1 2========= 3ID Mapper 4========= 5Id mapper is used by NFS to translate user and group ids into names, and to 6translate user and group names into ids. Part of this translation involves 7performing an upcall to userspace to request the information. Id mapper will 8user request-key to perform this upcall and cache the result. The program 9/usr/sbin/nfs.idmap should be called by request-key, and will perform the 10translation 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=========== 16Configuring 17=========== 18The file /etc/request-key.conf will need to be modified so /sbin/request-key can 19direct the upcall. The following line should be added: 20 21#OP TYPE DESCRIPTION CALLOUT INFO PROGRAM ARG1 ARG2 ARG3 ... 22#====== ======= =============== =============== =============================== 23create id_resolver * * /usr/sbin/nfs.idmap %k %d 600 24 25This will direct all id_resolver requests to the program /usr/sbin/nfs.idmap. 26The last parameter, 600, defines how many seconds into the future the key will 27expire. This parameter is optional for /usr/sbin/nfs.idmap. When the timeout 28is not specified, nfs.idmap will default to 600 seconds. 29 30id 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 36You can handle any of these individually, rather than using the generic upcall 37program. If you would like to use your own program for a uid lookup then you 38would edit your request-key.conf so it look similar to this: 39 40#OP TYPE DESCRIPTION CALLOUT INFO PROGRAM ARG1 ARG2 ARG3 ... 41#====== ======= =============== =============== =============================== 42create id_resolver uid:* * /some/other/program %k %d 600 43create id_resolver * * /usr/sbin/nfs.idmap %k %d 600 44 45Notice that the new line was added above the line for the generic program. 46request-key will find the first matching line and corresponding program. In 47this case, /some/other/program will handle all uid lookups and 48/usr/sbin/nfs.idmap will handle gid, user, and group lookups. 49 50See <file:Documentation/keys-request-keys.txt> for more information about the 51request-key function. 52 53 54========= 55nfs.idmap 56========= 57nfs.idmap is designed to be called by request-key, and should not be run "by 58hand". This program takes two arguments, a serialized key and a key 59description. The serialized key is first converted into a key_serial_t, and 60then passed as an argument to keyctl_instantiate (both are part of keyutils.h). 61 62The actual lookups are performed by functions found in nfsidmap.h. nfs.idmap 63determines the correct function to call by looking at the first part of the 64description string. For example, a uid lookup description will appear as 65"uid:user@domain". 66 67nfs.idmap will return 0 if the key was instantiated, and non-zero otherwise. 68