return errno;
char data[1024*128];
// TODO: compressing filesystems would require random data
+ // FIPS zeroization audit 20191115: this memset is not security related.
memset(data, 0x42, sizeof(data));
for (off_t off = 0; off < len; off += sizeof(data)) {
if (off + static_cast<off_t>(sizeof(data)) > len)