[gparted] Stop over rounding up of signature zeroing lengths (#756829)

[Curtis Gedak <gedakc src gnome org>]

commit eec78cd2b203d9e895c730a547345e4acafc40cf
Author: Mike Fleetwood <mike fleetwood googlemail com>
Date:   Sat Oct 31 10:14:03 2015 +0000

    Stop over rounding up of signature zeroing lengths (#756829)
    
    Following the previous commit "Add erasing of SWRaid metadata 0.90 and
    1.0 super blocks (#756829)" signature zeroing specified to write 4 KiB
    of zeros at position end - 64 KiB, aligned to 64 KiB.  Example operation
    details from formatting a 1 GiB partition to cleared:
    
        Format /dev/sdb8 as cleared
        + calibrate /dev/sdb8
        + clear old file system signatures in /dev/sdb8
          + write 68.00 KiB of zeros as byte offset 0
          + wite 4.00 KiB of zeros at byte offset 67108864
          + wite 64.00 KiB of zeros at byte offset 1073676288
          + write 8.00 KiB of zeros at byte offset 1073733632
          + flush operating system cache of /dev/sdb
    
    However it actually wrote 64 KiB.  This is because the rounding /
    alignment was also applied to the zeroing length.  Before this commit
    rounding / alignment was always less than or equal to the length so this
    wasn't seen before.  Instead just apply device sector size rounding up
    to the length.
    
    Bug 756829 - SWRaid member detection enhancements

 src/GParted_Core.cc |   10 ++++++----
 1 files changed, 6 insertions(+), 4 deletions(-)
---
diff --git a/src/GParted_Core.cc b/src/GParted_Core.cc
index 7616e24..87f9578 100644
--- a/src/GParted_Core.cc
+++ b/src/GParted_Core.cc
@@ -3667,19 +3667,21 @@ bool GParted_Core::erase_filesystem_signatures( const Partition & partition, Ope
                Byte_Value byte_offset ;
                Byte_Value byte_len ;
 
-               //Compute range to be erased taking into minimum desired rounding requirements and
-               //  negative offsets.  Range may become larger, but not smaller than requested.
+               // Compute range to be erased.  Starting position takes into account
+               // negative offsets from the end of the partition and minimum desired
+               // rounding requirements.  Length is only rounded to device sector size.
+               // Ranges may become larger, but not smaller than requested.
                if ( ranges[i] .offset >= 0LL )
                {
                        byte_offset = Utils::floor_size( ranges[i] .offset, rounding_size ) ;
-                       byte_len    = Utils::ceil_size( ranges[i] .offset + ranges[i] .length, rounding_size )
+                       byte_len    = Utils::ceil_size( ranges[i].offset + ranges[i].length, 
lp_device->sector_size )
                                      - byte_offset ;
                }
                else //Negative offsets
                {
                        Byte_Value notional_offset = Utils::floor_size( partition .get_byte_length() + 
ranges[i] .offset, ranges[i]. rounding ) ;
                        byte_offset = Utils::floor_size( notional_offset, rounding_size ) ;
-                       byte_len    = Utils::ceil_size( notional_offset + ranges[i] .length, rounding_size )
+                       byte_len    = Utils::ceil_size( notional_offset + ranges[i].length, 
lp_device->sector_size )
                                      - byte_offset ;
                }