shred and odd partition sizes

[Bruno Haible]

Hi,

I'm using shred-4.5.7 to clean disk partitions. Often a partition has an odd
number of 512-byte blocks; Linux fdisk indicates such partitions with a '+'.
Shred, when used on such a partition, gives three error messages:

  attempt to access beyond end of device
  03:06: rw=0, want=4200968, (=0x401a08), limit=4200966
  attempt to access beyond end of device
  03:06: rw=0, want=4200968, (=0x401a08), limit=4200966
  /usr/bin/shred: /dev/hda6: error writing at offset 4301787136: Input/output 
error
  attempt to access beyond end of device
  03:06: rw=0, want=4200968, (=0x401a08), limit=4200966
  /usr/bin/shred: /dev/hda6: error writing at offset 4301787137: Input/output 
error

and stops after the first pass. I had left the machine unattended, hoping for
all 25 passes to complete.

The -x option does not help. (Therefore probably the 2003-03-08 modification
to shred.c wouldn't have helped either in this case.)

The only option that helps is to use the --size option with a value of the
limit mentioned above (4200966), minus 2, times 1024. Unfortunately this is
a bit complicated, because I don't know where the "minus 2" comes from,
and also because I need 'bc' to compute this, but it is on the root
partition that I just erased through pass 1/25... OK, the offset from the
first error message does it as well...

Suggestion: Could shred, when encountering this error on a block device file,
print the error message but nevertheless continue with the remaining passes?
That would be more useful than the current behaviour.

Bruno