Query size of block device file in Python

Question

I have a Python script that reads a file (typically from optical media) marking the unreadable sectors, to allow a re-attempt to read said unreadable sectors on a different

Answer 1

Linux-specific ioctl-based solution:

import fcntl
import struct

device_path = '/dev/sr0'

req = 0x80081272 # BLKGETSIZE64, result is bytes as unsigned 64-bit integer (uint64)
buf = ' ' * 8
fmt = 'L'

with open(device_path) as dev:
    buf = fcntl.ioctl(dev.fileno(), req, buf)
bytes = struct.unpack('L', buf)[0]

print device_path, 'is about', bytes / (1024 ** 2), 'megabytes'

Other unixes will have different values for req, buf, fmt of course.