Re: Creating EFI System Partition

[Rod Smith <rodsmith@rodsbooks.com>]

On 06/15/2018 11:01 AM, Andrew Fish wrote:
> 
>> On Jun 15, 2018, at 6:17 AM, Rod Smith <rodsmith@rodsbooks.com 
>> <mailto:rodsmith@rodsbooks.com>> wrote:
>> 
>> but AFAIK, any common tool for creating a FAT32 filesystem should
>> work. I generally do it with mkdosfs in Linux, but equivalent tools
>> in macOS, Windows, or the BSDs also work. In practice, FAT16 and
>> FAT12 usually work, too, although the EFI spec does explicitly say
>> at one point that the filesystem should be FAT32, and I know of at
>> least one implementation that gets a little flaky with FAT16, so
>> I'd stick with FAT32.
>> 
> 
> I seem to remember that the FAT32 spec also defined FAT16 and FAT12.
> it also defines when FAT32, FAT16, or FAT12 should be used for
> media.
> 
> If the edk2 FAT driver has an issue with media that conform to the
> FAT32 spec we should fix that. If the issue is non conferment, then
> we need to decide if the fix can be made that will follow the FAT
> Spec. See that CYA was useful after all :).

No, I didn't mean to imply that the EDK2 FAT driver gets flaky with 12-
or 16-bit FAT filesystems. The EFI in question was an early
EFI-over-BIOS implementation on a Gigabyte motherboard from 2011 or
2012. That thing was a horror, and I wrote up my experiences at the time:

http://www.rodsbooks.com/gb-hybrid-efi/

I no longer have that motherboard, so I can't do any more tests with it
or double-check my findings from 2012. From that page, though:

: A FAT-16 ESP, on the other hand, seems problematic. Ubuntu 11.04 (and
: 11.10) in EFI mode creates a dinky FAT-16 ESP, and after my test
: install of Ubuntu 11.04, the board hung on reboot until I reworked
: the ESP as FAT-32. Thus, if you plan to install Ubuntu, or any other
: OS that creates a FAT-16 ESP, be prepared to fix it, preferably
: before the system reboots!

Note that Ubuntu no longer creates a "dinky FAT-16 ESP;" it now creates
a 512MiB FAT-32 ESP. The experience remains a relevant cautionary tale,
though, for anybody who's trying to write an OS installer, particularly
if the system must be installable on some random computer -- systems
from that period are still in use today, so a FAT-16 ESP could cause
problems in the real world. That said, I've not encountered this problem
on any modern (say, 2014 or later) EFI.

-- 
Rod Smith
rodsmith@rodsbooks.com
http://www.rodsbooks.com