Documentation/filesystems/nfs/idmapper.txt

   1
   2 =========
   3 ID Mapper
   4 =========
   5 Id mapper is used by NFS to translate user and group ids into names, and to
   6 translate user and group names into ids.  Part of this translation involves
   7 performing an upcall to userspace to request the information.  Id mapper will
   8 user request-key to perform this upcall and cache the result.  The program
   9 /usr/sbin/nfs.upcall should be called by request-key, and will perform the
  10 translation and initialize a key with the resulting information.
  11
  12  NFS_USE_NEW_IDMAPPER must be selected when configuring the kernel to use this
  13  feature.
  14
  15 ===========
  16 Configuring
  17 ===========
  18 The file /etc/request-key.conf will need to be modified so /sbin/request-key can
  19 direct the upcall.  The following line should be added:
  20
  21 #OP     TYPE    DESCRIPTION     CALLOUT INFO    PROGRAM ARG1 ARG2 ARG3 ...
  22 #====== ======= =============== =============== ===============================
  23 create  id_resolver     *       *               /usr/sbin/nfs.upcall %k %d 600
  24
  25 This will direct all id_resolver requests to the program /usr/sbin/nfs.upcall.
  26 The last parameter, 600, defines how many seconds into the future the key will
  27 expire.  This parameter is optional for /usr/sbin/nfs.upcall.  When the timeout
  28 is not specified, nfs.upcall will default to 600 seconds.
  29
  30 id mapper uses for key descriptions:
  31           uid:  Find the UID for the given user
  32           gid:  Find the GID for the given group
  33          user:  Find the user  name for the given UID
  34         group:  Find the group name for the given GID
  35
  36 You can handle any of these individually, rather than using the generic upcall
  37 program.  If you would like to use your own program for a uid lookup then you
  38 would edit your request-key.conf so it look similar to this:
  39
  40 #OP     TYPE    DESCRIPTION     CALLOUT INFO    PROGRAM ARG1 ARG2 ARG3 ...
  41 #====== ======= =============== =============== ===============================
  42 create  id_resolver     uid:*   *               /some/other/program  %k %d 600
  43 create  id_resolver     *       *               /usr/sbin/nfs.upcall %k %d 600
  44
  45 Notice that the new line was added above the line for the generic program.
  46 request-key will find the first matching line and corresponding program.  In
  47 this case, /some/other/program will handle all uid lookups and
  48 /usr/sbin/nfs.upcall will handle gid, user, and group lookups.
  49
  50 See <file:Documentation/keys-request-keys.txt> for more information about the
  51 request-key function.
  52
  53
  54 ==========
  55 nfs.upcall
  56 ==========
  57 nfs.upcall is designed to be called by request-key, and should not be run "by
  58 hand".  This program takes two arguments, a serialized key and a key
  59 description.  The serialized key is first converted into a key_serial_t, and
  60 then passed as an argument to keyctl_instantiate (both are part of keyutils.h).
  61
  62 The actual lookups are performed by functions found in nfsidmap.h.  nfs.upcall
  63 determines the correct function to call by looking at the first part of the
  64 description string.  For example, a uid lookup description will appear as
  65 "uid:user@domain".
  66
  67 nfs.upcall will return 0 if the key was instantiated, and non-zero otherwise.