linux-kernel - Re: [PATCH v4 00/34] Printbufs - new data structure for building strings

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Date:   Tue, 19 Jul 2022 20:05:07 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Kent Overstreet <kent.overstreet@...il.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org, pmladek@...e.com,
        enozhatsky@...omium.org, linux@...musvillemoes.dk,
        willy@...radead.org
Subject: Re: [PATCH v4 00/34] Printbufs - new data structure for building
 strings

On Tue, 19 Jul 2022 19:43:46 -0400
Kent Overstreet <kent.overstreet@...il.com> wrote:

> On 7/19/22 19:15, Steven Rostedt wrote:
> > On Sun, 19 Jun 2022 20:41:59 -0400
> > Kent Overstreet <kent.overstreet@...il.com> wrote:
> >   
> >> Core idea: Wouldn't it be nice if we had a common data structure and calling
> >> convention for outputting strings?  
> > 
> > Because seq_buf gives us this already, the cover letter really just needs
> > to state exactly what the benefit is to replace seq_buf with printbuf (and
> > why seq_buf can not be simply extended to do some extra features).  
> 
>   - seq_buf has the wrong semantics on overflow for what vsnprintf needs.

More specific please.

>   - seq_buf is somewhat unnecessarily coupled to tracing needs - the 
> readpos member has nothing to do with outputting formatting strings, and 
> some of the pretty-printers are tracing specific and don't really belong 
> in a generic pretty-printing library.

That's not really a benefit between the two.

> 
> And, when I tried to talk to you about changing seq_buf to be more 
> suitable you didn't respond - you just dropped off the IRC discussion we 
> were having.

I told you I've been swamped and this wasn't the best time for me. I
can't drop everything for you.

> 
> > 
> > I just applied your series and ran the tracing selftests and several of
> > them failed.
> > 
> >   # cd tools/testing/selftests/ftrace/
> >   # ./ftracetest  
> 
> Thank you for telling me where to find the tests. It would've saved us 
> some back and forth (and I could've gotten on this sooner) if you'd 
> responded when I asked before.

It's in kernel selftests, they are not hard to find.

> 
> It may seem like the perfectly natural place to look to you - who works 
> on the code - but to someone who works on a variety of subsystems, each 
> of which puts their test code (if they have any!) in a different place, 
> it wasn't.

All the subsystems tests should be in tools/testing/selftests this
isn't just where tracing goes. It's the standard place.

> 
> However, when I enabled all the tracing kernel config options, your 
> tests are now failing to run at all with:
> 
> db_root: cannot open: /etc/target
> 
> So now I've got to debug your tests, too. Gah.

WTF?

-- Steve