Date: Tue, 26 Jan 1999 14:02:51 -0800 From: John Plevyak <jplevyak@inktomi.com> To: Robert Nordier <rnordier@nordier.com>, John Plevyak <jplevyak@inktomi.com> Cc: freebsd-hackers@FreeBSD.ORG Subject: Re: raw devices and disk geometry Message-ID: <19990126140251.G19158@proxydev.inktomi.com> In-Reply-To: <199901222319.BAA02045@ceia.nordier.com>; from Robert Nordier on Sat, Jan 23, 1999 at 01:19:07AM %2B0200 References: <19990122124309.C11064@proxydev.inktomi.com> <199901222319.BAA02045@ceia.nordier.com>
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Thanx, but I am not sure this allows me to get the size of a raw partition.
If I call:
fd = open("/dev/rwd2c", O_RDONLY, 0);
ioctl(fd, DIOCGDINFO, &dl)
I get
> /dev/rwd0c:
> a: 65536
> b: 282304
> c: 4305357
> d: 0
> e: 65536
> f: 3891981
> g: 0
> h: 0
The "c:" portion of which does not match the "c:" portion of the
whole disk in your example:
> /dev/rwd0:
> a: 0
> b: 0
> c: 8438850
> d: 0
> e: 0
> f: 0
> g: 0
> h: 0
So this does not seem to be sufficient to determine the size
of /dev/rwd0c on your system. What I really need to know
is a way to determine from /dev/rwd0c
1. the main disk (/dev/rwd0) so I can get its table
2. which partition of the main disk corresponds to /dev/rwd0c
On my disk which does not have a FreeBSD slice, the program returns:
/dev/rwd2
a: 0
b: 0
c: 4124736
d: 0
e: 0
f: 0
g: 0
h: 0
/dev/rwd2c
a: 0
b: 0
c: 4124736
d: 0
e: 0
f: 0
g: 0
h: 0
Which is helpful if I assume that c: on /dev/rwd2c is the whole
disk, but given your counter example above I am not enclined to do that.
Any hints you could give me would be much appreciated.
Also, why shouldn't lseek work on a device? Is this something
we would like FreeBSD to do, or is the current undefined behavior
what we want? Given that this would solve my problem I would consider
making a patch if there was some expectation that it would be accepted.
Thanx again,
john
On Sat, Jan 23, 1999 at 01:19:07AM +0200, Robert Nordier wrote:
> John Plevyak wrote:
>
> > I am trying to find the disk of a raw disk partition (/dev/rwd2c).
> >
> > I have noticed the following in 3.0-CURRENT Jan 12:
> >
> > 1) DIOCGPART does not seem to return valid pointers:
>
> >
> > 2) lseek on raw disks does not seem to produce an error
> > when the size is exceeded. In fact, it acts very
> > oddly when given SEEK_END
>
> > 3) lseek followed by read *can* be used to determine the size of
> > the partition of course this requires a binary search.
> >
> > Are these known issues? Is there a better way of determining
> > the size of a partition from a program?
>
> DIOCGPART is for internal use and not used outside the kernel.
> You can't necessarily rely on lseek() when applied to a device.
>
> However, what you want to do seems fairly simple:
>
> if (ioctl(fd, DIOCGDINFO, &dl) == -1)
> errx(1, "%s: IOCTL(DIOCGDINFO)", argv[1]);
> for (i = 0; i < dl.d_npartitions; i++)
> printf("%c: %u\n", 'a' + i, dl.d_partitions[i].p_size);
>
> With sample output:
>
> /dev/rwd0:
> a: 0
> b: 0
> c: 8438850
> d: 0
> e: 0
> f: 0
> g: 0
> h: 0
>
> /dev/rwd0c:
> a: 65536
> b: 282304
> c: 4305357
> d: 0
> e: 65536
> f: 3891981
> g: 0
> h: 0
>
> The 'c' (raw) partitions give, respectively, the size of the whole
> disk, and of the FreeBSD slice ("fdisk partition").
>
> --
> Robert Nordier
--
John Bradley Plevyak, PhD, jplevyak@inktomi.com, PGP KeyID: 051130BD
Inktomi Corporation, 1900 S. Norfolk Street, Suite 110, San Mateo, CA 94403
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