NSDISPATCH(3)

NSDISPATCH(3) | 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 missing 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 function (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 function 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 database is.

## Callback function return values

The callback functions should return one of the following values depending 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

getaddrinfo
  char *name, const struct addrinfo *pai
  Returns struct addrinfo * via void *cbrv.
gethostbyaddr
  unsigned char *addr, int addrlen, int af
  Returns struct getnamaddr * via void *cbrv.
gethostbyname
  char *name, int namelen, int af
  Returns struct getnamaddr * via void *cbrv.

The struct getnamaddr is defined internally in libc as:

    struct getnamaddr {
            struct hostent *hp;
            char *buf;
            size_t buflen;
            int *he;
    };

## 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 otherwise.
  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(3) 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 dynamically-loaded modules first appeared in NetBSD 3.0.

# AUTHORS

Luke Mewburn <lukem@NetBSD.org> wrote this freely distributable name-service 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.

January 4, 2015 | NetBSD 8.3