[dm-crypt] How to find out about mapped device name?

Arno Wagner arno at wagner.name
Tue Feb 5 01:42:22 CET 2013


Attached is a Python-script I wrote some time ago, that 
traverses /dev/mapper/* and finds all the relevant information, 
including mount-point (or absence of).

Arno

On Mon, Feb 04, 2013 at 03:32:21PM -0800, David Li wrote:
> Hi Experts,
> 
> I have already called luksFormat on a raw block dev and luksOpen to set up
> mapped device in /dev/mapper. Is there a command to find out about the
> mapping between the raw dev and mapped dev?

> _______________________________________________
> dm-crypt mailing list
> dm-crypt at saout.de
> http://www.saout.de/mailman/listinfo/dm-crypt


-- 
Arno Wagner,     Dr. sc. techn., Dipl. Inform.,    Email: arno at wagner.name
GnuPG: ID: CB5D9718  FP: 12D6 C03B 1B30 33BB 13CF  B774 E35C 5FA1 CB5D 9718
----
One of the painful things about our time is that those who feel certainty
are stupid, and those with any imagination and understanding are filled
with doubt and indecision. -- Bertrand Russell
-------------- next part --------------
#!/usr/bin/python

# cryptstat.py

# Displays all matching devices in /dev/ for a cryptsetup target

# Calls "cryptsetup status <target>" to get the initial info,
# then determines major/minor of the reported device and does
# a traversal of /dev/ to find all matches.
# Reports an augemented result of "cryptsetup status", also
# including mount points.

# Arguments are any number of cryptsetup targets. Does a validity
# check and refuses targets not found in /dev/mapper/
# Without argument, displays info on all targets found in /dev/mapper/

# (c) Arno Wagner 2010, distributed under the modified BSD license.
# Version 0.03 
# Version history
# 0.03 Adjustments for cryptsrtup 1.2.0
# 0.02 fixed error on unmounted but mapped devices

import sys, os, stat, subprocess, re

dev_path = '/dev' 
mapper_path = '/dev/mapper'
cryptsetup_path = '/usr/sbin/cryptsetup'

# IEC function
def str_iec(v):

  n = float(v)
  if n < 0 :
    raise ValueError, 'Argument of str_iec() must not be negative'

  prefix = '  '     # Actually the postfix of the output, but the
                    # prefix of the unit, if one is attached.

  if n < 1024:
    pass
  elif n < 1024 * 1024:
    n = n / 1024
    prefix = 'ki'
  elif n < 1024 * 1024 * 1024:
    n = n / ( 1024 * 1024 )
    prefix = 'Mi'
  elif n < 1024 * 1024 * 1024 * 1024:
    n = n / ( 1024 * 1024 * 1024 )
    prefix = 'Gi'
  elif n < 1024 * 1024 * 1024 * 1024 * 1024:
    n = n / ( 1024 * 1024 * 1024 * 1024 )
    prefix = 'Ti'
  elif n < 1024 * 1024 * 1024 * 1024 * 1024 * 1024:
    n = n / ( 1024 * 1024 * 1024 * 1024 * 1024 )
    prefix = 'Ei'
  else:
    raise ValueError, 'Argument of str_iec() larger than (2^50)-1'

  s = "%(n)5.1f " % {'n': n}
  s = s + prefix
  return s

# Utility functions

def normalize_path(path):
    """Replaces any number of occurences of '/' with a single '/'"""
    # Note: INefficient, but should not matter
    while path.find('//') > -1:
        path = path.replace('//','/')
    return(path)    

def dir_walk(dir):
    """Returns a list of all filenames with full paths
       (including dirs, specials, etc.) below the argument.
       "." and ".." are omitted. Does not follow symblinks
       to avoid loops, but there is no real loop prevention."""
    names = []
    dir = normalize_path(dir)
    # process current directory 
    current = os.listdir(dir)
    for d in current:
        d = dir + '/' + d
        # Test whether d is a directory. If so, recurse.
        s = os.lstat(d)
        if stat.S_ISDIR( s[stat.ST_MODE] ):
            names.extend(dir_walk(d))  
        else:
            names.append(d)
    return(names)        

def dir_walk_block(dir):
    """Returns the names of all block devices in the subtree at dir"""
    names = dir_walk(dir)
    block_dev = []
    for n in names:
        if stat.S_ISBLK(os.lstat(n)[stat.ST_MODE]):
            block_dev.append(n)
    return(block_dev)

