source: branches/wsgi/packages/sipb-xen-console/files/usr/bin/sipb-xen-consolefs @ 1441

#!/usr/bin/python

import fuse
from fuse import Fuse

from time import time

import stat     # for file properties
import os         # for filesystem modes (O_RDONLY, etc)
import errno   # for error number codes (ENOENT, etc)
                           # - note: these must be returned as negatives

from syslog import *

import sipb_xen_database

fuse.fuse_python_api = (0, 2)

realpath = "/home/machines/"

def getDepth(path):
        """
        Return the depth of a given path, zero-based from root ('/')
        """
        if path == '/':
                return 0
        else:
                return path.count('/')

def getParts(path):
        """
        Return the slash-separated parts of a given path as a list
        """
        if path == '/':
                return ['/']
        else:
                # [1:] because otherwise you get an empty list element from the
                # initial '/'
                return path[1:].split('/')

class MyStat:
        def __init__(self):
                self.st_mode = 0
                self.st_ino = 0
                self.st_dev = 0
                self.st_nlink = 0
                self.st_uid = 0
                self.st_gid = 0
                self.st_size = 0
                self.st_atime = 0
                self.st_mtime = 0
                self.st_ctime = 0
        
        def toTuple(self):
                return (self.st_mode, self.st_ino, self.st_dev, self.st_nlink, self.st_uid, self.st_gid, self.st_size, self.st_atime, self.st_mtime, self.st_ctime)

class ConsoleFS(Fuse):
        """
        ConsoleFS creates a series of subdirectories each mirroring the same real
        directory, except for a single file - the .k5login - which is dynamically
        generated for each subdirectory
        
        This filesystem only implements the getattr, getdir, read, and readlink
        calls, beacuse this is a read-only filesystem
        """
        
        def __init__(self, *args, **kw):
                """Initialize the filesystem and set it to allow_other access besides
                the user who mounts the filesystem (i.e. root)
                """
                Fuse.__init__(self, *args, **kw)
                self.lasttime = time()
                self.allow_other = 1
                
                openlog('sipb-xen-consolefs ', LOG_PID, LOG_DAEMON)
                
                syslog(LOG_DEBUG, 'Init complete.')
        
        def mirrorPath(self, path):
                """Translate a virtual path to its real path counterpart"""
                return realpath + "/".join(getParts(path)[1:])
        
        def getMachines(self):
                """Get the list of VMs in the database, clearing the cache if it's 
                older than 15 seconds"""
                if time() - self.lasttime > 15:
                        self.lasttime = time()
                        sipb_xen_database.clear_cache()
                return [machine.name for machine in sipb_xen_database.Machine.select()]
        
        def getUid(self, machine_name):
                """Calculate the UID of a machine-account, which is just machine_id+1000
                """
                return sipb_xen_database.Machine.get_by(name=machine_name).machine_id + 1000
        
        def getK5login(self, machine_name):
                """Build the ACL for a machine and turn it into a .k5login file
                """
                machine = sipb_xen_database.Machine.get_by(name=machine_name)
                users = [acl.user for acl in machine.acl]
                return "\n".join(map(self.userToPrinc, users) + [''])
        
        def userToPrinc(self, user):
                """Convert Kerberos v4-style names to v5-style and append a default
                realm if none is specified
                """
                if '@' in user:
                        (princ, realm) = user.split('@')
                else:
                        princ = user
                        realm = "ATHENA.MIT.EDU"
                
                return princ.replace('.', '/') + '@' + realm
        
        def getattr(self, path):
                """
                - st_mode (protection bits)
                - st_ino (inode number)
                - st_dev (device)
                - st_nlink (number of hard links)
                - st_uid (user ID of owner)
                - st_gid (group ID of owner)
                - st_size (size of file, in bytes)
                - st_atime (time of most recent access)
                - st_mtime (time of most recent content modification)
                - st_ctime (platform dependent; time of most recent metadata change on Unix,
                                        or the time of creation on Windows).
                """
                
                syslog(LOG_DEBUG, "*** getattr: " + path)
                
                depth = getDepth(path)
                parts = getParts(path)
                
