lib/openat-priv.h

   1 /* Internals for openat-like functions.
   2
   3    Copyright (C) 2005-2006, 2009-2025 Free Software Foundation, Inc.
   4
   5    This program is free software: you can redistribute it and/or modify
   6    it under the terms of the GNU General Public License as published by
   7    the Free Software Foundation, either version 3 of the License, or
   8    (at your option) any later version.
   9
  10    This program 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
  13    GNU General Public License for more details.
  14
  15    You should have received a copy of the GNU General Public License
  16    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  17
  18 /* written by Jim Meyering */
  19
  20 #ifndef _GL_HEADER_OPENAT_PRIV
  21 #define _GL_HEADER_OPENAT_PRIV
  22
  23 #include <errno.h>
  24 #include <limits.h>
  25 #include <stdlib.h>
  26
  27 #ifdef __cplusplus
  28 extern "C" {
  29 #endif
  30
  31
  32 /* Maximum number of bytes that it is safe to allocate as a single
  33    array on the stack, and that is known as a compile-time constant.
  34    The assumption is that we'll touch the array very quickly, or a
  35    temporary very near the array, provoking an out-of-memory trap.  On
  36    some operating systems, there is only one guard page for the stack,
  37    and a page size can be as small as 4096 bytes.  Subtract 64 in the
  38    hope that this will let the compiler touch a nearby temporary and
  39    provoke a trap.  */
  40 #define SAFER_ALLOCA_MAX (4096 - 64)
  41
  42 #define SAFER_ALLOCA(m) ((m) < SAFER_ALLOCA_MAX ? (m) : SAFER_ALLOCA_MAX)
  43
  44 #if defined PATH_MAX
  45 # define OPENAT_BUFFER_SIZE SAFER_ALLOCA (PATH_MAX)
  46 #elif defined _XOPEN_PATH_MAX
  47 # define OPENAT_BUFFER_SIZE SAFER_ALLOCA (_XOPEN_PATH_MAX)
  48 #else
  49 # define OPENAT_BUFFER_SIZE SAFER_ALLOCA (1024)
  50 #endif
  51
  52 char *openat_proc_name (char buf[OPENAT_BUFFER_SIZE], int fd, char const *file);
  53
  54 /* Trying to access a BUILD_PROC_NAME file will fail on systems without
  55    /proc support, and even on systems *with* ProcFS support.  Return
  56    nonzero if the failure may be legitimate, e.g., because /proc is not
  57    readable, or the particular .../fd/N directory is not present.  */
  58 #define EXPECTED_ERRNO(Errno)                   \
  59   ((Errno) == ENOTDIR || (Errno) == ENOENT      \
  60    || (Errno) == EPERM || (Errno) == EACCES     \
  61    || (Errno) == ENOSYS /* Solaris 8 */         \
  62    || (Errno) == EOPNOTSUPP /* FreeBSD */)
  63
  64 /* Wrapper function shared among linkat and renameat.  */
  65 int at_func2 (int fd1, char const *file1,
  66               int fd2, char const *file2,
  67               int (*func) (char const *file1, char const *file2));
  68
  69
  70 #ifdef __cplusplus
  71 }
  72 #endif
  73
  74 #endif /* _GL_HEADER_OPENAT_PRIV */