Re: [PATCH] Don't create grubenv on ZFS

[Jordan Uggla]

On Thu, Feb 2, 2012 at 3:16 AM, Richard Laager <address@hidden> wrote:
> GRUB can't write to ZFS.  Creating a grubenv file leads to a misleading
> "sparse file not allowed" error on boot.  The attached patch for
> grub-install skips the creation of a grubenv file on ZFS.

I think that not writing /boot/grub/grubenv is a poor work around for
the problem of grubenv not being writable.

1: Even if it doesn't now, I would expect an error message when
save_env is run and no grubenv is present, so there should be an error
message either way.

2: There are uses for grubenv that do not involve writing to it at
boot. Fedora's grub2 documentation recommends grub-set-default as the
best way to change the default menu entry:
http://fedoraproject.org/wiki/Grub2#Setting_default_entry and if I
understand correctly this should continue to work on any filesystem
which grub can read.

3: It can't be determined with certainty that grubenv will be
writeable at boot. I have run into problems where I installed grub to
an SD card and then flipped the write protect switch on the card,
which could not have been anticipated at grub-install time. For this
reason I think the focus should be on graceful degradation and
understandable error messages when save_env is called with a read only
grubenv (and possibly there should be ways to disable calls to grubenv
in grub-mkconfig, especially in the case of Ubuntu's recordfail
modifications).

I do however think that some utilities should warn (but not otherwise
change their behavior) when grubenv does not appear to be writable.
The prime example of this would be grub-reboot. When grub-reboot is
called with a filesytem / abstraction which will prevent grub from
writing to the grubenv at boot, grub-reboot cannot possibly function.
It already degrades to basically having no effect, so there is no harm
in making the changes to grubenv on the off chance the user knows
better, but it should produce a clear warning that grub-reboot cannot
function without a grubenv writeable by grub at boot.

-- 
Jordan Uggla (Jordan_U on irc.freenode.net)