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executable file 136 lines (124 sloc) 5.451 kb
#!/usr/bin/python -tt
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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