Date: Thu, 29 Aug 1996 17:58:54 +1000 From: Bruce Evans <bde@zeta.org.au> To: bde@zeta.org.au, hackers@FreeBSD.org, rnordier@iafrica.com Subject: Re: Determining disk type & size Message-ID: <199608290758.RAA01914@godzilla.zeta.org.au>
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>>./fdtest /dev/fd0
>>sectors per cylinder: 158 [<-- 30 expected]
>> if (ioctl(fd, DIOCGDINFO, &dl) == -1)
>> err(1, argv[1]);
>> printf("sectors per cylinder: %lu\n", dl.d_secpercyl);
I wrote:
>DIOCGDINFO for floppies just returns whatever happens to be in the label
>area on the disk (*). The label is garbage unless the disk actually has
>a label. There is no way to tell from the ioctl() return value whether
>the label is garbage.
Oops, DIOCGDINFO checks the label magic number and checksum, so
d_secpercyl is probably correct if the label is valid. However,
it's extremely unlikely that a DOS floppy would contain a valid label.
Sector 2 normally contains part of the FAT, and it is very unlikely that
the bytes in the FAT form a valid label.
Bruce
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