netdev - Re: [PATCH v2 bpf-next 1/2] bpf: introduce BPF_F_PRESERVE

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Date:   Wed, 30 Sep 2020 16:49:27 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Song Liu <songliubraving@...com>, netdev@...r.kernel.org,
        bpf@...r.kernel.org
Cc:     kernel-team@...com, ast@...nel.org, john.fastabend@...il.com,
        kpsingh@...omium.org
Subject: Re: [PATCH v2 bpf-next 1/2] bpf: introduce BPF_F_PRESERVE_ELEMS for
 perf event array

On 9/29/20 11:56 PM, Song Liu wrote:
[...]
>   
> +static void bpf_fd_array_map_clear(struct bpf_map *map);
> +
> +static void perf_event_fd_array_map_free(struct bpf_map *map)
> +{
> +	if (map->map_flags & BPF_F_PRESERVE_ELEMS)
> +		bpf_fd_array_map_clear(map);
> +	fd_array_map_free(map);
> +}

Not quite sure why you place that here and added the fwd declaration? If you
place perf_event_fd_array_map_free() near perf_event_array_map_ops, then you
also don't need the additional bpf_fd_array_map_clear declaration.

>   static void *prog_fd_array_get_ptr(struct bpf_map *map,
>   				   struct file *map_file, int fd)
>   {
> @@ -1134,6 +1148,9 @@ static void perf_event_fd_array_release(struct bpf_map *map,
>   	struct bpf_event_entry *ee;
>   	int i;
>   
> +	if (map->map_flags & BPF_F_PRESERVE_ELEMS)
> +		return;
> +
>   	rcu_read_lock();
>   	for (i = 0; i < array->map.max_entries; i++) {
>   		ee = READ_ONCE(array->ptrs[i]);
> @@ -1148,7 +1165,7 @@ const struct bpf_map_ops perf_event_array_map_ops = {
>   	.map_meta_equal = bpf_map_meta_equal,
>   	.map_alloc_check = fd_array_map_alloc_check,
>   	.map_alloc = array_map_alloc,
> -	.map_free = fd_array_map_free,
> +	.map_free = perf_event_fd_array_map_free,
>   	.map_get_next_key = array_map_get_next_key,
>   	.map_lookup_elem = fd_array_map_lookup_elem,
>   	.map_delete_elem = fd_array_map_delete_elem,
> diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
> index 82522f05c0213..ea78eb89f8d67 100644
> --- a/tools/include/uapi/linux/bpf.h
> +++ b/tools/include/uapi/linux/bpf.h
> @@ -414,6 +414,9 @@ enum {
>   
>   /* Enable memory-mapping BPF map */
>   	BPF_F_MMAPABLE		= (1U << 10),
> +
> +/* Share perf_event among processes */
> +	BPF_F_PRESERVE_ELEMS	= (1U << 11),
>   };
>   
>   /* Flags for BPF_PROG_QUERY. */
>