#!/usr/bin/python

import sys
import os
import setns

from argparse import ArgumentParser

drop_capabilities='cap_sys_admin,cap_sys_boot,cap_sys_module'

# can set to True here, but also use the -d option
debug = False

def getarch(f):
    output = os.popen('readelf -h %s 2>&1'%f).readlines()
    classlines = [x for x in output if ('Class' in x.split(':')[0])]
    line = classlines[0]
    c = line.split(':')[1]
    if ('ELF64' in c):
        return 'x86_64'
    elif ('ELF32' in c):
        return 'i686'
    else:
        raise Exception('Could not determine architecture')

def umount(fs_dir, opts=''):
    output = os.popen('/bin/umount %s %s 2>&1'%(opts, fs_dir)).read()
    return ('device is busy' not in output)

def main ():
    parser = ArgumentParser()
    parser.add_argument("-n", "--nonet",
                                        action="store_true", dest="netns", default=False,
                                        help="Don't enter network namespace")
    parser.add_argument("-m", "--nomnt",
                                        action="store_true", dest="mntns", default=False,
                                        help="Don't enter mount namespace")
    parser.add_argument("-p", "--nopid",
                                        action="store_true", dest="pidns", default=False,
                                        help="Don't enter pid namespace")
    parser.add_argument("-r", "--root",
                                        action="store_true", dest="root", default=False,
                                        help="Enter as root: be careful")
    parser.add_argument("-i","--internal",
                                        action="store_true", dest="internal", default=False,
                                        help="does *not* prepend '-- -c' to arguments - or invoke lxcsu-internal")
    parser.add_argument("-d","--debug",
                                        action='store_true', dest='debug', default=False,
                                        help="debug option")
    parser.add_argument("-s","--nosliceuid",
                                        action='store_true', dest="nosliceuid", default=False,
                                        help="do not change to slice uid inside of slice")
    parser.add_argument("-o","--noslicehome",
                                        action='store_true', dest="noslicehome", default=False,
                                        help="do not change to slice home directory inside of slice")

    if os.path.exists("/etc/lxcsu_default"):
        defaults = parser.parse_args(file("/etc/lxcsu_default","r").read().split())
        parser.set_defaults(**defaults.__dict__)

        parser.add_argument ("slice_name")
        parser.add_argument ("command_to_run",nargs="*")

        args = parser.parse_args()
        slice_name=args.slice_name

        # unless we run the symlink 'lxcsu-internal', or we specify the -i option, prepend '--' '-c'
        if sys.argv[0].find('internal')>=0: args.internal=True

        if len(args.command_to_run)>0 and (args.command_to_run[0] == "/sbin/service"):
            # A quick hack to support nodemanager interfaces.py when restarting
            # networking in a slice.
            args.nosliceuid = True

        # plain lxcsu
        if not args.internal:
            # no command given: enter interactive shell
            if not args.command_to_run: args.command_to_run=['/bin/sh']
            args.command_to_run = [ '-c' ] + [" ".join(args.command_to_run)]

        # support for either setting debug at the top of this file, or on the command-line
        if args.debug:
            global debug
            debug=True

        try:
            cmd = 'grep %s /proc/*/cgroup | grep freezer'%slice_name
            output = os.popen(cmd).readlines()
        except:
            print "Error finding slice %s"%slice_name
            exit(1)

        slice_spec = None

        # provide a default as this is not always properly computed
        arch = None

        for e in output:
            try:
                l = e.rstrip()
                path = l.split(':')[0]  
                comp = l.rsplit(':')[-1]
                slice_name_check = comp.rsplit('/')[-1]
                if debug: print "dealing with >%s<"%slice_name_check
                
                if (slice_name_check == slice_name):
                    if debug: print "found %s"%slice_name
                    slice_path = path
                    pid = slice_path.split('/')[2]
                    cmdline = open('/proc/%s/cmdline'%pid).read().rstrip('\n\x00')
                    if (cmdline == '/sbin/init') or (cmdline.startswith("init [")):
                        slice_spec = slice_path
                        arch = getarch('/proc/%s/exe'%pid)
                        break
            except Exception,e:
                if debug: 
                    import traceback
                    print "BEG lxcsu - ignoring exception"
                    traceback.print_exc()
                    print "END lxcsu - ignoring exception"
                    pass

        if (not slice_spec or not pid):
            print "lxcsu: domain not started: %s"%slice_name
            exit(1)

        if arch is None:
            arch = 'x86_64'

        # Set sysctls specific to slice
        sysctls = []
        sysctl_dir = '/etc/planetlab/vsys-attributes/%s'%slice_name
        if (os.access(sysctl_dir,0)):
            entries = os.listdir(sysctl_dir)
            for e in entries:
                prefix = 'vsys_sysctl.'
                if (e.startswith(prefix)):
                    sysctl_file = '/'.join([sysctl_dir,e])
                    sysctl_name = e[len(prefix):]
                    sysctl_val = open(sysctl_file).read()
                    sysctls.append((sysctl_file, sysctl_name, sysctl_val))

