func, bpf_dynptr_is_null)
 BTF_ID_FLAGS(func, bpf_dynptr_is_rdonly)
 BTF_ID_FLAGS(func, bpf_dynptr_size)
 BTF_ID_FLAGS(func, bpf_dynptr_clone)
+#ifdef CONFIG_RELAY
+BTF_ID_FLAGS(func, bpf_relay_output)
+#endif
 BTF_SET8_END(common_btf_ids)
 
 static const struct btf_kfunc_id_set common_kfunc_set = {
diff --git a/kernel/bpf/relaymap.c b/kernel/bpf/relaymap.c
index 02b33a8e6b6c..37280d60133c 100644
--- a/kernel/bpf/relaymap.c
+++ b/kernel/bpf/relaymap.c
@@ -6,6 +6,7 @@
 #include <linux/slab.h>
 #include <linux/bpf.h>
 #include <linux/err.h>
+#include <linux/btf.h>
 
 #define RELAY_CREATE_FLAG_MASK (BPF_F_OVERWRITE)
 
@@ -197,3 +198,24 @@ const struct bpf_map_ops relay_map_ops = {
 	.map_mem_usage = relay_map_mem_usage,
 	.map_btf_id = &relay_map_btf_ids[0],
 };
+
+__bpf_kfunc_start_defs();
+
+__bpf_kfunc int bpf_relay_output(struct bpf_map *map,
+				   void *data, u64 data__sz, u32 flags)
+{
+	struct bpf_relay_map *rmap;
+
+	/* not support any flag now */
+	if (unlikely(!map || 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, data__sz);
+	return 0;
+}
+
+__bpf_kfunc_end_defs();
-- 
2.32.0.3.g01195cf9f