                st = MyStat()
                # / is a directory
                if path == '/':
                        st.st_mode = stat.S_IFDIR | 0755
                        st.st_nlink = 2
                # /foo is a directory if foo is a machine - otherwise it doesn't exist
                elif depth == 1:
                        if parts[-1] in self.getMachines():
                                st.st_mode = stat.S_IFDIR | 0755
                                st.st_nlink = 2
                                # Homedirs should be owned by the user whose homedir it is
                                st.st_uid = st.st_gid = self.getUid(parts[0])
                        else:
                                return -errno.ENOENT
                # Catch the .k5login file, because it's a special case
                elif depth == 2 and parts[-1] == '.k5login':
                        st.st_mode = stat.S_IFREG | 0444
                        st.st_nlink = 1
                        st.st_size = len(self.getK5login(parts[0]))
                        # The .k5login file should be owned by the user whose homedir it is
                        st.st_uid = st.st_gid = self.getUid(parts[0])
                # For anything else, we get the mirror path and call out to the OS
                else:
                        stats = list(os.lstat(self.mirrorPath(path)))
                        # Shadow the UID and GID from the original homedir
                        stats[4:6] = [self.getUid(parts[0])] * 2
                        return tuple(stats)
                return st.toTuple()
        
        # This call isn't actually used in the version of Fuse on console, but we
        # wanted to leave it implemented to ease the transition in the future
        def readdir(self, path, offset):
                """Return a generator with the listing for a directory
                """
                syslog(LOG_DEBUG, '*** readdir %s %s' % (path, offset))
                for (value, zero) in self.getdir(path):
                        yield fuse.Direntry(value)
        
        def getdir(self, path):
                """Return a list of tuples of the form (item, 0) with the contents of
                the directory path
                
                Fuse doesn't add '.' or '..' on its own, so we have to
                """
                syslog(LOG_DEBUG, '*** getdir %s' % path)
                
                # '/' contains a directory for each machine
                if path == '/':
                        contents = self.getMachines()
                # The directory for each machine contains the same files as the realpath
                # but also the .k5login
                #
                # The list is converted to a set so that we can handle the case where 
                # there is already a .k5login in the realpath gracefully
                elif getDepth(path) == 1:
                        contents = set(os.listdir(self.mirrorPath(path)) + ['.k5login'])
                # If it's not the root of the homedir, just pass the call onto the OS
                # for realpath
                else:
                        contents = os.listdir(self.mirrorPath(path))
                # Format the list the way that Fuse wants it - and don't forget to add
                # '.' and '..'
                return [(i, 0) for i in (list(contents) + ['.', '..'])]
        
        def read(self, path, length, offset):
                """Read length bytes starting at offset of path. In most cases, this
                just gets passed on to the OS
                """
                syslog(LOG_DEBUG, '*** read %s %s %s' % (path, length, offset))
                
                parts = getParts(path)
                
                # If the depth is less than 2, then either it's a directory or the file
                # doesn't exist
                # (realistically this doesn't appear to ever happen)
                if getDepth(path) < 2:
                        return -errno.ENOENT
                # If we're asking for a real .k5login file, then create it and return
                # the snippet requested
                elif parts[1:] == ['.k5login']:
                        if parts[0] not in self.getMachines():
                                return -errno.ENOENT
                        else:
                                return self.getK5login(parts[0])[offset:length + offset]
                # Otherwise, pass the call onto the OS
                # (note that the file will get closed when this call returns and the
                # file descriptor goes out of scope)
                else:
                        fname = self.mirrorPath(path)
                        if not os.path.isfile(fname):
                                return -errno.ENOENT
                        else:
                                f = open(fname)
                                f.seek(offset)
                                return f.read(length)
        
        def readlink(self, path):
                syslog(LOG_DEBUG, '*** readlink %s' % path)
                
                # There aren't any symlinks here
                if getDepth(path) < 2:
                        return -errno.ENOENT
                # But there might be here
                else:
                        return os.readlink(self.mirrorPath(path))

if __name__ == '__main__':
        sipb_xen_database.connect('postgres://sipb-xen@sipb-xen-dev.mit.edu/sipb_xen')
        usage="""
ConsoleFS [mount_path]
"""
        server = ConsoleFS()
        server.flags = 0
        server.main()