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Hey ironic-ers,

My team has a patch [1] up for enabling PXE for petitboot [2]. It's been 
around for awhile, and we actually use it in our PowerKVM CI ironic job 
(as our OpenPOWER target boxes run petitboot). I was hoping to get some 
eyes on it as we'd like to eventually get it upstream. I've recently 
stripped it down to what I think could be a reasonable change.

In short, this patch adds the use of DHCP option 210 [3] (TFTP path 
prefix) in the PXE module. The path-prefix points to where the 
pxelinux.cfg folder lives.

Petitboot is different from other PXE clients in that it doesn't use the 
pxelinux.0 boot file (or any boot file for that matter). Instead, 
petitboot handles all PXE functionality itself. The issue that arises 
from this is that pxelinux.0 by default derives the path-prefix from 
it's own location. Since petitboot doesn't use this boot file, the 
information must be specified through DHCP option 210.

I've tested this patch against target systems that use petitboot and 
systems that use the pxelinux.0 boot file and it seems to function properly.

While this is an arguably small change, I'm wondering is this should be 
going through the spec process. As well, I'm also wondering if there a 
better/preferred approach (ie - maybe providing path-prefix as a config 
option rather than always using it). I'd really appreciate any feedback!

Thanks,
Mike Turek

[1] https://review.openstack.org/#/c/185987
[2] 
https://www.kernel.org/pub/linux/kernel/people/geoff/petitboot/petitboot.html
[3] https://tools.ietf.org/html/rfc5071#section-5