1  /* Read symbolic links into a buffer without size limitation, relative to fd.
       2  
       3     Copyright (C) 2011-2023 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 */