careadlinkat.h 2.49 KB
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/* Read symbolic links into a buffer without size limitation, relative to fd.

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   Copyright (C) 2011-2020 Free Software Foundation, Inc.
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   This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
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   along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
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/* Written by Paul Eggert, Bruno Haible, and Jim Meyering.  */

#ifndef _GL_CAREADLINKAT_H
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#define _GL_CAREADLINKAT_H
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#include <fcntl.h>
#include <unistd.h>

struct allocator;

/* Assuming the current directory is FD, get the symbolic link value
   of FILENAME as a null-terminated string and put it into a buffer.
   If FD is AT_FDCWD, FILENAME is interpreted relative to the current
   working directory, as in openat.

   If the link is small enough to fit into BUFFER put it there.
   BUFFER's size is BUFFER_SIZE, and BUFFER can be null
   if BUFFER_SIZE is zero.

   If the link is not small, put it into a dynamically allocated
   buffer managed by ALLOC.  It is the caller's responsibility to free
   the returned value if it is nonnull and is not BUFFER.

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   The PREADLINKAT function specifies how to read links.  It operates
   like POSIX readlinkat()
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   <https://pubs.opengroup.org/onlinepubs/9699919799/functions/readlink.html>
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   but can assume that its first argument is the same as FD.
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   If successful, return the buffer address; otherwise return NULL and
   set errno.  */

char *careadlinkat (int fd, char const *filename,
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                    char *restrict buffer, size_t buffer_size,
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                    struct allocator const *alloc,
                    ssize_t (*preadlinkat) (int, char const *,
                                            char *, size_t));

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/* Suitable value for careadlinkat's FD argument.  */
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#if HAVE_READLINKAT
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/* AT_FDCWD is declared in <fcntl.h>.  */
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#else
/* Define AT_FDCWD independently, so that the careadlinkat module does
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   not depend on the fcntl-h module.  We might as well use the same value
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   as fcntl-h.  */
# ifndef AT_FDCWD
#  define AT_FDCWD (-3041965)
# endif
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#endif
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#endif /* _GL_CAREADLINKAT_H */