Date: Tue, 26 Jan 2010 10:24:57 -0800 From: Marcel Moolenaar <xcllnt@mac.com> To: ia64@freebsd.org Subject: About /boot being a symlink to /efi/boot and ZFS Message-ID: <AA18FBE5-DF42-4B2B-B473-1BCAF3FC8472@mac.com>
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All,
Due to limitations of the EFI loader, files under /boot had to
be on the EFI system partition for the boot process to work.
And in order to boot the new kernel after building an installing
a new kernel, the only viable option for that was to make /boot
a symlink to /efi/boot and mount the EFI system partition under
/efi by default.
While initially this was mostly preventing us from having more
than 1 FreeBSD installation on a single machine, over time this
showed to cause bigger problems.
The first and foremost problem is that it causes the kernel to
panic when you use ZFS. The reason for the panic is that ZFS
maintains a cache file that lives under /boot/zfs on FreeBSD.
This is because /boot/zfs really is /efi/boot/zfs on ia64 and
/efi is a FAT file system that needs the Giant lock, which ZFS
simply does not deal with well or at all.
To solve this issue, I had 3 choices:
ZFS-1 Teach ZFS about Giant for the time that Giant is still
around
ZFS-2 Fix the FAT file system implement by not needing Giant
ZFS-3 Eliminate /boot as a symlink to /efi/boot
A second problem recently popped up when mergemaster started to
compare file and directory types and started to complain about
/boot not being a directory like it should be. While this isn't
a big issue, mergemaster has no way of ignoring directories so
it'll will always come up.
To solve the mergemaster issue, I had 2 choices:
MM-1 Extend mergemaster to allow it to ignore directories
without ignoring the files in them
MM-2 Eliminate /boot as a symlink to /efi/boot
It has always been nice to be able to install multiple versions
of FreeBSD, especially for development and maintenance, and for
that to happen, I had to eliminate /boot as a symlink to /efi/boot.
You get the drift...
So, I changed to not use the EFI file system protocol, but rather
the EFI block I/O protocol. This make the loader aware of the
partitions on the disk. Using FreeBSD's file system support on
top of that, we were able to read from the EFI system partition,
a FreeBSD UFS file system and even ISO9660s.
Secondly, I added a command line argument to the loader (a boot
option in EFIs boot manager terminology) so that one can select
the default partition to boot from.
With these 2 changes, the loader can boot FreeBSD directly from
the UFS root file system and consequently /boot does not have to
be a symlink onto /efi and both ZFS and mergemaster are happy
campers.
To migrate your existing installation to the new scheme, follow
the following instructions:
1. Upgrade to the latest 8-STABLE or 9-CURRENT sources.
2. Perform a full 'make buildworld' and 'make buildkernel'
3. Perform a 'make installworld' only
[after step 3 you have the latest loader on /efi]
4. Remove the /boot symlink (and only the symlink)
5. Perform a 'make installworld' again -- a bit excessive,
but easier for the instructions.
[after step 5 you have a minimally populated /boot on the
root file system]
6. Perform a 'make installkernel' -- this installs the
latest kernel in /boot on the root file system.
[after step 6 the EFI file system holds the preview kernel
and the UFS root file system holds the latest kernel]
7. Copy /efi/boot/loader.conf and /efi/boot/device.hints to
/boot/loader.conf and /boot/device.hinst (resp).
8. From /boot/loader.conf, remove the vfs.root.mountfrom
line.
9. Copy the FreeBSD loader to a more proper directory. Type:
# mkdir /efi/FreeBSD
# cp /efi/boot/loader.efi /efi/FreeBSD
10. Reboot.
11. In the EFI boot manager, add a new entry for FreeBSD by
using "FreeBSD/loader.efi" as the loader and "-dev part2:"
as the boot option string (can be either Unicode or ASCII).
12. Boot FreeBSD. Check that the loader version is 2.1. If not,
you're not using the right loader. If the loader version
is right but the loader cannot find a kernel, run 'lsdev'
in the loader to list all partitions and try them until
you find the right one. Note that part0: can be expected
to be the EFI system partition, so you that only if you
can't find a kernel on any other partitons. Remember to
update the EFI boot manager accordingly.
[In FreeBSD, running the latest kernel]
13. Cleanup the EFI system partition:
# rm -rf /efi/boot
NOTE: The installation process has not been changed yet, so a
new installation still makes /boot a symlink to /efi/boot. This
is being worked on -- the installation needs to add a boot
entry to the EFI boot menu to make sure the loader knows which
partition to boot from.
FYI,
--
Marcel Moolenaar
xcllnt@mac.com
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