cvs commit: src/sys/fs/msdosfs msdosfs_vfsops.c

Bruce Evans brde at
Sat Jul 14 05:42:50 UTC 2007

On Fri, 13 Jul 2007, Ben Kaduk wrote:

> I recently got a patch committed to the installation chapter of the
> handbook, which included two occasions of clarifying ``MS-DOS
> filesystem'' as ``FAT16 or FAT32'' [1,2 for present incarnation].  I
> am too young to remember the existence of FAT12, so I'll have to defer
> to others as to whether the handbook should mention FAT12 in the same
> breath as FAT16 and FAT32.  What do you think?

I think FAT* is newspeak :-).  The file system is named msdosfs, not FAT.
Anyway, the number of bits per FAT entry is of no interest in most cases,
so it shouldn't be emphasized.  newfs_msdos will choose the best number,
or if you tell it, any number that can work.  newfs_msdos(8) says
"construct a new MS-DOS (FAT) file system ... creates a FAT12, FAT16 or
FAT32 file system".  It doesn't say anything about how newfs_msdos chooses
the best FAT size or other important parameters.  newfs_msdos still hasn't
caught up with the renaming of file systems from foo to foofs.

> [1] 
> [2] 

A quick reading showed some bugs in [2]:
- just after "FAT16 and FAT32", it says "The utility most common usage is
   # mount_msdosfs /dev/ad0s1 /mnt".  It should say something like "This
   utility's most common usage is indirectly via a line in /etc/fstab or
   mount -t msdosfs.  [Example line in fstab, and the above command line
   with direct use of mount_msdosfs fixed.]  This [section of?] the
   handbook is too small to describe utilities in not most common usage
   like newfs_msdos."

- a little later, it says It says "Extended MS-DOS file systems are usually
   mapped after FreeBSD partitions ... with the extended MS-DOS partition
   located on /dev/ad0s3", but there is no such thing as an extended MS-DOS
   file system.  It should say something like "MS-DOS logical drives are
   usually mapped after primary partitions ... with the first logical drive
   being /dev/ad0s3" and possibly add some details ("partition" here means
   an MS-DOS primary partition; MS-DOS extended partitions aren't mapped;
   MS-DOS logical drives correspond to FreeBSD slices, except for primary
   partitions the partitions correspond to slices; check that in MS-DOS
   speak, primary partitions aren't described as logical drives; logical
   drives may or may not contain a file system, but in this example
   /dev/ad0s3 has an MS-DOS file system, and I didn't reword things enough
   to describe this).


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