sysdeps/unix/opendir.c

   1 /* Copyright (C) 1991-1996,98,2000-2003,2005 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 Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the 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    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, write to the Free
  16    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  17    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 #include <string.h>
  30
  31 #include <dirstream.h>
  32 #include <not-cancel.h>
  33
  34
  35 /* opendir() must not accidentally open something other than a directory.
  36    Some OS's have kernel support for that, some don't.  In the worst
  37    case we have to stat() before the open() AND fstat() after.
  38
  39    We have to test at runtime for kernel support since libc may have
  40    been compiled with different headers to the kernel it's running on.
  41    This test can't be done reliably in the general case.  We'll use
  42    /dev/null, which if it's not a device lots of stuff will break, as
  43    a guinea pig.  It may be missing in chroot environments, so we
  44    make sure to fail safe. */
  45 #ifdef O_DIRECTORY
  46 # ifdef O_DIRECTORY_WORKS
  47 #  define o_directory_works 1
  48 #  define tryopen_o_directory() while (1) /* This must not be called.  */
  49 # else
  50 static int o_directory_works;
  51
  52 static void
  53 tryopen_o_directory (void)
  54 {
  55   int serrno = errno;
  56   int x = open_not_cancel_2 ("/dev/null", O_RDONLY|O_NDELAY|O_DIRECTORY);
  57
  58   if (x >= 0)
  59     {
  60       close_not_cancel_no_status (x);
  61       o_directory_works = -1;
  62     }
  63   else if (errno != ENOTDIR)
  64     o_directory_works = -1;
  65   else
  66     o_directory_works = 1;
  67
  68   __set_errno (serrno);
  69 }
  70 # endif
  71 # define EXTRA_FLAGS O_DIRECTORY
  72 #else
  73 # define EXTRA_FLAGS 0
  74 #endif
  75
  76
  77 /* Open a directory stream on NAME.  */
  78 DIR *
  79 __opendir (const char *name)
  80 {
  81   struct stat64 statbuf;
  82
  83   if (__builtin_expect (name[0], '\1') == '\0')
  84     {
  85       /* POSIX.1-1990 says an empty name gets ENOENT;
  86          but `open' might like it fine.  */
  87       __set_errno (ENOENT);
  88       return NULL;
  89     }
  90
  91 #ifdef O_DIRECTORY
  92   /* Test whether O_DIRECTORY works.  */
  93   if (o_directory_works == 0)
  94     tryopen_o_directory ();
  95
  96   /* We can skip the expensive `stat' call if O_DIRECTORY works.  */
  97   if (o_directory_works < 0)
  98 #endif
  99     {
 100       /* We first have to check whether the name is for a directory.  We
 101          cannot do this after the open() call since the open/close operation
 102          performed on, say, a tape device might have undesirable effects.  */
 103       if (__builtin_expect (__xstat64 (_STAT_VER, name, &statbuf), 0) < 0)
 104         return NULL;
 105       if (__builtin_expect (! S_ISDIR (statbuf.st_mode), 0))
 106         {
 107           __set_errno (ENOTDIR);
 108           return NULL;
 109          }
 110     }
 111
 112   int fd = open_not_cancel_2 (name, O_RDONLY|O_NDELAY|EXTRA_FLAGS|O_LARGEFILE);
 113   if (__builtin_expect (fd, 0) < 0)
 114     return NULL;
 115
 116   /* Now make sure this really is a directory and nothing changed since
 117      the `stat' call.  We do not have to perform the test for the
 118      descriptor being associated with a directory if we know the
 119      O_DIRECTORY flag is honored by the kernel.  */
 120   if (__builtin_expect (__fxstat64 (_STAT_VER, fd, &statbuf), 0) < 0)
 121     goto lose;
 122 #ifdef O_DIRECTORY
 123   if (o_directory_works <= 0)
 124 #endif
 125     {
 126       if (__builtin_expect (! S_ISDIR (statbuf.st_mode), 0))
 127         {
 128           __set_errno (ENOTDIR);
 129         lose:
 130           close_not_cancel_no_status (fd);
 131           return NULL;
 132         }
 133     }
 134
 135   return __alloc_dir (fd, true, &statbuf);
 136 }
 137 weak_alias (__opendir, opendir)
 138
 139
 140 DIR *
 141 internal_function
 142 __alloc_dir (int fd, bool close_fd, const struct stat64 *statp)
 143 {
 144   if (__builtin_expect (__fcntl (fd, F_SETFD, FD_CLOEXEC), 0) < 0)
 145     goto lose;
 146
 147   size_t allocation;
 148 #ifdef _STATBUF_ST_BLKSIZE
 149   if (__builtin_expect ((size_t) statp->st_blksize >= sizeof (struct dirent64),
 150                         1))
 151     allocation = statp->st_blksize;
 152   else
 153 #endif
 154     allocation = (BUFSIZ < sizeof (struct dirent64)
 155                   ? sizeof (struct dirent64) : BUFSIZ);
 156
 157   const int pad = -sizeof (DIR) % __alignof__ (struct dirent64);
 158
 159   DIR *dirp = (DIR *) malloc (sizeof (DIR) + allocation + pad);
 160   if (dirp == NULL)
 161   lose:
 162     {
 163       if (close_fd)
 164         {
 165           int save_errno = errno;
 166           close_not_cancel_no_status (fd);
 167           __set_errno (save_errno);
 168         }
 169       return NULL;
 170     }
 171   memset (dirp, '\0', sizeof (DIR));
 172   dirp->data = (char *) (dirp + 1) + pad;
 173   dirp->allocation = allocation;
 174   dirp->fd = fd;
 175
 176   __libc_lock_init (dirp->lock);
 177
 178   return dirp;
 179 }