nss_common.h revision 7c478bd95313f5f23a4c958a745db2134aa03244
/*
* CDDL HEADER START
*
* The contents of this file are subject to the terms of the
* Common Development and Distribution License, Version 1.0 only
* (the "License"). You may not use this file except in compliance
* with the License.
*
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* See the License for the specific language governing permissions
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*
* When distributing Covered Code, include this CDDL HEADER in each
* file and include the License file at usr/src/OPENSOLARIS.LICENSE.
* If applicable, add the following below this CDDL HEADER, with the
* fields enclosed by brackets "[]" replaced with your own identifying
* information: Portions Copyright [yyyy] [name of copyright owner]
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*/
/*
* Copyright (c) 1992-1999 by Sun Microsystems, Inc.
* All rights reserved.
*/
/*
*
* NOTE: The interfaces documented in this file may change in a minor
* release. It is intended that in the future a stronger committment
* will be made to these interface definitions which will guarantee
* them across minor releases.
*/
#ifndef _NSS_COMMON_H
#define _NSS_COMMON_H
#pragma ident "%Z%%M% %I% %E% SMI"
#include <synch.h>
#ifdef __cplusplus
extern "C" {
#endif
/*
* The name-service switch
* -----------------------
*
* From nsswitch.conf(4):
*
* The operating system uses a number of ``databases'' of information
* these can come from a variety of ``sources'': host-names and
* DNS. One or more sources may be used for each database; the
* sources and their lookup order are specified in the
* /etc/nsswitch.conf file.
*
* The implementation of this consists of:
*
* - a ``frontend'' for each database, which provides a programming
* interface for that database [for example, the "passwd" frontend
* consists of getpwnam_r(), getpwuid_r(), getpwent_r(), setpwent(),
* endpwent(), and the old MT-unsafe routines getpwnam() and getpwuid()]
* and is implemented by calls to...
*
* - the common core of the switch (``switch engine''); it determines
* which sources to use and invokes...
*
* - A ``backend'' for each useful <database, source> pair. Each backend
* consists of whatever private data it needs and a set of functions
* that the switch engine may invoke on behalf of the frontend
* [e.g. the "nis" backend for "passwd" provides routines to lookup
* The set of functions, and their expected arguments and results,
* constitutes a (database-specific) interface between a frontend and
* all its backends. The switch engine knows as little as possible
* about these interfaces.
*
* (The term ``backend'' is used ambiguously; it may also refer to a
* particular instantiation of a backend, or to the set of all backends
* for a particular source, e.g. "the nis backend").
*
* This header file defines the interface between the switch engine and the
* frontends and backends. Interfaces between specific frontends and
* backends are defined elsewhere; many are in <nss_dbdefs.h>.
*
*
* Switch-engine outline
* ---------------------
*
* Frontends may call the following routines in the switch engine:
*
* nss_search() does getXXXbyYYY, e.g. getpwnam_r(), getpwuid_r()
* nss_getent() does getXXXent, e.g. getpwent_r()
* nss_setent() does setXXXent, e.g. setpwent()
* nss_endent() does endXXXent, e.g. endpwent()
* nss_delete() releases resources, in the style of endpwent().
*
* A getpwnam_r() call might proceed thus (with many details omitted):
*
* calls nss_search(),
* (2) nss_search looks up configuration info, gets "passwd: files nis",
* (3) nss_search decides to try first source ("files"),
* (a) nss_search locates code for <"passwd", "files"> backend,
* (b) nss_search creates instance of backend,
* (c) nss_search calls get-by-name routine in backend,
* returns "not found" status to nss_search,
* (4) nss_search examines status and config info, decides to try
* next source ("nis"),
* (a) nss_search locates code for <"passwd", "nis"> backend,
* (b) nss_search creates instance of backend,
* (c) nss_search calls get-by-name routine in backend,
* (d) backend searches passwd.byname, finds the desired entry,
* fills in the result part of the getpwnam-specific
* struct, returns "success" status to nss_search,
* (5) nss_search examines status and config info, decides to return
* to caller,
* (6) getpwnam_r extracts result from getpwnam-specific struct,
* returns to caller.
