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aufs initramfs question

From: Philipp Wehrheim <flipstar@gm...> - 2007-10-19 15:39

Hey List,

I'm trying to use aufs in combination with initramfs and a mtd-flash
device but I can't really figure out how to do it.

What I want is:

- boot the kernel that starts the initramfs.
- the initramfs init checks if it can find a partition on the hd via
findfs
- and if it finds the partition mounts a squashfs(ro) and the hd
partition (rw) to /newroot
mount <hd> /aufs
cat <mtd> > /squashfs.img
mount -n /squashfs.img /squash
mount -n -t aufs -o br=/aufs:/squash none /newroot

- if the partition is not found it mounts some tmpfs and the squashfs
mount -n -t tmpfs /aufs
mount -n <mtd> /squash
mount -n -t aufs -o br=/aufs:/squash none /newroot

- in the end init calls
exec switch_root /newroot /sbin/init

Can this work?
Because there are some active mount when I call switchroot?

Can anybody share some experience please.

--
flip

Re: aufs initramfs question

From: Michael Towers <mt.42@we...> - 2007-10-19 16:49

Hi Philipp,

Yes, something like that should work - it's more or less how most live
CDs do it (though I can't speak for the details, I haven't used this
method for a while - I am now using klibc instead of busybox and
mounting aufs later).

If you need example scripts you could look at linux-live, for example.

As to the active mounts, so long as you don't want to manipulate them
afterwards, that seems to be no big problem.

Best wishes,
mt

Philipp Wehrheim wrote:
> Hey List,
>
>
> I'm trying to use aufs in combination with initramfs and a mtd-flash
> device but I can't really figure out how to do it.
>
> What I want is:
>
> - boot the kernel that starts the initramfs.
> - the initramfs init checks if it can find a partition on the hd via
> findfs
> - and if it finds the partition mounts a squashfs(ro) and the hd
> partition (rw) to /newroot
> mount <hd> /aufs
> cat <mtd> > /squashfs.img
> mount -n /squashfs.img /squash
> mount -n -t aufs -o br=/aufs:/squash none /newroot
>
> - if the partition is not found it mounts some tmpfs and the squashfs
> mount -n -t tmpfs /aufs
> mount -n <mtd> /squash
> mount -n -t aufs -o br=/aufs:/squash none /newroot
>
> - in the end init calls
> exec switch_root /newroot /sbin/init
>
> Can this work?
> Because there are some active mount when I call switchroot?
>
> Can anybody share some experience please.
>
> --
> flip
>
>
> -------------------------------------------------------------------------
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Re: aufs initramfs question

From: <flipstar@gm...> - 2007-10-19 18:44

Hey Michael,

thanks for your quick reply.

> Hi Philipp,
>
> Yes, something like that should work - it's more or less how most live
> CDs do it (though I can't speak for the details, I haven't used this
> method for a while - I am now using klibc instead of busybox and
> mounting aufs later).
>
> If you need example scripts you could look at linux-live, for example.
>
> As to the active mounts, so long as you don't want to manipulate them
> afterwards, that seems to be no big problem.

Yes I will have to manipulate the mountpoints I guess.
It is possible that I'll have to unmount aufs, which will
be "one layer below".
Do you/anybody see a way how this could be achieved?

--
flip

>
> Best wishes,
> mt
>
> Philipp Wehrheim wrote:
> > Hey List,
> >
> >
> > I'm trying to use aufs in combination with initramfs and a mtd-flash
> > device but I can't really figure out how to do it.
> >
> > What I want is:
> >
> > - boot the kernel that starts the initramfs.
> > - the initramfs init checks if it can find a partition on the hd via
> > findfs
> > - and if it finds the partition mounts a squashfs(ro) and the hd
> > partition (rw) to /newroot
> > mount <hd> /aufs
> > cat <mtd> > /squashfs.img
> > mount -n /squashfs.img /squash
> > mount -n -t aufs -o br=/aufs:/squash none /newroot
> >
> > - if the partition is not found it mounts some tmpfs and the squashfs
> > mount -n -t tmpfs /aufs
> > mount -n <mtd> /squash
> > mount -n -t aufs -o br=/aufs:/squash none /newroot
> >
> > - in the end init calls
> > exec switch_root /newroot /sbin/init
> >
> > Can this work?
> > Because there are some active mount when I call switchroot?
> >
> > Can anybody share some experience please.
> >
> > --
> > flip
> >
> >
> >
> -------------------------------------------------------------------------
> > This SF.net email is sponsored by: Splunk Inc.
> > Still grepping through log files to find problems? Stop.
> > Now Search log events and configuration files using AJAX and a browser.
> > Download your FREE copy of Splunk now >> http://get.splunk.com/
> >
>
>
> -------------------------------------------------------------------------
> This SF.net email is sponsored by: Splunk Inc.
> Still grepping through log files to find problems? Stop.
> Now Search log events and configuration files using AJAX and a browser.
> Download your FREE copy of Splunk now >> http://get.splunk.com/

