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

[Tomasz Nowicki]

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@xxxxxxxxxx>
> >
> > 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)

> 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.

Regards,
Tomasz

> > 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@xxxxxxxxxx>
> > Signed-off-by: Tomasz Nowicki <tomasz.nowicki@xxxxxxxxxx>
> > Signed-off-by: Hanjun Guo <hanjun.guo@xxxxxxxxxx>
> > ---
> >   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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