def special_dev_major_minor(n):
    """Returns (major,minor) for a device special file name"""
    s = os.lstat(n)
    if not stat.S_ISBLK(s[stat.ST_MODE]) and \
       not stat.S_ISCHR(s[stat.ST_MODE]) :
       return None
    else:
       maj = os.major(s.st_rdev)
       min = os.minor(s.st_rdev)
       return (maj, min)

def build_block_major_minor_tables(dir):
    """Returns 
       1) a table of filenames that are all block special files
       2) a dict mapping each name to (major,minor)
       3) a dict mapping each (major,minor) pair to a table of filenames"""
    names = []
    name2pair = {}
    pair2name = {}

    names = dir_walk_block(dir)
    for n in names:
        maj, min = special_dev_major_minor(n)
        name2pair[n] = (maj, min)
        if (maj, min) not in pair2name:
            pair2name[(maj, min)] = [n]
        else:
            pair2name[(maj, min)].append(n) 
        
    return (names, name2pair, pair2name)


# Start of main action

# determine list of targets to be processed
targets = []
# first get all in mapper_path except 'control'
mapper_targets = []
mapper_entries = os.listdir(mapper_path)
tmp = []
for e in mapper_entries:
    if e != 'control':
        tmp.append(e)
mapper_entries = tmp

# if argument list empty, copy mapper_entries
if len(sys.argv) == 1:
    targets = mapper_entries
    targets.sort()
else:
    targets = sys.argv[1:]

# Make sure all targets are in mapper_entries 
tbl = {}
for e in mapper_entries:
    tbl[e] = None
for e in targets:
    if e not in tbl:
        print '\nError: Command argument "'+e+'" is not present in '+\
              'mapper dir '+mapper_path+'!\nAborting\n'
        sys.exit(1)    

# print targets

# Create mappings (major,minor) <-> name
names, name2pair, pair2names = build_block_major_minor_tables(dev_path)

print

for t in targets:
    # do call to "cryptsetup status"
    cmd = cryptsetup_path + ' status ' + t
#    print 'calling "' + cmd + '"'
    p = subprocess.Popen(cmd, shell=True, bufsize=0,
             stdin=subprocess.PIPE, stdout=subprocess.PIPE,
             stderr=subprocess.PIPE, close_fds=True)
    (out, err) = p.communicate()
    out_lines = out.splitlines()
    if (p.returncode != 0): raise IOError(p.returncode, err)  
#    print('command output = [' + out + ']')
    # check output line 7 for '  device:  <device name>'
    if not re.match('\ \ device\:\ \ \S+', out_lines[4]):
        print '\nError: Line 7 of cryptsetup output has unexpected form'
        print 'Expected: "  device:  <device name>'
        print 'found: [' + out_lines[4]+ ']'
        print 'complete cryptsetup output:\m'
        print out
        print '\nAborting!\n'
        sys.exit(1)
    device = out_lines[4][11:]
#    print 'device found: [' + device + ']'
    (maj, min) = name2pair[device]
#    print '(maj, min) = ', (maj, min)
    devices = pair2names[(maj, min)]
    dev_str = ''
    for d in devices: dev_str = dev_str + d + '  '
#    print 'devices: ', dev_str
    out_lines[4] = '  devices: '+str((maj, min))+'  '+dev_str
    for l in out_lines: 
      if re.match('\s+size:\s+(\d+)\ssectors.*', l):
        m = re.match('\s+size:\s+(\d+)\ssectors.*', l)
        s = int(m.group(1))
        l = l.rstrip('\n')
        print l + '   ( '+ str_iec(s * 512) + ' Bytes )'
      else:
        print l
    # determine mounts and print them
    mounts = '  mounted:'
    # ';echo' in next command is so that we have at least one line
    # of output to avoid an error from subprocess
    cmd = 'mount | grep '+mapper_path+'/'+t+'; echo'
#    print 'calling "' + cmd + '"'
    p = subprocess.Popen(cmd, shell=True, bufsize=0,
             stdin=subprocess.PIPE, stdout=subprocess.PIPE,
             stderr=subprocess.PIPE, close_fds=True)
    (out, err) = p.communicate()
    out_lines = out.splitlines()
#    print('command output = [' + out + ']')
    if (p.returncode != 0): raise IOError(p.returncode, err)  
    if len(out_lines) == 1:
        mounts = mounts + ' not mounted'
    else:
        for l in out_lines:       
#           print 'l = ', l
           match = re.search(' on (\S+) type', l)
           if match != None:
               mounts = mounts + ' ' + match.group(1)
    print mounts
    print














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