Mount btrfs from initramfs as /

Mount btrfs from initramfs as /

[Paul Schyska]

Hello,

i recently tried copy my ubuntu intrepid installation to a btrfs file s=
ystem.
This is what I did:
- Download 0.16 tarballs of kernel and progs, build them and install th=
em
Note: I was unable to build the hg trunk. I am using a 2.6.27-rc1 kerne=
l build
with reiser4 patches. The error i got is:=20
/home/pschyska/btrfs/kernel-unstable/extent_io.c: In function
=E2=80=98read_extent_buffer_pages=E2=80=99:
/home/pschyska/btrfs/kernel-unstable/extent_io.c:2942: error: implicit
declaration of function =E2=80=98trylock_page=E2=80=99
However, I was able to build 0.16 release tarballs.
- Next, I copied btrfs.ko to :/lib/modules/2.6.27-rc1-reiser4/kernel/fs=
 and ran
depmod.
- I create an btrfs fs with mkfs.btrfs /dev/sd/lib/modules/2.6.27-rc1-r=
eiser4/a3
and added it to fstab
- After reboot, the btrfs fs was mounted and writable
- I booted into btrfs 0.16 enabled beta of sysresccd and
cp -a /mnt/sda3/* /mnt/sda4
- I modified fstab on /mnt/sda4/etc/fstab to mount the btrfs volume as =
/
- I modified grub/menu.lst accordingly (root=3D/dev/sda3) and update-gr=
ub
- i update etc/initrams-tools/modules to include btrfs and crc32_le and=
 ran
update-initramfs

Unfortunately, i get the error similar to "could not find /dev/sda3" an=
d after a
while drop to busybox (or whatever its called) when booting. In the bus=
ybox
shell i can=20
mount /dev/sda3 /tmp and /tmp shows my btrfs file system
Also, /proc/cmdline shows correct root=3D/dev/sda3
/proc/modules include btrfs and crc32_le.

Am I missing something?
P.S.: I dont have an UUID symlink for /dev/sda3, as I don't know how to=
 find out
the UUID of the new volume. Thats why I didn't specify UUID in fstab bu=
t
/dev/sda3 device.

thank you very much for your help!

P.P.S.: I used a similar process with cp -a from livecd to move my ubun=
tu from
an ext3 volume to reiser4 initially. So it should work!

Best regards,

Paul

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Re: Mount btrfs from initramfs as /

[Jeff Schroeder]

On Fri, Aug 22, 2008 at 7:52 AM, Paul Schyska <pschyska@googlemail.com> wrote:
...snip...
> P.S.: I dont have an UUID symlink for /dev/sda3, as I don't know how to find out
> the UUID of the new volume. Thats why I didn't specify UUID in fstab but
> /dev/sda3 device.

You can find out the UUID with either of these commands
# blkid /dev/sda3
# vol_id -u /dev/sda3

-- 
Jeff Schroeder

Don't drink and derive, alcohol and analysis don't mix.
http://www.digitalprognosis.com

Re: Mount btrfs from initramfs as /

[Paul Schyska]

Jeff Schroeder <jeffschroed <at> gmail.com> writes:

> You can find out the UUID with either of these commands
> # blkid /dev/sda3
> # vol_id -u /dev/sda3
> 

Thank you for this info. 
blkid shows:
/dev/sda3: UUID="59d5f4f0-b746-4147-900c-a1ca0af47c85" TYPE="xfs"
while df -T shows:
/dev/sda3    btrfs    40001848  20046168  19955680  51% /mnt/sda3

how is that possible?
Also, I just had a very odd situation where i accidentally changed fstab on
/dev/sda4 to mount /dev/sda3 as /.
The initramfs with root=/dev/sda4 then booted me to /dev/sda3 as /. However,

initramfs with root=/dev/sda4 did not boot and showed the error described above.
I think I can nail down that problem to the initramfs now ...

Re: Mount btrfs from initramfs as /

[Paul Schyska]

Paul Schyska <pschyska <at> googlemail.com> writes:

> 
> Jeff Schroeder <jeffschroed <at> gmail.com> writes:
> 
> > You can find out the UUID with either of these commands
> > # blkid /dev/sda3
> > # vol_id -u /dev/sda3
> > 
> 
> Thank you for this info. 
> blkid shows:
> /dev/sda3: UUID="59d5f4f0-b746-4147-900c-a1ca0af47c85" TYPE="xfs"
> while df -T shows:
> /dev/sda3    btrfs    40001848  20046168  19955680  51% /mnt/sda3
> 
> how is that possible?

OK, it seems that i got some kind of cached information there. xfs was the fs
type before i remorfatted to btrfs.
After doing vol_id -u /dev/sda3 as root it shows
/dev/sda3: unknown volume type
and since then sudo blkid /dev/sda3
shows an empty line.
Also, blkid /dev/sda4 showed nothing befor but after
sudo vol_id -u /dev/sda4
sudo blkid /dev/sda4 show the correct:
/dev/sda4: UUID="0a7a1695-2e80-486c-ba38-f8d4598cb28b" TYPE="reiser4"