Determining block device's sector size in Linux+Python

block_device_sector_size.py

#!/usr/bin/python
import fcntl
import os
import struct
import array
import sys

BLKGETSIZE=0x1260
BLKGETSIZE64=0x80081272
BLKSSZGET=0x1268
BLKPBSZGET=0x127b

def ioctl_read_uint32(fd, req):
    buf = array.array('c', [chr(0)] * 4)
    fcntl.ioctl(fd, req, buf)
    return struct.unpack('I',buf)[0]

def ioctl_read_uint64(fd, req):
    buf = array.array('c', [chr(0)] * 8)
    fcntl.ioctl(fd, req, buf)
    return struct.unpack('L',buf)[0]

if __name__ == '__main__':
    if len(sys.argv) < 2:
        print "Usage: %s block_device" % sys.argv[0]
        sys.exit(1)
    device = sys.argv[1]
    fd = os.open(device, os.O_RDONLY)
    logical_sector_size = ioctl_read_uint32(fd, BLKSSZGET)
    physical_sector_size = ioctl_read_uint32(fd, BLKPBSZGET)
    try:
        device_size = ioctl_read_uint64(fd, BLKGETSIZE64)
    except IOError as e: # Some platform doesn't support BLKGETSIZE64
        if e.errno == 25: # "Inappropreate ioctl for device"
            device_size = ioctl_read_uint32(fd, BLKGETSIZE) * logical_sector_size
	else: raise
    os.close(fd)
    print "Block device: %s" % device
    print "  Entire device capacity: %d" % device_size
    print "  Logical sector size: %d" % logical_sector_size
    print "  Physical sector size: %d" % physical_sector_size