linux-kernel - Re: [PATCH] tools/perf/util: Document and clean up readn() a bit

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Date:	Wed, 27 Nov 2013 16:54:12 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	David Ahern <dsahern@...il.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	linux-kernel@...r.kernel.org,
	Frederic Weisbecker <fweisbec@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Mike Galbraith <efault@....de>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH] tools/perf/util: Document and clean up readn() a bit


* Jiri Olsa <jolsa@...hat.com> wrote:

> On Wed, Nov 27, 2013 at 08:19:13AM -0700, David Ahern wrote:
> > On 11/27/13, 4:57 AM, Ingo Molnar wrote:
> > >Okay, I thought this was an intentional 'all or nothing' interface -
> > >but looking at the readn() users they can tolerate partial results
> > >just fine.
> > 
> > I believe that is the intent -- an all or nothing interface.
> 
> all the users either checks the returned value with the size
> or do (ret < 0) and fail

so, a 'ret < 0' check would actually be sensitive to whether readn() 
is an all-or-nothing interface (today), or a partial interface (the 
suggestion).

So it appears keeping it all-or-nothing (i.e. my patch) is the right 
approach.

> and one instance in the read_attr does not check anything and 
> blindly hopes it will read all ;-)
> 
> I have similar patch that also change callers to use proper ssize_t 
> instead of int.. I can rebase and send it separately or combine it 
> with yours.. let me know

Sure ... I just noticed a few patterns. Feel free to use all (or none 
;-) of my patch in your series.

Thanks,

	Ingo
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