Date: Wed, 3 Oct 2001 21:47:49 +1000 (EST) From: Bruce Evans <bde@zeta.org.au> To: Mike Silbersack <silby@silby.com> Cc: Dan Nelson <dnelson@allantgroup.com>, <freebsd-arch@FreeBSD.ORG> Subject: Re: Reading physical memory in a cross-platform way Message-ID: <20011003212829.R97858-100000@delplex.bde.org> In-Reply-To: <20011002122651.P16126-200000@achilles.silby.com>
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On Tue, 2 Oct 2001, Mike Silbersack wrote:
> On Mon, 1 Oct 2001, Dan Nelson wrote:
>
> > > physmem != hw.physmem. The sysctl is actually the output of a function,
> > > not a simple int or the like.
> >
> > Yeah, but look at the function (i386 as an example):
> >
> > static int
> > sysctl_hw_physmem(SYSCTL_HANDLER_ARGS)
> > {
> > int error = sysctl_handle_int(oidp, 0, ctob(physmem), req);
> > return (error);
> > }
> >
> > So the physmem value is just in pages; even though the different
> > platforms use ctob() or <mach>_ptob(), the macros all expand to
> > ((x) << PAGE_SHIFT).
Using ptob() (pages to bytes) would be correct, except ptob() doesn't
exist. There are "only" <mach>_ptob(), ptoa() (pages to address) and
the anachronism ctob() (clicks to bytes), not to mention explicit shifts
and multiplications, to do this conversion.
> True, but I still don't want to spread MD-ish code across the kernel. So,
> I whipped up the patch I proposed. This introduces "maxmembytes", which
> contains the size of ram in bytes. I think I've updated all architectures
> properly, but I've only tested on i386. Could someone working on
> alpha/ia64/sparc check to make sure that it doesn't break compilation?
>
> Unless there are objections, I'll probably commit it in a few days.
No thanks. This spreads MI-ish code across all arches.
Note that physmem is already used in MI code, in vfs_bio_alloc() and
vm_ksubmap_init(). vfs_bio_alloc() is not actually MI -- machine-
dependencies in this code include the magic number 16384 (64MB in
i386 pages). vm_ksubmap_init() uses btoc() (bytes to clicks) to
do the reverse conversion to the one you want.
Bruce
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