        # Enter cgroups
        try:
            for subsystem in ['cpuset','memory','blkio']:
                open('/sys/fs/cgroup/%s/libvirt/lxc/%s/tasks'%(subsystem,slice_name),'w').write(str(os.getpid()))

        except:
            print "Error assigning resources: %s"%slice_name
            exit(1)

        try:
            open('/sys/fs/cgroup/cpuacct/system/libvirtd.service/libvirt/lxc/%s/tasks'%slice_name,'w').write(str(os.getpid()))
        except:
            print "Error assigning cpuacct: %s" % slice_name
            exit(1)

        # If the slice is frozen, then we'll get an EBUSY when trying to write to the task
        # list for the freezer cgroup. Since the user couldn't do anything anyway, it's best
        # in this case to error out the shell. (an alternative would be to un-freeze it,
        # add the task, and re-freeze it)
        try:
            f=open('/sys/fs/cgroup/freezer/libvirt/lxc/%s/tasks'%(slice_name),'w')
            f.write(str(os.getpid()))
            # note: we need to call f.close() explicitly, or we'll get an exception in
            # the object destructor, which will not be caught
            f.close()
        except:
            print "Error adding task to freezer cgroup. Slice is probably frozen: %s" % slice_name
            exit(1)

        setns.chcontext('/proc/%s/ns/uts'%pid)
        setns.chcontext('/proc/%s/ns/ipc'%pid)
        
        if (not args.pidns):
            setns.chcontext('/proc/%s/ns/pid'%pid)

        if (not args.netns):
            setns.chcontext('/proc/%s/ns/net'%pid)

        if (not args.mntns):
            setns.chcontext('/proc/%s/ns/mnt'%pid)

        proc_mounted = False
        if (not os.access('/proc/self',0)):
            proc_mounted = True
            setns.proc_mount()

        for (sysctl_file, sysctl_name, sysctl_val) in sysctls:
            for fn in ["/sbin/sysctl", "/usr/sbin/sysctl", "/bin/sysctl", "/usr/bin/sysctl"]:
                if os.path.exists(fn):
                    os.system('%s -w %s=%s  >/dev/null 2>&1'%(fn, sysctl_name,sysctl_val))
                    break
                else:
                    print "Error: image does not have a sysctl binary"

        # cgroups is not yet LXC-safe, so we need to use the coarse grained access control
        # strategy of unmounting the filesystem

        umount_result = True
        for subsystem in ['cpuset','cpu,cpuacct','memory','devices','freezer','net_cls','blkio','perf_event','systemd']:
            fs_path = '/sys/fs/cgroup/%s'%subsystem
            if (not umount(fs_path,'-l')):
                pass
            # Leaving these comments for historical reference
                        #print "Error disabling cgroup access"
                        #exit(1) - Don't need this because failure here implies failure in the call to umount /sys/fs/cgroup

        if (not umount('/sys/fs/cgroup')):
            print "Error disabling cgroup access"
            exit(1)

        pid = os.fork()

        # capsh has a --user option starting with f14
        # so if only for f12 we need to fake this one
        #
        # capsh.c does essentially the following when invoked with --user:
        #               pwd = getpwnam(user); ...
        #               ngroups = MAX_GROUPS; 
        #               status = getgrouplist(user, pwd->pw_gid, groups, &ngroups); ...
        #               status = setgroups(ngroups, groups); ...
        #               status = setgid(pwd->pw_gid); ...
        #               status = setuid(pwd->pw_uid); ...
        # however we cannot simulate that ourselves because if we did in this process then
        # capsh could not be allowed to mess with caps any more

        def getuid (slicename):
            import pwd
            try:
                return pwd.getpwnam(slicename).pw_uid
            except:
                return

        if (pid == 0):
            cap_arg = '--drop='+drop_capabilities

            if (not args.root):
                if (args.nosliceuid):
                    # we still want to drop capabilities, but don't want to switch UIDs
                    exec_args = [arch,'/usr/sbin/capsh',cap_arg,'--','--login',]+args.command_to_run
                else:
                    uid = getuid (slice_name)
                    if not uid:
                        print "lxcsu could not spot %s in /etc/passwd - exiting"%slice_name
                        exit(1)
                        exec_args = [arch,'/usr/sbin/capsh',cap_arg,'--uid=%s'%uid,'--','--login',]+args.command_to_run
# once we can drop f12, it would be nicer to instead go for
#                                exec_args = [arch,'/usr/sbin/capsh',cap_arg,'--user=%s'%slice_name,'--','--login',]+args.command_to_run
                    else:
                        exec_args = [arch,'/usr/sbin/capsh','--','--login']+args.command_to_run

                os.environ['SHELL'] = '/bin/sh'
                if os.path.exists('/etc/planetlab/lib/bind_public.so'):
                    os.environ['LD_PRELOAD'] = '/etc/planetlab/lib/bind_public.so'
                if not args.noslicehome:
                    os.environ['HOME'] = '/home/%s'%slice_name
                    os.chdir("/home/%s"%(slice_name))
                if debug: print 'lxcsu:execv:','/usr/bin/setarch',exec_args
                os.execv('/usr/bin/setarch',exec_args)
        else:
            setns.proc_umount()
            _,status = os.waitpid(pid,0)
            exit(os.WEXITSTATUS(status))

if __name__ == '__main__':
    main()