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

/* Determine current working directory.  Linux version.
   Copyright (C) 1997, 1998, 1999, 2000, 2002 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 Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 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
   Lesser General Public License for more details.

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

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

#include <sysdep.h>
#include <sys/syscall.h>
#include <bp-checks.h>

#include "kernel-features.h"


#if __ASSUME_GETCWD_SYSCALL > 0
/* Kernel 2.1.92 introduced a third way to get the current working
   directory: a syscall.  We've got to be careful that even when
   compiling under 2.1.92+ the libc still runs under older kernels. */
extern int __syscall_getcwd (char *__unbounded buf, unsigned long size);
# define no_syscall_getcwd 0
# define have_new_dcache 1
/* This is a trick since we don't define generic_getcwd.  */
# define generic_getcwd getcwd
#else
/* 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) internal_function;

# if __NR_getcwd
/* Kernel 2.1.92 introduced a third way to get the current working
   directory: a syscall.  We've got to be careful that even when
   compiling under 2.1.92+ the libc still runs under older kernels. */
extern int __syscall_getcwd (char *__unbounded buf, unsigned long size);
static int no_syscall_getcwd;
static int have_new_dcache;
# else
#  define no_syscall_getcwd 1
static int have_new_dcache = 1;
# endif
#endif

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

  if (no_syscall_getcwd && !have_new_dcache)
    return generic_getcwd (buf, size);

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

      alloc_size = PATH_MAX;
    }

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

#if defined __NR_getcwd || __LINUX_GETCWD_SYSCALL > 0
  if (!no_syscall_getcwd)
    {
      int retval;

      retval = INLINE_SYSCALL (getcwd, 2, CHECK_STRING (path), alloc_size);
      if (retval >= 0)
	{
	  if (buf == NULL && size == 0)
	    /* Ensure that the buffer is only as large as necessary.  */
	    buf = realloc (path, (size_t) retval);

	  if (buf == NULL)
	    /* Either buf was NULL all along, or `realloc' failed but
	       we still have the original string.  */
	    buf = path;

	  return buf;
	}

# if __ASSUME_GETCWD_SYSCALL
      /* It should never happen that the `getcwd' syscall failed because
	 the buffer is too small if we allocated the buffer ourselves
	 large enough.  */
      assert (errno != ERANGE || buf != NULL || size != 0);

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

      return NULL;
# else
      if (errno == ENOSYS)
	{
	   no_syscall_getcwd = 1;
	   have_new_dcache = 1;	/* Now we will try the /proc method.  */
	}
      else if (errno != ERANGE || buf != NULL)
	{
	  if (buf == NULL)
	    free (path);
	  return NULL;
	}
# endif
    }
#endif

  n = __readlink ("/proc/self/cwd", path, alloc_size - 1);
  if (n != -1)
    {
      if (path[0] == '/')
	{
	  if ((size_t) n >= alloc_size - 1)
	    {
	      if (buf == NULL)
		free (path);
	      return NULL;
	    }

	  path[n] = '\0';
	  if (buf == NULL && size == 0)
	    /* Ensure that the buffer is only as large as necessary.  */
	    buf = realloc (path, (size_t) n + 1);
	  if (buf == NULL)
	    /* Either buf was NULL all along, or `realloc' failed but
	       we still have the original string.  */
	    buf = path;

	  return buf;
	}
#ifndef have_new_dcache
      else
	have_new_dcache = 0;
#endif
    }

#if __ASSUME_GETCWD_SYSCALL == 0
  /* Set to have_new_dcache only if error indicates that proc doesn't
     exist.  */
  if (errno != EACCES && errno != ENAMETOOLONG)
    have_new_dcache = 0;
#endif

  /* Don't put restrictions on the length of the path unless the user does.  */
  if (size == 0)
    {
      free (path);
      path = NULL;
    }

  result = generic_getcwd (path, size);

  if (result == NULL && buf == NULL && size != 0)
    free (path);

  return result;
}
weak_alias (__getcwd, getcwd)

#if __ASSUME_GETCWD_SYSCALL == 0
/* Get the code for the generic version.  */
# define GETCWD_RETURN_TYPE	static char * internal_function
# define __getcwd		generic_getcwd
# include <sysdeps/posix/getcwd.c>
#endif