linux-kernel - Re: [PATCH v2 01/28] lib/printbuf: New data structure for printing strings

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Message-ID: <20220526152127.gw7gb4jnoikop4hl@moria.home.lan>
Date:   Thu, 26 May 2022 11:21:27 -0400
From:   Kent Overstreet <kent.overstreet@...il.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...r.kernel.org,
        rostedt@...dmis.org, senozhatsky@...omium.org,
        andriy.shevchenko@...ux.intel.com, willy@...radead.org
Subject: Re: [PATCH v2 01/28] lib/printbuf: New data structure for printing
 strings

On Thu, May 26, 2022 at 05:06:15PM +0200, Petr Mladek wrote:
> On Thu 2022-05-19 13:23:54, Kent Overstreet wrote:
> > This adds printbufs: a printbuf points to a char * buffer and knows the
> > size of the output buffer as well as the current output position.
> > 
> > Future patches will be adding more features to printbuf, but initially
> > printbufs are targeted at refactoring and improving our existing code in
> > lib/vsprintf.c - so this initial printbuf patch has the features
> > required for that.
> 
> > diff --git a/include/linux/printbuf.h b/include/linux/printbuf.h
> > new file mode 100644
> > index 0000000000..40dc07040d
> > --- /dev/null
> > +++ b/include/linux/printbuf.h
> > +static inline void pr_chars(struct printbuf *out, char c, unsigned n)
> > +{
> > +	memset(out->buf + out->pos,
> > +	       c,
> > +	       min(n, printbuf_remaining(out)));
> > +	out->pos += n;
> > +	printbuf_nul_terminate(out);
> > +}
> 
> This function is not later used. Please, do not add API
> that will not have users in the same patchset.
> 
> There are several other cases. I am not going to comment
> all of them.

It is used in this patchset, in lib/vsnprintf.c. You sure about the other cases?

> > +static inline void __pr_char(struct printbuf *out, char c)
> > +{
> > +	if (printbuf_remaining(out))
> > +		out->buf[out->pos] = c;
> > +	out->pos++;
> > +}
> > +
> > +static inline void pr_char(struct printbuf *out, char c)
> > +{
> > +	__pr_char(out, c);
> > +	printbuf_nul_terminate(out);
> > +}
> 
> The "pr_" prefix is a nightmare for me because the same prefix
> is used also for printk() API ;-)
> 
> Could we please use "pb_" instead?

I'm not entirely against that, but I see printbufs as already in this patchset
tightly coupled to vsprintf.c and thus quite related to printk, as well - and
there aren't that many different pr_ things. So I think the shared prefix makes
some sense, I'd like to hear what others think before making that change.