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

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Message-ID: <20181030093842.0e174ea6@xeon-e3>
Date:   Tue, 30 Oct 2018 09:38:42 -0700
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     David Ahern <dsahern@...il.com>
Cc:     Stefano Brivio <sbrivio@...hat.com>,
        "Yoann P." <yoann.p.public@...il.com>, 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:

> On 10/30/18 9:05 AM, Stefano Brivio wrote:
> > Now that we have an abstraction for columns, it's relatively easy to
> > selectively display only some of them, and Yoann has a use case for it.
> > 
> > Patch 1/3 fixes a rendering issue that shows up only when display of
> > arbitrary columns is disabled. Patch 2/3 implements the relevant option,
> > and patch 3/3 makes the output more readable when some columns are
> > disabled.
> > 
> >  
> 
> I like the intent, and I have prototyped something similar for 'ip'.
> 
> 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"
> 
> or for csv output: "%S,%Qr,%Qs,%Al,%Pl,%Ar,%Pr,%p\n"
> 
> I have not had time to look into an implementation for ip. Conceptually
> - and scanning the kernel's vsprintf code - it does not look that
> difficult, just time consuming on the frontend with the initial setup.

The problem with custom formats is that you lose all ability for Gcc
to check format strings.