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Re: aufs initramfs question

From: Michael Towers <mt.42@we...> - 2007-10-19 20:12

flipstar@gm... wrote:
> Hey Michael,
>
> thanks for your quick reply.
>
>> Hi Philipp,
>>
>> Yes, something like that should work - it's more or less how most live
>> CDs do it (though I can't speak for the details, I haven't used this
>> method for a while - I am now using klibc instead of busybox and
>> mounting aufs later).
>>
>> If you need example scripts you could look at linux-live, for example.
>>
>> As to the active mounts, so long as you don't want to manipulate them
>> afterwards, that seems to be no big problem.
>
> Yes I will have to manipulate the mountpoints I guess.
> It is possible that I'll have to unmount aufs, which will
> be "one layer below".
> Do you/anybody see a way how this could be achieved?
>

I think here you need to consider very carefully what you want to
achieve. Your situation as I understand it is that you intend to make
the aufs your root filesystem (that's what the switch_root does). As far
as I know (which, I admit, is not very far!) there is no way back to the
initramfs root. But why would you want to get out of the aufs?

I did consider several variations on the theme while working on a live
CD construction kit (larch) for Archlinux. The current version doesn't
use an aufs root but uses separate aufs mounts for all the root
directories (/bin, /etc, /usr, and so on). It's quite a bit more
complicated than the basic approach, using multistage system
initialization and shutdown, but it does allow the aufs mounts to be
unmounted in a fairly orderly manner at shutdown.

This allows me to add sessions to the boot CD/DVD at shutdown, but -
especially in view of the fact that many computers can't boot from
multisession CD - I'm not completely convinced that the extra complexity
is justified.

There may of course be simpler ways to achieve this sort of thing. I,
too, would be glad to hear of them!

>> Philipp Wehrheim wrote:
>>> Hey List,
>>>
>>>
>>> I'm trying to use aufs in combination with initramfs and a mtd-flash
>>> device but I can't really figure out how to do it.
>>>
>>> What I want is:
>>>
>>> - boot the kernel that starts the initramfs.
>>> - the initramfs init checks if it can find a partition on the hd via
>>> findfs
>>> - and if it finds the partition mounts a squashfs(ro) and the hd
>>> partition (rw) to /newroot
>>> mount <hd> /aufs
>>> cat <mtd> > /squashfs.img
>>> mount -n /squashfs.img /squash
>>> mount -n -t aufs -o br=/aufs:/squash none /newroot
>>>
>>> - if the partition is not found it mounts some tmpfs and the squashfs
>>> mount -n -t tmpfs /aufs
>>> mount -n <mtd> /squash
>>> mount -n -t aufs -o br=/aufs:/squash none /newroot
>>>
>>> - in the end init calls
>>> exec switch_root /newroot /sbin/init
>>>
>>> Can this work?
>>> Because there are some active mount when I call switchroot?
>>>
>>> Can anybody share some experience please.
>>>
>>> --
>>> flip
>>>

Re: aufs initramfs question

From: <sfjro@us...> - 2007-10-20 03:33

Michael Towers:
> flipstar@gm... wrote:
:::
> > Yes I will have to manipulate the mountpoints I guess.
> > It is possible that I'll have to unmount aufs, which will
> > be "one layer below".
> > Do you/anybody see a way how this could be achieved?
:::
> initramfs root. But why would you want to get out of the aufs?

The same question came to my mind.
But I think what you need is 'mount --move' before switch_root.
See also CVS_TREE/aufs/sample/diskless/linuxrc.

