On 2023/12/23 19:28, Hou Tao wrote:
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 ?
I think a unique directory is enough for a relay map, so currently users can use map_update_elem to set the directory name. Thus $map_name/${value_name}xxx may be better than $map_name/$value_name/xxx.
As for whether map_name or value_name is better to be used as the directory name, I think it more likely that different bpf programs share a same map_name. So value_name is currently used.
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.
Got it. I will fix it in the next version. Thanks.
+ /* 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)
