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SubjectRe: What is the right type to store virtual address ?


On Thu, 19 Aug 1999, Petr Vandrovec wrote:
>
> if we are talking about endianess, I have one related small
> question: in variable of which type I should store return
> value from ioremap() ?

It shouldn't much matter for the simple reason that the only thing you can
do with the return value from ioremap() is to pass it in to read[bwl]()
and friends, and they (for historical reasons) accept both a pointer and a
integer.

So you might as well toss a coin - it has to be something you can do
arithmetic on because I want people to be able to just say "base+offset",
but again "unsigned long" and "void *" are equivalent on gcc in that
regard. If it wasn't for the arithmetic issue I'd just make it a special
type altogether to make the compiler warn about misuses.

For _true_ cleanliness, it should probably be something like

typedef struct {
unsigned long base;
} io_base_t;
/*
* The ISA legacy region 640kB-1M is always mapped,
* here's the base
*/
extern io_base_t isa_io_base;
extern io_base_t ioremap(unsigned long addr, unsigned long len);
extern unsigned char readb(io_base_t base, unsigned int offset);
...

but while I'd potentially like to see that I also wonder about just the
pain of doing the conversion.

Linus


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