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From: Robert Nordier <rnordier@nordier.com>
Message-Id: <199901222319.BAA02045@ceia.nordier.com>
Subject: Re: raw devices and disk geometry
In-Reply-To: <19990122124309.C11064@proxydev.inktomi.com> from John Plevyak at "Jan 22, 99 12:43:09 pm"
To: jplevyak@inktomi.com (John Plevyak)
Date: Sat, 23 Jan 1999 01:19:07 +0200 (SAT)
Cc: freebsd-hackers@FreeBSD.ORG
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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

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