/* xreadlink.c -- readlink wrapper to return the link name in malloc'd storage   Copyright 2001 Free Software Foundation, Inc.   This program is free software; you can redistribute it and/or modify   it under the terms of the GNU General Public License as published by   the Free Software Foundation; either version 2, or (at your option)   any later version.   This program is distributed in the hope that it will be useful,   but WITHOUT ANY WARRANTY; without even the implied warranty of   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the   GNU General Public License for more details.   You should have received a copy of the GNU General Public License   along with this program; see the file COPYING.   If not, write to the Free Software Foundation,   59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  *//* Written by Jim Meyering <jim@meyering.net>  */#if HAVE_CONFIG_H# include <config.h>#endif#include <stdio.h>#include <errno.h>#ifndef errnoextern int errno;#endif#if HAVE_LIMITS_H# include <limits.h>#endif#if HAVE_SYS_TYPES_H# include <sys/types.h>#endif#if HAVE_STDLIB_H# include <stdlib.h>#endif#if HAVE_UNISTD_H# include <unistd.h>#endif#ifndef SIZE_MAX# define SIZE_MAX ((size_t) -1)#endif#ifndef SSIZE_MAX# define SSIZE_MAX ((ssize_t) (SIZE_MAX / 2))#endif#include "xalloc.h"#include "xreadlink.h"/* Call readlink to get the symbolic link value of FILENAME.   Return a pointer to that NUL-terminated string in malloc'd storage.   If readlink fails, return NULL (caller may use errno to diagnose).   If realloc fails, or if the link value is longer than SIZE_MAX :-),   give a diagnostic and exit.  */char *xreadlink (char const *filename){  /* The initial buffer size for the link value.  A power of 2     detects arithmetic overflow earlier, but is not required.  */  size_t buf_size = 128;  while (1)    {      char *buffer = xmalloc (buf_size);      ssize_t link_length = readlink (filename, buffer, buf_size);      if (link_length < 0)	{	  int saved_errno = errno;	  free (buffer);	  errno = saved_errno;	  return NULL;	}      if ((size_t) link_length < buf_size)	{	  buffer[link_length] = 0;	  return buffer;	}      free (buffer);      buf_size *= 2;      if (SSIZE_MAX < buf_size || (SIZE_MAX / 2 < SSIZE_MAX && buf_size == 0))	xalloc_die ();    }}