Revert "Use native python truncate for privsep"

This reverts commit 2e292ddeb4148e12b8972fa0a25c03ab4c5e61a8.

Related-Bug: #1818504
Change-Id: I3df664d16ed8af4471619904c8af9e3427891ac4

cinder/privsep/fs.py

@@ -20,39 +20,9 @@ Helpers for filesystem related routines.
 
 
 from oslo_concurrency import processutils
-from oslo_log import log as logging
 
 import cinder.privsep
 
-LOG = logging.getLogger(__name__)
-
-mult_table = {'K': 1024}
-mult_table['M'] = mult_table['K'] * 1024
-mult_table['G'] = mult_table['M'] * 1024
-mult_table['T'] = mult_table['G'] * 1024
-mult_table['P'] = mult_table['T'] * 1024
-mult_table['E'] = mult_table['P'] * 1024
-
-
-def _convert_sizestr(sizestr):
-    try:
-        ret = int(sizestr)
-        return ret
-    except ValueError:
-        pass
-
-    error = ValueError(sizestr + " is not a valid sizestr")
-
-    unit = sizestr[-1:].upper()
-    if unit in mult_table:
-        try:
-            ret = int(sizestr[:-1]) * mult_table[unit]
-        except ValueError:
-            raise error
-        return ret
-
-    raise error
-
 
 @cinder.privsep.sys_admin_pctxt.entrypoint
 def umount(mountpoint):
@@ -60,18 +30,5 @@ def umount(mountpoint):
 
 
 @cinder.privsep.sys_admin_pctxt.entrypoint
-def _truncate(size, path):
-    # On Python 3.6, os.truncate() can accept a path arg.
-    # For now, do it this way.
-    with open(path, 'a+b') as f:
-        f.truncate(size)
-
-
-def truncate(sizestr, path):
-    # TODO(eharney): change calling code to use bytes instead size strings
-    size = _convert_sizestr(sizestr)
-
-    LOG.debug('truncating file %(path)s to %(size)s bytes', {'path': path,
-                                                             'size': size})
-
-    _truncate(size, path)
+def truncate(size, path):
+    processutils.execute('truncate', '-s', size, path)