Refactor clean_grub_dir() to create a backup of all the files, instead
of just irrevocably removing them as the first action. If available,
register atexit() handler to restore the backup if errors occur before
point of no return, or remove the backup if everything was successful.
If atexit() is not available, the backup remains on disk for manual
recovery.
Some platforms defined a point of no return, i.e. after modules & core
images were updated. Failures from any commands after that stage are
ignored, and backup is cleaned up. For example, on EFI platforms update
is not reverted when efibootmgr fails.
Extra care is taken to ensure atexit() handler is only invoked by the
parent process and not any children forks. Some older GRUB codebases
can invoke parent atexit() hooks from forks, which can mess up the
backup.
This allows safer upgrades of MBR & modules, such that
modules/images/fonts/translations are consistent with MBR in case of
errors. For example accidental grub-install /dev/non-existent-disk
currently clobbers and upgrades modules in /boot/grub, despite not
actually updating any MBR.
This patch only handles backup and restore of files copied to /boot/grub.
This patch does not perform backup (or restoration) of MBR itself or
blocklists. Thus when installing i386-pc platform, corruption may still
occur with MBR and blocklists which will not be attempted to be
automatically recovered.
Also add modinfo.sh and *.efi to the cleanup/backup/restore code path,
to ensure it is also cleaned, backed up and restored.
Signed-off-by: Dimitri John Ledkov <xnox@ubuntu.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
8ddbdc3bc2