Re: do_mmap

[Thomas 'Dent' Mirlacher]

--snip/snip

> >> is it possible to have 0 as a valid address? - if not, this should
> >> be the return on errors.
> >
> >SuS explicitly says that 0 is not a valid mmap return address.
> 
> But if so, SuS is _very_ _very_ wrong.
> 
> The fact is, if you use something like vm86 mode, you absolutely _need_
> to be able to explicitly mmap at address 0. 
> 
> So it is correct (and in fact there is no other sane way to do it) to
> say
> 
> 	addr = mmap(NULL, 1024*1024,
> 		PROT_READ | PROT_WRITE ,
> 		MAP_ANONYMOUS | MAP_PRIVATE | MAP_FIXED,
> 		-1, 0);
> 
> and if SuS says that mmap must not return NULL for this case, then SuS
> is so full of sh*t that it's not worth worrying about.
> 
> In short, under Linux 0 _is_, and will always be (at least on x86) a
> perfectly valid return address from mmap() and friends. It's only going
> to be returned when you explicitly ask for it with MAP_FIXED, but it
> absolutely is a valid return.

ok. so 0 or (NULL) is not an option, and also unnneccessary once someone
know how the error retun is used. - wouldn't it be much more cleaner
to convert this _ugly_ unsigned long vals into void * wherever these vals
are carrying an address? (well at least for do_mmap*) and use ERR_PTR
for returning, and IS_ERR for checking for an error?

btw, is err should (according to alans explaination be):

	return (unsigned long)ptr > (unsigned long)-1024UL;

	tm

-- 
in some way i do, and in some way i don't.