[PATCH RFC bpf-next v2 07/18] bpf: Implement batch ops for resizable hashtab

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

From: Mykyta Yatsenko <yatsenko@meta.com>

Add batch operations for BPF_MAP_TYPE_RHASH.

Batch operations:
 * rhtab_map_lookup_batch: Bulk lookup of elements by bucket
 * rhtab_map_lookup_and_delete_batch: Atomic bulk lookup and delete

The batch implementation uses rhashtable_walk_enter_from() to resume
iteration from the last collected key. When the buffer fills, the last
key becomes the cursor for the next batch call.

Also implements rhtab_map_mem_usage() to report memory consumption.

Signed-off-by: Mykyta Yatsenko <yatsenko@meta.com>
---
 kernel/bpf/hashtab.c | 137 +++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 134 insertions(+), 3 deletions(-)

diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index e79c194e2779..a79d434dc626 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -3051,19 +3051,150 @@ static long bpf_each_rhash_elem(struct bpf_map *map, bpf_callback_t callback_fn,
 
 static u64 rhtab_map_mem_usage(const struct bpf_map *map)
 {
-	return 0;
+	struct bpf_rhtab *rhtab = container_of(map, struct bpf_rhtab, map);
+	u64 num_entries;
+
+	num_entries = atomic_read(&rhtab->ht.nelems);
+	return sizeof(struct bpf_rhtab) + rhtab->elem_size * num_entries;
+}
+
+static int __rhtab_map_lookup_and_delete_batch(struct bpf_map *map,
+					       const union bpf_attr *attr,
+					       union bpf_attr __user *uattr,
+					       bool do_delete)
+{
+	struct bpf_rhtab *rhtab = container_of(map, struct bpf_rhtab, map);
+	void __user *uvalues = u64_to_user_ptr(attr->batch.values);
+	void __user *ukeys = u64_to_user_ptr(attr->batch.keys);
+	void __user *ubatch = u64_to_user_ptr(attr->batch.in_batch);
+	void *buf = NULL, *keys = NULL, *values = NULL, *dst_key, *dst_val;
+	struct rhtab_elem **del_elems = NULL;
+	u32 max_count, total, key_size, value_size, i;
+	struct rhashtable_iter iter;
+	struct rhtab_elem *elem;
+	u64 elem_map_flags, map_flags;
+	int ret = 0;
+
+	elem_map_flags = attr->batch.elem_flags;
+	if ((elem_map_flags & ~BPF_F_LOCK) ||
+	    ((elem_map_flags & BPF_F_LOCK) &&
+	     !btf_record_has_field(map->record, BPF_SPIN_LOCK)))
+		return -EINVAL;
+
+	map_flags = attr->batch.flags;
+	if (map_flags)
+		return -EINVAL;
+
+	max_count = attr->batch.count;
+	if (!max_count)
+		return 0;
+
+	if (put_user(0, &uattr->batch.count))
+		return -EFAULT;
+
+	key_size = map->key_size;
+	value_size = map->value_size;
+
+	keys = kvmalloc_array(max_count, key_size, GFP_USER | __GFP_NOWARN);
+	values = kvmalloc_array(max_count, value_size, GFP_USER | __GFP_NOWARN);
+	if (do_delete)
+		del_elems = kvmalloc_array(max_count, sizeof(void *),
+					   GFP_USER | __GFP_NOWARN);
+
+	if (!keys || !values || (do_delete && !del_elems)) {
+		ret = -ENOMEM;
+		goto free;
+	}
+
+	/*
+	 * Use the last key from the previous batch as cursor.
+	 * enter_from positions at that key's bucket, walk_next
+	 * returns the successor in O(1).
+	 * First call (ubatch == NULL): starts from bucket 0.
+	 */
+	if (ubatch) {
+		buf = kmalloc(key_size, GFP_USER | __GFP_NOWARN);
+		if (!buf) {
+			ret = -ENOMEM;
+			goto free;
+		}
+		if (copy_from_user(buf, ubatch, key_size)) {
+			ret = -EFAULT;
+			goto free;
+		}
+	}
+
+	scoped_guard(rcu) {
+		rhashtable_walk_enter_from(&rhtab->ht, &iter, buf, rhtab->params);
+		rhashtable_walk_start(&iter);
+	}
+
+	dst_key = keys;
+	dst_val = values;
+	total = 0;
+
+	while (total < max_count) {
+		elem = rhtab_iter_next(&iter);
+		if (!elem)
+			break;
+
+		memcpy(dst_key, elem->data, key_size);
+		rhtab_read_elem_value(map, dst_val, elem, elem_map_flags);
+		check_and_init_map_value(map, dst_val);
+
+		if (do_delete)
+			del_elems[total] = elem;
+
+		dst_key += key_size;
+		dst_val += value_size;
+		total++;
+	}
+
+	if (do_delete) {
+		for (i = 0; i < total; i++)
+			rhtab_delete_elem(rhtab, del_elems[i]);
+	}
+
+	rhashtable_walk_stop(&iter);
+	rhashtable_walk_exit(&iter);
+
+	if (total == 0) {
+		ret = -ENOENT;
+		goto free;
+	}
+
+	/* Signal end of table when we collected fewer than requested */
+	if (total < max_count)
+		ret = -ENOENT;
+
+	/* Write last key as cursor for the next batch call */
+	if (copy_to_user(ukeys, keys, total * key_size) ||
+	    copy_to_user(uvalues, values, total * value_size) ||
+	    put_user(total, &uattr->batch.count) ||
+	    copy_to_user(u64_to_user_ptr(attr->batch.out_batch),
+			 dst_key - key_size, key_size)) {
+		ret = -EFAULT;
+		goto free;
+	}
+
+free:
+	kfree(buf);
+	kvfree(keys);
+	kvfree(values);
+	kvfree(del_elems);
+	return ret;
 }
 
 static int rhtab_map_lookup_batch(struct bpf_map *map, const union bpf_attr *attr,
 				  union bpf_attr __user *uattr)
 {
-	return 0;
+	return __rhtab_map_lookup_and_delete_batch(map, attr, uattr, false);
 }
 
 static int rhtab_map_lookup_and_delete_batch(struct bpf_map *map, const union bpf_attr *attr,
 					     union bpf_attr __user *uattr)
 {
-	return 0;
+	return __rhtab_map_lookup_and_delete_batch(map, attr, uattr, true);
 }
 
 struct bpf_iter_seq_rhash_map_info {

-- 
2.52.0