Linux Certif

Toute la documentation sur la certification Linux LPI

lfc_python

NAME

lfc - Python interface to the LFC
lfcthr - Thread enabled version of Python interface to the LFC

SYNOPSIS

import lfc

import lfcthr
lfcthr.init()

DESCRIPTION

The lfc module permits you to access the LFC client interface from python programs. The lfc module is a swig wrapping of the standard C interface. For detailed descriptions of each function see the individual man page of each function.

The lfcthr module is a version of the lfc module supporting multi-threaded Python clients. Its usage is similar to the usage of the lfc module except the obligatory initialisation call lfcthr.init() in the main program before threads are started.
  There follows a series of examples of how to use selected functions and how to retrieve the information returned by them: Examples are finding the GUID of an existing entry, listing the replicas of a given GUID and setting and retrieving the comment associated with an entry.

EXAMPLE

 #!/usr/bin/python
 
 import sys
 import lfc
 
 """
 # stat an existing entry in the LFC and print the GUID
 """
 
 name = "/grid/dteam/my.test"
 
 stat = lfc.lfc_filestatg()
 res = lfc.lfc_statg(name,"",stat)
 
 if res == 0:
    guid = stat.guid
    print "The GUID for " + name + " is " + guid
 else:
    err_num = lfc.cvar.serrno
    err_string = lfc.sstrerror(err_num)
    print "There was an error while looking for " + name + ": Error " + str(err_num) \
                 + " (" + err_string + ")"
    sys.exit(1)
 

EXAMPLE

 #!/usr/bin/python
 
 import lfc
 
 """
 # list the replicas of a given entry, starting from the GUID
 """
 
 guid = "6a3164e0-a4d7-4abe-9f76-e3b8882735d1"
 
 listp = lfc.lfc_list()
 flag = lfc.CNS_LIST_BEGIN
 
 print "Listing replicas for GUID " + guid
 
 num_replicas=0
 
 while(1):
    res = lfc.lfc_listreplica("",guid,flag,listp)
    flag = lfc.CNS_LIST_CONTINUE
 
    if res == None:
       break
    else:
       rep_name = res.sfn
       print "Replica: " + rep_name
       num_replicas = num_replicas + 1
 
 lfc.lfc_listreplica("",guid,lfc.CNS_LIST_END,listp)
 print "Found " + str(num_replicas) + " replica(s)"
 

EXAMPLE

 #!/usr/bin/python
 
 import sys
 import lfc
 import re
 
 """
 # setting and retrieving a comment on a file
 """
 
 file = "/grid/dteam/my.test"
 
 comment = "MyComment"
 res = lfc.lfc_setcomment(file,comment)
 
 if res != 0:
    err_num = lfc.cvar.serrno
    err_string = lfc.sstrerror(err_num)
    print "Problem while setting comment for " + file + ": Error " + str(err_num) \
                 + " (" + err_string + ")"
    sys.exit(1)
 
 buffer=""
 for i in range(0,lfc.CA_MAXCOMMENTLEN+1):
   buffer=buffer + " "
   
 res = lfc.lfc_getcomment(file,buffer)
 
 if res != 0:
    err_num = lfc.cvar.serrno
    err_string = lfc.sstrerror(err_num)
    print "Problem while reading the comment for " + file + ": Error " + str(err_num) \
                 + " (" + err_string + ")"
    sys.exit(1)
 
 r = re.compile("(.*?) ", re.DOTALL)
 comment = r.findall(buffer)[0]
 
 print "Read back comment " + comment
 
 

 

EXAMPLE

 #!/usr/bin/python
 
 """
 # Using the lfc_readdirxr method
 """
 
 import sys
 import lfc
 
 name = "/grid/dteam/my.test"
 
 dir = lfc.lfc_opendirg(name,"")
 if (dir == None) or (dir == 0):
         err_num = lfc.cvar.serrno
         err_string = lfc.sstrerror(err_num)
         print "Error while looking for " + name + ": Error " + str(err_num) \
                         + " (" + err_string + ")"
         sys.exit(1)
 
 while 1:
         read_pt = lfc.lfc_readdirxr(dir,"")
         if (read_pt == None) or (read_pt == 0):
                 break
         entry, list = read_pt
         print entry.d_name
         try:
                 for i in range(len(list)):
                         print " ==> %s" % list[i].sfn
         except TypeError, x:
                 print " ==> None"
 
 lfc.lfc_closedir(dir)
 

EXAMPLE

 #!/usr/bin/python
 
 import lfc
 
 """
 # Using the lfc_getlinks method
 """
 
 result, list = lfc.lfc_getlinks("/grid/dteam/antotests/extratests/dir2/f105", "")
 print result
 print len(list)
 if (result == 0):
         for i in list:
                 print i.path
 

