libstdc++-v3/src/filesystem/dir-common.h

   1 // Filesystem directory iterator utilities -*- C++ -*-
   2
   3 // Copyright (C) 2014-2022 Free Software Foundation, Inc.
   4 //
   5 // This file is part of the GNU ISO C++ Library.  This library is free
   6 // software; you can redistribute it and/or modify it under the
   7 // terms of the GNU General Public License as published by the
   8 // Free Software Foundation; either version 3, or (at your option)
   9 // any later version.
  10
  11 // This library is distributed in the hope that it will be useful,
  12 // but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 // GNU General Public License for more details.
  15
  16 // Under Section 7 of GPL version 3, you are granted additional
  17 // permissions described in the GCC Runtime Library Exception, version
  18 // 3.1, as published by the Free Software Foundation.
  19
  20 // You should have received a copy of the GNU General Public License and
  21 // a copy of the GCC Runtime Library Exception along with this program;
  22 // see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
  23 // <http://www.gnu.org/licenses/>.
  24
  25 #ifndef _GLIBCXX_DIR_COMMON_H
  26 #define _GLIBCXX_DIR_COMMON_H 1
  27
  28 #include <stdint.h>  // uint32_t
  29 #include <string.h>  // strcmp
  30 #include <errno.h>
  31 #if _GLIBCXX_FILESYSTEM_IS_WINDOWS
  32 #include <wchar.h>  // wcscmp
  33 #endif
  34 #ifdef _GLIBCXX_HAVE_DIRENT_H
  35 # ifdef _GLIBCXX_HAVE_SYS_TYPES_H
  36 #  include <sys/types.h>
  37 # endif
  38 # include <dirent.h> // opendir, readdir, fdopendir, dirfd
  39 # ifdef _GLIBCXX_HAVE_FCNTL_H
  40 #  include <fcntl.h>  // open, openat, fcntl, AT_FDCWD, O_NOFOLLOW etc.
  41 #  include <unistd.h> // close, unlinkat
  42 # endif
  43 #endif
  44
  45 namespace std _GLIBCXX_VISIBILITY(default)
  46 {
  47 _GLIBCXX_BEGIN_NAMESPACE_VERSION
  48 namespace filesystem
  49 {
  50 namespace __gnu_posix
  51 {
  52 #if _GLIBCXX_FILESYSTEM_IS_WINDOWS
  53 // Adapt the Windows _wxxx functions to look like POSIX xxx, but for wchar_t*.
  54 using char_type = wchar_t;
  55 using DIR = ::_WDIR;
  56 using dirent = _wdirent;
  57 inline DIR* opendir(const wchar_t* path) { return ::_wopendir(path); }
  58 inline dirent* readdir(DIR* dir) { return ::_wreaddir(dir); }
  59 inline int closedir(DIR* dir) { return ::_wclosedir(dir); }
  60 #elif defined _GLIBCXX_HAVE_DIRENT_H
  61 using char_type = char;
  62 using DIR = ::DIR;
  63 typedef struct ::dirent dirent;
  64 using ::opendir;
  65 using ::readdir;
  66 using ::closedir;
  67 #else
  68 using char_type = char;
  69 struct dirent { const char* d_name; };
  70 struct DIR { };
  71 inline DIR* opendir(const char*) { return nullptr; }
  72 inline dirent* readdir(DIR*) { return nullptr; }
  73 inline int closedir(DIR*) { return -1; }
  74 #undef _GLIBCXX_HAVE_DIRFD
  75 #undef _GLIBCXX_HAVE_UNLINKAT
  76 #endif
  77 } // namespace __gnu_posix
  78
  79 namespace posix = __gnu_posix;
  80
  81 inline bool
  82 is_permission_denied_error(int e)
  83 {
  84   if (e == EACCES)
  85     return true;
  86 #ifdef __APPLE__
  87   if (e == EPERM) // See PR 99533
  88     return true;
  89 #endif
  90   return false;
  91 }
  92
  93 struct _Dir_base
  94 {
  95   // As well as the full pathname (including the directory iterator's path)
  96   // this type contains a file descriptor for a directory and a second pathname
  97   // relative to that directory. The file descriptor and relative pathname
  98   // can be used with POSIX openat and unlinkat.
