Date: Mon, 04 Nov 2002 01:07:22 -0700 (MST) From: "M. Warner Losh" <imp@bsdimp.com> To: jhay@icomtek.csir.co.za Cc: n_hibma@van-laarhoven.org, current@FreeBSD.ORG, phk@critter.freebsd.dk Subject: Re: umass CF geometry problems, was Re: fdisk -BI ob clean disk broken Message-ID: <20021104.010722.110976721.imp@bsdimp.com> In-Reply-To: <200211040802.gA482oJj093121@zibbi.icomtek.csir.co.za> References: <20021104084214.D17734-100000@uitsmijter.van-laarhoven.org> <200211040802.gA482oJj093121@zibbi.icomtek.csir.co.za>
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In message: <200211040802.gA482oJj093121@zibbi.icomtek.csir.co.za>
John Hay <jhay@icomtek.csir.co.za> writes:
: > What is the GET_GEOMETRY used for anyway?
:
: Well the short version of the problem is that "fdisk -BI <disk>" works
: on -stable to get a FreeBSD partition on the Compact Flash. This does
: not work on -current anymore. I have traced that back to the commit
: in umass.c rev 1.61 that removed the fake geometry setting and just
: leave the cylinders, heads and sectors_per_track zero. This cause
: fdisk to coredump with a floating point error.
fdisk is using them, btw, to create a MBR which needs these fields to
be somewhat sane. The floating point error likely is because we're
dividing by zero on this case:
#define RoundCyl(x) ((((x) + cylsecs - 1) / cylsecs) * cylsecs)
if cylsecs is 0, guess what happens. We do similar things with
dos_cylsecs in init_sector0. There's also code in get_params() that
devides by dos_heads * 512 * dos_sectors:
static int
get_params()
{
int error;
u_int u;
off_t o;
error = ioctl(fd, DIOCGFWSECTORS, &u);
if (error == 0)
sectors = dos_sectors = u;
error = ioctl(fd, DIOCGFWHEADS, &u);
if (error == 0)
heads = dos_heads = u;
dos_cylsecs = cylsecs = heads * sectors;
disksecs = cyls * heads * sectors;
error = ioctl(fd, DIOCGSECTORSIZE, &u);
if (error != 0)
u = 512;
error = ioctl(fd, DIOCGMEDIASIZE, &o);
if (error == 0) {
disksecs = o / u;
cyls = dos_cyls = o / (u * dos_heads * dos_sectors);
}
return (disksecs);
}
fdisk likely should do something sane in the face of such insanity,
but it is unclear what and fdisk is a royal pita to work on anyway :-(
Warner
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