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

static void
internal_unload_library(const char *libname)
{
	DynamicFileList *file_scanner,
			   *prv,
			   *nxt;
	struct stat stat_buf;
	PG_fini_t	PG_fini;

	/*
	 * We need to do stat() in order to determine whether this is the same
	 * file as a previously loaded file; it's also handy so as to give a good
	 * error message if bogus file name given.
	 */
	if (stat(libname, &stat_buf) == -1)
		ereport(ERROR,
				(errcode_for_file_access(),
				 errmsg("could not access file \"%s\": %m", libname)));

	/*
	 * We have to zap all entries in the list that match on either filename or
	 * inode, else internal_load_library() will still think it's present.
	 */
	prv = NULL;
	for (file_scanner = file_list; file_scanner != NULL; file_scanner = nxt)
	{
		nxt = file_scanner->next;
		if (strcmp(libname, file_scanner->filename) == 0 ||
			SAME_INODE(stat_buf, *file_scanner))
		{
			if (prv)
				prv->next = nxt;
			else
				file_list = nxt;

			/*
			 * If the library has a _PG_fini() function, call it.
			 */
			PG_fini = (PG_fini_t) pg_dlsym(file_scanner->handle, "_PG_fini");
			if (PG_fini)
				(*PG_fini) ();

			clear_external_function_hash(file_scanner->handle);
			pg_dlclose(file_scanner->handle);
			free((char *) file_scanner);
			/* prv does not change */
		}
		else
			prv = file_scanner;
	}
}

static bool
file_exists(const char *name)
{
	struct stat st;

	AssertArg(name != NULL);

	if (stat(name, &st) == 0)
		return S_ISDIR(st.st_mode) ? false : true;
	else if (!(errno == ENOENT || errno == ENOTDIR || errno == EACCES))
		ereport(ERROR,
				(errcode_for_file_access(),
				 errmsg("could not access file \"%s\": %m", name)));

	return false;
}


/* Example format: ".so" */
#ifndef DLSUFFIX
#error "DLSUFFIX must be defined to compile this file."
#endif

/*
 * If name contains a slash, check if the file exists, if so return
 * the name.  Else (no slash) try to expand using search path (see
 * find_in_dynamic_libpath below); if that works, return the fully
 * expanded file name.	If the previous failed, append DLSUFFIX and
 * try again.  If all fails, just return the original name.
 *
 * The result will always be freshly palloc'd.
 */
static char *
expand_dynamic_library_name(const char *name)
{
	bool		have_slash;
	char	   *new;
	char	   *full;

	AssertArg(name);

	have_slash = (first_dir_separator(name) != NULL);

	if (!have_slash)
	{
		full = find_in_dynamic_libpath(name);
		if (full)
			return full;
	}
	else
	{
		full = substitute_libpath_macro(name);
		if (file_exists(full))
			return full;
		pfree(full);
	}

	new = palloc(strlen(name) + strlen(DLSUFFIX) + 1);
	strcpy(new, name);
	strcat(new, DLSUFFIX);

	if (!have_slash)
	{
		full = find_in_dynamic_libpath(new);
		pfree(new);
		if (full)
			return full;
	}
	else
	{
		full = substitute_libpath_macro(new);
		pfree(new);
		if (file_exists(full))
			return full;
		pfree(full);
	}

	/*
	 * If we can't find the file, just return the string as-is. The ensuing
	 * load attempt will fail and report a suitable message.
	 */
	return pstrdup(name);
}

/*
 * Check a restricted library name.  It must begin with "$libdir/plugins/"
 * and there must not be any directory separators after that (this is
 * sufficient to prevent ".." style attacks).
 */
static void
check_restricted_library_name(const char *name)
{
	if (strncmp(name, "$libdir/plugins/", 16) != 0 ||
		first_dir_separator(name + 16) != NULL)
		ereport(ERROR,
				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
				 errmsg("access to library \"%s\" is not allowed",
						name)));
}

/*
 * Substitute for any macros appearing in the given string.
 * Result is always freshly palloc'd.
 */
static char *
substitute_libpath_macro(const char *name)
{
	const char *sep_ptr;
	char	   *ret;

