Re: [PATCH] Add support for specifying the boot device by label

[Nicholas Vinson]

On 9/11/23 07:15, darkpenguin wrote:
> Hmmm, this is actually a good idea. Grub does determine the boot device
> by analyzing fstab, doesn't it? Why does it then use either UUIDs or
> device paths, based on a configuration in a separate file, instead of
> simply reusing exactly what it has found specified in fstab? That would
> have been understandable in the past, when maybe Grub did not support
> UUIDs or labels, so the algorithm would have been "find the specified
> device, then find its path and use that". But now we can simply reuse
> exactly what's specified in fstab, can't we? (Though I'm afraid figuring
> out that process is beyond my skill or capacity at the moment.)
You can write an entry into /etc/fstab that identifies the the rootfs by 
label, uuid, or something else that's supported by `mount`, the init 
system will correctly remount the rootfs using that entry, but if you 
told the kernel to do it, it'd panic with an error (most likely "unknown 
block-device") because the kernel is limited to supporting a very small 
subset of methods.The same argument hold with initramfs images too; 
however, the de-facto standard is that initramfs images support 
root=UUID=... where the UUID is the fs UUID. Therefore, it's assumed 
that with an initramfs, you can mount with device name, partition uuid, 
or fs-uuid. Without an initramfs, booting can only be done using device 
name and partition uuid.

Put simply, the rootfs entry in /etc/fstab (assuming it has one) cannot 
be used to determine how to mount the device at boot time because the 
entry might use a method that neither the kernel nor the initramfs supports.

> On 11/09/23 14:44, Olaf Hering wrote:
> > Sun, 10 Sep 2023 09:30:24 +0000 darkpenguin <darkpenguin@posteo.de>:
> >
> > > Specifying the boot device by its label rather than its UUID can be
> > > pretty useful in various situations (e.g. multiple test VMs).
> > Yes, this is very true.
> >
> > It is up to the local admin to decide how the various block devices
> > are supposed to be mounted. The details how it must be done is
> > configured by the local admin via the well establish file /etc/fstab,
> > and of course other block device related configuration files.
> >
> > As you have noted, any such decision is outright ignored by grub2.
> >
> > So instead of adding more to the existing arrogance, please remove
> > the offending code and implement something that respects the local
> > configuration files.
> >
> > Thank you.
> >
> >
> > Olaf
> >
> >
> >
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