*
*
* Data structures
* ---------------
*
* Both databases and sources are represented by case-sensitive strings
* (the same strings that appear in the configuration file).
*
* The switch engine maintains a per-frontend data structure so that the
* results of steps (2), (a) and (b) can be cached. The frontend holds a
* handle (nss_db_root_t) to this structure and passes it in to the
* nss_*() routines.
*
* The nss_setent(), nss_getent() and nss_endent() routines introduce another
* variety of state (the current position in the enumeration process).
* Within a single source, this information is maintained by private data
* in the backend instance -- but, in the presence of multiple sources, the
* switch engine must keep track of the current backend instance [e.g either
* <"passwd", "files"> or <"passwd", "nis"> instances]. The switch engine
* has a separate per-enumeration data structure for this; again, the
* frontend holds a handle (nss_getent_t) and passes it in, along with the
* nss_db_root_t handle, to nss_setent(), nss_getent() and nss_endent().
*
*
* Multithreading
* --------------
*
* The switch engine takes care of locking; frontends should be written to
* be reentrant, and a backend instance may assume that all calls to it are
* serialized.
*
* If multiple threads simultaneously want to use a particular backend, the
* switch engine creates multiple backend instances (up to some limit
* specified by the frontend). Backends must of course lock any state that
* is shared between instances, and must serialize calls to any MT-unsafe
* code.
*
* The switch engine has no notion of per-thread state.
*
* Frontends can use the nss_getent_t handle to define the scope of the
* (which is what Posix has specified for the getXXXent_r routines), handles
* in Thread-Specific Data give per-thread state, and handles on the stack
* give per-invocation state.
*/
/*
* Backend instances
* -----------------
*
* As far as the switch engine is concerned, an instance of a backend is a
* struct whose first two members are:
* - A pointer to a vector of function pointers, one for each
* database-specific function,
* - The length of the vector (an int), used for bounds-checking.
* There are four well-known function slots in the vector:
* [0] is a destructor for the backend instance,
* [1] is the endXXXent routine,
* [2] is the setXXXent routine,
* [3] is the getXXXent routine.
* Any other slots are database-specific getXXXbyYYY routines; the frontend
* specifies a slot-number to nss_search().
*
* The functions take two arguments:
* - a pointer to the backend instance (like a C++ "this" pointer)
* structure (the contents are opaque to the switch engine).
* The four well-known functions ignore the (void *) pointer.
*
* Backend routines return one of five status codes to the switch engine:
* SUCCESS, UNAVAIL, NOTFOUND, TRYAGAIN (these are the same codes that may
* be specified in the config information; see nsswitch.conf(4)), or
* NSS_NISSERVDNS_TRYAGAIN (should only be used by the NIS backend for
* NIS server in DNS forwarding mode to indicate DNS server non-response).
*/
typedef enum {
} nss_status_t;
struct nss_backend;
#if defined(__STDC__)
#else
typedef nss_status_t (*nss_backend_op_t)();
#endif
struct nss_backend {
int n_ops;
};
typedef struct nss_backend nss_backend_t;
typedef int nss_dbop_t;
#define NSS_DBOP_DESTRUCTOR 0
#define NSS_DBOP_ENDENT 1
#define NSS_DBOP_SETENT 2
#define NSS_DBOP_GETENT 3
#define NSS_LOOKUP_DBOP(instp, n) \
: NSS_UNAVAIL)
/*
* Locating and instantiating backends
* -----------------------------------
*
* To perform step (a), the switch consults a list of backend-finder routines,
* passing a <database, source> pair.
*
* There is a standard backend-finder; frontends may augment or replace this
* in order to, say, indicate that some backends are "compiled in" with the
* frontend.
*
* Backend-finders return a pointer to a constructor function for the backend.
