sysdeps/unix/opendir.c

   1 /* Copyright (C) 1991, 92, 93, 94, 95, 96, 98 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Library General Public License as
   6    published by the Free Software Foundation; either version 2 of the
   7    License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Library General Public License for more details.
  13
  14    You should have received a copy of the GNU Library General Public
  15    License along with the GNU C Library; see the file COPYING.LIB.  If not,
  16    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  17    Boston, MA 02111-1307, USA.  */
  18
  19 #include <errno.h>
  20 #include <limits.h>
  21 #include <stddef.h>
  22 #include <stdlib.h>
  23 #include <dirent.h>
  24 #include <fcntl.h>
  25 #include <sys/types.h>
  26 #include <sys/stat.h>
  27 #include <unistd.h>
  28 #include <stdio.h>
  29
  30 #include <dirstream.h>
  31
  32 /* opendir() must not accidentally open something other than a directory.
  33    Some OS's have kernel support for that, some don't.  In the worst
  34    case we have to stat() before the open() AND fstat() after.
  35
  36    We have to test at runtime for kernel support since libc may have
  37    been compiled with different headers to the kernel it's running on.
  38    This test can't be done reliably in the general case.  We'll use
  39    /dev/null, which if it's not a device lots of stuff will break, as
  40    a guinea pig.  It may be missing in chroot environments, so we
  41    make sure to fail safe. */
  42 #ifdef O_DIRECTORY
  43 static int o_directory_works;
  44
  45 static void
  46 tryopen_o_directory (void)
  47 {
  48   int serrno = errno;
  49   int x = __open ("/dev/null", O_RDONLY|O_NDELAY|O_DIRECTORY);
  50
  51   if (x >= 0)
  52     {
  53       __close (x);
  54       o_directory_works = -1;
  55     }
  56   else if (errno != ENOTDIR)
  57     o_directory_works = -1;
  58   else
  59     o_directory_works = 1;
  60
  61   __set_errno (serrno);
  62 }
  63 # define EXTRA_FLAGS O_DIRECTORY
  64 #else
  65 # define EXTRA_FLAGS 0
  66 #endif
  67
  68
  69 /* Open a directory stream on NAME.  */
  70 DIR *
  71 __opendir (const char *name)
  72 {
  73   DIR *dirp;
  74   struct stat statbuf;
  75   int fd;
  76   size_t allocation;
  77   int save_errno;
  78
  79   if (name[0] == '\0')
  80     {
  81       /* POSIX.1-1990 says an empty name gets ENOENT;
  82          but `open' might like it fine.  */
  83       __set_errno (ENOENT);
  84       return NULL;
  85     }
  86
  87 #ifdef O_DIRECTORY
  88   /* Test whether O_DIRECTORY works.  */
  89   if (o_directory_works == 0)
  90     tryopen_o_directory ();
  91
  92   /* We can skip the expensive `stat' call if O_DIRECTORY works.  */
  93   if (o_directory_works < 0)
  94 #endif
  95     {
  96       /* We first have to check whether the name is for a directory.  We
  97          cannot do this after the open() call since the open/close operation
  98          performed on, say, a tape device might have undesirable effects.  */
  99       if (__xstat (_STAT_VER, name, &statbuf) < 0)
 100         return NULL;
 101       if (! S_ISDIR (statbuf.st_mode))
 102         {
 103           __set_errno (ENOTDIR);
 104           return NULL;
 105          }
 106     }
 107
 108   fd = __open (name, O_RDONLY|O_NDELAY|EXTRA_FLAGS);
 109   if (fd < 0)
 110     return NULL;
 111
 112   /* Now make sure this really is a directory and nothing changed since
 113      the `stat' call.  */
 114   if (__fstat (fd, &statbuf) < 0)
 115     goto lose;
 116   if (! S_ISDIR (statbuf.st_mode))
 117     {
 118       save_errno = ENOTDIR;
 119       goto lose;
 120     }
 121
 122   if (__fcntl (fd, F_SETFD, FD_CLOEXEC) < 0)
 123     goto lose;
 124
 125 #ifdef _STATBUF_ST_BLKSIZE
 126   if (statbuf.st_blksize < sizeof (struct dirent))
 127     allocation = sizeof (struct dirent);
 128   else
 129     allocation = statbuf.st_blksize;
 130 #else
 131   allocation = (BUFSIZ < sizeof (struct dirent)
 132                 ? sizeof (struct dirent) : BUFSIZ);
 133 #endif
 134
 135   dirp = (DIR *) calloc (1, sizeof (DIR) + allocation); /* Zero-fill.  */
 136   if (dirp == NULL)
 137   lose:
 138     {
 139       save_errno = errno;
 140       (void) __close (fd);
 141       __set_errno (save_errno);
 142       return NULL;
 143     }
 144   dirp->data = (char *) (dirp + 1);
 145   dirp->allocation = allocation;
 146   dirp->fd = fd;
 147
 148   __libc_lock_init (dirp->lock);
 149
 150   return dirp;
 151 }
 152 weak_alias (__opendir, opendir)