On Thu, Oct 09, 2025 at 01:24:24AM -0400, Chris Murphy wrote:
> 
> XBOOTLDR is being formatted either ext4 or XFS for a while now in Fedora.
> 
> UEFI spec supports file system drivers.

Yea, and tianocore even has a ext4 driver (see edk2-ext4.rpm and
https://github.com/tianocore/edk2-platforms/tree/master/Features/Ext4Pkg).

But that helps how exactly?

vfat is the only filesystem required by the spec, so that is the one you
can rely on being universally supported.  The ESP must be vfat anyway.

You could place the ext4 driver on the ESP.  Problem one is this is
fragile.  You must arrange for the driver getting loaded.  Either via
UEFI boot configuration (aka efi variables) which may get lost, or using
bootloader specific ways to do so.  Problem two is the drivers are not
signed, so with secure boot turned on this will not work.

I could bake the driver into tho OVMF firmware images.  That would get
us around the secure boot signature requirement.  This obviously would
work for virtual machines only, not your laptop.  It would make virtual
machines have slightly different behavior than bare metal machines,
which can be a source of obscure bugs.  Also virtual machines do not
really need XBOOTLDR, you rarely have to deal with an existing ESP which
is too small, so you can just make the ESP big enough on your images and
be done with it.

take care,
  Gerd

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