cygwin-1.5.19-2: mkdir returns inconsistent errno

[Eric Blake]

> mkdir (also syscall) return "Permission denied" when its argument refers to
> a mountpoint  at the top of windows drive (probably also a windows mount,
> I haven't tried).
> For example:
> $ mount d: /d
> $ mkdir /
> mkdir: cannot create directory `/': File exists
> $ mkdir /d
> mkdir: cannot create directory `/d': Permission denied
> $ mkdir /d/tmp
> mkdir: cannot create directory `/d/tmp': File exists

I raised this issue before, and the conclusion was that
POSIX permits this behavior (the mkdir must fail, but
is permitted to fail for ANY of the permissible errno
values that apply to the situation when more than
one failure mode is present).  Therefore, it is highly
likely that no change will be made to cygwin.

> 
> This is highly unexpected, does not match linux behaviour (it returns EEXIST),
> and actually breaks git (git clone, creation of pathnames, to be precise).

Then git has a bug.  Report it there.  To be portable
when making pathnames, you must first check
for directory existance rather than relying on an
errno of EEXIST to tell you the directory exists.

This is not even cygwin-specific.  It is possible on
Linux to have /usr mounted on a read-only filesystem,
then /usr/local mounted in a writable location,
such that the call "mkdir -p /usr/local/dir" will get
EROFS on the /usr component rather than EEXIST
(trust me - the coreutils code for mkdir faced this
very same issue in 5.90, and was fixed in time for
the current 5.93).

--
Eric Blake
volunteer cygwin coreutils maintainer

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