Re: UEFI booting survey

On Dec 19, 2017 10:58 AM, "Mark Millard" <markmi_at_dsl-only.net> wrote:

On 2017-Dec-18, at 2:37 PM, Warner Losh <imp at bsdimp.com> wrote:

> . . .
>
> Or the following pseudo-code with all the weird special cases removed for
clarity
>
> load loader.efi from ESP
> if BootXXXX uefi variable holds a second path, use that for root/kernel
> otherwise if an override variable holds a kernel/root path, use that
> otherwise scan for a usable ZFS pool, use that if it exists
> otherwise use the same partition loader.efi was booted from for
root/kernel if it's usable
> otherwise use the first UFS partition on the ESP that's usable.
>
> A partition is usable if /boot/loader.rc exists on that path.

What will be the role of /etc/fstab in establishing
were the kernel is loaded from? Where world is
loaded from? Where/how does use of /etc/fstab for
specifying the root file system mount fit in the
above pseudo-code?


Same as today: it is what the boot loader passes to the kernel as the Unix
name of /. I have no plans to change that. It's of almost no use to the
boot loader, since it can't know what BIOS device da3 is, for example, if
that's in fstab. Or even more complex examples like /dev/mirror/primary.
Efibootmgr can take Unix devices and paths and turn them into UEFI paths so
we know what devices to use for what. In the absence of those, or an
equivalent fallback, we are quite limited in what we can do since we don't
have the context needed to translate.

Warner

(For my particular interest the context uses UFS, not
ZFS.)

> What is being deleted is one final step: "otherwise use the first UFS
partition on any drive in a random order that's usable." which used to be
at the end of the boot1.efi psuedo code. It's my belief that no such
installations actually use this due to the random factor today (plug in a
new USB drive and it might take over). If my belief is wrong, it's my
belief that efibootmgr will solve it, and failing that, the fallback
mechanism (for platforms that use u-boot + EFI where UEFI variables don't
work) will allow the two or three people that are doing this today.


===
Mark Millard
markmi at dsl-only.net