========= ID Mapper ========= Id mapper is used by NFS to translate user and group ids into names, and to translate user and group names into ids. Part of this translation involves performing an upcall to userspace to request the information. Id mapper will user request-key to perform this upcall and cache the result. The program /usr/sbin/nfs.upcall should be called by request-key, and will perform the translation and initialize a key with the resulting information. NFS_USE_NEW_IDMAPPER must be selected when configuring the kernel to use this feature. =========== Configuring =========== The file /etc/request-key.conf will need to be modified so /sbin/request-key can direct the upcall. The following line should be added: #OP TYPE DESCRIPTION CALLOUT INFO PROGRAM ARG1 ARG2 ARG3 ... #====== ======= =============== =============== =============================== create id_resolver * * /usr/sbin/nfs.upcall %k %d 600 This will direct all id_resolver requests to the program /usr/sbin/nfs.upcall. The last parameter, 600, defines how many seconds into the future the key will expire. This parameter is optional for /usr/sbin/nfs.upcall. When the timeout is not specified, nfs.upcall will default to 600 seconds. id mapper uses for key descriptions: uid: Find the UID for the given user gid: Find the GID for the given group user: Find the user name for the given UID group: Find the group name for the given GID You can handle any of these individually, rather than using the generic upcall program. If you would like to use your own program for a uid lookup then you would edit your request-key.conf so it look similar to this: #OP TYPE DESCRIPTION CALLOUT INFO PROGRAM ARG1 ARG2 ARG3 ... #====== ======= =============== =============== =============================== create id_resolver uid:* * /some/other/program %k %d 600 create id_resolver * * /usr/sbin/nfs.upcall %k %d 600 Notice that the new line was added above the line for the generic program. request-key will find the first matching line and corresponding program. In this case, /some/other/program will handle all uid lookups and /usr/sbin/nfs.upcall will handle gid, user, and group lookups. See <file:Documentation/keys-request-keys.txt> for more information about the request-key function. ========== nfs.upcall ========== nfs.upcall is designed to be called by request-key, and should not be run "by hand". This program takes two arguments, a serialized key and a key description. The serialized key is first converted into a key_serial_t, and then passed as an argument to keyctl_instantiate (both are part of keyutils.h). The actual lookups are performed by functions found in nfsidmap.h. nfs.upcall determines the correct function to call by looking at the first part of the description string. For example, a uid lookup description will appear as "uid:user@domain". nfs.upcall will return 0 if the key was instantiated, and non-zero otherwise.
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