NSDISPATCH(3)           NetBSD Library Functions Manual          NSDISPATCH(3)

NAME
     nsdispatch -- name-service switch dispatcher routine

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <nsswitch.h>

     int
     nsdispatch(void *nsdrv, const ns_dtab dtab[], const char *database,
         const char *name, const ns_src defaults[], ...);

DESCRIPTION
     The nsdispatch() function invokes the callback functions specified in
     dtab in the order given in /etc/nsswitch.conf for the database database
     until the action criteria for a source of that database is fulfilled.

     nsdrv is passed to each callback function to use as necessary (to pass
     back to the caller of nsdispatch()).

     dtab is an array of ns_dtab structures, which have the following format:


           typedef struct {
                   const char *src;
                   nss_method cb;
                   void *cb_data;
           } ns_dtab;

           The dtab array should consist of one entry for each source type
           that has a static implementation, with src as the name of the
           source, cb as a callback function which handles that source, and
           cb_data as a pointer to arbitrary data to be passed to the callback
           function.  The last entry in dtab should contain NULL values for
           src, cb, and cb_data.

           The callback function signature is described by the typedef:

                 typedef int (*nss_method)(void *cbrv, void *cbdata,
                 va_list ap);

                 cbrv    The nsdrv that nsdispatch() was invoked with.

                 cbdata  The cb_data member of the array entry for the source
                         that this callback function implements in the dtab
                         argument of nsdispatch().

                 ap      The ... arguments to nsdispatch(), converted to a
                         va_list.

     database and name are used to select methods from optional per-source
     dynamically-loaded modules.  name is usually the name of the function
     calling nsdispatch().  Note that the callback functions provided by dtab
     take priority over those implemented in dynamically-loaded modules in the
     event of a conflict.

     defaults contains a list of default sources to try in the case of a miss-
     ing or corrupt nsswitch.conf(5), or if there isn't a relevant entry for
     database.  It is an array of ns_src structures, which have the following
     format:


           typedef struct {
                   const char *src;
                   uint32_t flags;
           } ns_src;

           The defaults array should consist of one entry for each source to
           consult by default indicated by src, and flags set to the desired
           behavior (usually NS_SUCCESS; refer to Callback function return
           values for more information).  The last entry in defaults should
           have src set to NULL and flags set to 0.

           Some invokers of nsdispatch() (such as setgrent(3)) need to force
           all callback functions to be invoked, irrespective of the action
           criteria listed in nsswitch.conf(5).  This can be achieved by
           adding NS_FORCEALL to defaults[0].flags before invoking
           nsdispatch().  The return value of nsdispatch() will be the result
           of the final callback function invoked.

           For convenience, a global variable defined as:
                 extern const ns_src __nsdefaultsrc[];
           exists which contains a single default entry for `files' for use by
           callers which don't require complicated default rules.

     ... are optional extra arguments, which are passed to the appropriate
     callback function as a stdarg(3) variable argument list of the type
     va_list.

     nsdispatch returns the value of the callback function that caused the
     dispatcher to finish, or NS_NOTFOUND otherwise.

   Dynamically-loaded module interface
     The nsdispatch() function loads callback functions from the run-time
     link-editor's search path using the following naming convention:


           nss_<source>.so.<version>

           <source>   The source that the module implements.

           <version>  The nsdispatch module interface version, which is
                      defined by the integer NSS_MODULE_INTERFACE_VERSION,
                      which has the value 0.

     When a module is loaded, nsdispatch() looks for and calls the following
     function in the module:

           ns_mtab * nss_module_register(const char *source, u_int *nelems,
           nss_module_unregister_fn *unreg);

           source  The name of the source that the module implements, as used
                   by nsdispatch() to construct the module's name.

           nelems  A pointer to an unsigned integer that nss_module_register()
                   should set to the number of elements in the ns_mtab array
                   returned by nss_module_register(), or 0 if there was a
                   failure.

           unreg   A pointer to a function pointer that nss_module_register()
                   can optionally set to an unregister function to be invoked
                   when the module is unloaded, or NULL if there isn't one.

     The unregister function signature is described by the typedef:

           typedef void (*nss_module_unregister_fn)(ns_mtab *mtab,
           u_int nelems);

           mtab    The array of ns_mtab structures returned by
                   nss_module_register().

           nelems  The *nelems value set by nss_module_register().

     nss_module_register() returns an array of ns_mtab structures (with
     *nelems entries), or NULL if there was a failure.  The ns_mtab structures
     have the following format:


           typedef struct {
                   const char *database;
                   const char *name;
                   nss_method method;
                   void *mdata;
           } ns_mtab;

           The mtab array should consist of one entry for each callback func-
           tion (method) that is implemented, with database as the name of the
           database, name as the name of the callback function, method as the
           nss_method callback function that implements the method, and mdata
           as a pointer to arbitrary data to be passed to the callback func-
           tion as its cbdata argument.