When you use aufs as a root filesystem, you need to pay attention at
shutdown. Generally the shutdown script remount the root filesystem as
readonly because it cannot be unmounted.
In aufs world, you also need to remount your writable branch filesystem
as readonly, in order to flush/write-back to the branch.

(from the aufs manual)
----------------------------------------------------------------------
When your aufs is the root directory of your system, and your system
tells you some of the filesystem were not unmounted cleanly, try these
procedure when you shutdown your system.
.nf
# mount -no remount,ro /
# for i in $writable_branches
# do mount -no remount,ro $i
# done
.fi
If your xino file is on a hard drive, you also need to specify
`noxino' option or `xino=/your/tmpfs/xino' at remounting root
directory.
----------------------------------------------------------------------

Junjiro Okajima

Re: aufs initramfs question

From: Michael Towers <mt.42@we...> - 2007-10-20 05:03

sfjro@us... wrote:
> Michael Towers:
>> flipstar@gm... wrote:
> :::
>>> Yes I will have to manipulate the mountpoints I guess.
>>> It is possible that I'll have to unmount aufs, which will
>>> be "one layer below".
>>> Do you/anybody see a way how this could be achieved?
> :::
>> initramfs root. But why would you want to get out of the aufs?
>
> The same question came to my mind.
> But I think what you need is 'mount --move' before switch_root.
> See also CVS_TREE/aufs/sample/diskless/linuxrc.
>

I see you are using initrd there. I am not at all sure about this, but I
think the situation is a bit different with initramfs because it's not a
'real' filesystem. I could even imagine it's possible to return to the
initrd at shutdown, but I think with initramfs this won't work. Please
correct me if I am wrong.

Regards,
mt

> When you use aufs as a root filesystem, you need to pay attention at
> shutdown. Generally the shutdown script remount the root filesystem as
> readonly because it cannot be unmounted.
> In aufs world, you also need to remount your writable branch filesystem
> as readonly, in order to flush/write-back to the branch.
>
> (from the aufs manual)
> ----------------------------------------------------------------------
> When your aufs is the root directory of your system, and your system
> tells you some of the filesystem were not unmounted cleanly, try these
> procedure when you shutdown your system.
> .nf
> # mount -no remount,ro /
> # for i in $writable_branches
> # do mount -no remount,ro $i
> # done
> .fi
> If your xino file is on a hard drive, you also need to specify
> `noxino' option or `xino=/your/tmpfs/xino' at remounting root
> directory.
> ----------------------------------------------------------------------
>
>
> Junjiro Okajima
>

Re: aufs initramfs question

From: <sfjro@us...> - 2007-10-20 05:05

Michael Towers:
> I see you are using initrd there. I am not at all sure about this, but I
:::

The sample in aufs cvs tree supports initramfs too.

Junjiro Okajima

Re: aufs initramfs question

From: Michael Towers <mt.42@we...> - 2007-10-20 05:17

sfjro@us... wrote:
> Michael Towers:
>> I see you are using initrd there. I am not at all sure about this, but I
> :::
>
> The sample in aufs cvs tree supports initramfs too.
>
>
> Junjiro Okajima
>

Could it be that there is a difference in regard to this in pivot_root
and switch_root? I haven't used root aufs for a while so I'm not sure
exactly what code I used but I don't remember using mount --move and I
don't remember any problems.

Regards,
mt

Re: aufs initramfs question

From: <sfjro@us...> - 2007-10-20 05:27

Michael Towers:
> Could it be that there is a difference in regard to this in pivot_root
> and switch_root? I haven't used root aufs for a while so I'm not sure
> exactly what code I used but I don't remember using mount --move and I
> don't remember any problems.

In the case of pivot_root, you can still see the contents of old root
which is the second parameter of pivot_root.
In switch_root, which is basically equivalent to
mount(".", "/", NULL, MS_MOVE, NULL)
chroot(".")
you can't see the contents of old root dir unless you move or copy them
before switch_root. You can access the aufs branch filesystems if you
mount --move them into under new root.
If you don't need accessing branches manually after switch_root, you
don't have move them. Aufs can access them if you don't move.

Junjiro Okajima

Re: aufs initramfs question

From: <flipstar@gm...> - 2007-10-20 10:21

Hey everybody,

thanks for your suggestions!

I'll try on monday (when I have access to the SOC).

