Re: [PATCH 0/13] maps: pagemap, kpagemap, and related cleanups

Matt Mackall
2007-04-13T00:38:09Z

On Fri, Apr 13, 2007 at 10:15:24AM +1000, Nick Piggin wrote:
> Andrew Morton wrote:
> >On Thu, 12 Apr 2007 16:10:50 -0700
> >William Lee Irwin III <wli@holomorphy.com> wrote:
>
> >>+ while (count > 0) {
> >>+ chunk = min_t(size_t, count, PAGE_SIZE);
> >>+ i = 0;
> >>+
> >>+ if (pfn == -1) {
> >>+ page[0] = 0;
> >>+ page[1] = 0;
> >>+ ((char *)page)[0] = (ntohl(1) != 1);
> >
> >
> >OK.
> >
> >
> >>+ ((char *)page)[1] = PAGE_SHIFT;
> >
> >
> >OK.
>
> Shouldn't we just expose page size and endianness by other means? (another
> file or
> syscall).

If I send you this file dumped from a random machine, you won't know
what to make of it.

I'm planning to write a trivial server to sit on, say, my embedded
target and spew this over the wire to a client.

> >Not a good idea to expose raw flags in this manner - it changes at the drop
> >of a hat. We'd need to also expose the kernel's PG_foo-to-bitnumber
> >mapping to make this viable.
>
> I don't think it is viable because that makes the flags part of the
> userspace ABI. I wonder what they are needed for.

Basically: to show what the hell's going on in the VM.

--
Mathematics is the supreme nostalgia of our time.