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 16:16:55 +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 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?


> >> NOTE: This change has no impact to x86 and ia64 archs since existing code
> >> checks for error occurrence only (acpi_parse_entries(...,0) < 0).
> >>
> >> Acked-by: Grant Likely <grant.likely@...aro.org>
> >> Signed-off-by: Tomasz Nowicki <tomasz.nowicki@...aro.org>
> >> Signed-off-by: Hanjun Guo <hanjun.guo@...aro.org>
> >> ---
> >>   drivers/acpi/tables.c |    5 ++++-
> >>   1 file changed, 4 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/acpi/tables.c b/drivers/acpi/tables.c
> >> index 21ae521..b18e45e 100644
> >> --- a/drivers/acpi/tables.c
> >> +++ b/drivers/acpi/tables.c
> >> @@ -225,10 +225,13 @@ acpi_parse_entries(unsigned long table_size,
> >>   	while (((unsigned long)entry) + sizeof(struct acpi_subtable_header) <
> >>   	       table_end) {
> >>   		if (entry->type == entry_id
> >> -		    && (!max_entries || count++ < max_entries))
> >> +		    && (!max_entries || count < max_entries)) {
> >>   			if (handler(entry, table_end))
> >>   				return -EINVAL;
> >>
> >> +			count++;
> >> +		}
> >> +
> >>   		/*
> >>   		 * If entry->length is 0, break from this loop to avoid
> >>   		 * infinite loop.
> >>
> >
> --
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-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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