Re: Problem with pg_upgrade's directory write check on Windows

On 07/23/2011 08:45 AM, Bruce Momjian wrote:
> Pg_upgrade writes temporary files (e.g. _dumpall output) into the
> current directory, rather than a temporary directory or the user's home
> directory.  (This was decided by community discussion.)
>
> I have a check in pg_upgrade 9.1 to make sure pg_upgrade has write
> permission in the current directory:
>
>         if (access(".", R_OK | W_OK
>     #ifndef WIN32
>     
>         /*
>          * Do a directory execute check only on Unix because execute permission on
>          * NTFS means "can execute scripts", which we don't care about. Also, X_OK
>          * is not defined in the Windows API.
>          */
>                    | X_OK
>     #endif
>                    ) != 0)
>             pg_log(PG_FATAL,
>               "You must have read and write access in the current directory.\n");
>
> Unfortunately, I have received a bug report from EnterpriseDB testing
> that this does not trigger the FATAL exit on Windows even if the user
> does not have write permission in the current directory, e.g. C:\.
>
> I think I see the cause of the problem.  access() on Windows is
> described here:
>
>     http://msdn.microsoft.com/en-us/library/1w06ktdy%28v=vs.80%29.aspx
>
> It specifically says:
>
>     When used with directories, _access determines only whether the
>     specified directory exists; in Windows NT 4.0 and Windows 2000, all
>     directories have read and write access.
>     ...
>     This function only checks whether the file and directory are read-only
>     or not, it does not check the filesystem security settings.  For
>     that you need an access token.
>
> We do use access() in a few other places in our code, but not for
> directory permission checks.
>
> Any ideas on a solution?  Will checking stat() work?  Do I have to try
> creating a dummy file and delete it?

That looks like the obvious solution - it's what came to my mind even 
before reading this sentence.

cheers

andrew