[systemd-devel] [PATCH] fstab-generator: Honor usr=, usrfstype= and usrflags=

[Lennart Poettering]

On Thu, 09.10.14 09:37, Tobias Hunger (tobias.hunger at gmail.com) wrote:

> On Oct 8, 2014 2:15 PM, "Harald Hoyer" <harald.hoyer at gmail.com> wrote:
> > > What is the rationale of this patch?
> > > Supporting systems without /etc/fstab in the root device?
> > > Overriding the /etc/fstab settings?
> > >
> > > In a systemd initrd (e.g. in dracut) as soon as initrd-root-fs.target is
> > > reached, initrd-parse-etc.service is executed, which retriggers the
> > > fstab-generator and reads fstab from the real root and generates units
> for /usr.
> 
> Hello Harald,
> 
> The use case is exactly the one Lennart described in his blog about
> deploying Linux in the future.
> 
> My setup now looks like this: I got a Btrfs partition for my Linux
> installations. This partition has a subvol root:somename:someid:x86_64
> containing a Linux installation minus /use.
> 
> Then I have several versions of /use for that distribution in more
> subvolumes named usr:someid:x86_64:version (all with different versions,
> basically getting incremented whenever a new set of packages gets
> installed).
> 
> The idea is to now be able to write bootloader entries for all versions the
> somename-installation.
> 
> For that the initrd needs to know which /usr to mount on top of the root
> partition.
> 
> I can not use the fstab from the root drive here, because that would always
> point to the same version of /use, preventing me to roll back/forward when
> something breaks during an upgrade.
> 
> What I could do instead is to put the information about which subvol to
> mount at /use into the initrd. But I actually think the way of passing this
> into initrd in the same way as the rootfs is more consistent and it also
> saves me from having a new initrd in /boot when libreoffice gets updated.
> That *might* be necessary when using secure boot, but only then.
> 
> Does this explain my motivation for this patch sufficiently?

Hmm, so I think this should be merged, but I'd like to ask for one
more change. We really want to avoid inventing new non-namespaced
kernel command line options, that's really something we should leave
to the kernel guys...

Hence, I'd propose using "mount.usr=", "mount.usrflags=" and
"mount.usrfstype="... Or maybe "fs." as prefix? Or "mnt."? But I think
"mount." is the nicest one, even if it is slightly more to type.

Hope that make sense?

(OTOH I just yesterday merged a patch that introduced a new
un-namespaced kernel cmdline option "rescue", so I am not totall fair
here, but I think that's a special case...)

Lennart

-- 
Lennart Poettering, Red Hat