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

[Nick Piggin]

Matt Mackall wrote:
> 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@xxxxxxxxxxxxxx> 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.

That's a good reason ;)

> 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.

kprobes / systemtap isn't good enough?

--
SUSE Labs, Novell Inc.
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