sysdeps/unix/opendir.c

   1 /* Copyright (C) 1991-1996,98,2000,2001 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 # ifdef O_DIRECTORY_WORKS
  44 #  define o_directory_works 1
  45 #  define tryopen_o_directory() while (1) /* This must not be called.  */
  46 # else
  47 static int o_directory_works;
  48
  49 static void
  50 tryopen_o_directory (void)
  51 {
  52   int serrno = errno;
  53   int x = __open ("/dev/null", O_RDONLY|O_NDELAY|O_DIRECTORY);
  54
  55   if (x >= 0)
  56     {
  57       __close (x);
  58       o_directory_works = -1;
  59     }
  60   else if (errno != ENOTDIR)
  61     o_directory_works = -1;
  62   else
  63     o_directory_works = 1;
  64
  65   __set_errno (serrno);
  66 }
  67 # endif
  68 # define EXTRA_FLAGS O_DIRECTORY
  69 #else
  70 # define EXTRA_FLAGS 0
  71 #endif
  72
  73
  74 /* Open a directory stream on NAME.  */
  75 DIR *
  76 __opendir (const char *name)
  77 {
  78   DIR *dirp;
  79   struct stat64 statbuf;
  80   int fd;
  81   size_t allocation;
  82   int save_errno;
  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   fd = __open64 (name, O_RDONLY|O_NDELAY|EXTRA_FLAGS);
 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           save_errno = ENOTDIR;
 130           goto lose;
 131         }
 132     }
 133
 134   if (__builtin_expect (__fcntl (fd, F_SETFD, FD_CLOEXEC), 0) < 0)
 135     goto lose;
 136
 137 #ifdef _STATBUF_ST_BLKSIZE
 138   if (__builtin_expect ((size_t) statbuf.st_blksize < sizeof (struct dirent),
 139                         0))
 140     allocation = sizeof (struct dirent);
 141   else
 142     allocation = statbuf.st_blksize;
 143 #else
 144   allocation = (BUFSIZ < sizeof (struct dirent)
 145                 ? sizeof (struct dirent) : BUFSIZ);
 146 #endif
 147
 148   dirp = (DIR *) calloc (1, sizeof (DIR) + allocation); /* Zero-fill.  */
 149   if (dirp == NULL)
 150   lose:
 151     {
 152       save_errno = errno;
 153       (void) __close (fd);
 154       __set_errno (save_errno);
 155       return NULL;
 156     }
 157   dirp->data = (char *) (dirp + 1);
 158   dirp->allocation = allocation;
 159   dirp->fd = fd;
 160
 161   __libc_lock_init (dirp->lock);
 162
 163   return dirp;
 164 }
 165 weak_alias (__opendir, opendir)