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

[Philo Lu]

On 2023/12/22 22:45, Jiri Olsa wrote:

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 <lu...@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?

OK, will do it.

jirka

+
+       return 0;
  }

static long relay_map_delete_elem(struct bpf_map *map, void *key)

--
2.32.0.3.g01195cf9f