KFunc `bpf_iter_css_new`

Initialize a cgroup iterator.

Definition

it should be a stack allocated struct bpf_iter_css that is used to iterate over cgroups. The start parameter is the cgroup subsystem state to start the iteration from. The flags parameter is a bitmask of flags that control the behavior of the iterator. The following flags are supported:

BPF_CGROUP_ITER_DESCENDANTS_PRE: Walk descendants of the cgroup in pre-order.
BPF_CGROUP_ITER_DESCENDANTS_POST: Walk descendants of the cgroup in post-order.
BPF_CGROUP_ITER_ANCESTORS_UP: Walk ancestors of the cgroup upward.

int bpf_iter_css_new(struct bpf_iter_css *it, struct cgroup_subsys_state *start, unsigned int flags)

Note

This kfunc is RCU protected. This means that the kfunc can be called from RCU read-side critical section. If a program isn't called from RCU read-side critical section, such as sleepable programs, the bpf_rcu_read_lock and bpf_rcu_read_unlock to protect the calls to such KFuncs.

Usage

Docs could be improved

This part of the docs is incomplete, contributions are very welcome

Program types

The following program types can make use of this kfunc:

Example

// SPDX-License-Identifier: GPL-2.0
/* Copyright (C) 2023 Chuyi Zhou <zhouchuyi@bytedance.com> */

#include "vmlinux.h"
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_tracing.h>
#include "bpf_misc.h"
#include "bpf_experimental.h"

char _license[] SEC("license") = "GPL";

pid_t target_pid;
u64 root_cg_id, leaf_cg_id;
u64 first_cg_id, last_cg_id;

int pre_order_cnt, post_order_cnt, tree_high;

struct cgroup *bpf_cgroup_from_id(u64 cgid) __ksym;
void bpf_cgroup_release(struct cgroup *p) __ksym;
void bpf_rcu_read_lock(void) __ksym;
void bpf_rcu_read_unlock(void) __ksym;

SEC("fentry.s/" SYS_PREFIX "sys_getpgid")
int iter_css_for_each(const void *ctx)
{
    struct task_struct *cur_task = bpf_get_current_task_btf();
    struct cgroup_subsys_state *root_css, *leaf_css, *pos;
    struct cgroup *root_cgrp, *leaf_cgrp, *cur_cgrp;

    if (cur_task->pid != target_pid)
        return 0;

    root_cgrp = bpf_cgroup_from_id(root_cg_id);

    if (!root_cgrp)
        return 0;

    leaf_cgrp = bpf_cgroup_from_id(leaf_cg_id);

    if (!leaf_cgrp) {
        bpf_cgroup_release(root_cgrp);
        return 0;
    }
    root_css = &root_cgrp->self;
    leaf_css = &leaf_cgrp->self;
    pre_order_cnt = post_order_cnt = tree_high = 0;
    first_cg_id = last_cg_id = 0;

    bpf_rcu_read_lock();
    bpf_for_each(css, pos, root_css, BPF_CGROUP_ITER_DESCENDANTS_POST) {
        cur_cgrp = pos->cgroup;
        post_order_cnt++;
        last_cg_id = cur_cgrp->kn->id;
    }

    bpf_for_each(css, pos, root_css, BPF_CGROUP_ITER_DESCENDANTS_PRE) {
        cur_cgrp = pos->cgroup;
        pre_order_cnt++;
        if (!first_cg_id)
            first_cg_id = cur_cgrp->kn->id;
    }

    bpf_for_each(css, pos, leaf_css, BPF_CGROUP_ITER_ANCESTORS_UP)
        tree_high++;

    bpf_for_each(css, pos, root_css, BPF_CGROUP_ITER_ANCESTORS_UP)
        tree_high--;
    bpf_rcu_read_unlock();
    bpf_cgroup_release(root_cgrp);
    bpf_cgroup_release(leaf_cgrp);
    return 0;
}

KFunc bpf_iter_css_new

Definition

Usage

Program types

Example

KFunc `bpf_iter_css_new`