Recent libpciaccess changes

[Damien Zammit]

Hi folks,

I upgraded my hurd system and got the following error trying to boot with 
rumpdisk:

ext2fs: part:2:device:wd0: No such device or address

libpciaccess:
I have not been able to prove it yet, but I think the function call
pci_device_hurd_map_range() attempts to look up _SERVERS_BUS_PCI during
bootstrap and fails because it does not exist (no root filesystem exists).

Joan, I heard we are not supposed to use the hurd access method during 
bootstrap,
only the x86 access method.  Is this the problem, and if so, how can we fix 
this?
How did you envisage your mapping of regions to work during bootstrap when there
is no filesystem access?

Samuel suggested on IRC that we could make it try the x86 map range function 
first
and then fall back to hurd method, is there any problem with that?

Perhaps there is a better solution to make the access method selectable via a 
parameter,
instead of implementing fallback mechanisms and making assumptions about what 
is running?
Would that work better?

In any case, we do need better testing of changes in different scenarios
to not put a burden on Samuel to fix everything we break.

Cheers,
Damien