1/* Header for directory for shm/sem files.
2 Copyright (C) 2014-2021 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
9
10 The GNU C Library 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 GNU
13 Lesser General Public License for more details.
14
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see
17 <https://www.gnu.org/licenses/>. */
18
19#ifndef _SHM_DIRECTORY_H
20
21#include <errno.h>
22#include <limits.h>
23#include <stdbool.h>
24#include <stdlib.h>
25#include <string.h>
26
27extern const char *__shm_directory (size_t *len);
28
29/* This defines local variables SHM_DIR and SHM_DIRLEN, giving the
30 directory prefix (with trailing slash) and length (not including '\0'
31 terminator) of the directory used for shm files. If that cannot be
32 determined, it sets errno to ENOSYS and returns RETVAL_FOR_INVALID.
33
34 This uses the local variable NAME as an lvalue, and increments it past
35 any leading slashes. It then defines the local variable NAMELEN, giving
36 strlen (NAME) + 1. If NAME is invalid, it sets errno to
37 ERRNO_FOR_INVALID and returns RETVAL_FOR_INVALID. Finally, it defines
38 the local variable SHM_NAME, giving the absolute file name of the shm
39 file corresponding to NAME. PREFIX is a string constant used as a
40 prefix on NAME. */
41
42#define SHM_GET_NAME(errno_for_invalid, retval_for_invalid, prefix) \
43 size_t shm_dirlen; \
44 const char *shm_dir = __shm_directory (&shm_dirlen); \
45 /* If we don't know what directory to use, there is nothing we can do. */ \
46 if (__glibc_unlikely (shm_dir == NULL)) \
47 { \
48 __set_errno (ENOSYS); \
49 return retval_for_invalid; \
50 } \
51 /* Construct the filename. */ \
52 while (name[0] == '/') \
53 ++name; \
54 size_t namelen = strlen (name) + 1; \
55 /* Validate the filename. */ \
56 if (namelen == 1 || namelen >= NAME_MAX || strchr (name, '/') != NULL) \
57 { \
58 __set_errno (errno_for_invalid); \
59 return retval_for_invalid; \
60 } \
61 char *shm_name = __alloca (shm_dirlen + sizeof prefix - 1 + namelen); \
62 __mempcpy (__mempcpy (__mempcpy (shm_name, shm_dir, shm_dirlen), \
63 prefix, sizeof prefix - 1), \
64 name, namelen)
65
66#endif /* shm-directory.h */
67