dos filesystem check

[Richard Hirst]

Hi,
  If you create a file system with an odd number of sectors and then use
the linux mkdosfs to create a FAT filesystem on it, and then do a parted
check on that, you get:

> address@hidden:/build/dosfstools/dosfstools-2.8$ sudo parted -s /dev/sdc
> check 1
> Warning: Partition size (64197 sectors) and filesystem size (64196 sectors) 
> do not match.
> You found a bug in GNU Parted.  Please email a bug report to address@hidden 
> containing the version (1.4.24), and the following message:
> 
> There are no possible configurations for this FAT type.
> address@hidden:/build/dosfstools/dosfstools-2.8$ echo $?
> 0


mkdosfs actually does a binary search up the disk to find the highest
numbered sector it can read, and linux doesn't let you read the last odd
sector of a block device directly.  So, mkdosfs concludes that the
partition size is one sector less than the real size.  A bug in mkdosfs,
maybe; parted behaves like Microsoft s/w in this case.

Anyway, I didn't investigate whether it is just this that parted is
treating as a bug, or whether something else goes wrong as a result.

Also, having decided there is a bug, parted really shouldn't exit with
code 0.

In addition:

> (parted) p
> Disk geometry for /dev/sdc: 0.000-4095.856 megabytes
> Disk label type: msdos
> Minor    Start       End     Type      Filesystem  Flags
> 1          0.031     31.376  primary   FAT         
> 2        101.975    196.105  primary   FAT         
> 3        298.081    902.087  primary   FAT         
> 4        996.218   4000.561  primary   FAT         
> (parted) mkfs 3 fat  
> Warning: Would you like to use FAT32 for this filesystem?  It is much more 
> efficient with your disk space, but is not compatible with early versions of 
> Windows 95 and Windows NT.  Only select yes if you only use Linux, BSD, MS 
> Windows 98 and/or MS Windows 95 B.
> Yes No Cancel ? y
> (parted) check 3
> Warning: File system is reporting the free space as 154493 clusters, not 
> 154318 clusters.
> Ignore Cancel ? 

So something seems amiss with it's creation/checking of FAT32.  All this
with parted 1.4.

Richard