1// Copyright (C) 2015 Konstantin Ritt <ritt.ks@gmail.com>
2// Copyright (C) 2016 The Qt Company Ltd.
3// Copyright (C) 2015 Klarälvdalens Datakonsult AB, a KDAB Group company, info@kdab.com, author Tobias Koenig <tobias.koenig@kdab.com>
4// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
5
6#include "qsharedmemory.h"
7#include "qsharedmemory_p.h"
8#include "qtipccommon_p.h"
9#include <qfile.h>
10
11#include <errno.h>
12
13#if QT_CONFIG(sharedmemory)
14#if QT_CONFIG(posix_shm)
15#include <sys/types.h>
16#include <sys/mman.h>
17#include <sys/stat.h>
18#include <fcntl.h>
19#include <unistd.h>
20
21#include "private/qcore_unix_p.h"
22
23#ifndef O_CLOEXEC
24# define O_CLOEXEC 0
25#endif
26
27QT_BEGIN_NAMESPACE
28
29using namespace Qt::StringLiterals;
30using namespace QtIpcCommon;
31
32bool QSharedMemoryPosix::runtimeSupportCheck()
33{
34 static const bool result = []() {
35 (void)shm_open(name: "", oflag: 0, mode: 0); // this WILL fail
36 return errno != ENOSYS;
37 }();
38 return result;
39}
40
41bool QSharedMemoryPosix::handle(QSharedMemoryPrivate *self)
42{
43 // don't allow making handles on empty keys
44 if (self->nativeKey.isEmpty()) {
45 self->setError(e: QSharedMemory::KeyError,
46 message: QSharedMemory::tr(s: "%1: key is empty").arg(a: "QSharedMemory::handle"_L1));
47 return false;
48 }
49
50 return true;
51}
52
53bool QSharedMemoryPosix::cleanHandle(QSharedMemoryPrivate *)
54{
55 if (hand != -1)
56 qt_safe_close(fd: hand);
57 hand = -1;
58
59 return true;
60}
61
62bool QSharedMemoryPosix::create(QSharedMemoryPrivate *self, qsizetype size)
63{
64 if (!handle(self))
65 return false;
66
67 const QByteArray shmName = QFile::encodeName(fileName: self->nativeKey.nativeKey());
68
69 int fd;
70 QT_EINTR_LOOP(fd, ::shm_open(shmName.constData(), O_RDWR | O_CREAT | O_EXCL | O_CLOEXEC, 0600));
71 if (fd == -1) {
72 const int errorNumber = errno;
73 const auto function = "QSharedMemory::attach (shm_open)"_L1;
74 switch (errorNumber) {
75 case EINVAL:
76 self->setError(e: QSharedMemory::KeyError,
77 message: QSharedMemory::tr(s: "%1: bad name").arg(a: function));
78 break;
79 default:
80 self->setUnixErrorString(function);
81 }
82 return false;
83 }
84
85 // the size may only be set once
86 int ret;
87 QT_EINTR_LOOP(ret, QT_FTRUNCATE(fd, size));
88 if (ret == -1) {
89 self->setUnixErrorString("QSharedMemory::create (ftruncate)"_L1);
90 qt_safe_close(fd);
91 return false;
92 }
93
94 qt_safe_close(fd);
95
96 return true;
97}
98
99bool QSharedMemoryPosix::attach(QSharedMemoryPrivate *self, QSharedMemory::AccessMode mode)
100{
101 const QByteArray shmName = QFile::encodeName(fileName: self->nativeKey.nativeKey());
102
103 const int oflag = (mode == QSharedMemory::ReadOnly ? O_RDONLY : O_RDWR);
104 const mode_t omode = (mode == QSharedMemory::ReadOnly ? 0400 : 0600);
105
106 QT_EINTR_LOOP(hand, ::shm_open(shmName.constData(), oflag | O_CLOEXEC, omode));
107 if (hand == -1) {
108 const int errorNumber = errno;
109 const auto function = "QSharedMemory::attach (shm_open)"_L1;
110 switch (errorNumber) {
111 case EINVAL:
112 self->setError(e: QSharedMemory::KeyError,
113 message: QSharedMemory::tr(s: "%1: bad name").arg(a: function));
114 break;
115 default:
116 self->setUnixErrorString(function);
117 }
118 hand = -1;
119 return false;
120 }
121
122 // grab the size
123 QT_STATBUF st;
124 if (QT_FSTAT(fd: hand, buf: &st) == -1) {
125 self->setUnixErrorString("QSharedMemory::attach (fstat)"_L1);
126 cleanHandle(self);
127 return false;
128 }
129 self->size = qsizetype(st.st_size);
130
131 // grab the memory
132 const int mprot = (mode == QSharedMemory::ReadOnly ? PROT_READ : PROT_READ | PROT_WRITE);
133 self->memory = QT_MMAP(addr: 0, len: size_t(self->size), prot: mprot, MAP_SHARED, fd: hand, offset: 0);
134 if (self->memory == MAP_FAILED || !self->memory) {
135 self->setUnixErrorString("QSharedMemory::attach (mmap)"_L1);
136 cleanHandle(self);
137 self->memory = 0;
138 self->size = 0;
139 return false;
140 }
141
142#ifdef F_ADD_SEALS
143 // Make sure the shared memory region will not shrink
144 // otherwise someone could cause SIGBUS on us.
145 // (see http://lwn.net/Articles/594919/)
146 fcntl(fd: hand, F_ADD_SEALS, F_SEAL_SHRINK);
147#endif
148
149 return true;
150}
151
152bool QSharedMemoryPosix::detach(QSharedMemoryPrivate *self)
153{
154 // detach from the memory segment
155 if (::munmap(addr: self->memory, len: size_t(self->size)) == -1) {
156 self->setUnixErrorString("QSharedMemory::detach (munmap)"_L1);
157 return false;
158 }
159 self->memory = 0;
160 self->size = 0;
161
162#ifdef Q_OS_QNX
163 // On QNX the st_nlink field of struct stat contains the number of
164 // active shm_open() connections to the shared memory file, so we
165 // can use it to automatically clean up the file once the last
166 // user has detached from it.
167
168 // get the number of current attachments
169 int shm_nattch = 0;
170 QT_STATBUF st;
171 if (QT_FSTAT(hand, &st) == 0) {
172 // subtract 2 from linkcount: one for our own open and one for the dir entry
173 shm_nattch = st.st_nlink - 2;
174 }
175
176 cleanHandle(self);
177
178 // if there are no attachments then unlink the shared memory
179 if (shm_nattch == 0) {
180 const QByteArray shmName = QFile::encodeName(self->nativeKey.nativeKey());
181 if (::shm_unlink(shmName.constData()) == -1 && errno != ENOENT)
182 self->setUnixErrorString("QSharedMemory::detach (shm_unlink)"_L1);
183 }
184#else
185 // On non-QNX systems (tested Linux and Haiku), the st_nlink field is always 1,
186 // so we'll simply leak the shared memory files.
187 cleanHandle(self);
188#endif
189
190 return true;
191}
192
193QT_END_NAMESPACE
194
195#endif // QT_CONFIG(posix_shm)
196#endif // QT_CONFIG(sharedmemory)
197

source code of qtbase/src/corelib/ipc/qsharedmemory_posix.cpp