netdev - Re: [PATCH 0/3] ss: pretty-printing BPF socket-local storage

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Date: Tue, 28 Nov 2023 14:43:59 -0800
From: Stephen Hemminger <stephen@...workplumber.org>
To: Quentin Deslandes <qde@...cy.de>
Cc: <netdev@...r.kernel.org>, David Ahern <dsahern@...il.com>, Martin KaFai
 Lau <martin.lau@...nel.org>
Subject: Re: [PATCH 0/3] ss: pretty-printing BPF socket-local storage

On Mon, 27 Nov 2023 18:30:55 -0800
Quentin Deslandes <qde@...cy.de> wrote:

> BPF allows programs to store socket-specific data using
> BPF_MAP_TYPE_SK_STORAGE maps. The data is attached to the socket itself,
> and Martin added INET_DIAG_REQ_SK_BPF_STORAGES, so it can be fetched
> using the INET_DIAG mechanism.
> 
> Currently, ss doesn't request the socket-local data, this patch aims to
> fix this.
> 
> The first patch fixes a bug where the "Process" column would always be
> printed on ss' output, even if --processes/-p is not used.
> 
> Patch #2 requests the socket-local data for the requested map ID
> (--bpf-map-id=) or all the maps (--bpf-maps). It then prints the map_id
> in a dedicated column.
> 
> Patch #3 uses libbpf and BTF to pretty print the map's content, like
> `bpftool map dump` would do.
> 
> While I think it makes sense for ss to provide the socket-local storage
> content for the sockets, it's difficult to conciliate the column-based
> output of ss and having readable socket-local data. Hence, the
> socket-local data is printed in a readable fashion over multiple lines
> under its socket statistics, independently of the column-based approach.
> 
> Here is an example of ss' output with --bpf-maps:
> [...]
> ESTAB                  2960280             0 [...]
>     map_id: 259 [
>         (struct my_sk_storage) {
>             .field_hh = (char)127,
>             .<anon> = (union <anon>) {
>                 .a = (int)0,
>                 .b = (int)0,
>             },
>         },
>     ]
> 
> Quentin Deslandes (3):
>   ss: prevent "Process" column from being printed unless requested
>   ss: add support for BPF socket-local storage
>   ss: pretty-print BPF socket-local storage
> 
>  misc/ss.c | 822 +++++++++++++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 818 insertions(+), 4 deletions(-)


Useful, but ss is growing into a huge monolithic program and may need some
refactoring. Also, this cries out for a json output format. Which ss doesn't
have yet.