dfmgr.c

来自「postgresql8.3.4源码,开源数据库」· C语言 代码 · 共 625 行 · 第 1/2 页

/*-------------------------------------------------------------------------
 *
 * dfmgr.c
 *	  Dynamic function manager code.
 *
 * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  $PostgreSQL: pgsql/src/backend/utils/fmgr/dfmgr.c,v 1.96 2008/01/01 19:45:53 momjian Exp $
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include <sys/stat.h>

#ifndef WIN32_ONLY_COMPILER
#include "dynloader.h"
#else
#include "port/dynloader/win32.h"
#endif
#include "miscadmin.h"
#include "utils/dynamic_loader.h"
#include "utils/hsearch.h"


/* signatures for PostgreSQL-specific library init/fini functions */
typedef void (*PG_init_t) (void);
typedef void (*PG_fini_t) (void);

/* hashtable entry for rendezvous variables */
typedef struct
{
	char		varName[NAMEDATALEN];	/* hash key (must be first) */
	void	   *varValue;
} rendezvousHashEntry;

/*
 * List of dynamically loaded files (kept in malloc'd memory).
 */

typedef struct df_files
{
	struct df_files *next;		/* List link */
	dev_t		device;			/* Device file is on */
#ifndef WIN32					/* ensures we never again depend on this under
								 * win32 */
	ino_t		inode;			/* Inode number of file */
#endif
	void	   *handle;			/* a handle for pg_dl* functions */
	char		filename[1];	/* Full pathname of file */

	/*
	 * we allocate the block big enough for actual length of pathname.
	 * filename[] must be last item in struct!
	 */
} DynamicFileList;

static DynamicFileList *file_list = NULL;
static DynamicFileList *file_tail = NULL;

/* stat() call under Win32 returns an st_ino field, but it has no meaning */
#ifndef WIN32
#define SAME_INODE(A,B) ((A).st_ino == (B).inode && (A).st_dev == (B).device)
#else
#define SAME_INODE(A,B) false
#endif

char	   *Dynamic_library_path;

static void *internal_load_library(const char *libname);
static void internal_unload_library(const char *libname);
static bool file_exists(const char *name);
static char *expand_dynamic_library_name(const char *name);
static void check_restricted_library_name(const char *name);
static char *substitute_libpath_macro(const char *name);
static char *find_in_dynamic_libpath(const char *basename);

/* Magic structure that module needs to match to be accepted */
static const Pg_magic_struct magic_data = PG_MODULE_MAGIC_DATA;


/*
 * Load the specified dynamic-link library file, and look for a function
 * named funcname in it.
 *
 * If the function is not found, we raise an error if signalNotFound is true,
 * else return (PGFunction) NULL.  Note that errors in loading the library
 * will provoke ereport() regardless of signalNotFound.
 *
 * If filehandle is not NULL, then *filehandle will be set to a handle
 * identifying the library file.  The filehandle can be used with
 * lookup_external_function to lookup additional functions in the same file
 * at less cost than repeating load_external_function.
 */
PGFunction
load_external_function(char *filename, char *funcname,
					   bool signalNotFound, void **filehandle)
{
	char	   *fullname;
	void	   *lib_handle;
	PGFunction	retval;

	/* Expand the possibly-abbreviated filename to an exact path name */
	fullname = expand_dynamic_library_name(filename);

	/* Load the shared library, unless we already did */
	lib_handle = internal_load_library(fullname);

	/* Return handle if caller wants it */
	if (filehandle)
		*filehandle = lib_handle;

	/* Look up the function within the library */
	retval = (PGFunction) pg_dlsym(lib_handle, funcname);

	if (retval == NULL && signalNotFound)
		ereport(ERROR,
				(errcode(ERRCODE_UNDEFINED_FUNCTION),
				 errmsg("could not find function \"%s\" in file \"%s\"",
						funcname, fullname)));

	pfree(fullname);
	return retval;
}

/*
 * This function loads a shlib file without looking up any particular
 * function in it.	If the same shlib has previously been loaded,
 * unload and reload it.
 *
 * When 'restricted' is true, only libraries in the presumed-secure
 * directory $libdir/plugins may be referenced.
 */
void
load_file(const char *filename, bool restricted)
{
	char	   *fullname;

	/* Apply security restriction if requested */
	if (restricted)
		check_restricted_library_name(filename);

	/* Expand the possibly-abbreviated filename to an exact path name */
	fullname = expand_dynamic_library_name(filename);

	/* Unload the library if currently loaded */
	internal_unload_library(fullname);

