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// Copyright (C) 2015 Konstantin Ritt <ritt.ks@gmail.com>
// Copyright (C) 2016 The Qt Company Ltd.
// Copyright (C) 2015 Klarälvdalens Datakonsult AB, a KDAB Group company, info@kdab.com, author Tobias Koenig <tobias.koenig@kdab.com>
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
#include "qsharedmemory.h"
#include "qsharedmemory_p.h"
#include "qtipccommon_p.h"
#include <qfile.h>
#include <errno.h>
#if QT_CONFIG(sharedmemory)
#if QT_CONFIG(posix_shm)
#include <sys/types.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include "private/qcore_unix_p.h"
#ifndef O_CLOEXEC
# define O_CLOEXEC 0
#endif
QT_BEGIN_NAMESPACE
using namespace Qt::StringLiterals;
using namespace QtIpcCommon;
bool QSharedMemoryPosix::runtimeSupportCheck()
{
static const bool result = []() {
(void)shm_open("", 0, 0); // this WILL fail
return errno != ENOSYS;
}();
return result;
}
bool QSharedMemoryPosix::handle(QSharedMemoryPrivate *self)
{
// don't allow making handles on empty keys
if (self->nativeKey.isEmpty()) {
self->setError(QSharedMemory::KeyError,
QSharedMemory::tr("%1: key is empty").arg("QSharedMemory::handle"_L1));
return false;
}
return true;
}
bool QSharedMemoryPosix::cleanHandle(QSharedMemoryPrivate *)
{
if (hand != -1)
qt_safe_close(hand);
hand = -1;
return true;
}
bool QSharedMemoryPosix::create(QSharedMemoryPrivate *self, qsizetype size)
{
if (!handle(self))
return false;
const QByteArray shmName = QFile::encodeName(self->nativeKey.nativeKey());
int fd;
QT_EINTR_LOOP(fd, ::shm_open(shmName.constData(), O_RDWR | O_CREAT | O_EXCL | O_CLOEXEC, 0600));
if (fd == -1) {
const int errorNumber = errno;
const auto function = "QSharedMemory::attach (shm_open)"_L1;
switch (errorNumber) {
case EINVAL:
self->setError(QSharedMemory::KeyError,
QSharedMemory::tr("%1: bad name").arg(function));
break;
default:
self->setUnixErrorString(function);
}
return false;
}
// the size may only be set once
int ret;
QT_EINTR_LOOP(ret, QT_FTRUNCATE(fd, size));
if (ret == -1) {
self->setUnixErrorString("QSharedMemory::create (ftruncate)"_L1);
qt_safe_close(fd);
return false;
}
qt_safe_close(fd);
return true;
}
bool QSharedMemoryPosix::attach(QSharedMemoryPrivate *self, QSharedMemory::AccessMode mode)
{
const QByteArray shmName = QFile::encodeName(self->nativeKey.nativeKey());
const int oflag = (mode == QSharedMemory::ReadOnly ? O_RDONLY : O_RDWR);
const mode_t omode = (mode == QSharedMemory::ReadOnly ? 0400 : 0600);
QT_EINTR_LOOP(hand, ::shm_open(shmName.constData(), oflag | O_CLOEXEC, omode));
if (hand == -1) {
const int errorNumber = errno;
const auto function = "QSharedMemory::attach (shm_open)"_L1;
switch (errorNumber) {
case EINVAL:
self->setError(QSharedMemory::KeyError,
QSharedMemory::tr("%1: bad name").arg(function));
break;
default:
self->setUnixErrorString(function);
}
hand = -1;
return false;
}
// grab the size
QT_STATBUF st;
if (QT_FSTAT(hand, &st) == -1) {
self->setUnixErrorString("QSharedMemory::attach (fstat)"_L1);
cleanHandle(self);
return false;
}
self->size = qsizetype(st.st_size);
// grab the memory
const int mprot = (mode == QSharedMemory::ReadOnly ? PROT_READ : PROT_READ | PROT_WRITE);
self->memory = QT_MMAP(0, size_t(self->size), mprot, MAP_SHARED, hand, 0);
if (self->memory == MAP_FAILED || !self->memory) {
self->setUnixErrorString("QSharedMemory::attach (mmap)"_L1);
cleanHandle(self);
self->memory = 0;
self->size = 0;
return false;
}
#ifdef F_ADD_SEALS
// Make sure the shared memory region will not shrink
// otherwise someone could cause SIGBUS on us.
// (see http://lwn.net/Articles/594919/)
fcntl(hand, F_ADD_SEALS, F_SEAL_SHRINK);
#endif
return true;
}
bool QSharedMemoryPosix::detach(QSharedMemoryPrivate *self)
{
// detach from the memory segment
if (::munmap(self->memory, size_t(self->size)) == -1) {
self->setUnixErrorString("QSharedMemory::detach (munmap)"_L1);
return false;
}
self->memory = 0;
self->size = 0;
#ifdef Q_OS_QNX
// On QNX the st_nlink field of struct stat contains the number of
// active shm_open() connections to the shared memory file, so we
// can use it to automatically clean up the file once the last
// user has detached from it.
// get the number of current attachments
int shm_nattch = 0;
QT_STATBUF st;
if (QT_FSTAT(hand, &st) == 0) {
// subtract 2 from linkcount: one for our own open and one for the dir entry
shm_nattch = st.st_nlink - 2;
}
cleanHandle(self);
// if there are no attachments then unlink the shared memory
if (shm_nattch == 0) {
const QByteArray shmName = QFile::encodeName(self->nativeKey.nativeKey());
if (::shm_unlink(shmName.constData()) == -1 && errno != ENOENT)
self->setUnixErrorString("QSharedMemory::detach (shm_unlink)"_L1);
}
#else
// On non-QNX systems (tested Linux and Haiku), the st_nlink field is always 1,
// so we'll simply leak the shared memory files.
cleanHandle(self);
#endif
return true;
}
QT_END_NAMESPACE
#endif // QT_CONFIG(posix_shm)
#endif // QT_CONFIG(sharedmemory)
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