linux-kernel - Re: [PATCH v5 03/18] ACPI / table: Count matched and successfully parsed entries without specifying max entries

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Date:	Mon, 24 Nov 2014 16:37:19 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Tomasz Nowicki <tomasz.nowicki@...aro.org>
Cc:	Hanjun Guo <hanjun.guo@...aro.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Mark Rutland <mark.rutland@....com>,
	Olof Johansson <olof@...om.net>,
	Grant Likely <grant.likely@...aro.org>,
	Will Deacon <will.deacon@....com>,
	Graeme Gregory <graeme.gregory@...aro.org>,
	Arnd Bergmann <arnd@...db.de>,
	Sudeep Holla <Sudeep.Holla@....com>,
	Jon Masters <jcm@...hat.com>,
	Jason Cooper <jason@...edaemon.net>,
	Marc Zyngier <marc.zyngier@....com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Mark Brown <broonie@...nel.org>, Rob Herring <robh@...nel.org>,
	Robert Richter <rric@...nel.org>,
	Lv Zheng <lv.zheng@...el.com>,
	Robert Moore <robert.moore@...el.com>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Liviu Dudau <Liviu.Dudau@....com>,
	Randy Dunlap <rdunlap@...radead.org>,
	Charles.Garcia-Tobin@....com, Kangkang.Shen@...wei.com,
	linux-acpi@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, linaro-acpi@...ts.linaro.org
Subject: Re: [PATCH v5 03/18] ACPI / table: Count matched and successfully parsed entries without specifying max entries

On Monday, November 24, 2014 04:01:24 PM Tomasz Nowicki wrote:
> On 24.11.2014 16:16, Rafael J. Wysocki wrote:
> > On Monday, November 24, 2014 09:34:24 AM Tomasz Nowicki wrote:
> >> On 24.11.2014 02:45, Rafael J. Wysocki wrote:
> >>> On Friday, October 17, 2014 09:36:59 PM Hanjun Guo wrote:
> >>>> From: Tomasz Nowicki <tomasz.nowicki@...aro.org>
> >>>>
> >>>> It is very useful to traverse all available table entries without max
> >>>> number of expected entries type. Current acpi_parse_entries()
> >>>> implementation gives that feature but it does not count those entries,
> >>>> it returns 0 instead, so fix it to count matched and successfully
> >>>> entries and return it.
> >>>
> >>> Hmm.  I guess that the goal is for count to only be incremented when the
> >>> condition is satisfied entirely, while without the patch it may be incremented
> >>> even if that isn't the case.
> >>
> >> That would be our goal if patch would look like:
> >> -		    && (!max_entries || count++ < max_entries))
> >> +		    && (!max_entries && count++ < max_entries)) {
> >> but then we can not walk through all available entries (with max_entries==0)
> >
> > No, that's not what I was trying to say. :-)
> >
> >>>
> >>> I'm not sure how that is related to the above paragraph, however.
> >>>
> >>
> >> Previous changelog is not clear, let me rewrite it:
> >>
> >> acpi_parse_entries() allows to traverse all available table entries (aka
> >> subtables) by passing max_entries parameter equal to 0. But for that use
> >> case acpi_parse_entries() does not inform caller how many entries were
> >> matched and for how many entries handler was run against. That patch is
> >> going to fix it.
> >
> > Do I understand correctly that count is only ever incremented by current code
> > if max_entries is different from 0?
> 
> Right. Currently "count" is incremented only if max_entries > 0.

So can you say that in the changelog, please?

Something like:

"acpi_parse_entries() allows to traverse all available table entries (aka
 subtables) by passing max_entries parameter equal to 0, but since its count
 variable is only incremented if max_entries is not 0, the function always
 returns 0 for max_entries equal to 0.  It would be more useful if it returned
 the number of entries matched instead, so make it increment count in that
 case too".

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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