Autoconfiguring root device and fstab(5) (wedges?)

[Jean-Yves Migeon <jeanyves.migeon%free.fr@localhost>]

Hi list,

I am currently adding support for Xen dom0/domU with anita, our
automated installation and testing tool.

The current system uses QEMU to install a full-fledged OS to run ATF
tests. For convenience, I would like to reuse the same image for testing
native, dom0 and domU environments.

Thing is: the root device is different for domU and native/dom0 (xbd0 vs
wd0). This causes failures everywhere during boot, due to improper
fstab(5) entry for /.

Andreas suggested me to try wedges. They do work, as they autoconfigure
properly, but current kernels do not have DKWEDGE_METHOD_BSDLABEL turned
on by default (and won't have it in the near future I believe, given all
the breakage it imposes with current setups).

Any other way to autodetect root device while keeping fstab(5)
untouched? I want to avoid newbtconf(8) (this will need a couple extract
commands in anita to use it), or playing dirty tricks with symlinks to
different fstab(5) depending on boot device...

I tried to use dkscan_bsdlabel(8) together with sysctl kern.root_device
very early during boot (/etc/rc.conf.d/fsck_root), however it returns
"Device busy", so I can't use it to circumvent the missing
DKWEDGE_METHOD_BSDLABEL options(4).

Thanks!

-- 
Jean-Yves Migeon
jeanyves.migeon%free.fr@localhost