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Date:   Tue, 21 Mar 2023 11:18:16 -0700
MIME-Version: 1.0
Subject: Re: [PATCH bpf-next v9 5/8] bpf: Update the struct_ops of a bpf_link.
Content-Language: en-US
To:     Kui-Feng Lee <kuifeng@meta.com>
References: <20230320195644.1953096-1-kuifeng@meta.com>
 <20230320195644.1953096-6-kuifeng@meta.com>
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From:   Martin KaFai Lau <martin.lau@linux.dev>
Cc:     bpf@vger.kernel.org, ast@kernel.org, song@kernel.org,
        kernel-team@meta.com, andrii@kernel.org, sdf@google.com
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On 3/20/23 12:56 PM, Kui-Feng Lee wrote:
> +static int bpf_struct_ops_map_link_update(struct bpf_link *link, struct bpf_map *new_map,
> +					  struct bpf_map *expected_old_map)
> +{
> +	struct bpf_struct_ops_map *st_map, *old_st_map;
> +	struct bpf_map *old_map;
> +	struct bpf_struct_ops_link *st_link;
> +	int err = 0;
> +
> +	st_link = container_of(link, struct bpf_struct_ops_link, link);
> +	st_map = container_of(new_map, struct bpf_struct_ops_map, map);
> +
> +	if (!bpf_struct_ops_valid_to_reg(new_map))
> +		return -EINVAL;
> +
> +	mutex_lock(&update_mutex);
> +
> +	old_map = rcu_dereference_protected(st_link->map, lockdep_is_held(&update_mutex));
> +	if (expected_old_map && old_map != expected_old_map) {
> +		err = -EINVAL;
> +		goto err_out;
> +	}
> +
> +	old_st_map = container_of(old_map, struct bpf_struct_ops_map, map);
> +	/* The new and old struct_ops must be the same type. */
> +	if (st_map->st_ops != old_st_map->st_ops) {
> +		err = -EINVAL;

Other ".update_prog" implementation returns -EPERM. eg. take a look at 
cgroup_bpf_replace().

> +		goto err_out;
> +	}
> +
> +	err = st_map->st_ops->update(st_map->kvalue.data, old_st_map->kvalue.data);
> +	if (err)
> +		goto err_out;
> +
> +	bpf_map_inc(new_map);
> +	rcu_assign_pointer(st_link->map, new_map);
> +	bpf_map_put(old_map);
> +
> +err_out:
> +	mutex_unlock(&update_mutex);
> +
> +	return err;
> +}
> +