glibc/sysdeps/unix/sysv/linux/getcwd.c

/* Determine current working directory.  Linux version.
   Copyright (C) 1997 Free Software Foundation, Inc.
   This file is part of the GNU C Library.
   Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Library General Public License as
   published by the Free Software Foundation; either version 2 of the
   License, or (at your option) any later version.

   The GNU C Library 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
   Library General Public License for more details.

   You should have received a copy of the GNU Library General Public
   License along with the GNU C Library; see the file COPYING.LIB.  If not,
   write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
   Boston, MA 02111-1307, USA.  */

#include <errno.h>
#include <limits.h>
#include <stdlib.h>
#include <unistd.h>

/* #define NDEBUG 1 */
#include <assert.h>

/* The "proc" filesystem provides an easy method to retrieve the value.
   For each process, the corresponding directory contains a symbolic link
   named `cwd'.  Reading the content of this link immediate gives us the
   information.  But we have to take care for systems which do not have
   the proc filesystem mounted.  Use the POSIX implementation in this case.  */
static char *generic_getcwd (char *buf, size_t size);

char *
__getcwd (char *buf, size_t size)
{
  int save_errno;
  char *path;
  int n;
  char *result;

  if (size == 0)
    {
      if (buf != NULL)
	{
	  __set_errno (EINVAL);
	  return NULL;
	}

      size = PATH_MAX + 1;
    }

  if (buf != NULL)
    path = buf;
  else
    {
      path = malloc (size);
      if (path == NULL)
	return NULL;
    }

  save_errno = errno;
  n = __readlink ("/proc/self/cwd", path, size);
  if (n != -1)
    {
      if (n >= size)
	{
	  /* This should never happen when we allocate the buffer here.  */
	  assert (buf == NULL);
	  __set_errno (ERANGE);
	  return NULL;
	}
      path[n] = '\0';
      return buf ?: (char *) realloc (path, (size_t) n + 1);
    }

  /* Something went wrong.  Restore the error number and use the generic
     version.  */
  __set_errno (save_errno);
  result = generic_getcwd (path, size);

  if (result == NULL && buf == NULL)
    free (path);

  return result;
}
weak_alias (__getcwd, getcwd)

/* Get the code for the generic version.  */
#define GETCWD_STORAGE_CLASS	static
#define __getcwd		generic_getcwd
#include <sysdeps/posix/getcwd.c>