glibc/sysdeps/unix/opendir.c

/* Copyright (C) 1991,92,93,94,95,96,98,2000 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   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 <stddef.h>
#include <stdlib.h>
#include <dirent.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <stdio.h>

#include <dirstream.h>

/* opendir() must not accidentally open something other than a directory.
   Some OS's have kernel support for that, some don't.  In the worst
   case we have to stat() before the open() AND fstat() after.

   We have to test at runtime for kernel support since libc may have
   been compiled with different headers to the kernel it's running on.
   This test can't be done reliably in the general case.  We'll use
   /dev/null, which if it's not a device lots of stuff will break, as
   a guinea pig.  It may be missing in chroot environments, so we
   make sure to fail safe. */
#ifdef O_DIRECTORY
# ifdef O_DIRECTORY_WORKS
#  define o_directory_works 1
#  define tryopen_o_directory() while (1) /* This must not be called.  */
# else
static int o_directory_works;

static void
tryopen_o_directory (void)
{
  int serrno = errno;
  int x = __open ("/dev/null", O_RDONLY|O_NDELAY|O_DIRECTORY);

  if (x >= 0)
    {
      __close (x);
      o_directory_works = -1;
    }
  else if (errno != ENOTDIR)
    o_directory_works = -1;
  else
    o_directory_works = 1;

  __set_errno (serrno);
}
# endif
# define EXTRA_FLAGS O_DIRECTORY
#else
# define EXTRA_FLAGS 0
#endif


/* Open a directory stream on NAME.  */
DIR *
__opendir (const char *name)
{
  DIR *dirp;
  struct stat64 statbuf;
  int fd;
  size_t allocation;
  int save_errno;

  if (__builtin_expect (name[0], '\1') == '\0')
    {
      /* POSIX.1-1990 says an empty name gets ENOENT;
	 but `open' might like it fine.  */
      __set_errno (ENOENT);
      return NULL;
    }

#ifdef O_DIRECTORY
  /* Test whether O_DIRECTORY works.  */
  if (o_directory_works == 0)
    tryopen_o_directory ();

  /* We can skip the expensive `stat' call if O_DIRECTORY works.  */
  if (o_directory_works < 0)
#endif
    {
      /* We first have to check whether the name is for a directory.  We
	 cannot do this after the open() call since the open/close operation
	 performed on, say, a tape device might have undesirable effects.  */
      if (__builtin_expect (__xstat64 (_STAT_VER, name, &statbuf), 0) < 0)
	return NULL;
      if (__builtin_expect (! S_ISDIR (statbuf.st_mode), 0))
	{
	  __set_errno (ENOTDIR);
	  return NULL;
	 }
    }

  fd = __open (name, O_RDONLY|O_NDELAY|EXTRA_FLAGS);
  if (__builtin_expect (fd, 0) < 0)
    return NULL;

  /* Now make sure this really is a directory and nothing changed since
     the `stat' call.  We do not have to perform the test for the
     descriptor being associated with a directory if we know the
     O_DIRECTORY flag is honored by the kernel.  */
  if (__builtin_expect (__fxstat64 (_STAT_VER, fd, &statbuf), 0) < 0)
    goto lose;
  if (o_directory_works <= 0
      && __builtin_expect (! S_ISDIR (statbuf.st_mode), 0))
    {
      save_errno = ENOTDIR;
      goto lose;
    }

  if (__builtin_expect (__fcntl (fd, F_SETFD, FD_CLOEXEC), 0) < 0)
    goto lose;

#ifdef _STATBUF_ST_BLKSIZE
  if (__builtin_expect (statbuf.st_blksize < sizeof (struct dirent), 0))
    allocation = sizeof (struct dirent);
  else
    allocation = statbuf.st_blksize;
#else
  allocation = (BUFSIZ < sizeof (struct dirent)
		? sizeof (struct dirent) : BUFSIZ);
#endif

  dirp = (DIR *) calloc (1, sizeof (DIR) + allocation); /* Zero-fill.  */
  if (dirp == NULL)
  lose:
    {
      save_errno = errno;
      (void) __close (fd);
      __set_errno (save_errno);
      return NULL;
    }
  dirp->data = (char *) (dirp + 1);
  dirp->allocation = allocation;
  dirp->fd = fd;

  __libc_lock_init (dirp->lock);

  return dirp;
}
weak_alias (__opendir, opendir)