Messages in this thread | | | Date | Fri, 15 Apr 2011 19:07:01 +0300 | From | Phil Carmody <> | Subject | Re: [PATCH] mm: make read-only accessors take const parameters |
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On 15/04/11 09:51 -0500, ext Christoph Lameter wrote: > On Fri, 15 Apr 2011, Phil Carmody wrote: > > > +++ b/include/linux/mm.h > > @@ -353,9 +353,16 @@ static inline struct page *compound_head(struct page *page) > > return page; > > } > > > > -static inline int page_count(struct page *page) > > +static inline const struct page *compound_head_ro(const struct page *page) > > { > > - return atomic_read(&compound_head(page)->_count); > > + if (unlikely(PageTail(page))) > > + return page->first_page; > > + return page; > > +} > > Can you make compound_head take a const pointer too to avoid this?
Not in C, alas. As it returns what it's given I wouldn't want it to lie about the type of what it returns, and some of its clients want it to return something writeable.
The simplest macro would have multiple-evaluation issues:
#define compound_head(page) (PageTail(page) ? (page)->first_page : (page))
Not that there are any clients who would misuse that currently, but setting traps isn't a good way to make things cleaner.
Phil
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