Re: GPT boot has less features than legacy MBR-based one (Was: UEFI, loader.efi and /boot.config)

> > On 18 Jan 2019, at 21:33, Rodney W. Grimes <freebsd-rwg_at_pdx.rh.CN85.dnsmgr.net> wrote:
> > 
> >> 
> >> 
> >>> On 18 Jan 2019, at 19:57, Lev Serebryakov <lev_at_FreeBSD.org> wrote:
> >>> 
> >>> On 18.01.2019 20:13, Warner Losh wrote:
> >>> 
> >>>>> Also, there are same problems with GPT/BIOS setup (which uses GPT but
> >>>>> legacy boot) :-(
> >>>>> 
> >>>> 
> >>>> What same problems? I don't think we've touched how gptboot has handed off
> >>>> to /boot/loader in a long, long time. It there's an issue here, it's a
> >>>> different issue.
> >>> Ok, strictly speaking it is different issue with same "high-level"
> >>> description: pmbr/gptboot has less features than simplest oldest boot0.
> >>> 
> >>> pmbr/gptbood doesn't have any way to select partition to boot from, as
> >>> "boot0" has. No, setting "nextboot" from live system is not a solution.
> >>> I speak about NanoBSD situation when there is tow partitions, both
> >>> bootable, one marked as "active" ("bootme" on GPT parlance) but it is
> >>> completely broken and user need to boot from other one form very
> >>> beginning. This task is trivially solved by "boot0" in pure-MBR case.
> >>> What about GPT/Legacy and GPT/UEFI?
> >>> 
> >>> -- 
> >>> // Lev Serebryakov
> >>> 
> >> 
> >> errm.. you press a key and enter device and or loader path. if it is not working - the code is there to be fixed.
> >> GPT does not have the concept of active partition.
> > 
> > It certainly does, it is called the attribute bootme,
> > and the above correctly states that.
> > 
> 
> Shall you give the reference to specification?:) 

You can bury yourself in that paradigm, but the fact is even the wiki documents
gpt attribute bit 2 as "legacy bootable, equivelant to active flag".

> 
> I am very well aware about the ?vendor? attributes, and I guess You can make a difference about vendor extensions and specification?  
> 
> And regarding to GPT attributes, I personally would avoid writing partition table from the boot loader?

I never advocated writing to anything from the loader.


-- 
Rod Grimes                                                 rgrimes_at_freebsd.org