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bpf: add new BPF_CGROUP_ITER_CHILDREN control option

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Currently, the BPF cgroup iterator supports walking descendants in
either pre-order (BPF_CGROUP_ITER_DESCENDANTS_PRE) or post-order
(BPF_CGROUP_ITER_DESCENDANTS_POST). These modes perform an exhaustive
depth-first search (DFS) of the hierarchy. In scenarios where a BPF
program may need to inspect only the direct children of a given parent
cgroup, a full DFS is unnecessarily expensive.

This patch introduces a new BPF cgroup iterator control option,
BPF_CGROUP_ITER_CHILDREN. This control option restricts the traversal
to the immediate children of a specified parent cgroup, allowing for
more targeted and efficient iteration, particularly when exhaustive
depth-first search (DFS) traversal is not required.

Signed-off-by: Matt Bobrowski <mattbobrowski@google.com>
Link: https://lore.kernel.org/r/20260127085112.3608687-1-mattbobrowski@google.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Matt Bobrowski
2026-01-27 08:51:10 +00:00
committed by Alexei Starovoitov
parent 8016abd631
commit 752b807028
3 changed files with 37 additions and 5 deletions
Download Patch File Download Diff File Expand all files Collapse all files

8
include/uapi/linux/bpf.h
View File

@@ -119,6 +119,14 @@ enum bpf_cgroup_iter_order {
BPF_CGROUP_ITER_DESCENDANTS_PRE, /* walk descendants in pre-order. */
BPF_CGROUP_ITER_DESCENDANTS_POST, /* walk descendants in post-order. */
BPF_CGROUP_ITER_ANCESTORS_UP, /* walk ancestors upward. */
/*
* Walks the immediate children of the specified parent
* cgroup_subsys_state. Unlike BPF_CGROUP_ITER_DESCENDANTS_PRE,
* BPF_CGROUP_ITER_DESCENDANTS_POST, and BPF_CGROUP_ITER_ANCESTORS_UP
* the iterator does not include the specified parent as one of the
* returned iterator elements.
*/
BPF_CGROUP_ITER_CHILDREN,
};
union bpf_iter_link_info {

26
kernel/bpf/cgroup_iter.c
View File

@@ -8,12 +8,13 @@
#include "../cgroup/cgroup-internal.h" /* cgroup_mutex and cgroup_is_dead */
/* cgroup_iter provides four modes of traversal to the cgroup hierarchy.
/* cgroup_iter provides five modes of traversal to the cgroup hierarchy.
*
* 1. Walk the descendants of a cgroup in pre-order.
* 2. Walk the descendants of a cgroup in post-order.
* 3. Walk the ancestors of a cgroup.
* 4. Show the given cgroup only.
* 5. Walk the children of a given parent cgroup.
*
* For walking descendants, cgroup_iter can walk in either pre-order or
* post-order. For walking ancestors, the iter walks up from a cgroup to
@@ -78,6 +79,8 @@ static void *cgroup_iter_seq_start(struct seq_file *seq, loff_t *pos)
return css_next_descendant_pre(NULL, p->start_css);
else if (p->order == BPF_CGROUP_ITER_DESCENDANTS_POST)
return css_next_descendant_post(NULL, p->start_css);
else if (p->order == BPF_CGROUP_ITER_CHILDREN)
return css_next_child(NULL, p->start_css);
else /* BPF_CGROUP_ITER_SELF_ONLY and BPF_CGROUP_ITER_ANCESTORS_UP */
return p->start_css;
}
@@ -113,6 +116,8 @@ static void *cgroup_iter_seq_next(struct seq_file *seq, void *v, loff_t *pos)
return css_next_descendant_post(curr, p->start_css);
else if (p->order == BPF_CGROUP_ITER_ANCESTORS_UP)
return curr->parent;
else if (p->order == BPF_CGROUP_ITER_CHILDREN)
return css_next_child(curr, p->start_css);
else /* BPF_CGROUP_ITER_SELF_ONLY */
return NULL;
}
@@ -200,11 +205,16 @@ static int bpf_iter_attach_cgroup(struct bpf_prog *prog,
int order = linfo->cgroup.order;
struct cgroup *cgrp;
if (order != BPF_CGROUP_ITER_DESCENDANTS_PRE &&
order != BPF_CGROUP_ITER_DESCENDANTS_POST &&
order != BPF_CGROUP_ITER_ANCESTORS_UP &&
order != BPF_CGROUP_ITER_SELF_ONLY)
switch (order) {
case BPF_CGROUP_ITER_DESCENDANTS_PRE:
case BPF_CGROUP_ITER_DESCENDANTS_POST:
case BPF_CGROUP_ITER_ANCESTORS_UP:
case BPF_CGROUP_ITER_SELF_ONLY:
case BPF_CGROUP_ITER_CHILDREN:
break;
default:
return -EINVAL;
}
if (fd && id)
return -EINVAL;
@@ -257,6 +267,8 @@ show_order:
seq_puts(seq, "order: descendants_post\n");
else if (aux->cgroup.order == BPF_CGROUP_ITER_ANCESTORS_UP)
seq_puts(seq, "order: ancestors_up\n");
else if (aux->cgroup.order == BPF_CGROUP_ITER_CHILDREN)
seq_puts(seq, "order: children\n");
else /* BPF_CGROUP_ITER_SELF_ONLY */
seq_puts(seq, "order: self_only\n");
}
@@ -320,6 +332,7 @@ __bpf_kfunc int bpf_iter_css_new(struct bpf_iter_css *it,
case BPF_CGROUP_ITER_DESCENDANTS_PRE:
case BPF_CGROUP_ITER_DESCENDANTS_POST:
case BPF_CGROUP_ITER_ANCESTORS_UP:
case BPF_CGROUP_ITER_CHILDREN:
break;
default:
return -EINVAL;
@@ -345,6 +358,9 @@ __bpf_kfunc struct cgroup_subsys_state *bpf_iter_css_next(struct bpf_iter_css *i
case BPF_CGROUP_ITER_DESCENDANTS_POST:
kit->pos = css_next_descendant_post(kit->pos, kit->start);
break;
case BPF_CGROUP_ITER_CHILDREN:
kit->pos = css_next_child(kit->pos, kit->start);
break;
case BPF_CGROUP_ITER_ANCESTORS_UP:
kit->pos = kit->pos ? kit->pos->parent : kit->start;
}

8
tools/include/uapi/linux/bpf.h
View File

@@ -119,6 +119,14 @@ enum bpf_cgroup_iter_order {
BPF_CGROUP_ITER_DESCENDANTS_PRE, /* walk descendants in pre-order. */
BPF_CGROUP_ITER_DESCENDANTS_POST, /* walk descendants in post-order. */
BPF_CGROUP_ITER_ANCESTORS_UP, /* walk ancestors upward. */
/*
* Walks the immediate children of the specified parent
* cgroup_subsys_state. Unlike BPF_CGROUP_ITER_DESCENDANTS_PRE,
* BPF_CGROUP_ITER_DESCENDANTS_POST, and BPF_CGROUP_ITER_ANCESTORS_UP
* the iterator does not include the specified parent as one of the
* returned iterator elements.
*/
BPF_CGROUP_ITER_CHILDREN,
};
union bpf_iter_link_info {