ftruncate under ZFS incorrectly checks permissions

[Mark Martinec]

Any takers for the:

  http://www.freebsd.org/cgi/query-pr.cgi?pr=154873

?

Summary:
  ftruncate under ZFS requires W file access permission,
  instead of testing file open mode (O_RDWR),
  (violating POSIX.1-2008 and breaking Postfix mailer)

(FreeBSD 8.2, ZFS: pool version 15, ZFS version 4, and earlier)

  Mark