First of all there was missing ']'. Bu additionally change that rule to
detect partitioned loop devices instead of device-mapper.
(cherry picked from commit 68bbd408d7)
When file opened with O_TMPFILE but use_tmpfile==0, the file will not be
linked to the directory (the code at the end of process_one_file_reg).
Additionally it is waste of time trying using O_TMPFILE when it's
already known it shouldn't be.
Also use_tmpfile==0 can mean we don't have access to /proc
(set_procfs_fd wasn't called), so even if linking the file to its
directory would be attempted, it would fail. This is the case for
dom0-updates copy.
Otherwise source domain can modify (append) the file while the user
already is accessing it. While incoming files should be treated as
untrusted, this problem could allow file modification after the user
makes some sanity checks.