Populate the used, unused and unallocated figures in the Partition
object for a LUKS formatted partition. See comment in
luks::set_used_sectors() for the rational of what is used, unused and
unallocated.
As that rational mentions, a LUKS header does not store the size of the
encrypted data and is assumed to extend to the end of the partition by
the tools which start the mapping.
An underlying block device of 128 MiB (131072 KiB).
# sfdisk -s /dev/sde
131072
An active LUKS mapping at offset 2 MiB (4096 512-byte sectors) and
length 126 MiB (129024 KiB, 258048 512-byte sectors).
# sfdisk -s /dev/mapper/sde_crypt
129024
# cryptsetup status sde_crypt
/dev/mapper/sde_crypt is active.
type: LUKS1
cipher: aes-cbc-essiv:sha256
keysize: 256 bits
device: /dev/sde
offset: 4096 sectors
size: 258048 sectors
mode: read/write
No size/length reported when dumping the LUKS header, just (payload)
offset.
# cryptsetup luksDump /dev/sde
LUKS header information for /dev/sde
Version: 1
Cipher name: aes
Cipher mode: cbc-essiv:sha256
Hash spec: sha1
Payload offset: 4096
MK bits: 256
MK digest: 7f fb ba 40 7e ba e4 3b 2f c6 d0 93 7b f7 05 49 7b 72 d4 ad
MK salt: 4a 5b 54 f9 7b 67 af 6e ef 16 31 0a fe d9 7e 5f
c3 66 dc 8a ed e0 07 f4 45 c3 7c 1a 8d 7d ac f4
MK iterations: 37750
UUID: 0a337705-434a-4994-a842-5b4351cb3778
...
Shrink the LUKS mapping to 64 MiB (65536 KiB, 131072 512-byte sectors).
# cryptsetup resize --size 131072 sde_crypt
# sfdisk -s /dev/mapper/sde_crypt
65536
# cryptsetup status sde_crypt
/dev/mapper/sde_crypt is active.
type: LUKS1
cipher: aes-cbc-essiv:sha256
keysize: 256 bits
device: /dev/sde
offset: 4096 sectors
size: 131072 sectors
mode: read/write
Stop and start the LUKS mapping.
# cryptsetup luksClose sde_crypt
# cryptsetup luksOpen /dev/sde sde_crypt
The size of the LUKS mapping is back to 126 MiB (129024 KiB, 258048
512-byte sectors), extending to the end of the partition.
# sfdisk -s /dev/mapper/sde_crypt
129024
# cryptsetup status sde_crypt
/dev/mapper/sde_crypt is active.
type: LUKS1
cipher: aes-cbc-essiv:sha256
keysize: 256 bits
device: /dev/sde
offset: 4096 sectors
size: 258048 sectors
mode: read/write
Bug 760080 - Implement read-only LUKS support
317114ffcb