> > what's the semantics of it?  "can access any disks"?
> 
> Well, I was thinking the semantics should be the "worse case" because we
> don't really know anything more than that raw disk access was required
> and the access modes -- we can't tell if it's mounted or not, etc.

i agree.
and it's why i don't think it's a good idea.
it's better to require caller to specify a device.

YAMAMOTO Takashi