   Valid source types
     While there is support for arbitrary sources, the following #defines for
     commonly implemented sources are provided:

           #define         Value
           NSSRC_FILES     "files"
           NSSRC_DNS       "dns"
           NSSRC_NIS       "nis"
           NSSRC_COMPAT    "compat"

     Refer to nsswitch.conf(5) for a complete description of what each source
     type is.

   Valid database types
     While there is support for arbitrary databases, the following #defines
     for currently implemented system databases are provided:

           #define               Value
           NSDB_HOSTS            "hosts"
           NSDB_GROUP            "group"
           NSDB_GROUP_COMPAT     "group_compat"
           NSDB_NETGROUP         "netgroup"
           NSDB_NETWORKS         "networks"
           NSDB_PASSWD           "passwd"
           NSDB_PASSWD_COMPAT    "passwd_compat"
           NSDB_SHELLS           "shells"

     Refer to nsswitch.conf(5) for a complete description of what each data-
     base is.

   Callback function return values
     The callback functions should return one of the following values depend-
     ing upon status of the lookup:

           Return value   Status code
           NS_SUCCESS     The requested entry was found.
           NS_NOTFOUND    The entry is not present at this source.
           NS_TRYAGAIN    The source is busy, and may respond to retries.
           NS_UNAVAIL     The source is not responding, or entry is corrupt.

CALLBACK FUNCTION API FOR STANDARD DATABASES
     The organization of the ap argument for an nss_method() callback function
     for a standard method in a standard database is:
           1.   Pointer to return value of the standard function.
           2.   First argument of the standard function.
           3.   (etc.)

     For example, given the standard function getgrnam(3):
           struct group * getgrnam(const char *name)
     the ap organization used by the callback functions is:
           1.   struct group **
           2.   const char *

     NOTE: Not all standard databases are using this calling convention yet;
     those that aren't are noted below.  These will be changed in the future.

     The callback function names and va_list organization for various standard
     database callback functions are:

   Methods for hosts database
     NOTE: The method APIs for this database will be changing in the near
     future.

     getaddrinfo
          char *name, const struct addrinfo *pai

          Returns struct addrinfo * via void *cbrv.

     gethostbyaddr
          unsigned char *addr, int addrlen, int af

          Returns struct hostent * via void *cbrv.

     gethostbyname
          char *name, int namelen, int af

          Returns struct hostent * via void *cbrv.

   Methods for group and group_compat databases
     endgrent
          Empty ap.

          All methods for all sources are invoked for this method name.

     getgrent
          struct group **retval

          *retval should be set to a pointer to an internal static struct
          group on success, NULL otherwise.

          getgrent(3) returns *retval if nsdispatch() returns NS_SUCCESS, NULL
          otherwise.

     getgrent_r
          int *retval, struct group *grp, char *buffer, size_t buflen, struct
          group **result

          *retval should be set to an appropriate errno(2) on failure.

          getgrent_r(3) returns 0 if nsdispatch() returns NS_SUCCESS or
          NS_NOTFOUND, and *retval otherwise.

     getgrgid
          struct group **retval, gid_t gid

          *retval should be set to a pointer to an internal static struct
          group on success, NULL otherwise.

          getgrgid(3) returns *retval if nsdispatch() returns NS_SUCCESS, NULL
          otherwise.

     getgrgid_r
          int *retval, gid_t gid, struct group *grp, char *buffer, size_t
          buflen, struct group **result

          *retval should be set to an appropriate errno(2) on failure.

          getgrgid_r(3) returns 0 if nsdispatch() returns NS_SUCCESS or
          NS_NOTFOUND, and *retval otherwise.

     getgrnam
          struct group **retval, const char *name

          *retval should be set to a pointer to an internal static struct
          group on success, NULL otherwise.

          getgrnam(3) returns *retval if nsdispatch() returns NS_SUCCESS, NULL
          otherwise.

     getgrnam_r
          int *retval, const char *name, struct group *grp, char *buffer,
          size_t buflen, struct group **result

          *retval should be set to an appropriate errno(2) on failure.

          getgrnam_r(3) returns 0 if nsdispatch() returns NS_SUCCESS or
          NS_NOTFOUND, and *retval otherwise.

     getgroupmembership
          int *retval, const char *name, gid_t basegid, gid_t *groups, int
          maxgrp, int *groupc

          retval is unused.

          Lookups for group_compat are also stopped if NS_SUCCESS was returned
          to prevent multiple ``+:'' compat entries from being expanded.

          getgroupmembership(3) returns is -1 if *groupc is greater than to
          maxgrp, and 0 otherwise.

     setgroupent
          int *retval, int stayopen

          retval should be set to 0 on failure and 1 on success.

