[CRIU] [PATCH 1/6] Replace PAGE_SIZE in vaddr_to_pfn

[Cyrill Gorcunov]

On Wed, Oct 08, 2014 at 07:05:28PM +0400, Pavel Emelyanov wrote:
> >>
> >> Here are the different possible uses of PAGE_SIZE and corresponding
> >> replacements that I came up with:
> >>
> >> PAGE_OR_LESS -- (local) compile-time constant minimum page size, guaranteed to
> >> be less than or equal to one page but not necessarily page aligned
> >>
> >> EXEC_PAGESIZE -- (libc) compile-time constant maximum page size, guaranteed to
> >> be greater than or equal to one page and page aligned
> >>
> >> sysconf(_SC_PAGESIZE) or page_size -- (libc or local) run-time determined
> >> value of the current page size
> >>
> >> (And maybe also something like BUFFER_SIZE, if I run into uses that really
> >> have no functional or performance connection to the page size:
> >> http://lists.busybox.net/pipermail/busybox/2011-June/075864.html)
> > 
> > I see. Indeed we've a number of places where PAGE_SIZE is assumed to be
> > a constant expanded at compile time. I like the idea of introducing
> > these variables. Pavel?
> 
> I've grep-ed around all the '\[PAGE_SIZE' lines. It looks like there's only
> one place that requires a page -- in memory restorer. All other places just
> declare a buffer big enough to fit what it needs (log message, proc file line,
> etc.).  That said, yes I agree that we might need another set of constants
> for such cases, but in all but one of them has nothing to do with a page :)

So lets start with changing buffers size then. I think my ideal scenario
would be to

 - left PAGE_SIZE as a macro (constant for x86 and helper for other archs if needed)
 - in pie code pass PAGE_SIZE as argument (because we can't call for any libc from
   inside of parasite code)
 - for internal buffers which require compiletime sizes simply use PAGE_OR_LESS
   or something like that

iow the less new vars we're introdusing then better. I'm not sure how easy it
would be to implement though.