[Bug 1491150] Re: 15.10: No SSD TRIM (allow-discards) support in update-initramfs

[TJ]

My fault, I copied the cryptsetup command-line option "--allow-discards"
into crypttab, instead of using the "discard" option as per "man
crypttab".

Interesting that despite the faulty option discard support was
automatically enabled, despite the strong security warning about using
"--allow-discards"  in "man cryptsetup".

** Changed in: cryptsetup (Ubuntu)
       Status: New => Invalid

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Title:
  15.10: No SSD TRIM (allow-discards) support in update-initramfs

Status in cryptsetup package in Ubuntu:
  Invalid

Bug description:
  With a LUKS > LVM > EXT4 rootfs the update-initramfs hooks scripts do
  not include the "allow-discards" option in the generated

  /conf/conf.d/cryptroot

  This prevents all file-systems contained in the LVM VG LVs from using
  the mount option 'discard'.

  $ journalctl | grep -B3 'Mounted /'
  Sep 01 19:48:08 hephaestion.lan.iam.tj systemd-fsck[547]: 14.04_var: recovering journal
  Sep 01 19:48:08 hephaestion.lan.iam.tj kernel: EXT4-fs (dm-3): mounting with "discard" option, but the device does not support discard
  Sep 01 19:48:08 hephaestion.lan.iam.tj kernel: EXT4-fs (dm-3): mounted filesystem with ordered data mode. Opts: discard
  Sep 01 19:48:08 hephaestion.lan.iam.tj systemd[1]: Mounted /usr/local.
  --
  Sep 01 19:48:08 hephaestion.lan.iam.tj systemd[1]: Started Cryptography Setup for LUKS_OS.
  Sep 01 19:48:08 hephaestion.lan.iam.tj kernel: EXT4-fs (dm-2): mounting with "discard" option, but the device does not support discard
  Sep 01 19:48:08 hephaestion.lan.iam.tj kernel: EXT4-fs (dm-2): mounted filesystem with ordered data mode. Opts: discard
  Sep 01 19:48:08 hephaestion.lan.iam.tj systemd[1]: Mounted /var.
  --
  Sep 01 19:48:11 hephaestion.lan.iam.tj systemd[1]: Mounting /boot...
  Sep 01 19:48:11 hephaestion.lan.iam.tj kernel: EXT4-fs (dm-4): mounting ext3 file system using the ext4 subsystem
  Sep 01 19:48:11 hephaestion.lan.iam.tj kernel: EXT4-fs (dm-4): mounted filesystem with ordered data mode. Opts: discard
  Sep 01 19:48:11 hephaestion.lan.iam.tj systemd[1]: Mounted /boot.
  --
  Sep 01 19:48:11 hephaestion.lan.iam.tj systemd[1]: Mounting /home...
  Sep 01 19:48:11 hephaestion.lan.iam.tj kernel: EXT4-fs (dm-6): mounted filesystem with ordered data mode. Opts: discard
  Sep 01 19:48:11 hephaestion.lan.iam.tj systemd[1]: Mounted /home.

  Any encrypted VG that is unlocked by the init system later on
  correctly uses 'allow-discards'

  kernel: Command line: BOOT_IMAGE=/vmlinuz-4.1.0-3-lowlatency
  root=/dev/mapper/VG_OS-ubuntu_15.10_rootfs ro pci=use_crs

  $ cat /etc/crypttab 
  LUKS_OS   UUID=f7175e39-2594-4cb9-b842-de2e1c208f61 /path/to/key.file luks,allow-discards,keyscript=/usr/local/sbin/luks_keyfile.sh

  $ cat /tmp/initrd/conf/conf.d/cryptroot 
  target=LUKS_OS,source=UUID=f7175e39-2594-4cb9-b842-de2e1c208f61,key=/path/to/key.file,rootdev,lvm=VG_OS-ubuntu_14.04_rootfs,keyscript=/lib/cryptsetup/scripts/luks_keyfile.sh

  $ sudo dmsetup table | grep LUKS
  LUKS_DATA: 0 706482157 crypt aes-xts-plain64 0...0 0 8:5 4096 1 allow_discards
  LUKS_BOOT: 0 1568768 crypt aes-xts-plain64 0..0 0 8:3 4096 1 allow_discards
  LUKS_OS: 0 268431360 crypt aes-xts-plain64 0...0 0 8:4 4096

  $ grep discard /etc/fstab
  UUID=6a718a43-2187-49f4-99fd-3f696cb36c4c / ext4 defaults,errors=remount-ro,discard 0 1
  UUID=bd28407f-1ba5-412e-949d-230dab13437a /boot ext3 defaults,discard 0 2
  UUID=fa6d6717-2464-4250-9ba3-0a5cb14a7253 /var ext4 defaults,discard 0 2
  UUID=1d3fa07a-8200-4dd0-99b5-6a598a2636c2 /usr/local ext4 defaults,discard 0 2
  UUID=48a00384-04dc-4ea3-a753-7c68ab306cc7 /home ext4 defaults,discard 0 2

  $ apt-cache policy cryptsetup
  cryptsetup:
    Installed: 2:1.6.6-5ubuntu2

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