sysdeps/unix/opendir.c

   1 /* Copyright (C) 1991-1996,98,2000-2003,2005,2007
   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
  35
  36 /* opendir() must not accidentally open something other than a directory.
  37    Some OS's have kernel support for that, some don't.  In the worst
  38    case we have to stat() before the open() AND fstat() after.
  39
  40    We have to test at runtime for kernel support since libc may have
  41    been compiled with different headers to the kernel it's running on.
  42    This test can't be done reliably in the general case.  We'll use
  43    /dev/null, which if it's not a device lots of stuff will break, as
  44    a guinea pig.  It may be missing in chroot environments, so we
  45    make sure to fail safe. */
  46 #ifdef O_DIRECTORY
  47 # ifdef O_DIRECTORY_WORKS
  48 #  define o_directory_works 1
  49 #  define tryopen_o_directory() while (1) /* This must not be called.  */
  50 # else
  51 static int o_directory_works;
  52
  53 static void
  54 tryopen_o_directory (void)
  55 {
  56   int serrno = errno;
  57   int x = open_not_cancel_2 ("/dev/null", O_RDONLY|O_NDELAY|O_DIRECTORY);
  58
  59   if (x >= 0)
  60     {
  61       close_not_cancel_no_status (x);
  62       o_directory_works = -1;
  63     }
  64   else if (errno != ENOTDIR)
  65     o_directory_works = -1;
  66   else
  67     o_directory_works = 1;
  68
  69   __set_errno (serrno);
  70 }
  71 # endif
  72 # define EXTRA_FLAGS O_DIRECTORY
  73 #else
  74 # define EXTRA_FLAGS 0
  75 #endif
  76
  77
  78 /* Open a directory stream on NAME.  */
  79 DIR *
  80 __opendir (const char *name)
  81 {
  82   struct stat64 statbuf;
  83
  84   if (__builtin_expect (name[0], '\1') == '\0')
  85     {
  86       /* POSIX.1-1990 says an empty name gets ENOENT;
  87          but `open' might like it fine.  */
  88       __set_errno (ENOENT);
  89       return NULL;
  90     }
  91
  92 #ifdef O_DIRECTORY
  93   /* Test whether O_DIRECTORY works.  */
  94   if (o_directory_works == 0)
  95     tryopen_o_directory ();
  96
  97   /* We can skip the expensive `stat' call if O_DIRECTORY works.  */
  98   if (o_directory_works < 0)
  99 #endif
 100     {
 101       /* We first have to check whether the name is for a directory.  We
 102          cannot do this after the open() call since the open/close operation
 103          performed on, say, a tape device might have undesirable effects.  */
 104       if (__builtin_expect (__xstat64 (_STAT_VER, name, &statbuf), 0) < 0)
 105         return NULL;
 106       if (__builtin_expect (! S_ISDIR (statbuf.st_mode), 0))
 107         {
 108           __set_errno (ENOTDIR);
 109           return NULL;
 110          }
 111     }
 112
 113   int fd = open_not_cancel_2 (name, O_RDONLY|O_NDELAY|EXTRA_FLAGS|O_LARGEFILE);
 114   if (__builtin_expect (fd, 0) < 0)
 115     return NULL;
 116
 117   /* Now make sure this really is a directory and nothing changed since
 118      the `stat' call.  We do not have to perform the test for the
 119      descriptor being associated with a directory if we know the
 120      O_DIRECTORY flag is honored by the kernel.  */
 121   if (__builtin_expect (__fxstat64 (_STAT_VER, fd, &statbuf), 0) < 0)
 122     goto lose;
 123 #ifdef O_DIRECTORY
 124   if (o_directory_works <= 0)
 125 #endif
 126     {
 127       if (__builtin_expect (! S_ISDIR (statbuf.st_mode), 0))
 128         {
 129           __set_errno (ENOTDIR);
 130         lose:
 131           close_not_cancel_no_status (fd);
 132           return NULL;
 133         }
 134     }
 135
 136   return __alloc_dir (fd, true, &statbuf);
 137 }
 138 weak_alias (__opendir, opendir)
 139
 140
 141 DIR *
 142 internal_function
 143 __alloc_dir (int fd, bool close_fd, const struct stat64 *statp)
 144 {
 145   if (__builtin_expect (__fcntl (fd, F_SETFD, FD_CLOEXEC), 0) < 0)
 146     goto lose;
 147
 148   size_t allocation;
 149 #ifdef _STATBUF_ST_BLKSIZE
 150   if (__builtin_expect ((size_t) statp->st_blksize >= sizeof (struct dirent64),
 151                         1))
 152     allocation = statp->st_blksize;
 153   else
 154 #endif
 155     allocation = (BUFSIZ < sizeof (struct dirent64)
 156                   ? sizeof (struct dirent64) : BUFSIZ);
 157
 158   const int pad = -sizeof (DIR) % __alignof__ (struct dirent64);
 159
 160   DIR *dirp = (DIR *) malloc (sizeof (DIR) + allocation + pad);
 161   if (dirp == NULL)
 162   lose:
 163     {
 164       if (close_fd)
 165         {
 166           int save_errno = errno;
 167           close_not_cancel_no_status (fd);
 168           __set_errno (save_errno);
 169         }
 170       return NULL;
 171     }
 172   memset (dirp, '\0', sizeof (DIR));
 173   dirp->data = (char *) (dirp + 1) + pad;
 174   dirp->allocation = allocation;
 175   dirp->fd = fd;
 176
 177 #ifndef NOT_IN_libc
 178   __libc_lock_init (dirp->lock);
 179 #endif
 180
 181   return dirp;
 182 }