	/* Load the shared library */
	(void) internal_load_library(fullname);

	pfree(fullname);
}

/*
 * Lookup a function whose library file is already loaded.
 * Return (PGFunction) NULL if not found.
 */
PGFunction
lookup_external_function(void *filehandle, char *funcname)
{
	return (PGFunction) pg_dlsym(filehandle, funcname);
}


/*
 * Load the specified dynamic-link library file, unless it already is
 * loaded.	Return the pg_dl* handle for the file.
 *
 * Note: libname is expected to be an exact name for the library file.
 */
static void *
internal_load_library(const char *libname)
{
	DynamicFileList *file_scanner;
	PGModuleMagicFunction magic_func;
	char	   *load_error;
	struct stat stat_buf;
	PG_init_t	PG_init;

	/*
	 * Scan the list of loaded FILES to see if the file has been loaded.
	 */
	for (file_scanner = file_list;
		 file_scanner != NULL &&
		 strcmp(libname, file_scanner->filename) != 0;
		 file_scanner = file_scanner->next)
		;

	if (file_scanner == NULL)
	{
		/*
		 * Check for same files - different paths (ie, symlink or link)
		 */
		if (stat(libname, &stat_buf) == -1)
			ereport(ERROR,
					(errcode_for_file_access(),
					 errmsg("could not access file \"%s\": %m",
							libname)));

		for (file_scanner = file_list;
			 file_scanner != NULL &&
			 !SAME_INODE(stat_buf, *file_scanner);
			 file_scanner = file_scanner->next)
			;
	}

	if (file_scanner == NULL)
	{
		/*
		 * File not loaded yet.
		 */
		file_scanner = (DynamicFileList *)
			malloc(sizeof(DynamicFileList) + strlen(libname));
		if (file_scanner == NULL)
			ereport(ERROR,
					(errcode(ERRCODE_OUT_OF_MEMORY),
					 errmsg("out of memory")));

		MemSet(file_scanner, 0, sizeof(DynamicFileList));
		strcpy(file_scanner->filename, libname);
		file_scanner->device = stat_buf.st_dev;
#ifndef WIN32
		file_scanner->inode = stat_buf.st_ino;
#endif
		file_scanner->next = NULL;

		file_scanner->handle = pg_dlopen(file_scanner->filename);
		if (file_scanner->handle == NULL)
		{
			load_error = (char *) pg_dlerror();
			free((char *) file_scanner);
			/* errcode_for_file_access might not be appropriate here? */
			ereport(ERROR,
					(errcode_for_file_access(),
					 errmsg("could not load library \"%s\": %s",
							libname, load_error)));
		}

		/* Check the magic function to determine compatibility */
		magic_func = (PGModuleMagicFunction)
			pg_dlsym(file_scanner->handle, PG_MAGIC_FUNCTION_NAME_STRING);
		if (magic_func)
		{
			const Pg_magic_struct *magic_data_ptr = (*magic_func) ();

			if (magic_data_ptr->len != magic_data.len ||
				memcmp(magic_data_ptr, &magic_data, magic_data.len) != 0)
			{
				/* copy data block before unlinking library */
				Pg_magic_struct module_magic_data = *magic_data_ptr;

				/* try to unlink library */
				pg_dlclose(file_scanner->handle);
				free((char *) file_scanner);

				/*
				 * Report suitable error.  It's probably not worth writing a
				 * separate error message for each field; only the most common
				 * case of wrong major version gets its own message.
				 */
				if (module_magic_data.version != magic_data.version)
					ereport(ERROR,
					 (errmsg("incompatible library \"%s\": version mismatch",
							 libname),
					  errdetail("Server is version %d.%d, library is version %d.%d.",
								magic_data.version / 100,
								magic_data.version % 100,
								module_magic_data.version / 100,
								module_magic_data.version % 100)));
				ereport(ERROR,
				 (errmsg("incompatible library \"%s\": magic block mismatch",
						 libname)));
			}
		}
		else
		{
			/* try to unlink library */
			pg_dlclose(file_scanner->handle);
			free((char *) file_scanner);
			/* complain */
			ereport(ERROR,
				  (errmsg("incompatible library \"%s\": missing magic block",
						  libname),
				   errhint("Extension libraries are required to use the PG_MODULE_MAGIC macro.")));
		}

		/*
		 * If the library has a _PG_init() function, call it.
		 */
		PG_init = (PG_init_t) pg_dlsym(file_scanner->handle, "_PG_init");
		if (PG_init)
			(*PG_init) ();

		/* OK to link it into list */
		if (file_list == NULL)
			file_list = file_scanner;
		else
			file_tail->next = file_scanner;
		file_tail = file_scanner;
	}

	return file_scanner->handle;
}

/*
 * Unload the specified dynamic-link library file, if it is loaded.
 *
 * Note: libname is expected to be an exact name for the library file.
 */