sysdeps/unix/opendir.c

   1 /* Copyright (C) 1991-1996,98,2000-2003,2005,2007,2009
   2    Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, write to the Free
  17    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  18    02111-1307 USA.  */
  19
  20 #include <errno.h>
  21 #include <limits.h>
  22 #include <stddef.h>
  23 #include <stdlib.h>
  24 #include <dirent.h>
  25 #include <fcntl.h>
  26 #include <sys/types.h>
  27 #include <sys/stat.h>
  28 #include <unistd.h>
  29 #include <stdio.h>
  30 #include <string.h>
  31
  32 #include <dirstream.h>
  33 #include <not-cancel.h>
  34 #include <kernel-features.h>
  35
  36
  37 /* opendir() must not accidentally open something other than a directory.
  38    Some OS's have kernel support for that, some don't.  In the worst
  39    case we have to stat() before the open() AND fstat() after.
  40
  41    We have to test at runtime for kernel support since libc may have
  42    been compiled with different headers to the kernel it's running on.
  43    This test can't be done reliably in the general case.  We'll use
  44    /dev/null, which if it's not a device lots of stuff will break, as
  45    a guinea pig.  It may be missing in chroot environments, so we
  46    make sure to fail safe. */
  47 #ifdef O_DIRECTORY
  48 # ifdef O_DIRECTORY_WORKS
  49 #  define o_directory_works 1
  50 #  define tryopen_o_directory() while (1) /* This must not be called.  */
  51 # else
  52 static int o_directory_works;
  53
  54 static void
  55 tryopen_o_directory (void)
  56 {
  57   int serrno = errno;
  58   int x = open_not_cancel_2 ("/dev/null", O_RDONLY|O_NDELAY|O_DIRECTORY);
  59
  60   if (x >= 0)
  61     {
  62       close_not_cancel_no_status (x);
  63       o_directory_works = -1;
  64     }
  65   else if (errno != ENOTDIR)
  66     o_directory_works = -1;
  67   else
  68     o_directory_works = 1;
  69
  70   __set_errno (serrno);
  71 }
  72 # endif
  73 # define EXTRA_FLAGS O_DIRECTORY
  74 #else
  75 # define EXTRA_FLAGS 0
  76 #endif
  77
  78
  79 /* Open a directory stream on NAME.  */
  80 DIR *
  81 __opendir (const char *name)
  82 {
  83   struct stat64 statbuf;
  84   struct stat64 *statp = NULL;
  85
  86   if (__builtin_expect (name[0], '\1') == '\0')
  87     {
  88       /* POSIX.1-1990 says an empty name gets ENOENT;
  89          but `open' might like it fine.  */
  90       __set_errno (ENOENT);
  91       return NULL;
  92     }
  93
  94 #ifdef O_DIRECTORY
  95   /* Test whether O_DIRECTORY works.  */
  96   if (o_directory_works == 0)
  97     tryopen_o_directory ();
  98
  99   /* We can skip the expensive `stat' call if O_DIRECTORY works.  */
 100   if (o_directory_works < 0)
 101 #endif
 102     {
 103       /* We first have to check whether the name is for a directory.  We
 104          cannot do this after the open() call since the open/close operation
 105          performed on, say, a tape device might have undesirable effects.  */
 106       if (__builtin_expect (__xstat64 (_STAT_VER, name, &statbuf), 0) < 0)
 107         return NULL;
 108       if (__builtin_expect (! S_ISDIR (statbuf.st_mode), 0))
 109         {
 110           __set_errno (ENOTDIR);
 111           return NULL;
 112          }
 113     }
 114
 115   int flags = O_RDONLY|O_NDELAY|EXTRA_FLAGS|O_LARGEFILE;
 116 #ifdef O_CLOEXEC
 117   flags |= O_CLOEXEC;
 118 #endif
 119   int fd = open_not_cancel_2 (name, flags);
 120   if (__builtin_expect (fd, 0) < 0)
 121     return NULL;
 122
 123 #ifdef O_DIRECTORY
 124   if (o_directory_works <= 0)
 125 #endif
 126     {
 127       /* Now make sure this really is a directory and nothing changed since
 128          the `stat' call.  */
 129       if (__builtin_expect (__fxstat64 (_STAT_VER, fd, &statbuf), 0) < 0)
 130         goto lose;
 131       if (__builtin_expect (! S_ISDIR (statbuf.st_mode), 0))
 132         {
 133           __set_errno (ENOTDIR);
 134         lose:
 135           close_not_cancel_no_status (fd);
 136           return NULL;
 137         }
 138       statp = &statbuf;
 139     }
 140
 141   return __alloc_dir (fd, true, statp);
 142 }
 143 weak_alias (__opendir, opendir)
 144
 145
 146 #ifdef __ASSUME_O_CLOEXEC
 147 # define check_have_o_cloexec(fd) 1
 148 #else
 149 static int
 150 check_have_o_cloexec (int fd)
 151 {
 152   if (__have_o_cloexec == 0)
 153     __have_o_cloexec = (__fcntl (fd, F_GETFD, 0) & FD_CLOEXEC) == 0 ? -1 : 1;
 154   return __have_o_cloexec > 0;
 155 }
 156 #endif
 157
 158
 159 DIR *
 160 internal_function
 161 __alloc_dir (int fd, bool close_fd, const struct stat64 *statp)
 162 {
 163   /* We always have to set the close-on-exit flag if the user provided
 164      the file descriptor.  Otherwise only if we have no working
 165      O_CLOEXEC support.  */
 166 #ifdef O_CLOEXEC
 167   if (! close_fd || ! check_have_o_cloexec (fd))
 168 #endif
 169     {
 170       if (__builtin_expect (__fcntl (fd, F_SETFD, FD_CLOEXEC), 0) < 0)
 171         goto lose;
 172     }
 173
 174   const size_t default_allocation = (4 * BUFSIZ < sizeof (struct dirent64)
 175                                      ? sizeof (struct dirent64) : 4 * BUFSIZ);
 176   const size_t small_allocation = (BUFSIZ < sizeof (struct dirent64)
 177                                    ? sizeof (struct dirent64) : BUFSIZ);
 178   size_t allocation = default_allocation;
 179 #ifdef _STATBUF_ST_BLKSIZE
 180   if (statp != NULL && default_allocation < statp->st_blksize)
 181     allocation = statp->st_blksize;
 182 #endif
 183
 184   DIR *dirp = (DIR *) malloc (sizeof (DIR) + allocation);
 185   if (dirp == NULL)
 186     {
 187       allocation = small_allocation;
 188       dirp = (DIR *) malloc (sizeof (DIR) + allocation);
 189
 190       if (dirp == NULL)
 191       lose:
 192         {
 193           if (close_fd)
 194             {
 195               int save_errno = errno;
 196               close_not_cancel_no_status (fd);
 197               __set_errno (save_errno);
 198             }
 199           return NULL;
 200         }
 201     }
 202
 203   dirp->fd = fd;
 204 #ifndef NOT_IN_libc
 205   __libc_lock_init (dirp->lock);
 206 #endif
 207   dirp->allocation = allocation;
 208   dirp->size = 0;
 209   dirp->offset = 0;
 210   dirp->filepos = 0;
 211
 212   return dirp;
 213 }