[PATCH RFC bpf-next v2 09/18] bpf: Implement alloc and free for resizable hashtab

[Mykyta Yatsenko <mykyta.yatsenko5@gmail.com>]

From: Mykyta Yatsenko <yatsenko@meta.com>

Initialize rhashtable with bpf_mem_alloc element cache. Require
BPF_F_NO_PREALLOC. Limit max_entries to 2^31. Free elements via
rhashtable_free_and_destroy() callback to handle internal structs.

Signed-off-by: Mykyta Yatsenko <yatsenko@meta.com>
---
 kernel/bpf/hashtab.c | 62 ++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 60 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index 492c6a9154b6..a62093d8d1ae 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -2762,16 +2762,74 @@ static inline void *rhtab_elem_value(struct rhtab_elem *l, u32 key_size)
 
 static struct bpf_map *rhtab_map_alloc(union bpf_attr *attr)
 {
-	return ERR_PTR(-EOPNOTSUPP);
+	struct bpf_rhtab *rhtab;
+	int err = 0;
+
+	rhtab = bpf_map_area_alloc(sizeof(*rhtab), NUMA_NO_NODE);
+	if (!rhtab)
+		return ERR_PTR(-ENOMEM);
+
+	bpf_map_init_from_attr(&rhtab->map, attr);
+
+	if (rhtab->map.max_entries > 1UL << 31) {
+		err = -E2BIG;
+		goto free_rhtab;
+	}
+
+	rhtab->elem_size = sizeof(struct rhtab_elem) + round_up(rhtab->map.key_size, 8) +
+			   round_up(rhtab->map.value_size, 8);
+
+	rhtab->params.head_offset = offsetof(struct rhtab_elem, node);
+	rhtab->params.key_offset = offsetof(struct rhtab_elem, data);
+	rhtab->params.key_len = rhtab->map.key_size;
+
+	err = rhashtable_init(&rhtab->ht, &rhtab->params);
+	if (err)
+		goto free_rhtab;
+
+	/* Set max_elems after rhashtable_init() since init zeroes the struct */
+	rhtab->ht.max_elems = rhtab->map.max_entries;
+
+	err = bpf_mem_alloc_init(&rhtab->ma, rhtab->elem_size, false);
+	if (err)
+		goto destroy_rhtab;
+
+	return &rhtab->map;
+
+destroy_rhtab:
+	rhashtable_destroy(&rhtab->ht);
+free_rhtab:
+	bpf_map_area_free(rhtab);
+	return ERR_PTR(err);
 }
 
 static int rhtab_map_alloc_check(union bpf_attr *attr)
 {
-	return -EOPNOTSUPP;
+	if (!(attr->map_flags & BPF_F_NO_PREALLOC))
+		return -EINVAL;
+
+	if (attr->map_flags & BPF_F_ZERO_SEED)
+		return -EINVAL;
+
+	return htab_map_alloc_check(attr);
+}
+
+static void rhtab_free_elem(void *ptr, void *arg)
+{
+	struct bpf_rhtab *rhtab = arg;
+	struct rhtab_elem *elem = ptr;
+
+	bpf_map_free_internal_structs(&rhtab->map, rhtab_elem_value(elem, rhtab->map.key_size));
+	bpf_mem_cache_free_rcu(&rhtab->ma, elem);
 }
 
 static void rhtab_map_free(struct bpf_map *map)
 {
+	struct bpf_rhtab *rhtab = container_of(map, struct bpf_rhtab, map);
+
+	rhashtable_free_and_destroy(&rhtab->ht, rhtab_free_elem, rhtab);
+	bpf_mem_alloc_destroy(&rhtab->ma);
+	bpf_map_area_free(rhtab);
 }
 
 static void *rhtab_lookup_elem(struct bpf_map *map, void *key)

-- 
2.52.0