clevis-luks-askpass.service does not decrypt with a loop way

[zhechen]

host envrioment:
   version: ubuntu-20.04.2 LTS
   kernel: 5.4.0-1043
   clevis-systemd: 12-1ubuntu2.2(amd64)

We want to mount the data disk automatically in NBDE way(ref: https://semanticlab.net/sysadmin/encryption/Network-bound-disk-encryption-in-ubuntu-20.04/), but it's failure when the tang server was temporarily inaccessible. and I found clevis-luks-askpass.service was not send request repeately! It does not meet our expectations.

The error message after reboot host:

  Mar 22 04:37:45 cz-ubuntu20 clevis-luks-askpass[509]: + TS=2022_03_22_04_37_45
  Mar 22 04:37:45 cz-ubuntu20 clevis-luks-askpass[509]: + echo '2022_03_22_04_37_45 [info] clevis unlock done..'
  Mar 22 04:37:45 cz-ubuntu20 clevis-luks-askpass[509]: + '[' true == true ']'
  Mar 22 04:37:45 cz-ubuntu20 clevis-luks-askpass[509]: + '[' false == true ']'
  Mar 22 04:37:45 cz-ubuntu20 clevis-luks-askpass[509]: + (( todo++ ))
  Mar 22 04:37:45 cz-ubuntu20 systemd[1]: clevis-luks-askpass.service: Main process exited, code=exited, status=1/FAILURE
  Mar 22 04:37:45 cz-ubuntu20 systemd[1]: clevis-luks-askpass.service: Failed with result 'exit-code'.

And there is a problem with the following code:

  // /usr/lib/x86_64-linux-gnu/clevis-luks-askpass
    1 #!/bin/bash -e
  ...
  ...
  108 [ "$metadata" == true ] || continue
  109 [ "$unlocked" == true ] && continue
  110 ((todo++)) # -> exit here
  111 done
  112
  113 if [ $todo -eq 0 ] || [ "$loop" != true ]; then
  114 break;
  115 fi

because clevis-luks-askpass enable '-e' at first line, and '((todo++))' return 1, so exit at line 110.

we can use the following method to fix this error:

  110 todo=$((todo+1))
    or
  110 ((todo=todo+1))