Re: [PATCH] BIOS boot vs EFI system partition mountpoint

[Taylor R Campbell <riastradh%NetBSD.org@localhost>]

> Date: Sat, 20 Aug 2022 20:45:29 +0700
> From: Robert Elz <kre%munnari.OZ.AU@localhost>
> 
> Of course they wouldn't if they have installed the new version of the PBR
> boot blocks, but I know of lots of people who essentially never do that.
> They have happily done NetBSD upgrades (major version upgrades) without
> touching anything outside the NetBSD filesystems.   At least since we
> stopped encoding the /boot block numbers in the PBR boot code.   The boot
> blocks work, updating them to something which should work, but who knows
> since this is all BIOS using code, and no-one can test against every
> ancient BOIS that ever existed, is dangerous.

Users who update these systems can either:

(a) leave the bootloader as is, and it will continue to work with no
change, or

(b) update the primary bootloader with installboot and move /boot to
/biosboot if they want to turn the existing image into a hybrid image
that can also be booted with EFI (assuming it's already on a GPT).

Nothing in this change will automatically move /boot to /biosboot.  It
will just cause new installations to use /biosboot instead of /boot
(but still support /boot if you, e.g., untar an old file system's
contents into a new file system).

What is the specific problem you foresee?

> Please leave /boot as it is (on x86 and arm and anything else that uses
> something of that name) and make a new standard place for mounting the ESP.
> That can be /efi (which I am currently using) or anywhere else that seems
> reasonable (I can easily update my fstab), just not /boot (not on arm
> systems either, unless there is some very good reason that it has to be
> that way, which I very much doubt - the ESP should contain nothing that
> is needed while the system is running, except when there is a need to
> update it - my /efi is "noauto" in fstab, and I almost never mount it).

The EFI system partition is already mounted by default at /boot on
evbarm and riscv.  That mount point serves a dual purpose both for efi
boot and for fdt boot, and for related things like creds_msdos(8), so
that, e.g., you can update device tree data by extracting a newer
dtb.tgz.  The evbmips generic and octeon images also use /boot for dtb
(not sure any of them boot with EFI).  x86 is the odd one out here.

Part of the purpose is to make a standard mount point so that
automatic upgrade tools can work more reliably.  Obviously if /boot is
not a directory then such tools would have to fall back to manual
intervention for legacy systems.