path: root/src/corelib/kernel/qsharedmemory_unix.cpp

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** Copyright (C) 2013 Digia Plc and/or its subsidiary(-ies).
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** This file is part of the QtCore module of the Qt Toolkit.
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** General Public License version 3.0 as published by the Free Software
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** packaging of this file.  Please review the following information to
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#include "qplatformdefs.h"

#include "qsharedmemory.h"
#include "qsharedmemory_p.h"

#include <qdebug.h>
#include <qfile.h>

#ifndef QT_NO_SHAREDMEMORY
#include <sys/types.h>
#include <sys/ipc.h>
#ifndef QT_POSIX_IPC
#include <sys/shm.h>
#else
#include <sys/mman.h>
#include <sys/stat.h>
#endif
#include <fcntl.h>
#include <unistd.h>
#endif // QT_NO_SHAREDMEMORY
#include <errno.h>

#include "private/qcore_unix_p.h"

#ifndef QT_NO_SHAREDMEMORY

//#define QSHAREDMEMORY_DEBUG

QT_BEGIN_NAMESPACE

QSharedMemoryPrivate::QSharedMemoryPrivate()
    : QObjectPrivate(), memory(0), size(0), error(QSharedMemory::NoError),
#ifndef QT_NO_SYSTEMSEMAPHORE
      systemSemaphore(QString()), lockedByMe(false),
#endif
#ifndef QT_POSIX_IPC
      unix_key(0)
#else
      hand(0)
#endif
{
}

void QSharedMemoryPrivate::setErrorString(const QString &function)
{
    // EINVAL is handled in functions so they can give better error strings
    switch (errno) {
    case EACCES:
    case EPERM:
        errorString = QSharedMemory::tr("%1: permission denied").arg(function);
        error = QSharedMemory::PermissionDenied;
        break;
    case EEXIST:
        errorString = QSharedMemory::tr("%1: already exists").arg(function);
        error = QSharedMemory::AlreadyExists;
        break;
    case ENOENT:
        errorString = QSharedMemory::tr("%1: doesn't exist").arg(function);
        error = QSharedMemory::NotFound;
        break;
    case EAGAIN:
    case EMFILE:
    case ENFILE:
    case ENOMEM:
    case ENOSPC:
        errorString = QSharedMemory::tr("%1: out of resources").arg(function);
        error = QSharedMemory::OutOfResources;
        break;
    case EOVERFLOW:
        errorString = QSharedMemory::tr("%1: invalid size").arg(function);
        error = QSharedMemory::InvalidSize;
        break;
    default:
        errorString = QSharedMemory::tr("%1: unknown error %2").arg(function).arg(errno);
        error = QSharedMemory::UnknownError;
#ifdef QSHAREDMEMORY_DEBUG
        qDebug() << errorString << "key" << key << "errno" << errno << EINVAL;
#endif
        break;
    }
}

/*!
    \internal

    If not already made create the handle used for accessing the shared memory.
*/
#ifndef QT_POSIX_IPC
key_t QSharedMemoryPrivate::handle()
{
    // already made
    if (unix_key)
        return unix_key;

    // don't allow making handles on empty keys
    if (nativeKey.isEmpty()) {
        errorString = QSharedMemory::tr("%1: key is empty").arg(QLatin1String("QSharedMemory::handle"));
        error = QSharedMemory::KeyError;
        return 0;
    }

    // ftok requires that an actual file exists somewhere
    if (!QFile::exists(nativeKey)) {
        errorString = QSharedMemory::tr("%1: UNIX key file doesn't exist").arg(QLatin1String("QSharedMemory::handle"));
        error = QSharedMemory::NotFound;
        return 0;
    }

    unix_key = ftok(QFile::encodeName(nativeKey).constData(), 'Q');
    if (-1 == unix_key) {
        errorString = QSharedMemory::tr("%1: ftok failed").arg(QLatin1String("QSharedMemory::handle"));
        error = QSharedMemory::KeyError;
        unix_key = 0;
    }
    return unix_key;
}
#else
int QSharedMemoryPrivate::handle()
{
    // don't allow making handles on empty keys
    QString safeKey = makePlatformSafeKey(key);
    if (safeKey.isEmpty()) {
        errorString = QSharedMemory::tr("%1: key is empty").arg(QLatin1String("QSharedMemory::handle"));
        error = QSharedMemory::KeyError;
        return 0;
    }

    return 1;
}
#endif // QT_POSIX_IPC

#endif // QT_NO_SHAREDMEMORY

#if !(defined(QT_NO_SHAREDMEMORY) && defined(QT_NO_SYSTEMSEMAPHORE))
/*!
    \internal
    Creates the unix file if needed.
    returns true if the unix file was created.

