We already have upstream pull request for this -- https://github.com/storaged-project/udisks/pull/474

Hi Vojtech,

How it could be used look like? Is there usage or example? Thanks!

There is a new "Resize" function in the "Encrypted" interface.

Resize /dev/vda (contains unlocked luks device) to 50 MiB
# busctl call org.freedesktop.UDisks2 /org/freedesktop/UDisks2/block_devices/vda org.freedesktop.UDisks2.Encrypted Resize "ta{sv}" $((50*1024*1024)) 0

$ lsblk /dev/vda
NAME                                        MAJ:MIN RM  SIZE RO TYPE  MOUNTPOINT
vda                                         252:0    0  512M  0 disk  
└─luks-d03c2b92-5454-42f8-b77e-85c995e2613f 253:2    0   50M  0 crypt 

Resize /dev/vda back to its original size (0 = max size/size of the underlying device)
# busctl call org.freedesktop.UDisks2 /org/freedesktop/UDisks2/block_devices/vda org.freedesktop.UDisks2.Encrypted Resize "ta{sv}" 0 0

$ lsblk /dev/vda
NAME                                        MAJ:MIN RM  SIZE RO TYPE  MOUNTPOINT
vda                                         252:0    0  512M  0 disk  
└─luks-d03c2b92-5454-42f8-b77e-85c995e2613f 253:2    0  510M  0 crypt

Thanks Vojtech for providing details. 

It works when I resized the unlocked luks device to 50M, but it doesn't work when I tried to resize it to 0. 

*************** snip ************************
# dd if=/dev/zero of=/tmp/tfile_loop0 iflag=fullblock bs=1M count=100
# udisksctl loop-setup -f /tmp/tfile_loop0
Mapped file /tmp/tfile_loop0 as /dev/loop0

# echo Redhat2018|cryptsetup --verbose --cipher aes-xts-plain64 --key-size 512 --hash sha512 --iter-time 5000 luksFormat /dev/loop0

# echo -n Redhat2018>/tmp/passwd.key

# udisksctl unlock -b /dev/loop0 --key-file /tmp/passwd.key
Unlocked /dev/loop0 as /dev/dm-3.

============== TEST START =====================
# lsblk -l 
NAME                                      MAJ:MIN RM  SIZE RO TYPE  MOUNTPOINT
luks-3bb93ed6-d796-4fd4-8736-0d50b242094d 253:3    0   98M  0 crypt

# busctl call org.freedesktop.UDisks2 /org/freedesktop/UDisks2/block_devices/loop0 org.freedesktop.UDisks2.Encrypted Resize "ta{sv}" $((50*1024*1024)) 0

lsblk -l
NAME                                      MAJ:MIN RM  SIZE RO TYPE  MOUNTPOINT
sda                                         8:0    0 68.3G  0 disk  
sda1                                        8:1    0    1G  0 part  /boot
sda2                                        8:2    0 67.3G  0 part  
rhel_storageqe--16-root                   253:0    0 40.7G  0 lvm   /
rhel_storageqe--16-swap                   253:1    0  6.9G  0 lvm   [SWAP]
rhel_storageqe--16-home                   253:2    0 19.9G  0 lvm   /home
loop0                                       7:0    0  100M  0 loop  
luks-3bb93ed6-d796-4fd4-8736-0d50b242094d 253:3    0   50M  0 crypt

# busctl call org.freedesktop.UDisks2 /org/freedesktop/UDisks2/block_devices/loop0 org.freedesktop.UDisks2.Encrypted Resize "ta{sv}" 0 0

# lsblk /dev/loop0'...
NAME                                      MAJ:MIN RM  SIZE RO TYPE  MOUNTPOINT
loop0                                       7:0    0  100M  0 loop  
luks-6a253ff8-8a7f-4d7e-90be-203f8bf74501 253:3    0   98M  0 crypt

============== TEST END =====================
*************** snip ************************

After confirmed with vtrefny@, the test result in #c7 are what we expected. Move it to VERIFIED.

vtrefny@: if you call resize with 0 as size it means to resize it to its maximum size -- e.g size of the underlying device (minus size of the metadata)

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHBA-2018:3271