          All methods for all sources are invoked for this method name.

     setgrent
          Empty ap.

          All methods for all sources are invoked for this method name.

   Methods for netgroup database
     NOTE: The method APIs for this database will be changing in the near
     future.

     endnetgrent
          Empty ap.

     lookup
          char *name, char **line, int bywhat

          Find the given name and return its value in line.  bywhat is one of
          _NG_KEYBYNAME, _NG_KEYBYUSER, or _NG_KEYBYHOST.

     getnetgrent
          int *retval, const char **host, const char **user, const char
          **domain

          *retval should be set to 0 for no more netgroup members and 1 other-
          wise.

          getnetgrent(3) returns *retval if nsdispatch() returns NS_SUCCESS, 0
          otherwise.

     innetgr
          int *retval, const char *grp, const char *host, const char *user,
          const char *domain

          *retval should be set to 1 for a successful match and 0 otherwise.

     setnetgrent
          const char *netgroup

   Methods for networks database
     getnetbyaddr
          struct netent **retval, uint32_t net, int type

          *retval should be set to a pointer to an internal static struct
          netent on success, NULL otherwise.

          getnetbyaddr(3) returns *retval if nsdispatch() returns NS_SUCCESS,
          NULL otherwise.

     getnetbyname
          struct netent **retval, const char *name

          *retval should be set to a pointer to an internal static struct
          netent on success, NULL otherwise.

          getnetbyname(3) returns *retval if nsdispatch() returns NS_SUCCESS,
          NULL otherwise.

   Methods for passwd and passwd_compat databases
     endpwent
          Empty ap.

          All methods for all sources are invoked for this method name.

     getpwent
          struct passwd **retval

          *retval should be set to a pointer to an internal static struct
          passwd on success, NULL otherwise.

          getpwent(3) returns *retval if nsdispatch() returns NS_SUCCESS, NULL
          otherwise.

     getpwent_r
          int *retval, struct passwd *pw, char *buffer, size_t buflen, struct
          passwd **result

          *retval should be set to an appropriate errno(2) on failure.

          getpwent_r(3) returns 0 if nsdispatch() returns NS_SUCCESS or
          NS_NOTFOUND, and *retval otherwise.

     getpwnam
          struct passwd **retval, const char *name

          *retval should be set to a pointer to an internal static struct
          passwd on success, NULL otherwise.

          getpwnam(3) returns *retval if nsdispatch() returns NS_SUCCESS, NULL
          otherwise.

     getpwnam_r
          int *retval, const char *name, struct passwd *pw, char *buffer,
          size_t buflen, struct passwd **result

          *retval should be set to an appropriate errno(2) on failure.

          getpwnam_r(3) returns 0 if nsdispatch() returns NS_SUCCESS or
          NS_NOTFOUND, and *retval otherwise.

     getpwuid
          struct passwd **retval, uid_t uid

          *retval should be set to a pointer to an internal static struct
          passwd on success, NULL otherwise.

          getpwuid(3) returns *retval if nsdispatch() returns NS_SUCCESS, NULL
          otherwise.

     getpwuid_r
          int *retval, uid_t uid, struct passwd *pw, char *buffer, size_t
          buflen, struct passwd **result

          *retval should be set to an appropriate errno(2) on failure.

          getpwuid_r returns 0 if nsdispatch() returns NS_SUCCESS or
          NS_NOTFOUND, and *retval otherwise.

     setpassent
          int *retval, int stayopen

          retval should be set to 0 on failure and 1 on success.

          All methods for all sources are invoked for this method name.

     setpwent
          Empty ap.

          All methods for all sources are invoked for this method name.

   Methods for shells database
     endusershell
          Empty ap.

          All methods for all sources are invoked for this method name.

     getusershell
          char **retval

          getusershell(3) returns *retval if nsdispatch() returns NS_SUCCESS,
          and 0 otherwise.

     setusershell
          Empty ap.

          All methods for all sources are invoked for this method name.

SEE ALSO
     ld.elf_so(1), hesiod(3), stdarg(3), ypclnt(3), nsswitch.conf(5)

HISTORY
     The nsdispatch routines first appeared in NetBSD 1.4.  Support for dynam-
     ically-loaded modules first appeared in NetBSD 3.0.

AUTHORS
     Luke Mewburn <lukem@NetBSD.org> wrote this freely distributable name-ser-
     vice switch implementation, using ideas from the ULTRIX svc.conf(5) and
     Solaris nsswitch.conf(4) manual pages.  Support for dynamically-loaded
     modules was added by Jason Thorpe <thorpej@NetBSD.org>, based on code
     developed by the FreeBSD Project.

NetBSD 5.1                        May 8, 2008                       NetBSD 5.1

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