to go to the FS image we are making cannot be read (e.g. EPERM).
Current behaviour when we issue waring but still proceeed and
return success is definitely not correct: masking out error
condition as well as making a slighly inconsistent FS where
attempt to access the file in question ends up in EBADF. See
linked DR for details.
MFC after: 1 month
Differential Revision: https://reviews.freebsd.org/D18584
781e78182d