    -1 error
     0 already existed
     1 created
*/
int QSharedMemoryPrivate::createUnixKeyFile(const QString &fileName)
{
#ifndef QT_POSIX_IPC
    if (QFile::exists(fileName))
        return 0;

    int fd = qt_safe_open(QFile::encodeName(fileName).constData(),
                          O_EXCL | O_CREAT | O_RDWR, 0640);
    if (-1 == fd) {
        if (errno == EEXIST)
            return 0;
        return -1;
    } else {
        qt_safe_close(fd);
    }
    return 1;
#else
    Q_UNUSED(fileName);
    // nothing to do
    return -1;
#endif
}
#endif // QT_NO_SHAREDMEMORY && QT_NO_SYSTEMSEMAPHORE

#ifndef QT_NO_SHAREDMEMORY

void QSharedMemoryPrivate::cleanHandle()
{
#ifndef QT_POSIX_IPC
    unix_key = 0;
#else
    qt_safe_close(hand);
    hand = 0;
#endif
}

bool QSharedMemoryPrivate::create(int size)
{
#ifndef QT_POSIX_IPC
    // build file if needed
    int built = createUnixKeyFile(nativeKey);
    if (built == -1) {
        errorString = QSharedMemory::tr("%1: unable to make key").arg(QLatin1String("QSharedMemory::create"));
        error = QSharedMemory::KeyError;
        return false;
    }
    bool createdFile = built == 1;

    // get handle
    if (!handle()) {
        if (createdFile)
            QFile::remove(nativeKey);
        return false;
    }

    // create
    if (-1 == shmget(unix_key, size, 0600 | IPC_CREAT | IPC_EXCL)) {
        QString function = QLatin1String("QSharedMemory::create");
        switch (errno) {
        case EINVAL:
            errorString = QSharedMemory::tr("%1: system-imposed size restrictions").arg(function);
            error = QSharedMemory::InvalidSize;
            break;
        default:
            setErrorString(function);
        }
        if (createdFile && error != QSharedMemory::AlreadyExists)
            QFile::remove(nativeKey);
        return false;
    }
#else
    if (!handle())
        return false;

    QByteArray shmName = QFile::encodeName(makePlatformSafeKey(key));

    int fd;
    EINTR_LOOP(fd, shm_open(shmName.constData(), O_RDWR | O_CREAT | O_EXCL, 0666));
    if (fd == -1) {
        QString function = QLatin1String("QSharedMemory::create");
        switch (errno) {
        case ENAMETOOLONG:
        case EINVAL:
            errorString = QSharedMemory::tr("%1: bad name").arg(function);
            error = QSharedMemory::KeyError;
            break;
        default:
            setErrorString(function);
        }
        return false;
    }

    // the size may only be set once; ignore errors
    int ret;
    EINTR_LOOP(ret, ftruncate(fd, size));
    if (ret == -1) {
        setErrorString(QLatin1String("QSharedMemory::create (ftruncate)"));
        qt_safe_close(fd);
        return false;
    }

    qt_safe_close(fd);
#endif // QT_POSIX_IPC

    return true;
}

bool QSharedMemoryPrivate::attach(QSharedMemory::AccessMode mode)
{
#ifndef QT_POSIX_IPC
    // grab the shared memory segment id
    int id = shmget(unix_key, 0, (mode == QSharedMemory::ReadOnly ? 0400 : 0600));
    if (-1 == id) {
        setErrorString(QLatin1String("QSharedMemory::attach (shmget)"));
        return false;
    }

