nss/nss_module.h

   1 /* Global list of NSS service modules.
   2    Copyright (c) 2020-2021 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 #ifndef _NSS_MODULE_H
  20 #define _NSS_MODULE_H
  21
  22 #include <nss.h>
  23 #include <stdbool.h>
  24
  25 /* See nss_database.h for a summary of how this relates.  */
  26
  27 /* Typed function pointers for all functions that can be defined by a
  28    service module.  */
  29 struct nss_module_functions
  30 {
  31 #undef DEFINE_NSS_FUNCTION
  32 #define DEFINE_NSS_FUNCTION(f) nss_##f *f;
  33 #include "function.def"
  34 };
  35
  36 /* Untyped version of struct nss_module_functions, for consistent
  37    processing purposes.  */
  38 typedef void *nss_module_functions_untyped[sizeof (struct nss_module_functions)
  39                                            / sizeof (void *)];
  40
  41 /* Initialization state of a NSS module.  */
  42 enum nss_module_state
  43 {
  44   nss_module_uninitialized,
  45   nss_module_loaded,
  46   nss_module_failed,
  47 };
  48
  49 /* A NSS service module (potentially unloaded).  Client code should
  50    use the functions below.  */
  51 struct nss_module
  52 {
  53   /* Actual type is enum nss_module_state.  Use int due to atomic
  54      access.  Used in a double-checked locking idiom.  */
  55   int state;
  56
  57   /* The function pointers in the module.  */
  58   union
  59   {
  60     struct nss_module_functions typed;
  61     nss_module_functions_untyped untyped;
  62   } functions;
  63
  64   /* Only used for __libc_freeres unloading.  */
  65   void *handle;
  66
  67   /* The next module in the list. */
  68   struct nss_module *next;
  69
  70   /* The name of the module (as it appears in /etc/nsswitch.conf).  */
  71   char name[];
  72 };
  73
  74 /* Allocates the NSS module NAME (of NAME_LENGTH bytes) and places it
  75    into the global list.  If it already exists in the list, return the
  76    pre-existing module.  This does not actually load the module.
  77    Returns NULL on memory allocation failure.  */
  78 struct nss_module *__nss_module_allocate (const char *name,
  79                                           size_t name_length) attribute_hidden;
  80
  81 /* Ensures that MODULE is in a loaded or failed state.  */
  82 bool __nss_module_load (struct nss_module *module) attribute_hidden;
  83
  84 /* Ensures that MODULE is loaded and returns a pointer to the function
  85    NAME defined in it.  Returns NULL if MODULE could not be loaded, or
  86    if the function NAME is not defined in the module.  */
  87 void *__nss_module_get_function (struct nss_module *module, const char *name)
  88   attribute_hidden;
  89
  90 /* Block attempts to dlopen any module we haven't already opened.  */
  91 void __nss_module_disable_loading (void);
  92
  93 /* Called from __libc_freeres.  */
  94 void __nss_module_freeres (void) attribute_hidden;
  95
  96 #endif /* NSS_MODULE_H */