linux-kernel - Re: [PATCH 2/3] ACPI: fix acpi_parse_entries

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Date:	Fri, 1 Jul 2016 23:46:27 +0200
From:	"Rafael J. Wysocki" <rafael@...nel.org>
To:	Al Stone <ahs3@...hat.com>
Cc:	"Rafael J. Wysocki" <rafael@...nel.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"Rafael J . Wysocki" <rjw@...ysocki.net>,
	Len Brown <lenb@...nel.org>
Subject: Re: [PATCH 2/3] ACPI: fix acpi_parse_entries_array() so it traverses
 all subtables

On Fri, Jul 1, 2016 at 11:41 PM, Al Stone <ahs3@...hat.com> wrote:
> On 07/01/2016 03:32 PM, Rafael J. Wysocki wrote:
>> On Fri, Jul 1, 2016 at 11:21 PM, Al Stone <ahs3@...hat.com> wrote:
>>> Without this patch, the acpi_parse_entries_array() function will return
>>> the very first time there is any error found in either the array of
>>> callback functions or if one of the callbacks returns an non-zero value.
>>> However, the array of callbacks could still have valid entries further
>>> on in the array, or the callbacks may be able to process subsequent
>>> subtables without error.  The change here makes the function consistent
>>> with its description so that it will properly return the sum of all
>>> matching entries for all proc handlers, instead of stopping abruptly
>>> as it does today.
>>
>> I'm not sure I follow.
>>
>> You seem to be saying that the function should process all of the
>> subtables etc even though errors have been found for some of them, but
>> it still will return an error in the end if there are any errors.  How
>> exactly does it help to continue processing in case of an error, then?
>
> The use case I have in mind is to simply count all of the subtables of
> a certain type.  If for some reason, the callback -- or any other callback
> -- fails, the traversal of all the subtables stops immediately.  So, I
> could have two callbacks, and if the first one fails on the first subtable
> of its type, traversal stops.  The count for the second callback will be
> zero which may or may not be correct.

It will be zero, because the callback has not been invoked at all.
Why is this incorrect?