  99   struct _At_path
 100   {
 101     // No file descriptor given, so interpret the pathname relative to the CWD.
 102     _At_path(const posix::char_type* p) noexcept
 103     : pathname(p), dir_fd(fdcwd()), offset(0)
 104     { }
 105
 106     _At_path(int fd, const posix::char_type* p, size_t offset) noexcept
 107     : pathname(p), dir_fd(fd), offset(offset)
 108     { }
 109
 110     const posix::char_type*
 111     path() const noexcept { return pathname; }
 112
 113     int
 114     dir() const noexcept { return dir_fd; }
 115
 116     const posix::char_type*
 117     path_at_dir() const noexcept { return pathname + offset; }
 118
 119   private:
 120     const posix::char_type* pathname; // Full path relative to CWD.
 121     int dir_fd; // A directory descriptor (either the parent dir, or AT_FDCWD).
 122     uint32_t offset; // Offset into pathname for the part relative to dir_fd.
 123
 124     // Special value representing the current working directory.
 125     // Not a valid file descriptor for an open directory stream.
 126     static constexpr int
 127     fdcwd() noexcept
 128     {
 129 #ifdef AT_FDCWD
 130       return AT_FDCWD;
 131 #else
 132       return -1; // Use invalid fd if AT_FDCWD isn't supported.
 133 #endif
 134     }
 135   };
 136
 137   // If no error occurs then dirp is non-null,
 138   // otherwise null (even if a permission denied error is ignored).
 139   _Dir_base(const _At_path& atp,
 140             bool skip_permission_denied, bool nofollow,
 141             error_code& ec) noexcept
 142   : dirp(_Dir_base::openat(atp, nofollow))
 143   {
 144     if (dirp)
 145       ec.clear();
 146     else if (is_permission_denied_error(errno) && skip_permission_denied)
 147       ec.clear();
 148     else
 149       ec.assign(errno, std::generic_category());
 150   }
 151
 152   _Dir_base(_Dir_base&& d) : dirp(std::exchange(d.dirp, nullptr)) { }
 153
 154   _Dir_base& operator=(_Dir_base&&) = delete;
 155
 156   ~_Dir_base() { if (dirp) posix::closedir(dirp); }
 157
 158   const posix::dirent*
 159   advance(bool skip_permission_denied, error_code& ec) noexcept
 160   {
 161     ec.clear();
 162
 163     int err = std::exchange(errno, 0);
 164     const posix::dirent* entp = posix::readdir(dirp);
 165     // std::swap cannot be used with Bionic's errno
 166     err = std::exchange(errno, err);
 167
 168     if (entp)
 169       {
 170         // skip past dot and dot-dot
 171         if (is_dot_or_dotdot(entp->d_name))
 172           return advance(skip_permission_denied, ec);
 173         return entp;
 174       }
 175     else if (err)
 176       {
 177         if (err == EACCES && skip_permission_denied)
 178           return nullptr;
 179         ec.assign(err, std::generic_category());
 180         return nullptr;
 181       }
 182     else
 183       {
 184         // reached the end
 185         return nullptr;
 186       }
 187   }
 188
 189   static bool is_dot_or_dotdot(const char* s) noexcept
 190   { return !strcmp(s, ".") || !strcmp(s, ".."); }
 191
 192 #if _GLIBCXX_FILESYSTEM_IS_WINDOWS
 193   static bool is_dot_or_dotdot(const wchar_t* s) noexcept
 194   { return !wcscmp(s, L".") || !wcscmp(s, L".."); }
 195 #endif
 196
 197   // Set the close-on-exec flag if not already done via O_CLOEXEC.