* (or NULL if they can't find the backend). The switch engine caches these
* function pointers; when it needs to perform step (b), it calls the
* constructor function, which returns a pointer to a new instance of the
* backend, properly initialized (or returns NULL).
*/
#if defined(__STDC__)
const char *src_name,
/* Hook for (unimplemented) args in nsswitch.conf */ const char *cfg_args);
#else
typedef nss_backend_t * (*nss_backend_constr_t)();
#endif
struct nss_backend_finder {
#if defined(__STDC__)
void (*delete)
(void *del_priv, nss_backend_constr_t);
#else
nss_backend_constr_t (*lookup)();
void (*delete)();
#endif
struct nss_backend_finder *next;
void *lookup_priv;
};
typedef struct nss_backend_finder nss_backend_finder_t;
extern nss_backend_finder_t *nss_default_finders;
/*
* Frontend parameters
* -------------------
*
* The frontend must tell the switch engine:
* - the database name,
* - the compiled-in default configuration entry.
* It may also override default values for:
* - the database name to use when looking up the configuration
* information (e.g. "shadow" uses the config entry for "passwd"),
* - a limit on the number of instances of each backend that are
* simultaneously active,
* - a limit on the number of instances of each backend that are
* simultaneously dormant (waiting for new requests),
* - a flag that tells the switch engine to use the default configuration
* entry and ignore any other config entry for this database,
* - backend-finders (see above)
* - a cleanup routine that should be called when these parameters are
* about to be deleted.
*
* In order to do this, the frontend includes a pointer to an initialization
* function (nss_db_initf_t) in every nss_*() call. When necessary (normally
* just on the first invocation), the switch engine allocates a parameter
* structure (nss_db_params_t), fills in the default values, then calls
* the initialization function, which should update the parameter structure
* as necessary.
*
* (This might look more natural if we put nss_db_initf_t in nss_db_root_t,
* or abolished nss_db_initf_t and put nss_db_params_t in nss_db_root_t.
* It's done the way it is for shared-library efficiency, namely:
* - keep the unshared data (nss_db_root_t) to a minimum,
* - keep the symbol lookups and relocations to a minimum.
* In particular this means that non-null pointers, e.g. strings and
* function pointers, in global data are a bad thing).
*/
enum nss_dbp_flags {
NSS_USE_DEFAULT_CONFIG = 0x1
};
struct nss_db_params {
const char *name; /* Mandatory: database name */
const char *config_name; /* config-file database name */
const char *default_config; /* Mandatory: default config */
unsigned max_active_per_src;
unsigned max_dormant_per_src;
enum nss_dbp_flags flags;
void *private; /* Not used by switch */
void (*cleanup)(struct nss_db_params *);
};
typedef struct nss_db_params nss_db_params_t;
#if defined(__STDC__)
typedef void (*nss_db_initf_t)(nss_db_params_t *);
#else
typedef void (*nss_db_initf_t)();
#endif
/*
* These structures are defined inside the implementation of the switch
* engine; the interface just holds pointers to them.
*/
struct nss_db_state;
struct nss_getent_context;
/*
* Finally, the two handles that frontends hold:
*/
struct nss_db_root {
struct nss_db_state *s;
};
typedef struct nss_db_root nss_db_root_t;
#define NSS_DB_ROOT_INIT { 0, DEFAULTMUTEX }
typedef struct {
struct nss_getent_context *ctx;
} nss_getent_t;
#define NSS_GETENT_INIT { 0, DEFAULTMUTEX }
#if defined(__STDC__)
int search_fnum, void *search_args);
void *getent_args);
/* ^^ superfluous but consistent */
extern void nss_delete(nss_db_root_t *);
#else
extern nss_status_t nss_search();
extern nss_status_t nss_getent();
extern void nss_setent();
extern void nss_endent();
extern void nss_delete();
#endif
#ifdef __cplusplus
}
#endif
#endif /* _NSS_COMMON_H */