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

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Message-ID: <7462e934-f746-eef7-ff92-0eeb8cc08b82@gmail.com>
Date:   Tue, 19 Jul 2022 19:43:46 -0400
From:   Kent Overstreet <kent.overstreet@...il.com>
To:     Steven Rostedt <rostedt@...dmis.org>
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 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.
  - 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.

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 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 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.

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.