mkdir semantics

[David Feuer]

I am working on rewriting mkdir to do smarter fchdir optimization when
multiple directories are being created.  The trouble is that if people
do really weird things, the results may be different than with the standard
mkdir.


Two such weird things:

umask 2
mkdir -m a+w -p foo/bar foo  (does foo absolutely need to be created
with permissions according to the umask, or is it acceptable to create
it with permissions according to the -m argument?)

mkdir /a
ln -s /a/c /a/b    (note that this creates a symbolic link into the
void)
mkdir /a/c /a/b/x  (can this be allowed to fail with an error?)

Would a new implementation of mkdir have to behave exactly like the
current one in such cases, or is the implementation allowed some
latitude in dealing with them?

David Feuer