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#!/usr/bin/python -tt

# Copyright 2009-2012 Eucalyptus Systems, Inc.
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; version 3 of the License.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see http://www.gnu.org/licenses/.
#
# Please contact Eucalyptus Systems, Inc., 6755 Hollister Ave., Goleta
# CA 93117, USA or visit http://www.eucalyptus.com/licenses/ if you need
# additional information or have any questions.
#
# This file may incorporate work covered under the following copyright
# and permission notice:
#
# Software License Agreement (BSD License)
#
# Copyright (c) 2008, Regents of the University of California
# All rights reserved.
#
# Redistribution and use of this software in source and binary forms,
# with or without modification, are permitted provided that the
# following conditions are met:
#
# Redistributions of source code must retain the above copyright
# notice, this list of conditions and the following disclaimer.
#
# Redistributions in binary form must reproduce the above copyright
# notice, this list of conditions and the following disclaimer
# in the documentation and/or other materials provided with the
# distribution.
#
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
# FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
# COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
# INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
# BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
# LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
# CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
# ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
# POSSIBILITY OF SUCH DAMAGE. USERS OF THIS SOFTWARE ACKNOWLEDGE
# THE POSSIBLE PRESENCE OF OTHER OPEN SOURCE LICENSED MATERIAL,
# COPYRIGHTED MATERIAL OR PATENTED MATERIAL IN THIS SOFTWARE,
# AND IF ANY SUCH MATERIAL IS DISCOVERED THE PARTY DISCOVERING
# IT MAY INFORM DR. RICH WOLSKI AT THE UNIVERSITY OF CALIFORNIA,
# SANTA BARBARA WHO WILL THEN ASCERTAIN THE MOST APPROPRIATE REMEDY,
# WHICH IN THE REGENTS' DISCRETION MAY INCLUDE, WITHOUT LIMITATION,
# REPLACEMENT OF THE CODE SO IDENTIFIED, LICENSING OF THE CODE SO
# IDENTIFIED, OR WITHDRAWAL OF THE CODE CAPABILITY TO THE EXTENT
# NEEDED TO COMPLY WITH ANY SUCH LICENSES OR RIGHTS.

import grp
import optparse
import os
import os.path
import platform
import stat
import warnings

try:
    import selinux
    HAVE_LIBSELINUX = True
except ImportError:
    HAVE_LIBSELINUX = False

def get_max_part():
    """
Linux 2.6.26 and later allow loop devices to contain partitions. When this
behavior is enabled by passing a max_part option to the loop driver, loop
devices' minor device numbers increase by that value plus 1 instead of just
1, so we need to know this value when creating loop devices so we don't
break things when max_part is nonzero.
"""

    if os.path.isfile('/sys/module/loop/parameters/max_part'):
        max_part_file = open('/sys/module/loop/parameters/max_part')
        max_part = int(max_part_file.readline().strip())
        max_part_file.close()
    else:
        # Linux 2's loop driver does not export its parameters to sysfs, so
        # guess the correct value by computing the difference between the
        # device numbers of /dev/loop0 and /dev/loop1. Hopefully they exist.
        loop0_minor = os.minor(os.stat('/dev/loop0').st_rdev)
        loop1_minor = os.minor(os.stat('/dev/loop1').st_rdev)
        max_part = loop1_minor - loop0_minor - 1
    assert max_part >= 0
    return max_part

def loop_devs_are_limited():
    """
Return whether or not the max_loop option for the driver is nonzero. When
is nonzero, two things happen:
- The driver creates a given number of loop devices automatically
- The driver sets a hard limit on the number of loop devices

The hard limit means that when max_loop is nonzero any device nodes we
create will be useless.

On Linux 2.6.22 and later this value defaults to 0. On earlier versions it
has a default value of 8, a minimum of 1, and a maximum of 256.
"""
    if os.path.isfile('/sys/module/loop/parameters/max_loop'):
        # Linux >= 3
        max_loop_file = open('/sys/module/loop/parameters/max_loop')
        max_loop = int(max_loop_file.readline().strip())
        max_loop_file.close()
    elif (int(platform.release().split('.')[0].split('-')[0]) == 2 and
          int(platform.release().split('.')[1].split('-')[0]) == 6 and
          int(platform.release().split('.')[2].split('-')[0]) >= 22):
        # Linux >= 2.6.22
        # Since Linux 2's loop driver doesn't export its parameters to sysfs we
        # have no easy way to query what the value of max_loop is. It might be
        # in the kernel parameters...
        kcmdline_file = open('/proc/cmdline')
        kcmdline = kcmdline_file.readline().strip()
        kcmdline_file.close()
        max_loop_opts = [opt for opt in kcmdline.split() if 'max_loop' in opt]
        for opt in max_loop_opts:
            if opt.startswith('max_loop=') or opt.startswith('loop.max_loop='):
                max_loop = int(opt.split('=')[-1])
        else:
            # At this point the only option is to try to find modprobe
            # configuration. That is a lot of work, so just assume 0. If
            # things don't work the worst that will happen is broken loop
            # devices, which doesn't break components any more than they
            # would already be if the devices did not exist.
            max_loop = 0
    else:
        # Linux < 2.6.22
        # It can't be 0, so the actual value doesn't actually matter.
        max_loop = 8
    return max_loop != 0

def create_loop_devices(total, max_part):
    """
Create devices /dev/loop0 through /dev/loopN, where N is total - 1.
"""
    try:
        for i in range(0, total):
            fname = '/dev/loop{0}'.format(i)
            major = 7
            minor = i * (max_part + 1)
            if minor < 2 ** 20:
                if not os.path.exists(fname):
                    os.mknod(fname, stat.S_IFBLK, os.makedev(major, minor))
                    # Set the permissions to something sane. These seem to be
                    # the defaults on pretty much every distro; a better source
                    # of information would be nice.
                    try:
                        gid = grp.getgrnam('disk').gr_gid
                        os.chown(fname, 0, gid)
                        os.chmod(fname, 0660)
                    except KeyError:
                        os.chown(fname, 0, 0)
                        os.chmod(fname, 0600)
                    try:
                        if HAVE_LIBSELINUX and selinux.is_selinux_enabled():
                            selinux.restorecon(fname)
                    except OSError:
                        warnings.warn('Failed to set SELinux context on ' +
fname, RuntimeWarning)
            else:
                warnings.warn(('Minor device numbers too large to create all '
                               'device nodes'), RuntimeWarning)
                break
    except OverflowError:
        # The native code can barf when given really big numbers for device
        # nodes. (i.e. when os.makedev(major, minor) > 2 ** 31 - 1)
        warnings.warn('Device numbers too large to create all device nodes',
                      RuntimeWarning)

def main():
    parser = optparse.OptionParser()
    (options, args) = parser.parse_args()
    if len(args) > 0:
        ndevs = int(args[0])
    else:
        ndevs = 256

    if not loop_devs_are_limited():
        create_loop_devices(ndevs, get_max_part())

if __name__ == '__main__':
    main()
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