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Re: [Patch] Robustly search for ZFS labels & uberblocks

From: Vladimir 'φ-coder/phcoder' Serbinenko
Subject: Re: [Patch] Robustly search for ZFS labels & uberblocks
Date: Sat, 28 Jan 2012 20:21:19 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:9.0) Gecko/20111222 Thunderbird/9.0

On 28.01.2012 19:33, Richard Laager wrote:
On Sat, 2012-01-28 at 13:51 +0100, Vladimir 'φ-coder/phcoder' Serbinenko
Index: grub/util/grub.d/
--- grub.orig/util/grub.d/   2012-01-24 23:44:10.530591000 -0600
+++ grub/util/grub.d/        2012-01-24 23:44:10.706928000 -0600
@@ -56,8 +56,10 @@

-if [ "x`${grub_probe} --device ${GRUB_DEVICE} --target=fs 2>/dev/null || 
true`" = xbtrfs ] \
-    || [ "x`stat -f --printf=%T /`" = xbtrfs ]; then
+LINUX_ROOT_FS=`${grub_probe} --device ${GRUB_DEVICE} --target=fs 2>/dev/null 
|| true`
+LINUX_ROOT_STAT=`stat -f --printf=%T / || true`
+if [ "x${LINUX_ROOT_FS}" = xbtrfs -o "x${LINUX_ROOT_STAT}" = xbtrfs ]; then
     rootsubvol="`make_system_path_relative_to_its_root /`"
     if [ "x${rootsubvol}" != x ]; then
@@ -76,6 +78,10 @@
       GRUB_CMDLINE_EXTRA="$GRUB_CMDLINE_EXTRA crashkernel=384M-2G:64M,2G-:128M"

+if [ "x${LINUX_ROOT_FS}" = xzfs ]; then
   linux_entry ()
@@ -114,6 +120,12 @@
       printf '%s\n' "${prepare_boot_cache}"
+  if [ "x${LINUX_ROOT_FS}" = xzfs ]; then
+    cat<<   EOF
+       insmod zfsinfo
+       zfs-bootfs (\$root) bootfs
This makes 3 wrong assumptions in a row:
- / and /boot may be different.
Despite the variable being called LINUX_ROOT_FS, this is really the
output from grub-probe --device ${GRUB_DEVICE}. When / != /boot, is
$GRUB_DEVICE the device of / or /boot?
Yes. But "zfs-bootfs (\$root) bootfs" will fill "bootfs" with the info for /boot.
- Linux may be in a non-root subvolume. Then the subvolid points to
wrong one.
By "Linux", you're talking about the kernel, as opposed to the root
filesystem, correct?
Sorry, I used wrong term. I meant "OS root".

What do you mean by "non-root subvolume"? That sounds like a btrfs term,
not a ZFS term, so I don't follow.
I refuse to use ZFS terminology due to its term misuse for marketing reasons (calling subvolume a "filesystem" just to say "we handle N*1000000 filesystems on the server" is pure marketing).
In short my system may be in mypool/OS/Debian and not just mypool/

- / may be unaccessible to GRUB altogether.
Are you talking about at grub-install time or boot time? Can you provide
an example of when this might happen, so I can understand.
boot time. Easy: ZFS on LUKS with a separate /boot and GRUB LUKS support disabled (like the default).
In short: this command line part has to be generated on grub-mkconfig
time and have a stable representation. I'd recommend UUID and subvolume
By "this command line part", are you talking about the path to the
The part "fs=zfs $bootfs"

Vladimir 'φ-coder/phcoder' Serbinenko

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