[PATCH bpf-next v3 4/7] bpf: Introduce css open-coded iterator kfuncs

Chuyi Zhou
2023-09-25T10:56:16Z

This Patch adds kfuncs bpf_iter_css_{new,next,destroy} which allow
creation and manipulation of struct bpf_iter_css in open-coded iterator
style. These kfuncs actually wrapps css_next_descendant_{pre, post}.
css_iter can be used to:

1) iterating a sepcific cgroup tree with pre/post/up order

2) iterating cgroup_subsystem in BPF Prog, like
for_each_mem_cgroup_tree/cpuset_for_each_descendant_pre in kernel.

The API design is consistent with cgroup_iter. bpf_iter_css_new accepts
parameters defining iteration order and starting css. Here we also reuse
BPF_CGROUP_ITER_DESCENDANTS_PRE, BPF_CGROUP_ITER_DESCENDANTS_POST,
BPF_CGROUP_ITER_ANCESTORS_UP enums.

Signed-off-by: Chuyi Zhou <zhouchuyi@bytedance.com>
---
kernel/bpf/cgroup_iter.c | 57 +++++++++++++++++++
kernel/bpf/helpers.c | 3 +
.../testing/selftests/bpf/bpf_experimental.h | 6 ++
3 files changed, 66 insertions(+)

diff --git a/kernel/bpf/cgroup_iter.c b/kernel/bpf/cgroup_iter.c
index 810378f04fbc..ebc3d9471f52 100644
--- a/kernel/bpf/cgroup_iter.c
+++ b/kernel/bpf/cgroup_iter.c
@@ -294,3 +294,60 @@ static int __init bpf_cgroup_iter_init(void)
}

late_initcall(bpf_cgroup_iter_init);
+
+struct bpf_iter_css {
+ __u64 __opaque[2];
+ __u32 __opaque_int[1];
+} __attribute__((aligned(8)));
+
+struct bpf_iter_css_kern {
+ struct cgroup_subsys_state *start;
+ struct cgroup_subsys_state *pos;
+ int order;
+} __attribute__((aligned(8)));
+
+__bpf_kfunc int bpf_iter_css_new(struct bpf_iter_css *it,
+ struct cgroup_subsys_state *start, enum bpf_cgroup_iter_order order)
+{
+ struct bpf_iter_css_kern *kit = (void *)it;
+ kit->start = NULL;
+ BUILD_BUG_ON(sizeof(struct bpf_iter_css_kern) != sizeof(struct bpf_iter_css));
+ BUILD_BUG_ON(__alignof__(struct bpf_iter_css_kern) != __alignof__(struct bpf_iter_css));
+ switch (order) {
+ case BPF_CGROUP_ITER_DESCENDANTS_PRE:
+ case BPF_CGROUP_ITER_DESCENDANTS_POST:
+ case BPF_CGROUP_ITER_ANCESTORS_UP:
+ break;
+ default:
+ return -EINVAL;
+ }
+
+ kit->start = start;
+ kit->pos = NULL;
+ kit->order = order;
+ return 0;
+}
+
+__bpf_kfunc struct cgroup_subsys_state *bpf_iter_css_next(struct bpf_iter_css *it)
+{
+ struct bpf_iter_css_kern *kit = (void *)it;
+ if (!kit->start)
+ return NULL;
+
+ switch (kit->order) {
+ case BPF_CGROUP_ITER_DESCENDANTS_PRE:
+ kit->pos = css_next_descendant_pre(kit->pos, kit->start);
+ break;
+ case BPF_CGROUP_ITER_DESCENDANTS_POST:
+ kit->pos = css_next_descendant_post(kit->pos, kit->start);
+ break;
+ default:
+ kit->pos = kit->pos ? kit->pos->parent : kit->start;
+ }
+
+ return kit->pos;
+}
+
+__bpf_kfunc void bpf_iter_css_destroy(struct bpf_iter_css *it)
+{
+}
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 556262c27a75..9c3af36249a2 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -2510,6 +2510,9 @@ BTF_ID_FLAGS(func, bpf_iter_css_task_destroy, KF_ITER_DESTROY)
BTF_ID_FLAGS(func, bpf_iter_task_new, KF_ITER_NEW | KF_TRUSTED_ARGS)
BTF_ID_FLAGS(func, bpf_iter_task_next, KF_ITER_NEXT | KF_RET_NULL)
BTF_ID_FLAGS(func, bpf_iter_task_destroy, KF_ITER_DESTROY)
+BTF_ID_FLAGS(func, bpf_iter_css_new, KF_ITER_NEW | KF_TRUSTED_ARGS)
+BTF_ID_FLAGS(func, bpf_iter_css_next, KF_ITER_NEXT | KF_RET_NULL)
+BTF_ID_FLAGS(func, bpf_iter_css_destroy, KF_ITER_DESTROY)
BTF_ID_FLAGS(func, bpf_dynptr_adjust)
BTF_ID_FLAGS(func, bpf_dynptr_is_null)
BTF_ID_FLAGS(func, bpf_dynptr_is_rdonly)
diff --git a/tools/testing/selftests/bpf/bpf_experimental.h b/tools/testing/selftests/bpf/bpf_experimental.h
index d989775dbdb5..aa247d1d81d1 100644
--- a/tools/testing/selftests/bpf/bpf_experimental.h
+++ b/tools/testing/selftests/bpf/bpf_experimental.h
@@ -174,4 +174,10 @@ extern int bpf_iter_task_new(struct bpf_iter_task *it, struct task_struct *task,
extern struct task_struct *bpf_iter_task_next(struct bpf_iter_task *it) __weak __ksym;
extern void bpf_iter_task_destroy(struct bpf_iter_task *it) __weak __ksym;

+struct bpf_iter_css;
+extern int bpf_iter_css_new(struct bpf_iter_css *it,
+ struct cgroup_subsys_state *start, enum bpf_cgroup_iter_order order) __weak __ksym;
+extern struct cgroup_subsys_state *bpf_iter_css_next(struct bpf_iter_css *it) __weak __ksym;
+extern void bpf_iter_css_destroy(struct bpf_iter_css *it) __weak __ksym;
+
#endif
--
2.20.1