Hi,
On 12/22/2023 8:21 PM, 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).
It is a little weird. Because the name of the relay file is
$debug_fs_root/$value_name/${map_name}xxx. Could we update it to
$debug_fs_root/$map_name/$value_name/xxx instead ?
> Signed-off-by: Philo Lu <lulie@xxxxxxxxxxxxxxxxx>
> ---
> 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);
> +
Lock is needed here, because .map_update_elem can be invoked concurrently.
> + /* 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;
> + }
> +
> + return 0;
> }
>
> static long relay_map_delete_elem(struct bpf_map *map, void *key)
