disk-deactivate

#!/usr/bin/env python

import sys
import os
import glob
import optparse

'''
usage: disk-scan
Similar to scsi-rescan in sg3_utils. Useful for eSATA disk hotplug.

Implementation:
echo '- - -' > /sys/class/scsi_host/host*/scan

usage: disk-deactivate DEVICE

It derives (Host, Bus, Target, Lun) from Linux device names then does:
echo 1 > /sys/bus/scsi/devices/12:0:0:0/block/sdc/device/delete

See:
* http://gurkulindia.com/main/2011/05/linux-dynamically-addremove-scsi-from-linux/
'''

# strace lscsi --kname
# <...>
# open("/sys/bus/scsi/devices/1:0:0:0/type", O_RDONLY) = 3
# open("/sys/bus/scsi/devices/1:0:0:0/vendor", O_RDONLY) = 3
# open("/sys/bus/scsi/devices/1:0:0:0/model", O_RDONLY) = 3
# open("/sys/bus/scsi/devices/1:0:0:0/rev", O_RDONLY) = 3
# openat(AT_FDCWD, "/sys/bus/scsi/devices/1:0:0:0", O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC) = 3
# openat(AT_FDCWD, "/sys/bus/scsi/devices/1:0:0:0/block", O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC) = 3
# stat("/sys/bus/scsi/devices/1:0:0:0/block/sda", {st_mode=S_IFDIR|0755, st_size=0, ...}) = 0
# chdir("/sys/bus/scsi/devices/1:0:0:0/block/sda") = 0
# getcwd("/sys/devices/pci0000:00/0000:00:1f.2/ata2/host1/target1:0:0/1:0:0:0/block/sda", 260) = 78
# -- start of next device --
# open("/sys/bus/scsi/devices/3:0:0:0/type", O_RDONLY) = 3
# <...>

def human_size(size_in_blocks):
    '''
    Number in "/sys/block/sda/size" -> "250G"

    >>> human_size(488397168)
    '250.0G'
    >>> human_size(625142448)
    '320.0G'
    '''
    units = [ 'K', 'M', 'G', 'T', 'P' ]
    block_size = 512

    (n, i) = (size_in_blocks / (1000.0/512 + .0005), 0)
    while n >= 1000:
        (n, i) = (n / 1000.0, i + 1)
    return '%.1f%s' % (n, units[i])

def disk_info(name):
    '-> [ (kernel_name, proc_name, vendor, model, size, (host, bus, target, lun)) ... ]'
    try:
        i = glob.glob('/sys/bus/scsi/devices/*/block/' + name)[0]
    except IndexError:
        return None
    f = i.split(os.path.sep)
    kname = f[-1]
    hbtl = tuple( int(x) for x in f[-3].split(':') )
    proc_name = open('/sys/class/scsi_host/host%d/proc_name' % (hbtl[0],)).read().strip()
    d = ('/sys/bus/scsi/devices/%d:%d:%d:%d' % hbtl)

    def read(key):
        return open(os.path.join(d, key)).read().strip()

    vendor = read('vendor')
    model = read('model')
    size = human_size(int(open(os.path.join(i, 'size')).read()))
    return (kname, proc_name, vendor, model, size, hbtl)

def disk_list():
    '-> [ disk_info() ... ]'
    # /sys/bus/scsi/devices/1:0:0:0/block/sda
    l = glob.glob('/sys/bus/scsi/devices/*/block/*')
    out = []
    for i in l:
        kname = os.path.basename(i)
        out.append(disk_info(kname))

    out.sort(key=lambda x: x[-1])
    return out

def host_bus_target_lun_from_name(name):
    '-> (host, bus, target, lun) or None'
    try:
        t = glob.glob('/sys/bus/scsi/devices/*/block/' + name)[0]
    except IndexError:
        return None

    f = t.split(os.path.sep)
    hbtl = tuple( int(x) for x in f[-3].split(':') )
    return hbtl

main_function_map = {}

def main_function(func):
    global main_function_map
    main_function_map[func.__name__.replace('_','-')] = func
    return func

@main_function
def disk_scan(args):
    p = optparse.OptionParser(usage='%prog')
    (options, args) = p.parse_args(args)

    old_disks = disk_list()

    for i in glob.glob('/sys/class/scsi_host/host*/scan'):
        with open(i, 'w') as f:
            f.write('- - -\n')

    new_disks = disk_list()

    delta = []
    for i in new_disks:
        if i in old_disks:
            continue
        delta.append(i)

    if not delta:
        sys.stdout.write('No new disks discovered\n')
        sys.exit(0)

    sys.stdout.write('New disk(s):\n')
    (name, proc_name, vendor, model, size, hbtl) = i
    sys.stdout.write('%s\t%s\t%s\t%s\t%s\t[%d:%d:%d:%d]\n' %
                     ((name, proc_name, vendor, model, size) + hbtl))

@main_function
def disk_deactivate(args):
    p = optparse.OptionParser(usage='%prog KERNEL_BLOCK_DEVICE_NAME')
    (options, args) = p.parse_args(args)
    try:
        (dev_name,) = args
    except ValueError:
        p.print_usage()
        sys.stderr.write('Current disks:\n')
        for (name, proc_name, vendor, model, size, hbtl) in disk_list():
            sys.stderr.write('%s\t%s\t%s\t%s\t%s\t[%d:%d:%d:%d]\n' %
                             ((name, proc_name, vendor, model, size) + hbtl))
        sys.exit(2)

    hbtl = host_bus_target_lun_from_name(dev_name)
    delete_fname = ('/sys/bus/scsi/devices/'
                    '%(host)d:%(bus)d:%(target)d:%(lun)d/block/'
                    '%(name)s/device/delete' %
                    dict(host=hbtl[0], bus=hbtl[1], target=hbtl[2], lun=hbtl[3], name=dev_name))
    with open(delete_fname, 'w') as f:
        f.write('1')

def main_function_dispatch(name, args):
    try:
        f = main_function_map[name]
    except KeyError:
        sys.stderr.write('%s is not a valid command name\n' % (name,))
        sys.exit(2)
    f(args)

def program_name():
    return os.path.basename(sys.argv[0])

if __name__ == '__main__':
    main_function_dispatch(program_name(), sys.argv[1:])