def wipe_file(path, reader=None, buflen=4 * 1024 * 1024, exclusive=True):
"""
wipe the existing file at path.
if reader is provided, it will be called as a 'reader(buflen)'
to provide data for each write. Otherwise, zeros are used.
writes will be done in size of buflen.
"""
if reader:
readfunc = reader
else:
buf = buflen * b'\0'
def readfunc(size):
return buf
size = util.file_size(path)
LOG.debug("%s is %s bytes. wiping with buflen=%s", path, size, buflen)
with exclusive_open(path, exclusive=exclusive) as fp:
while True:
pbuf = readfunc(buflen)
pos = fp.tell()
if len(pbuf) != buflen and len(pbuf) + pos < size:
raise ValueError(
"short read on reader got %d expected %d after %d" %
(len(pbuf), buflen, pos))
if pos + buflen >= size:
fp.write(pbuf[0:size - pos])
break
else:
fp.write(pbuf)
def check_dos_signature(device):
"""
check if there is a dos partition table signature present on device
"""
# the last 2 bytes of a dos partition table have the signature with the
# value 0xAA55. the dos partition table is always 0x200 bytes long, even if
# the underlying disk uses a larger logical block size, so the start of
# this signature must be at 0x1fe
# https://en.wikipedia.org/wiki/Master_boot_record#Sector_layout
devname = dev_path(path_to_kname(device))
return (is_block_device(devname) and util.file_size(devname) >= 0x200 and
(util.load_file(devname, decode=False, read_len=2, offset=0x1fe)
== b'\x55\xAA'))
def check_efi_signature(device):
"""
check if there is a gpt partition table signature present on device
"""
# the gpt partition table header is always on lba 1, regardless of the
# logical block size used by the underlying disk. therefore, a static
# offset cannot be used, the offset to the start of the table header is
# always the sector size of the disk
# the start of the gpt partition table header shoult have the signaure
# 'EFI PART'.
# https://en.wikipedia.org/wiki/GUID_Partition_Table
devname = dev_path(path_to_kname(device))
sector_size = get_blockdev_sector_size(devname)[0]
return (is_block_device(devname)
and util.file_size(devname) >= 2 * sector_size and (util.load_file(
devname, decode=False, read_len=8,
offset=sector_size) == b'EFI PART'))