To be more presiese of my setup:
Im talking about a NAS that my or may not have a HD installd.
The situation when I have to umount the HD (aufs) is when
the user decides to reformat the hd or even change the partition layout.

Mount move sounds promissing and I'll report if and how it works for me.

Im now also thinking about exchanging the squash image with
a ro jffs(2?) partition to save some space/ram.

Have a nice weekend.

--
flip

>
> Michael Towers:
> > Could it be that there is a difference in regard to this in pivot_root
> > and switch_root? I haven't used root aufs for a while so I'm not sure
> > exactly what code I used but I don't remember using mount --move and I
> > don't remember any problems.
>
> In the case of pivot_root, you can still see the contents of old root
> which is the second parameter of pivot_root.
> In switch_root, which is basically equivalent to
> mount(".", "/", NULL, MS_MOVE, NULL)
> chroot(".")
> you can't see the contents of old root dir unless you move or copy them
> before switch_root. You can access the aufs branch filesystems if you
> mount --move them into under new root.
> If you don't need accessing branches manually after switch_root, you
> don't have move them. Aufs can access them if you don't move.
>
>
> Junjiro Okajima
>
> -------------------------------------------------------------------------
> This SF.net email is sponsored by: Splunk Inc.
> Still grepping through log files to find problems? Stop.
> Now Search log events and configuration files using AJAX and a browser.
> Download your FREE copy of Splunk now >> http://get.splunk.com/

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Re: aufs initramfs question

From: Philipp Wehrheim <flipstar@gm...> - 2007-10-23 11:44

Hey everybody,

I just want to share my expirences with initramfs and aufs.
Again I have to say that the kind manner in this list
is something I really like.

my initramfs structur looks like this:

./
|-- aufs
|-- bin
| |-- busybox
| |-- cat -> busybox
| |-- cut -> busybox
| |-- echo -> busybox
| |-- findfs -> busybox
| |-- grep -> busybox
| |-- ls -> busybox
| |-- mdev -> busybox
| |-- mkdir -> busybox
| |-- mount -> busybox
| |-- msh -> busybox
| |-- sh -> busybox
| |-- switch_root -> busybox
| |-- test -> busybox
| `-- umount -> busybox
|-- dev
| `-- console
|-- flashroot
|-- init
|-- newroot
|-- proc
`-- sys

stuffed in a initramfs_data.cpio.gz its about 334K.

The init script can be found below.

--
flip

cat init
#!/bin/sh
#
# simple phase 1 init script
#
# by: Philipp Wehrheim 20071023
#
# This file is released under the GPLv2.
#
export PATH="/bin"
#
# OVERLAYLABEL is the filesystem lable
# of the overlay partition
OVERLAYLABEL="Overlay"
#
# mount
mount -n -t proc proc /proc
mount -n -t sysfs sysfs /sys
mount -n -t tmpfs tmpfs /dev
#
# mdev create devices
mdev -s

#
# find mtd Ramdisk
MTDRAMDISK=`cat /proc/mtd | grep Ramdisk | cut -d':' -f1`

#
# find the overlay partition
#
# WARNING: What happens if more than one Devices with the label is fond?
echo "searching for filesystem $OVERLAYLABEL"
PARTITION=`findfs LABEL=$OVERLAYLABEL 2>/dev/null`

echo "PARTITION: $PARTITION"

# if findfs found a partition try to mount it
if test $? -eq 0 ; then
echo "mounting /aufs partition"
mount $PARTITION /aufs >/dev/null 2>&1
fi

# if the mount did not succeed
if test $? -ne 0 ; then
echo "mounting /aufs with tmpfs"
mount -t tmpfs tmpfs -o size=10m /aufs >/dev/null 2>&1
fi

# extract squash image from flash
cat /dev/$MTDRAMDISK > /squash.img

# mount the squash.img
mount -n -t squashfs -o loop /squash.img /flashroot

# mount aufs and squash.img to newroot
mount -n -t aufs -o br=/aufs:/flashroot none /newroot

# create mountpoints for mount move
mkdir /newroot/system/aufs
mkdir /newroot/system/flashroot

# move the mountpoints
# into the new root
mount --move /aufs /newroot/system/aufs
mount --move /flashroot /newroot/system/flashroot

# clean up
umount -l /proc /sys /dev

# switch root
exec switch_root /newroot /sbin/init

aufs

Email Archive: aufs-users (read-only)

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