1  /* Internals for openat-like functions.
       2  
       3     Copyright (C) 2005-2006, 2009-2023 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  /* Maximum number of bytes that it is safe to allocate as a single
      28     array on the stack, and that is known as a compile-time constant.
      29     The assumption is that we'll touch the array very quickly, or a
      30     temporary very near the array, provoking an out-of-memory trap.  On
      31     some operating systems, there is only one guard page for the stack,
      32     and a page size can be as small as 4096 bytes.  Subtract 64 in the
      33     hope that this will let the compiler touch a nearby temporary and
      34     provoke a trap.  */
      35  #define SAFER_ALLOCA_MAX (4096 - 64)
      36  
      37  #define SAFER_ALLOCA(m) ((m) < SAFER_ALLOCA_MAX ? (m) : SAFER_ALLOCA_MAX)
      38  
      39  #if defined PATH_MAX
      40  # define OPENAT_BUFFER_SIZE SAFER_ALLOCA (PATH_MAX)
      41  #elif defined _XOPEN_PATH_MAX
      42  # define OPENAT_BUFFER_SIZE SAFER_ALLOCA (_XOPEN_PATH_MAX)
      43  #else
      44  # define OPENAT_BUFFER_SIZE SAFER_ALLOCA (1024)
      45  #endif
      46  
      47  char *openat_proc_name (char buf[OPENAT_BUFFER_SIZE], int fd, char const *file);
      48  
      49  /* Trying to access a BUILD_PROC_NAME file will fail on systems without
      50     /proc support, and even on systems *with* ProcFS support.  Return
      51     nonzero if the failure may be legitimate, e.g., because /proc is not
      52     readable, or the particular .../fd/N directory is not present.  */
      53  #define EXPECTED_ERRNO(Errno)                   \
      54    ((Errno) == ENOTDIR || (Errno) == ENOENT      \
      55     || (Errno) == EPERM || (Errno) == EACCES     \
      56     || (Errno) == ENOSYS /* Solaris 8 */         \
      57     || (Errno) == EOPNOTSUPP /* FreeBSD */)
      58  
      59  /* Wrapper function shared among linkat and renameat.  */
      60  int at_func2 (int fd1, char const *file1,
      61                int fd2, char const *file2,
      62                int (*func) (char const *file1, char const *file2));
      63  
      64  #endif /* _GL_HEADER_OPENAT_PRIV */