Commit 752b8070 authored by Matt Bobrowski's avatar Matt Bobrowski Committed by Alexei Starovoitov
Browse files

bpf: add new BPF_CGROUP_ITER_CHILDREN control option 



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: default avatarMatt Bobrowski <mattbobrowski@google.com>
Link: https://lore.kernel.org/r/20260127085112.3608687-1-mattbobrowski@google.com


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent 8016abd6

include/uapi/linux/bpf.h

+8 −0
Original line number Diff line number Diff line
@@ -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 {

kernel/bpf/cgroup_iter.c

+21 −5
Original line number Diff line number Diff line
@@ -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 @@ static void bpf_iter_cgroup_show_fdinfo(const struct bpf_iter_aux_info *aux, 
		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;

	}

tools/include/uapi/linux/bpf.h

+8 −0
Original line number Diff line number Diff line
@@ -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 {