Re: [PATCH bpf-next] bpftool: Print map_extra in map show

[Quentin Monnet]

2026-10-16 15:16 UTC+0800 ~ chenyuan_fl@xxxxxxx
> From: Yuan Chen <chenyuan@xxxxxxxxxx>
> 
> bpf_map_info::map_extra carries per-map-type creation attributes
> (hash function count for bloom filter, VMA start for arena). The
> kernel prints it in fdinfo, but bpftool does not. Print the raw
> value in plain and JSON output when non-zero, without interpreting
> it per map type, like map_flags. The attribute is already overloaded
> per map type, and bpftool must not grow per-type knowledge of it.


Why not? Do we expect the semantic of map_extra to change? Having
something like "nr_hash_funcs 7" in plain output in the case of a Bloom
filter would be easier to interpret?


> 
> Example (bloom filter with 7 hash functions):
> 
>     117665: bloom_filter  name featu_bloom  flags 0x0
>             key 0B  value 8B  max_entries 128  map_extra 0x7  memlock 520B
>             pids fixture(3543054)
> 
> Signed-off-by: Yuan Chen <chenyuan@xxxxxxxxxx>