[linux_distributions][chromium_os] DLC documentation

[LukeShortCloud]

• DLC location in Chromium OS: /opt/google/dlc/<DLC_NAME>/package/. There are always two files in here:
  • imageloader.json = Information about the image file that contains the package.
  • table = Information about the checksum hash.
• Binaries
  • dlcservice = A daemon that handles downloading DLC from remote servers (Google's Omaha server, by default).
  • dlcservice_util = An end-user tool to install DLCs.
• DLC packages available on Chrome OS:
  • borealis-dlc = For Steam. Not public yet.
  • pita = For Parallels Desktop for Chrome OS.
  • termina-dlc = For Crostini. Also available as DLC for Chromium OS.
• How to create DLC:
  • Latest guide: https://chromium.googlesource.com/chromiumos/platform2/+/HEAD/dlcservice/docs/developer.md
  • Older guide with a simpler example of a DLC package: https://github.com/colemickens/platform2-sommelier/blob/master/dlcservice/docs/developer.md

[LukeShortCloud]

Example of installing termina-dlc:

$ sudo dlcservice_util --id=termina-dlc --install

https://bugs.chromium.org/p/chromium/issues/detail?id=953544

[LukeShortCloud]

The DLC packages live in source code at src/third_party/chromiumos-overlay/chromeos-base/. Only sample-dlc, termina-dlc, and test-dlc exist (borealis-dlc and pita-dlc are missing upstream).

[LukeShortCloud]

For Crostini and Borealis, here are where the read-only kernel and root file system are stored:

$ mount | grep '/run/imageloader'
imageloader on /run/imageloader type tmpfs (rw,nosuid,nodev,noexec,relatime,seclabel,mode=755)
/dev/mapper/DAD94DD7E689D1B9613181CAEF439AFD3306347A3BE978BEA91105FFF4A58733 on /run/imageloader/termina-dlc/package type squashfs (ro,nosuid,nodev,relatime,seclabel)
/dev/mapper/97FAF558800146218A8FC01F8D9858A9816001B65A431ADCF0F273D18909E335 on /run/imageloader/borealis-dlc/package type squashfs (ro,nosuid,nodev,relatime,seclabel)
$ sudo ls -1 /run/imageloader/borealis-dlc/package/root/
credits.html
splash_logo.png
vm_kernel
vm_rootfs.img