linux-kernel - Re: [RFC][PATCH 1/3] trace_seq: Move the trace

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Date:	Sun, 22 Jun 2014 09:38:05 +0200
From:	Johannes Berg <johannes@...solutions.net>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>, Jiri Kosina <jkosina@...e.cz>,
	Michal Hocko <mhocko@...e.cz>, Jan Kara <jack@...e.cz>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Dave Anderson <anderson@...hat.com>,
	Petr Mladek <pmladek@...e.cz>
Subject: Re: [RFC][PATCH 1/3] trace_seq: Move the trace_seq code to lib/

On Fri, 2014-06-20 at 12:58 -0400, Steven Rostedt wrote:

> > > +#define HEX_CHARS		(MAX_MEMHEX_BYTES*2 + 1)
> > > +
> > > +int trace_seq_putmem_hex(struct trace_seq *s, const void *mem, size_t len)
> > > +{
> > > +	unsigned char hex[HEX_CHARS];
> > > +	const unsigned char *data = mem;
> > > +	int i, j;
> > > +
> > > +	if (s->full)
> > > +		return 0;
> > 
> > What's this ->full thing all about anyway?  Some central comment which
> > explains the design is needed.
> 
> Comment? What? Git blame isn't good enough for ya? ;-)
> 
> > 
> > Is this test really needed?  trace_seq_putmem() will handle this.
> 
> It was added as an optimization, because once it filled up, you could
> still have multiple calls to the trace_seq() functions that would waste
> time trying to write the buffer.
> 
> It seemed like a good idea at the time. I Cc'd Johannes Berg as he's
> the one that implemented.
> 
> Johannes, is this really needed, should we bother keeping it?

Honestly, I don't remember, sorry.

Looking at the code though, I'm not sure it's a pure optimisation - if
you do say putc() after a failed puts(), without this code the putc()
would succeed? I can't tell right now if that's really a problem, but it
seems you could get some odd behaviour out of it.

johannes

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