On Tue, Jun 4, 2019 at 1:01 PM Nayna [off-list ref] wrote:

It seems efivars were first implemented in sysfs and then later
separated out as efivarfs.
Refer - Documentation/filesystems/efivarfs.txt.

So, the reason wasn't that sysfs should not be used for exposing
firmware variables,
but for the size limitations which seems to come from UEFI Specification.

Is this limitation valid for the new requirement of secure variables ?

I don't think the size restriction is an issue now, but there's a lot
of complex semantics around variable deletion and immutability that
need to be represented somehow.