EXAMPLE

 #!/usr/bin/python
 
 import lfc
 
 """
 # Using the lfc_getreplica method
 """
 
 result, list = lfc.lfc_getreplica("/grid/dteam/antotests/extratests/dir2/f105", "", "")
 print result
 print len(list)
 if (result == 0):
         for i in list:
                 print i.host
                 print i.sfn
 

EXAMPLE

 #!/usr/bin/python
 
 import lfc
 
 """
 # Using the lfc_getacl and lfc_setacl methods to add a user ACL
 """
 
 nentries, acls_list = lfc.lfc_getacl("/grid/dteam/tests_sophie3", lfc.CA_MAXACLENTRIES)
 
 print nentries
 print len(acls_list)
 
 for i in acls_list:
         print i.a_type
         print i.a_id
         print i.a_perm
 
 # When adding a first ACL for a given user, you also need to add the mask
 # When adding the second user ACL, it is not necessary anymore
 
 acl_user = lfc.lfc_acl()
 acl_mask = lfc.lfc_acl()
 
 acl_user.a_type=2               # 2 corresponds to CNS_ACL_USER
 acl_user.a_id=18701             # user id
 acl_user.a_perm=5
 
 acl_mask.a_type=5               # 5 corresponds to CNS_ACL_MASK
 acl_mask.a_id=0                 # no user id specified
 acl_mask.a_perm=5
 
 acls_list.append(acl_user)
 acls_list.append(acl_mask)
 
 res = lfc.lfc_setacl("/grid/dteam/tests_sophie3", acls_list)
 
 if res == 0:
         print "OK"
 else:
         err_num = lfc.cvar.serrno
         err_string = lfc.sstrerror(err_num)
         print "There was an error : Error " + str(err_num) + " (" + err_string + ")"
         sys.exit(1)
 

EXAMPLE

 #!/usr/bin/python
 
 import lfc
 
 """
 # Using the lfc_getacl and lfc_setacl methods to remove a user ACL
 """
 
 nentries, acls_list = lfc.lfc_getacl("/grid/dteam/tests_sophie3", lfc.CA_MAXACLENTRIES)
 
 # Note : you cannot remove the owner ACL (i.e. for CNS_ACL_USER_OBJ type) if ACLs
 # ====== for other users exist. Ff all the other user ACLs are deleted, the owner
 # ====== ACL is automatically removed.
 
 for i in acls_list:
         print i.a_type
         print i.a_id
         print i.a_perm
 
 del acls_list[1]        # delete a given user ACL from the list of ACLs
 
 res = lfc.lfc_setacl("/grid/dteam/tests_sophie3", acls_list)
 
 if res == 0:
         print "OK"
 else:
         err_num = lfc.cvar.serrno
         err_string = lfc.sstrerror(err_num)
         print "There was an error : Error " + str(err_num) + " (" + err_string + ")"
         sys.exit(1)
 

EXAMPLE

 #!/usr/bin/env python
 import lfcthr 
 import os
 from threading import Thread
 
 class slave(Thread):
 
    def __init__ (self):
       Thread.__init__(self)
       
    def run(self):
         ....
         result = lfcthr.lfc_getreplica("", guid, "")
         ....
         return
         
 if __name__ == '__main__':
 
     os.environ['LFC_HOST'] = 'my_lfc.cern.ch'
 
     #   Threaded library initialisation
     lfcthr.init()
 
     ....
     #   Start up of threads
     for i in xrange(totalNumberOfSlaves):
         slv = slave(i)
         slv.start()
         
     ....
 
 

EXAMPLE

 #!/usr/bin/python
 
 import lfc
 
 """
 # Using the lfc_getusrmap method
 """
 
 result, list = lfc.lfc_getusrmap()
 print result
 print len(list)
 if (result == 0):
         for i in list:
                 print i.userid + " " + i.username
 

EXAMPLE

 #!/usr/bin/python
 
 import lfc
 
 """
 # Using the lfc_getgrpmap method
 """
 
 result, list = lfc.lfc_getgrpmap()
 print result
 print len(list)
 if (result == 0):
         for i in list:
                 print i.gid + " " + i.groupname
 

KNOWN BUGS

The current interface to the lfc_getcomment(3), lfc_getcwd(3), lfc_readlink(3), lfc_seterrbuf(3) requires the passing of str object which is modified to contain the result (in a similar way to the C functions, which accept a buffer). However this breaks the immutability of python str. This will be changed in the future.

SEE ALSO

LFC C interface man pages