Fixed the fixing of the backup boot sector in ntfsfix

ntfsfix now checks and update the backup boot sector on the last sector of
the partition (instead of the sector next to end of the file system). After
an ntfsresize the file system generally does not use the maximum size because
of different roundings and required alignments in the resizing and the
repartitioning.

diff --git a/ntfsprogs/ntfsfix.c b/ntfsprogs/ntfsfix.c
index 49c59e0..4a2fcac 100644 (file)
--- a/ntfsprogs/ntfsfix.c
+++ b/ntfsprogs/ntfsfix.c
@@ -1276,8 +1276,27 @@ static int try_alternate_boot(ntfs_volume *vol, char *full_bs,
 /*
  *             Check and fix the alternate boot sector
  *
- *     Fixing is only done if the volume could be mounted, and the
- *     last sector designated in the normal boot sector is reachable.
+ *     The alternate boot sector is usually in the last sector of a
+ *     partition, which should not be used by the file system
+ *     (the sector count in the boot sector should be less than
+ *     the total sector count in the partition).
+ *
+ *     chkdsk never changes the count in the boot sector.
+ *     - If this is less than the total count, chkdsk place the
+ *       alternate boot sector into the sector,
+ *     - if the count is the same as the total count, chkdsk place
+ *       the alternate boot sector into the middle sector (half
+ *       the total count rounded upwards)
+ *     - if the count is greater than the total count, chkdsk
+ *       declares the file system as raw, and refuses to fix anything.
+ *
+ *     Here, we check and fix the alternate boot sector, only in the
+ *     first situation where the file system does not overflow on the
+ *     last sector.
+ *
+ *     Note : when shrinking a partition, ntfsresize cannot determine
+ *     the future size of the partition. As a consequence the number of
+ *     sectors in the boot sectors may be less than the possible size.
  *
  *     Returns 0 if successful
  */
@@ -1285,6 +1304,7 @@ static int try_alternate_boot(ntfs_volume *vol, char *full_bs,
 static int check_alternate_boot(ntfs_volume *vol)
 {
        s64 got_sectors;
+       s64 actual_sectors;
        s64 last_sector_off;
        char *full_bs;
        char *alt_bs;
@@ -1305,10 +1325,18 @@ static int check_alternate_boot(ntfs_volume *vol)
        if (br == vol->sector_size) {
                bs = (NTFS_BOOT_SECTOR*)full_bs;
                got_sectors = le64_to_cpu(bs->number_of_sectors);
-               last_sector_off = got_sectors << vol->sector_size_bits;
-               ntfs_log_info("Checking the alternate boot sector... ");
-               br = ntfs_pread(vol->dev, last_sector_off, vol->sector_size,
-                                                       alt_bs);
+               actual_sectors = ntfs_device_size_get(vol->dev,
+                                               vol->sector_size);
+               if (actual_sectors > got_sectors) {
+                       last_sector_off = (actual_sectors - 1)
+                                               << vol->sector_size_bits;
+                       ntfs_log_info("Checking the alternate boot sector... ");
+                       br = ntfs_pread(vol->dev, last_sector_off,
+                                               vol->sector_size, alt_bs);
+               } else {
+                       ntfs_log_info("Checking file system overflow... ");
+                       br = -1;
+               }
                /* accept getting no byte, needed for short image files */
                if (br >= 0) {
                        if ((br != vol->sector_size)