Re: [PATCH bpf-next 2/3] bpf: implement map_update_elem to init relay file

[Jiri Olsa <olsajiri@gmail.com>]

On Fri, Dec 22, 2023 at 08:21:45PM +0800, Philo Lu wrote:
> map_update_elem is used to create relay files and bind them with the
> relay channel, which is created with BPF_MAP_CREATE. This allows users
> to set a custom directory name. It must be used with key=NULL and
> flag=0.
> 
> Here is an example:
> ```
> struct {
> __uint(type, BPF_MAP_TYPE_RELAY);
> __uint(max_entries, 4096);
> } my_relay SEC(".maps");
> ...
> char dir_name[] = "relay_test";
> bpf_map_update_elem(map_fd, NULL, dir_name, 0);
> ```
> 
> Then, directory `/sys/kerenl/debug/relay_test` will be created, which
> includes files of my_relay0...my_relay[#cpu]. Each represents a per-cpu
> buffer with size 8 * 4096 B (there are 8 subbufs by default, each with
> size 4096B).
> 
> Signed-off-by: Philo Lu <lulie@linux.alibaba.com>
> ---
>  kernel/bpf/relaymap.c | 32 +++++++++++++++++++++++++++++++-
>  1 file changed, 31 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/bpf/relaymap.c b/kernel/bpf/relaymap.c
> index d0adc7f67758..588c8de0a4bd 100644
> --- a/kernel/bpf/relaymap.c
> +++ b/kernel/bpf/relaymap.c
> @@ -117,7 +117,37 @@ static void *relay_map_lookup_elem(struct bpf_map *map, void *key)
>  static long relay_map_update_elem(struct bpf_map *map, void *key, void *value,
>  				   u64 flags)
>  {
> -	return -EOPNOTSUPP;
> +	struct bpf_relay_map *rmap;
> +	struct dentry *parent;
> +	int err;
> +
> +	if (unlikely(flags))
> +		return -EINVAL;
> +
> +	if (unlikely(key))
> +		return -EINVAL;
> +
> +	rmap = container_of(map, struct bpf_relay_map, map);
> +
> +	/* The directory already exists */
> +	if (rmap->relay_chan->has_base_filename)
> +		return -EEXIST;
> +
> +	/* Setup relay files. Note that the directory name passed as value should
> +	 * not be longer than map->value_size, including the '\0' at the end.
> +	 */
> +	((char *)value)[map->value_size - 1] = '\0';
> +	parent = debugfs_create_dir(value, NULL);
> +	if (IS_ERR_OR_NULL(parent))
> +		return PTR_ERR(parent);
> +
> +	err = relay_late_setup_files(rmap->relay_chan, map->name, parent);
> +	if (err) {
> +		debugfs_remove_recursive(parent);
> +		return err;
> +	}

looks like this patch could be moved to the previous one?

jirka

> +
> +	return 0;
>  }
>  
>  static long relay_map_delete_elem(struct bpf_map *map, void *key)
> -- 
> 2.32.0.3.g01195cf9f
> 
>