PostgreSQL插件hook机制

internal_load_library postgresql-> PG_init = (PG_init_t) pg_dlsym(file_scanner->handle, "_PG_init"); if (PG_init) (*PG_init) (); internal_unload_library(const char *libname)-> PG_fini = (PG_fini_t) pg_dlsym(file_scanner->handle, "_PG_fini"); if (PG_fini) (*PG_fini) (); 以ClientAuthentication_hook_type为例 auth.h: //声明插件使用的函数 extern void ClientAuthentication(Port *port); /* Hook for plugins to get control in ClientAuthentication() */ typedef void (*ClientAuthentication_hook_type) (Port *, int); extern PGDLLIMPORT ClientAuthentication_hook_type ClientAuthentication_hook; auth.c: //全局变量初始化为NULL，在_PG_init函数中进行初始化赋值，如果该插件加载，则ClientAuthentication_hook为 ClientAuthentication_hook_type ClientAuthentication_hook = NULL; //如果ClientAuthentication_hook被赋值则执行植入的代码 InitPostgres->PerformAuthentication->ClientAuthentication-> if (ClientAuthentication_hook) (*ClientAuthentication_hook) (port, status); auth_delay.c: static ClientAuthentication_hook_type original_client_auth_hook = NULL; /* * Module Load Callback */ void _PG_init(void) { /* Define custom GUC variables */ DefineCustomIntVariable("auth_delay.milliseconds", "Milliseconds to delay before reporting authentication failure", NULL, &auth_delay_milliseconds, 0, 0, INT_MAX / 1000, PGC_SIGHUP, GUC_UNIT_MS, NULL, NULL, NULL); /* Install Hooks */ original_client_auth_hook = ClientAuthentication_hook; ClientAuthentication_hook = auth_delay_checks; } /* 如果卸载则调用该函数，实际上是将ClientAuthentication_hook赋回原值 */ void _PG_fini(void) { ClientAuthentication_hook=original_client_auth_hook； } /* */ static void auth_delay_checks(Port *port, int status) { if (original_client_auth_hook) original_client_auth_hook(port, status); if (status != STATUS_OK){ pg_usleep(1000L * auth_delay_milliseconds); } }