lib/careadlinkat.h

   1 /* Read symbolic links into a buffer without size limitation, relative to fd.
   2
   3    Copyright (C) 2011-2024 Free Software Foundation, Inc.
   4
   5    This file is free software: you can redistribute it and/or modify
   6    it under the terms of the GNU Lesser General Public License as
   7    published by the Free Software Foundation; either version 2.1 of the
   8    License, or (at your option) any later version.
   9
  10    This file 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 Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public License
  16    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  17
  18 /* Written by Paul Eggert, Bruno Haible, and Jim Meyering.  */
  19
  20 #ifndef _GL_CAREADLINKAT_H
  21 #define _GL_CAREADLINKAT_H
  22
  23 /* This file uses HAVE_READLINKAT.  */
  24 #if !_GL_CONFIG_H_INCLUDED
  25  #error "Please include config.h first."
  26 #endif
  27
  28 #include <fcntl.h>
  29 #include <unistd.h>
  30
  31 struct allocator;
  32
  33 /* Assuming the current directory is FD, get the symbolic link value
  34    of FILENAME as a null-terminated string and put it into a buffer.
  35    If FD is AT_FDCWD, FILENAME is interpreted relative to the current
  36    working directory, as in openat.
  37
  38    If the link is small enough to fit into BUFFER put it there.
  39    BUFFER's size is BUFFER_SIZE, and BUFFER can be null
  40    if BUFFER_SIZE is zero.
  41
  42    If the link is not small, put it into a dynamically allocated
  43    buffer managed by ALLOC.  It is the caller's responsibility to free
  44    the returned value if it is nonnull and is not BUFFER.
  45
  46    The PREADLINKAT function specifies how to read links.  It operates
  47    like POSIX readlinkat()
  48    <https://pubs.opengroup.org/onlinepubs/9699919799/functions/readlink.html>
  49    but can assume that its first argument is the same as FD.
  50
  51    If successful, return the buffer address; otherwise return NULL and
  52    set errno.  */
  53
  54 char *careadlinkat (int fd, char const *filename,
  55                     char *restrict buffer, size_t buffer_size,
  56                     struct allocator const *alloc,
  57                     ssize_t (*preadlinkat) (int, char const *,
  58                                             char *, size_t));
  59
  60 /* Suitable value for careadlinkat's FD argument.  */
  61 #if HAVE_READLINKAT
  62 /* AT_FDCWD is declared in <fcntl.h>.  */
  63 #else
  64 /* Define AT_FDCWD independently, so that the careadlinkat module does
  65    not depend on the fcntl-h module.  We might as well use the same value
  66    as fcntl-h.  */
  67 # ifndef AT_FDCWD
  68 #  define AT_FDCWD (-3041965)
  69 # endif
  70 #endif
  71
  72 #endif /* _GL_CAREADLINKAT_H */