[PATCH v2 02/23] bpf: initial support for attaching struct ops to cgroups

Roman Gushchin
2025-10-27T23:17:47Z

When a struct ops is being attached and a bpf link is created,
allow to pass a cgroup fd using bpf attr, so that struct ops
can be attached to a cgroup instead of globally.

Attached struct ops doesn't hold a reference to the cgroup,
only preserves cgroup id.

Signed-off-by: Roman Gushchin <roman.gushchin@linux.dev>
---
include/linux/bpf.h | 1 +
kernel/bpf/bpf_struct_ops.c | 13 +++++++++++++
2 files changed, 14 insertions(+)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index eae907218188..7205b813e25f 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1849,6 +1849,7 @@ struct bpf_struct_ops_link {
struct bpf_link link;
struct bpf_map __rcu *map;
wait_queue_head_t wait_hup;
+ u64 cgroup_id;
};

struct bpf_link_primer {
diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c
index 45cc5ee19dc2..58664779a2b6 100644
--- a/kernel/bpf/bpf_struct_ops.c
+++ b/kernel/bpf/bpf_struct_ops.c
@@ -13,6 +13,7 @@
#include <linux/btf_ids.h>
#include <linux/rcupdate_wait.h>
#include <linux/poll.h>
+#include <linux/cgroup.h>

struct bpf_struct_ops_value {
struct bpf_struct_ops_common_value common;
@@ -1359,6 +1360,18 @@ int bpf_struct_ops_link_create(union bpf_attr *attr)
}
bpf_link_init(&link->link, BPF_LINK_TYPE_STRUCT_OPS, &bpf_struct_ops_map_lops, NULL,
attr->link_create.attach_type);
+#ifdef CONFIG_CGROUPS
+ if (attr->link_create.cgroup.relative_fd) {
+ struct cgroup *cgrp;
+
+ cgrp = cgroup_get_from_fd(attr->link_create.cgroup.relative_fd);
+ if (IS_ERR(cgrp))
+ return PTR_ERR(cgrp);
+
+ link->cgroup_id = cgroup_id(cgrp);
+ cgroup_put(cgrp);
+ }
+#endif /* CONFIG_CGROUPS */

err = bpf_link_prime(&link->link, &link_primer);
if (err)
--
2.51.0