1/****************************************************************************
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3** Copyright (C) 2015 Konstantin Ritt <ritt.ks@gmail.com>
4** Copyright (C) 2016 The Qt Company Ltd.
5** Copyright (C) 2015 Klarälvdalens Datakonsult AB, a KDAB Group company, info@kdab.com, author Tobias Koenig <tobias.koenig@kdab.com>
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40****************************************************************************/
41
42#include "qplatformdefs.h"
43
44#include "qsharedmemory.h"
45#include "qsharedmemory_p.h"
46#include "qsystemsemaphore.h"
47#include <qfile.h>
48
49#include <errno.h>
50
51#ifdef QT_POSIX_IPC
52
53#ifndef QT_NO_SHAREDMEMORY
54#include <sys/types.h>
55#include <sys/mman.h>
56#include <sys/stat.h>
57#include <fcntl.h>
58#include <unistd.h>
59
60#include "private/qcore_unix_p.h"
61
62QT_BEGIN_NAMESPACE
63
64int QSharedMemoryPrivate::handle()
65{
66 // don't allow making handles on empty keys
67 const QString safeKey = makePlatformSafeKey(key);
68 if (safeKey.isEmpty()) {
69 errorString = QSharedMemory::tr("%1: key is empty").arg(QLatin1String("QSharedMemory::handle"));
70 error = QSharedMemory::KeyError;
71 return 0;
72 }
73
74 return 1;
75}
76
77bool QSharedMemoryPrivate::cleanHandle()
78{
79 qt_safe_close(hand);
80 hand = -1;
81
82 return true;
83}
84
85bool QSharedMemoryPrivate::create(int size)
86{
87 if (!handle())
88 return false;
89
90 const QByteArray shmName = QFile::encodeName(makePlatformSafeKey(key));
91
92 int fd;
93#ifdef O_CLOEXEC
94 // First try with O_CLOEXEC flag, if that fails, fall back to normal flags
95 EINTR_LOOP(fd, ::shm_open(shmName.constData(), O_RDWR | O_CREAT | O_EXCL | O_CLOEXEC, 0600));
96 if (fd == -1)
97 EINTR_LOOP(fd, ::shm_open(shmName.constData(), O_RDWR | O_CREAT | O_EXCL, 0600));
98#else
99 EINTR_LOOP(fd, ::shm_open(shmName.constData(), O_RDWR | O_CREAT | O_EXCL, 0600));
100#endif
101 if (fd == -1) {
102 const int errorNumber = errno;
103 const QLatin1String function("QSharedMemory::attach (shm_open)");
104 switch (errorNumber) {
105 case ENAMETOOLONG:
106 case EINVAL:
107 errorString = QSharedMemory::tr("%1: bad name").arg(function);
108 error = QSharedMemory::KeyError;
109 break;
110 default:
111 setErrorString(function);
112 }
113 return false;
114 }
115
116 // the size may only be set once
117 int ret;
118 EINTR_LOOP(ret, QT_FTRUNCATE(fd, size));
119 if (ret == -1) {
120 setErrorString(QLatin1String("QSharedMemory::create (ftruncate)"));
121 qt_safe_close(fd);
122 return false;
123 }
124
125 qt_safe_close(fd);
126
127 return true;
128}
129
130bool QSharedMemoryPrivate::attach(QSharedMemory::AccessMode mode)
131{
132 const QByteArray shmName = QFile::encodeName(makePlatformSafeKey(key));
133
134 const int oflag = (mode == QSharedMemory::ReadOnly ? O_RDONLY : O_RDWR);
135 const mode_t omode = (mode == QSharedMemory::ReadOnly ? 0400 : 0600);
136
137#ifdef O_CLOEXEC
138 // First try with O_CLOEXEC flag, if that fails, fall back to normal flags
139 EINTR_LOOP(hand, ::shm_open(shmName.constData(), oflag | O_CLOEXEC, omode));
140 if (hand == -1)
141 EINTR_LOOP(hand, ::shm_open(shmName.constData(), oflag, omode));
142#else
143 EINTR_LOOP(hand, ::shm_open(shmName.constData(), oflag, omode));
144#endif
145 if (hand == -1) {
146 const int errorNumber = errno;
147 const QLatin1String function("QSharedMemory::attach (shm_open)");
148 switch (errorNumber) {
149 case ENAMETOOLONG:
150 case EINVAL:
151 errorString = QSharedMemory::tr("%1: bad name").arg(function);
152 error = QSharedMemory::KeyError;
153 break;
154 default:
155 setErrorString(function);
156 }
157 hand = -1;
158 return false;
159 }
160
161 // grab the size
162 QT_STATBUF st;
163 if (QT_FSTAT(hand, &st) == -1) {
164 setErrorString(QLatin1String("QSharedMemory::attach (fstat)"));
165 cleanHandle();
166 return false;
167 }
168 size = st.st_size;
169
170 // grab the memory
171 const int mprot = (mode == QSharedMemory::ReadOnly ? PROT_READ : PROT_READ | PROT_WRITE);
172 memory = QT_MMAP(0, size, mprot, MAP_SHARED, hand, 0);
173 if (memory == MAP_FAILED || !memory) {
174 setErrorString(QLatin1String("QSharedMemory::attach (mmap)"));
175 cleanHandle();
176 memory = 0;
177 size = 0;
178 return false;
179 }
180
181#ifdef F_ADD_SEALS
182 // Make sure the shared memory region will not shrink
183 // otherwise someone could cause SIGBUS on us.
184 // (see http://lwn.net/Articles/594919/)
185 fcntl(hand, F_ADD_SEALS, F_SEAL_SHRINK);
186#endif
187
188 return true;
189}
190
191bool QSharedMemoryPrivate::detach()
192{
193 // detach from the memory segment
194 if (::munmap(memory, size) == -1) {
195 setErrorString(QLatin1String("QSharedMemory::detach (munmap)"));
196 return false;
197 }
198 memory = 0;
199 size = 0;
200
201#ifdef Q_OS_QNX
202 // On QNX the st_nlink field of struct stat contains the number of
203 // active shm_open() connections to the shared memory file, so we
204 // can use it to automatically clean up the file once the last
205 // user has detached from it.
206
207 // get the number of current attachments
208 int shm_nattch = 0;
209 QT_STATBUF st;
210 if (QT_FSTAT(hand, &st) == 0) {
211 // subtract 2 from linkcount: one for our own open and one for the dir entry
212 shm_nattch = st.st_nlink - 2;
213 }
214
215 cleanHandle();
216
217 // if there are no attachments then unlink the shared memory
218 if (shm_nattch == 0) {
219 const QByteArray shmName = QFile::encodeName(makePlatformSafeKey(key));
220 if (::shm_unlink(shmName.constData()) == -1 && errno != ENOENT)
221 setErrorString(QLatin1String("QSharedMemory::detach (shm_unlink)"));
222 }
223#else
224 // On non-QNX systems (tested Linux and Haiku), the st_nlink field is always 1,
225 // so we'll simply leak the shared memory files.
226 cleanHandle();
227#endif
228
229 return true;
230}
231
232QT_END_NAMESPACE
233
234#endif // QT_NO_SHAREDMEMORY
235
236#endif // QT_POSIX_IPC
237

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