    // grab the memory
    memory = shmat(id, 0, (mode == QSharedMemory::ReadOnly ? SHM_RDONLY : 0));
    if ((void*) - 1 == memory) {
        memory = 0;
        setErrorString(QLatin1String("QSharedMemory::attach (shmat)"));
        return false;
    }

    // grab the size
    shmid_ds shmid_ds;
    if (!shmctl(id, IPC_STAT, &shmid_ds)) {
        size = (int)shmid_ds.shm_segsz;
    } else {
        setErrorString(QLatin1String("QSharedMemory::attach (shmctl)"));
        return false;
    }
#else
    QByteArray shmName = QFile::encodeName(makePlatformSafeKey(key));

    int oflag = (mode == QSharedMemory::ReadOnly ? O_RDONLY : O_RDWR);
    mode_t omode = (mode == QSharedMemory::ReadOnly ? 0444 : 0660);

    EINTR_LOOP(hand, shm_open(shmName.constData(), oflag, omode));
    if (hand == -1) {
        QString function = QLatin1String("QSharedMemory::attach (shm_open)");
        switch (errno) {
        case ENAMETOOLONG:
        case EINVAL:
            errorString = QSharedMemory::tr("%1: bad name").arg(function);
            error = QSharedMemory::KeyError;
            break;
        default:
            setErrorString(function);
        }
        hand = 0;
        return false;
    }

    // grab the size
    QT_STATBUF st;
    if (QT_FSTAT(hand, &st) == -1) {
        setErrorString(QLatin1String("QSharedMemory::attach (fstat)"));
        cleanHandle();
        return false;
    }
    size = st.st_size;

    // grab the memory
    int mprot = (mode == QSharedMemory::ReadOnly ? PROT_READ : PROT_READ | PROT_WRITE);
    memory = mmap(0, size, mprot, MAP_SHARED, hand, 0);
    if (memory == MAP_FAILED || !memory) {
        setErrorString(QLatin1String("QSharedMemory::attach (mmap)"));
        cleanHandle();
        memory = 0;
        size = 0;
        return false;
    }
#endif // QT_POSIX_IPC

    return true;
}

bool QSharedMemoryPrivate::detach()
{
#ifndef QT_POSIX_IPC
    // detach from the memory segment
    if (-1 == shmdt(memory)) {
        QString function = QLatin1String("QSharedMemory::detach");
        switch (errno) {
        case EINVAL:
            errorString = QSharedMemory::tr("%1: not attached").arg(function);
            error = QSharedMemory::NotFound;
            break;
        default:
            setErrorString(function);
        }
        return false;
    }
    memory = 0;
    size = 0;

    // Get the number of current attachments
    int id = shmget(unix_key, 0, 0400);
    cleanHandle();

    struct shmid_ds shmid_ds;
    if (0 != shmctl(id, IPC_STAT, &shmid_ds)) {
        switch (errno) {
        case EINVAL:
            return true;
        default:
            return false;
        }
    }
    // If there are no attachments then remove it.
    if (shmid_ds.shm_nattch == 0) {
        // mark for removal
        if (-1 == shmctl(id, IPC_RMID, &shmid_ds)) {
            setErrorString(QLatin1String("QSharedMemory::detach"));
            switch (errno) {
            case EINVAL:
                return true;
            default:
                return false;
            }
        }

        // remove file
        if (!QFile::remove(nativeKey))
            return false;
    }
#else
    // detach from the memory segment
    if (munmap(memory, size) == -1) {
        setErrorString(QLatin1String("QSharedMemory::detach (munmap)"));
        return false;
    }
    memory = 0;
    size = 0;

    // 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();
    // if there are no attachments then unlink the shared memory
    if (shm_nattch == 0) {
        QByteArray shmName = QFile::encodeName(makePlatformSafeKey(key));
        if (shm_unlink(shmName.constData()) == -1 && errno != ENOENT)
            setErrorString(QLatin1String("QSharedMemory::detach (shm_unlink)"));
    }
#endif // QT_POSIX_IPC

    return true;
}

QT_END_NAMESPACE

#endif // QT_NO_SHAREDMEMORY