Re: [PATCH bpf-next v8 1/2] bpftool: Add recursive map dumping

[Quentin Monnet <qmo@kernel.org>]

2026-09-26 02:44 UTC+0900 ~ Tianyi Chen <hi@tychen.cc>
> Dumping a map-of-maps currently shows inner map IDs without their
> contents. Add a recursive keyword to map dump to include referenced
> inner maps, leaving the default output unchanged. Show selected maps
> followed by distinct inner maps, preserving plain and BTF formatting
> and using an array of map objects for JSON output.
> 
> Holding every discovered inner-map FD open would make descriptor use
> grow with the number of maps and could exhaust RLIMIT_NOFILE. Keep the
> selected map FDs open, queue distinct inner map IDs, and open, dump and
> close each queued map in turn. This needs only one additional map FD.
> The tradeoff is deferred ID resolution: concurrently removed inner
> maps can disappear before they are opened, so the dump is not atomic.
> 
> Report failure when an inner map cannot be opened, retain per-entry
> lookup errors, and close JSON containers before returning.
> 
> Link: https://github.com/libbpf/bpftool/issues/58
> Assisted-by: LLM
> Signed-off-by: Tianyi Chen <hi@tychen.cc>
> ---
>  .../bpf/bpftool/Documentation/bpftool-map.rst |  15 +-
>  tools/bpf/bpftool/bash-completion/bpftool     |   3 +
>  tools/bpf/bpftool/map.c                       | 147 ++++++++++++++++--
>  3 files changed, 151 insertions(+), 14 deletions(-)
> 
> diff --git a/tools/bpf/bpftool/Documentation/bpftool-map.rst b/tools/bpf/bpftool/Documentation/bpftool-map.rst
> index e4ed7e701c9e..0b804926d829 100644
> --- a/tools/bpf/bpftool/Documentation/bpftool-map.rst
> +++ b/tools/bpf/bpftool/Documentation/bpftool-map.rst
> @@ -16,7 +16,8 @@ SYNOPSIS
>  
>  **bpftool** [*OPTIONS*] **map** *COMMAND*
>  
> -*OPTIONS* := { |COMMON_OPTIONS| | { **-f** | **--bpffs** } | { **-n** | **--nomount** } }
> +*OPTIONS* := { |COMMON_OPTIONS| |
> +{ **-f** | **--bpffs** } | { **-n** | **--nomount** } }


This hunk is no longer necessary now that we use a keyword rather than
an option, please drop the rewrap.

Looks mostly good otherwise, but Sashiko's finding seems correct, so
please look into it.

Thanks,
Quentin