netdev - Re: [PATCH iproute2 net-next 0/3] ss: Allow selection of columns to be displayed

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Message-ID: <20181030183420.181b3d51@redhat.com>
Date:   Tue, 30 Oct 2018 18:34:20 +0100
From:   Stefano Brivio <sbrivio@...hat.com>
To:     David Ahern <dsahern@...il.com>
Cc:     "Yoann P." <yoann.p.public@...il.com>,
        Stephen Hemminger <stephen@...workplumber.org>,
        netdev@...r.kernel.org
Subject: Re: [PATCH iproute2 net-next 0/3] ss: Allow selection of columns to
 be displayed

On Tue, 30 Oct 2018 10:34:45 -0600
David Ahern <dsahern@...il.com> wrote:

> A more flexible approach is to use format strings to allow users to
> customize the output order and whitespace as well. So for ss and your
> column list (winging it here):
> 
>     netid          = %N
>     state          = %S
>     recv Q         = %Qr
>     send Q         = %Qs
>     local address  = %Al
>     lport port     = %Pl
>     remote address = %Ar
>     remote port    = %Pr
>     process data   = %p
>     ...
> 
> then a format string could be: "%S  %Qr %Qs  %Al:%Pl %Ar:%Pr  %p\n"

I like the idea indeed, but I see two issues with ss:

- the current column abstraction is rather lightweight, things are
  already buffered in the defined column order so we don't have to jump
  back and forth in the buffer while rendering. Doing that needs some
  extra care to avoid a performance hit, but it's probably doable, I
  can put that on my to-do list

- how would you model automatic spacing in a format string? Should we
  support width specifiers? Disable automatic spacing if a format
  string is given? It might even make sense to allow partial automatic
  spacing with a special character in the format string, that is:

	"%S.%Qr.%Qs  %Al:%Pl %Ar:%Pr  %p\n"

  would mean "align everything to the right, distribute remaining
  whitespace between %S, %Qr and %Qs". But it looks rather complicated
  at a glance.

-- 
Stefano