Re: [PATCH bpf-next 3/3] selftests/bpf: libarena: Add rb_next()

[Emil Tsalapatis]

On Wed Oct 28, 2026 at 6:00 AM UTC, Changwoo Min wrote:
> Add rb_next(), the in-order successor through parent pointers.
>
> Add a selftest that walks a tree with repeated keys and checks the walk
> against the order in which the head leaves the tree.
>
> Signed-off-by: Changwoo Min <changwoo@xxxxxxxxxx>
> ---
>  .../bpf/libarena/include/libarena/rbtree.h    | 23 ++++++++
>  .../bpf/libarena/selftests/test_rbtree.bpf.c  | 54 +++++++++++++++++++
>  2 files changed, 77 insertions(+)
>
> diff --git a/tools/testing/selftests/bpf/libarena/include/libarena/rbtree.h b/tools/testing/selftests/bpf/libarena/include/libarena/rbtree.h
> index a8dd8c2e7596..956b4a24b52a 100644
> --- a/tools/testing/selftests/bpf/libarena/include/libarena/rbtree.h
> +++ b/tools/testing/selftests/bpf/libarena/include/libarena/rbtree.h
> @@ -103,6 +103,29 @@ void rb_node_free(struct rbnode __arena *rbnode);
>  
>  int rb_integrity_check(struct rbtree __arena *rbtree);
>  
> +/*
> + * Return the in-order successor of @node, or NULL if @node is the last one.
> + * Walking from rb_first() with it visits the tree in key order, equal keys in
> + * insertion order. Call it under the writer's lock.
> + */

Let's move this to the main *.bpf.c file, with the rest of the traversal functions.

> +static __always_inline struct rbnode __arena *rb_next(struct rbnode __arena *node)
> +{
> +	struct rbnode __arena *parent;
> +
> +	if (node->right) {
> +		node = node->right;
> +		while (node->left && can_loop)
> +			node = node->left;
> +		return node;
> +	}
> +
> +	/* Climb until we leave a left subtree; its parent comes next. */
> +	while ((parent = node->parent) && node == parent->right && can_loop)
> +		node = parent;
> +
> +	return parent;
> +}
> +
>  /*
>   * Lockless reads of the head and the node count. They need not be called
>   * under the writer's lock, so they are advisory: the tree may change before
> diff --git a/tools/testing/selftests/bpf/libarena/selftests/test_rbtree.bpf.c b/tools/testing/selftests/bpf/libarena/selftests/test_rbtree.bpf.c
> index 57c4395c046a..784cc9edea17 100644
> --- a/tools/testing/selftests/bpf/libarena/selftests/test_rbtree.bpf.c
> +++ b/tools/testing/selftests/bpf/libarena/selftests/test_rbtree.bpf.c
> @@ -425,6 +425,60 @@ __weak int test_rbtree_first_update(void)
>  	return rb_destroy(rbtree);
>  }
>  
> +#define NEXT_NR_NODES	64
> +
> +static struct rbnode __arena *next_nodes[NEXT_NR_NODES];
> +
> +SEC("syscall")
> +__weak int test_rbtree_next(void)
> +{
> +	struct rbtree __arena *rbtree;
> +	struct rbnode __arena *node;
> +	u64 seed = 0xcafe;
> +	int i;
> +
> +	rbtree = rb_create(RB_NOALLOC, RB_DUPLICATE);
> +	if (!rbtree)
> +		return 1;
> +
> +	/* Pseudo-random keys with repeats, so the walk crosses equal keys. */
> +	for (i = 0; i < NEXT_NR_NODES && can_loop; i++) {
> +		/* LCG using Knuth's MMIX constants for determinism. */
> +		seed = seed * 6364136223846793005ULL + 1442695040888963407ULL;
> +		node = rb_node_alloc((seed >> 33) % 16, i);
> +		if (!node)
> +			return 2;
> +
> +		if (rb_insert_node(rbtree, node))
> +			return 3;
> +	}
> +
> +	node = rb_first(rbtree);
> +	for (i = 0; i < NEXT_NR_NODES && can_loop; i++) {
> +		if (!node)
> +			return 4;
> +
> +		next_nodes[i] = node;
> +		node = rb_next(node);
> +	}
> +
> +	if (node)
> +		return 5;
> +
> +	for (i = 0; i < NEXT_NR_NODES && can_loop; i++) {
> +		node = rb_first(rbtree);
> +		if (node != next_nodes[i])
> +			return 6;
> +
> +		if (rb_remove_node(rbtree, node))
> +			return 7;
> +
> +		rb_node_free(node);
> +	}
> +
> +	return rb_destroy(rbtree);
> +}
> +
>  struct rb_embed {
>  	u64 pad;
>  	struct rbtree tree;