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To: gentoo-dev@g.o
From: Joost Roeleveld <joost@...>
Subject: Re: udev and /usr
Date: Fri, 16 Sep 2011 00:05:37 +0200
On Thursday, September 15, 2011 08:31:51 PM Robin H. Johnson wrote:
> On Thu, Sep 15, 2011 at 10:03:53PM +0200, Joost Roeleveld wrote:
> > On Thursday, September 15, 2011 09:27:06 AM Zac Medico wrote:
> > > On 09/15/2011 09:04 AM, Joost Roeleveld wrote:
> > > > Thank you for your response, however, I do have a few questions
> > > > about
> > > > this. Where will this default initramfs actually need to be
> > > > placed?
> > > 
> > > It should be similar to how sys-apps/v86d is used for uvesafb
> > > support.
> > > It installs /usr/share/v86d/initramfs and when you configure your
> > > kernel, you set CONFIG_INITRAMFS_SOURCE="/usr/share/v86d/initramfs"
> > > in
> > > order to have in included in your kernel image.
> > 
> > Will this be set somewhere globally to the initramfs automatically?
> > And doesn't this mean that a new kernel will need to be build just to
> > satisfy this?
> > 
> > I'm trying to think of how best to avoid users who are not aware to get
> > caught with non-booting systems.
> > 
> > Wouldn't automatic inclusion into grub.conf be a better approach? Not
> > sure if grub.conf can handle a "global" setting for initramfs.
> 
> Grub doesn't support a global initramfs setting, but you can build a
> static initramfs for v86d if needed.

Ok, was afraid there wasn't. If there was, it would make things easier.

> > > > Also, how will
> > > > we be able to deal with situations where this script fails?
> > > 
> > > It should drop you to a minimal shell.
> > 
> > But, with udev then failing, will there be the /dev-entries to mount the
> > different partitions to fix the environment?
> 
> Yes, /dev is provided by devtmpfs already, and that is populated by the
> kernel.

If /dev is already populated by devtmpfs with the stuff for mounting what can 
currently already be mounted without an initramfs. Won't that be sufficient to 
have udev started *after* localmount?

Eg. the following configuration:
Kernel has the "devtmpfs" option
localmount mounts the local filesystems using the devtmpfs /dev-tree
udev is configured to start after localmount

> > > > If Gentoo does decide to follow the initramfs-route, why not
> > > > simply
> > > > implement /etc/init.d/localmount in the initramfs?
> > > 
> > > I think that's pretty close to what we have planned, since the plan
> > > is
> > > to have the initramfs mount configuration stored on the root
> > > filesystem.> 
> > But still require a seperate configuration file for this?
> 
> The configuration file isn't actually required, but it's there in case
> you want to specify MORE filesystems to mount before switching to the
> rootfs init.
> 
> There are two files to load from the rootfs:
> 1. /etc/fstab
> 2. /etc/minimal-filesystems.cfg [exact name undecided]
> 
> The list is in the second file, just one mountpoint per line.
> Defaults to /usr, /var
> If the file is not available, the default is also /usr, /var.
> 
> For each filesystem for the minimal list, use the line from fstab to
> mount it. This covers getting the device, mountpoint and mount options.

Why not try to mount all the filesystems in /etc/fstab in the minimal script 
automatically unless there is a list (not commented out) in /etc/minimal-
filesystems.cfg ?

> There is a catch to this:
> If those non-root filesystems live on LVM or something complex, you're
> going to need to use a more advanced initramfs,
> genkernel/dracut/roll-your-own.

This means that on a system where I currently don't need an initramfs, I 
suddenly need a full-grown initramfs.

> > On my desktop, that would mean the following list:
> > /usr/
> > /var/
> 
> Only these two should be needed to early-boot the system successfully.
> 
> > True, but I don't have any scripts configured for udev on my desktop.
> > My server has some scripts related to Xen, and those are all under
> > /etc/xen/...
> > 
> > In this case, would it still be necessary to use an initramfs?
> 
> Where is /usr, and do you have any udev rules that need /var?

I followed the following guide:
http://www.gentoo.org/doc/en/gentoo-x86+raid+lvm2-quickinstall.xml

I have /usr on LVM which is on top of mdadm-raid1 on the server.
My desktop has the same, except for the raid1-part.

I don't have any udev-rules needing anything outside of /.
Eg. they don't need /usr or anything else that is not part of the root-
filesystem.
The xen-scripts might, but those devices only appear when starting the PV-
domains. And those don't start until well after everything else.

--
Joost


References:
udev and /usr
-- Joost Roeleveld
Re: udev and /usr
-- Joost Roeleveld
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