newfs_msdos and dvd-ram (fwsectors, fwheads)

Andriy Gapon avg at
Thu Feb 21 14:37:38 UTC 2008

on 21/02/2008 16:27 Bruce Evans said the following:
> On Thu, 21 Feb 2008, Andriy Gapon wrote:
>> on 17/02/2008 13:39 Andriy Gapon said the following:
>>> Should newfs_msdos be able to work on "whole" cdX/acdX device ?
>>> [ufs/ffs] newfs can do it.
>>> But with newfs_msdos I had to run disklabel first and then I could
>>> create a filesystem on cdXa, but I couldn't do it on the whole disk.
>> It seems that the reason for this newfs_msdos behavior is in the
>> following lines:
>> if (ioctl(fd, DIOCGSECTORSIZE, &dlp.d_secsize) == -1)
>>    errx(1, "Cannot get sector size, %s", strerror(errno));
>> if (ioctl(fd, DIOCGFWSECTORS, &dlp.d_nsectors) == -1)
>>    errx(1, "Cannot get number of sectors, %s", strerror(errno));
>> if (ioctl(fd, DIOCGFWHEADS, &dlp.d_ntracks)== -1)
>>    errx(1, "Cannot get number of heads, %s", strerror(errno));
>> While a failure to get sector size is a serious situation indeed, number
>> of sectors per track and number of heads are just relics of the past and
>> are not applicable to all types of should-be-supported media.
>> What's even more funny is that those values can be set via command line
>> options and in that case values from ioctl are not used at all.
> Also, it needs the BIOS geometry, but has been broken to ask for, and


you lost me after this. I understand that you speak about a general
case, but is there a "BIOS geometry" for DVD-RAM disk ?
Would any information about physical structure of DVD-RAM disk prove
useful for FAT on it ?
I thought that all those CHS parameters were useful only in times when
CHS was the disk access mode (and maybe for performance optimizations).
I don't see how those parameters can be of any real use now.

P.S. I must declare that I know zero about FAT.

Andriy Gapon

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