> On 5. mai 2017, at 22:07, Julian Elischer <jul...@freebsd.org> wrote:
> Subject says it all really, is this an option at this time?
> we'd like to try boot the main zfs root partition and then fall back to a 
> small UFS based recovery partition.. is that possible?
> I know we could use grub but I'd prefer keep it in the family.

it is, sure. but there is an compromise to be made for it.

Lets start with what I have done in illumos port, as the idea there is exactly 
about having as “universal” binaries as possible (just the binaries are listed 
below to get the size):

-r-xr-xr-x   1 root     sys       171008 apr 30 19:55 bootia32.efi
-r-xr-xr-x   1 root     sys       148992 apr 30 19:55 bootx64.efi
-r--r--r--   1 root     sys         1255 okt 25  2015 cdboot
-r--r--r--   1 root     sys       154112 apr 30 19:55 gptzfsboot
-r-xr-xr-x   1 root     sys       482293 mai  2 21:10 loader32.efi
-r-xr-xr-x   1 root     sys       499218 mai  2 21:10 loader64.efi
-r--r--r--   1 root     sys          512 okt 15  2015 pmbr
-r--r--r--   1 root     sys       377344 mai  2 21:10 pxeboot
-r--r--r--   1 root     sys       376832 mai  2 21:10 zfsloader

the loader (bios/efi) is built with full complement - zfs, ufs, dosfs, cd9660, 
nfs, tftp + gzipfs. The cdboot is starting zfsloader (thats trivial string 

The gptzfsboot in illumos case is only built with zfs, dosfs and ufs - as it 
has to support only disk based media to read out the loader. Also I am building 
gptzfsboot with libstand and libi386 to get as much shared code as possible - 
which has both good and bad sides, as usual;)

The gptzfsboot size means that with ufs the dedicated boot partition is needed 
(freebsd-boot), with zfs the illumos port is always using the 3.5MB boot area 
after first 2 labels (as there is no geli, the illumos does not need dedicated 
boot partition with zfs).

As the freebsd-boot is currently created 512k, the size is not an issue. Also 
using common code does allow the generic partition code to be used, so 
GPT/MBR/BSD (VTOC in illumos case) labels are not problem.

So, even just with cd boot (iso), starting zfsloader (which in fbsd has built 
in ufs, zfs etc), you already can get rescue capability. 

Now, even with just adding ufs reader to gptzfsboot, we can use gpt + 
freebsd-boot and ufs root but loading zfsloader on usb image, so it can be used 
for both live/install and rescue, because zfsloader itself has support for all 
file systems + partition types.

I have kept myself a bit off from freebsd gptzfsboot because of simple reason - 
the older setups have smaller size for freebsd boot, and not everyone is 
necessarily happy about size changes:D also in freebsd case there is another 
factor called geli - it most certainly does contribute some bits, but also 
needs to be properly addressed on IO call stack (as we have seen with 
zfsbootcfg bits). But then again, here also the shared code can help to reduce 
the complexity.

Yea, the zfsloader/loader*.efi in that listing above is actually built with 
framebuffer code and compiled in 8x16 default font (lz4 compressed 
ascii+boxdrawing basically - because zfs has lz4, the decompressor is always 
there), and ficl 4.1, so thats a bit of difference from fbsd loader.

Also note that we can still build the smaller dedicated blocks like boot2, just 
that we can not use those blocks for more universal cases and eventually those 
special cases will diminish.


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