Re: root-dev-ino.c limitation

[Eric Blake]

> So cygwin has are two root directories, / and //, with distinct dev/inode
> pairs?

Yes, as allowed by POSIX.

> If so, then we may need a new type that corresponds to a single
> pair on Unix-like systems, and to two dev/ino pairs on cygwin -- which
> is needed would be selected at configure time.

My already-proposed patch to fix basename/dirname introduced
DOUBLE_SLASH_IS_DISTINCT_ROOT, which sounds like the
right macro to base this decision on.  Note, however, that while
native compiles always define the macro correctly, a cross-compile
must be pessimistic and assume that // might be distinct from /
unless taught otherwise from config.cache, since there is no
compile time test that will expose the target's file system
characteristics in relation to / vs. // (at least not that I could
come up with).

> 
> It is not appropriate to change the dev_ino type, because it is used in
> other contexts where the added space would be a pointless waste.

Agreed, and I was planning on introducing a new type to
store info on a doubled root.  I'll work on a patch, and propose
it once I get it hammered out alongside a repost of my
basename/dirname patch.

-- 
Eric Blake