	AssertArg(name != NULL);

	/* Currently, we only recognize $libdir at the start of the string */
	if (name[0] != '$')
		return pstrdup(name);

	if ((sep_ptr = first_dir_separator(name)) == NULL)
		sep_ptr = name + strlen(name);

	if (strlen("$libdir") != sep_ptr - name ||
		strncmp(name, "$libdir", strlen("$libdir")) != 0)
		ereport(ERROR,
				(errcode(ERRCODE_INVALID_NAME),
				 errmsg("invalid macro name in dynamic library path: %s",
						name)));

	ret = palloc(strlen(pkglib_path) + strlen(sep_ptr) + 1);

	strcpy(ret, pkglib_path);
	strcat(ret, sep_ptr);

	return ret;
}


/*
 * Search for a file called 'basename' in the colon-separated search
 * path Dynamic_library_path.  If the file is found, the full file name
 * is returned in freshly palloc'd memory.  If the file is not found,
 * return NULL.
 */
static char *
find_in_dynamic_libpath(const char *basename)
{
	const char *p;
	size_t		baselen;

	AssertArg(basename != NULL);
	AssertArg(first_dir_separator(basename) == NULL);
	AssertState(Dynamic_library_path != NULL);

	p = Dynamic_library_path;
	if (strlen(p) == 0)
		return NULL;

	baselen = strlen(basename);

	for (;;)
	{
		size_t		len;
		char	   *piece;
		char	   *mangled;
		char	   *full;

		piece = first_path_separator(p);
		if (piece == p)
			ereport(ERROR,
					(errcode(ERRCODE_INVALID_NAME),
					 errmsg("zero-length component in parameter \"dynamic_library_path\"")));

		if (piece == 0)
			len = strlen(p);
		else
			len = piece - p;

		piece = palloc(len + 1);
		strlcpy(piece, p, len + 1);

		mangled = substitute_libpath_macro(piece);
		pfree(piece);

		canonicalize_path(mangled);

		/* only absolute paths */
		if (!is_absolute_path(mangled))
			ereport(ERROR,
					(errcode(ERRCODE_INVALID_NAME),
					 errmsg("component in parameter \"dynamic_library_path\" is not an absolute path")));

		full = palloc(strlen(mangled) + 1 + baselen + 1);
		sprintf(full, "%s/%s", mangled, basename);
		pfree(mangled);

		elog(DEBUG3, "find_in_dynamic_libpath: trying \"%s\"", full);

		if (file_exists(full))
			return full;

		pfree(full);

		if (p[len] == '\0')
			break;
		else
			p += len + 1;
	}

	return NULL;
}


/*
 * Find (or create) a rendezvous variable that one dynamically
 * loaded library can use to meet up with another.
 *
 * On the first call of this function for a particular varName,
 * a "rendezvous variable" is created with the given name.
 * The value of the variable is a void pointer (initially set to NULL).
 * Subsequent calls with the same varName just return the address of
 * the existing variable.  Once created, a rendezvous variable lasts
 * for the life of the process.
 *
 * Dynamically loaded libraries can use rendezvous variables
 * to find each other and share information: they just need to agree
 * on the variable name and the data it will point to.
 */
void	  **
find_rendezvous_variable(const char *varName)
{
	static HTAB *rendezvousHash = NULL;

	rendezvousHashEntry *hentry;
	bool		found;

	/* Create a hashtable if we haven't already done so in this process */
	if (rendezvousHash == NULL)
	{
		HASHCTL		ctl;

		MemSet(&ctl, 0, sizeof(ctl));
		ctl.keysize = NAMEDATALEN;
		ctl.entrysize = sizeof(rendezvousHashEntry);
		rendezvousHash = hash_create("Rendezvous variable hash",
									 16,
									 &ctl,
									 HASH_ELEM);
	}

	/* Find or create the hashtable entry for this varName */
	hentry = (rendezvousHashEntry *) hash_search(rendezvousHash,
												 varName,
												 HASH_ENTER,
												 &found);

	/* Initialize to NULL if first time */
	if (!found)
		hentry->varValue = NULL;

	return &hentry->varValue;
}