 198   static bool
 199   set_close_on_exec([[maybe_unused]] int fd)
 200   {
 201 #if ! defined O_CLOEXEC && defined FD_CLOEXEC
 202     int flags = ::fcntl(fd, F_GETFD);
 203     if (flags == -1 || ::fcntl(fd, F_SETFD, flags | FD_CLOEXEC) == -1)
 204       return false;
 205 #endif
 206     return true;
 207   }
 208
 209   static posix::DIR*
 210   openat(const _At_path& atp, bool nofollow)
 211   {
 212 #if _GLIBCXX_HAVE_FDOPENDIR && defined O_RDONLY && defined O_DIRECTORY \
 213     && ! _GLIBCXX_FILESYSTEM_IS_WINDOWS
 214
 215     // Any file descriptor we open here should be closed on exec.
 216 #ifdef O_CLOEXEC
 217     constexpr int close_on_exec = O_CLOEXEC;
 218 #else
 219     constexpr int close_on_exec = 0;
 220 #endif
 221
 222     int flags = O_RDONLY | O_DIRECTORY | close_on_exec;
 223
 224     // Directory iterators are vulnerable to race conditions unless O_NOFOLLOW
 225     // is supported, because a directory could be replaced with a symlink after
 226     // checking is_directory(symlink_status(f)). O_NOFOLLOW avoids the race.
 227 #ifdef O_NOFOLLOW
 228     if (nofollow)
 229       flags |= O_NOFOLLOW;
 230 #else
 231     nofollow = false;
 232 #endif
 233
 234     int fd;
 235
 236 #if _GLIBCXX_HAVE_OPENAT
 237     fd = ::openat(atp.dir(), atp.path_at_dir(), flags);
 238 #else
 239     // If we cannot use openat, there's no benefit to using posix::open unless
 240     // we will use O_NOFOLLOW, so just use the simpler posix::opendir.
 241     if (!nofollow)
 242       return posix::opendir(atp.path());
 243
 244     fd = ::open(atp.path(), flags);
 245 #endif
 246
 247     if (fd == -1)
 248       return nullptr;
 249     if (set_close_on_exec(fd))
 250       if (::DIR* dirp = ::fdopendir(fd))
 251         return dirp;
 252     int err = errno;
 253     ::close(fd);
 254     errno = err;
 255     return nullptr;
 256 #else
 257     return posix::opendir(atp.path());
 258 #endif
 259   }
 260
 261   posix::DIR*   dirp;
 262 };
 263
 264 } // namespace filesystem
 265
 266 // BEGIN/END macros must be defined before including this file.
 267 _GLIBCXX_BEGIN_NAMESPACE_FILESYSTEM
 268
 269 inline file_type
 270 get_file_type(const std::filesystem::__gnu_posix::dirent& d [[gnu::unused]])
 271 {
 272 #ifdef _GLIBCXX_HAVE_STRUCT_DIRENT_D_TYPE
 273   switch (d.d_type)
 274   {
 275   case DT_BLK:
 276     return file_type::block;
 277   case DT_CHR:
 278     return file_type::character;
 279   case DT_DIR:
 280     return file_type::directory;
 281   case DT_FIFO:
 282     return file_type::fifo;
 283   case DT_LNK:
 284     return file_type::symlink;
 285   case DT_REG:
 286     return file_type::regular;
 287   case DT_SOCK:
 288     return file_type::socket;
 289   case DT_UNKNOWN:
 290     return file_type::unknown;
 291   default:
 292     return file_type::none;
 293   }
 294 #else
 295   return file_type::none;
 296 #endif
 297 }
 298
 299 _GLIBCXX_END_NAMESPACE_FILESYSTEM
 300
 301 _GLIBCXX_END_NAMESPACE_VERSION
 302 } // namespace std
 303
 304 #endif // _GLIBCXX_DIR_COMMON_H