kernel panic booting from USB flash drive

Build Host: x86_64 LFS 11.3 SystemV running kernel 6.6.56

I'm building LFS 12.2 SystemD (also kernel 6.6.56, I prefer LTS kernels) to
a
USB flash drive (using shell scripts) with the intent of then booting from
the
USB flash drive to re-run my scripts to build it to a partition on the hd.

Everything is working well *except* the boot.

The flash drive is a single ext4 partition created by using fdisk (LFS
11.3) to
delete what the manufacturer put on it, create a single primary partition of
type Linux, and marking the partition bootable in fdisk.

I then format the single partition with mkfs.ext4 (I *probably* should have
used
ext2 but that's not the issue).

LFS builds on it (albeit slowly), kernel installs, grub-install on /dev/sdi
from
within the chroot after building kernel reports no problems.

This is the grub.cfg I initially tried:

    # Begin /boot/grub/grub.cfg
    set default=0
    set timeout=5

    insmod part_gpt
    insmod ext2
    search --set=root --fs-uuid add2119a-1a46-4c72-b212-863ee869ebd1

    #USB Flash Grub

    menuentry "USB Flash GNU/Linux, Linux 6.6.56-lfs-12.2-systemd" {
      linux /boot/vmlinuz-6.6.56-lfs-12.2-systemd root=PARTUUID=8d5d11ba-01
ro
    }

The UUID and PARTUUID are from the `blkid` command and are correct, and LFS
11.3
booting from a hard drive is just fine with me using them so that changes
in the
device name don't cause issues.

When booting off the flash drive, the grub menu appears and it actually
starts
to boot but I get

    [    0.605403]  msdos
    [    0.605474]  iso9660
    [    0.605545]
    [    0.605685] Kernel panic - not syncing: VFS: Unable to mount root fs
on unkno
    wn-block(0,0)
    [    0.605770] CPU: 5 PID: 1 Comm: swapper/0 Not tainted 6.6.56 #1
    [    0.605850] Hardware name: Supermicro X10SLH-F/X10SLM+-F/X10SLM+-F,
    BIOS 3.3 03/27/2020
    [    0.605934] Call Trace:
    [    0.606011]  <TASK>
    [    0.606077]  dump_stack_lvl+0x38/0x50
    [    0.606157]  panic+0x170/0x320
    [    0.606238]  mount_root_generic+0x24b/0x300
    [    0.606317]  ? rest_init+0xc0/0xc0
    [    0.606394]  prepare_namespace+0x5e/0x270
    [    0.606471]  kernel_init+0x11/0x1a0
    [    0.606567]  ret_from_fork+0x28/0x40
    [    0.606646]  ? rest_init+0xc0/0xc0
    [    0.606722]  ret_from_fork_asm+0x11/0x20
    [    0.606799]  </TASK>
    [    0.606897] Kernel Offset: 0x16c00000 from 0xffffffff81000000
(relocation ran
    ge: 0xffffffff80000000-0xffffffffbfffffff)
    [    0.606987] ---[ end Kernel panic - not syncing: VFS: Unable to
mount root fs
     on unknown- block(0,0) ]---

(above manually transcribed from photo)

It's definitely the Linux kernel and not a bios related kernel as the kernel
version is clearly visible.

I tried changing

    search --set=root --fs-uuid add2119a-1a46-4c72-b212-863ee869ebd1

to

    set root=(hd4,1)

and I tried changing

    root=PARTUUID=8d5d11ba-01

to

    /dev/sdi1

but when I do that, grub can't even find the kernel. Clearly one or both of
those relative device references is wrong when I try it, I suspect the
`set root=(hd4,1)` as I have four physical SATA drives which I think should
correspond to (hd0--hd3) but with bios boot order set to USB first, who
knows?

But anyway I think the `UUID` and `PARTUUID` should work and when used,
clearly
the kernel loads enough to panic.

Same kernel config used as what works with LFS 11.3 but I wonder if maybe
there
are some kernel options I need (or need as built-in instead of modular) to
boot
a kernel off of USB? Anyone know?

Would it be better to make an initramfs that lets kernel modules load
before the
filesystem is mounted and does anyone have a clear reference to that
process?

Thank you for your time.

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