Warning, file /frameworks/kdelibs4support/src/kdecore/klockfile_unix.cpp was not indexed or was modified since last indexation (in which case cross-reference links may be missing, inaccurate or erroneous).

 /*
    This file is part of the KDE libraries
    Copyright (c) 2004 Waldo Bastian <bastian@kde.org>
    Copyright (c) 2011 David Faure <faure@kde.org>
 
    This library is free software; you can redistribute it and/or
    modify it under the terms of the GNU Library General Public
    License version 2 as published by the Free Software Foundation.
 
    This library is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
    Library General Public License for more details.
 
    You should have received a copy of the GNU Library General Public License
    along with this library; see the file COPYING.LIB.  If not, write to
    the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
    Boston, MA 02110-1301, USA.
 */
 
 #include "klockfile.h"
 
 #include <config-klockfile.h>
 
 #include <sys/types.h>
 #if HAVE_SYS_STAT_H
 #include <sys/stat.h>
 #endif
 #if HAVE_SYS_TIME_H
 #include <sys/time.h>
 #endif
 #include <signal.h>
 #include <errno.h>
 #include <stdlib.h>
 #include <unistd.h>
 
 #include <qplatformdefs.h> // QT_STATBUF, QT_LSTAT, QT_OPEN
 #include <QDate>
 #include <QFile>
 #include <QCoreApplication>
 #include <QTextStream>
 #include <QTemporaryFile>
 
 #include "krandom.h"
 #include "kfilesystemtype.h"
 
 #include <unistd.h>
 #include <fcntl.h>
 
 // Related reading:
 // http://www.spinnaker.de/linux/nfs-locking.html
 // http://en.wikipedia.org/wiki/File_locking
 // http://apenwarr.ca/log/?m=201012
 
 // Related source code:
 // * lockfile-create, from the lockfile-progs package, uses the link() trick from lockFileWithLink
 // below, so it works over NFS but fails on FAT32 too.
 // * the flock program, which uses flock(LOCK_EX), works on local filesystems (including FAT32),
 //    but not NFS.
 //  Note about flock: don't unlink, it creates a race. http://world.std.com/~swmcd/steven/tech/flock.html
 
 // fcntl(F_SETLK) is not a good solution.
 // It locks other processes but locking out other threads must be done by hand,
 // and worse, it unlocks when just reading the file in the same process (!).
 // See the apenwarr.ca article above.
 
 // open(O_EXCL) seems to be the best solution for local files (on all filesystems),
 // it only fails over NFS (at least with old NFS servers).
 // See http://www.informit.com/guides/content.aspx?g=cplusplus&seqNum=144
 
 // Conclusion: we use O_EXCL by default, and the link() trick over NFS.
 
 class Q_DECL_HIDDEN KLockFile::Private
 {
 public:
     Private(const QString &componentName)
         : staleTime(30), // 30 seconds
           isLocked(false),
           linkCountSupport(true),
           mustCloseFd(false),
           m_pid(-1),
           m_componentName(componentName)
     {
     }
 
     // The main method
     KLockFile::LockResult lockFile(QT_STATBUF &st_buf);
 
     // Two different implementations
     KLockFile::LockResult lockFileOExcl(QT_STATBUF &st_buf);
     KLockFile::LockResult lockFileWithLink(QT_STATBUF &st_buf);
 
     KLockFile::LockResult deleteStaleLock();
     KLockFile::LockResult deleteStaleLockWithLink();
 
     void writeIntoLockFile(QFile &file);
     void readLockFile();
     bool isNfs() const;
 
     QFile m_file;
     QString m_fileName;
     int staleTime;
     bool isLocked;
     bool linkCountSupport;
     bool mustCloseFd;
     QTime staleTimer;
     QT_STATBUF statBuf;
     int m_pid;
     QString m_hostname;
     QString m_componentName; // as set for this instance
     QString m_componentNameFromFile; // as read from the lock file
 };
 
 KLockFile::KLockFile(const QString &file, const QString &componentName)
     : d(new Private(componentName))
 {
     d->m_fileName = file;
 }
 
 KLockFile::~KLockFile()
 {
     unlock();
     delete d;
 }
 
 int
 KLockFile::staleTime() const
 {
     return d->staleTime;
 }
 
 void
 KLockFile::setStaleTime(int _staleTime)
 {
     d->staleTime = _staleTime;
 }
 
 static bool operator==(const QT_STATBUF &st_buf1,
                        const QT_STATBUF &st_buf2)
 {
 #define FIELD_EQ(what)       (st_buf1.what == st_buf2.what)
     return FIELD_EQ(st_dev) && FIELD_EQ(st_ino) &&
            FIELD_EQ(st_uid) && FIELD_EQ(st_gid) && FIELD_EQ(st_nlink);
 #undef FIELD_EQ
 }
 
 static bool operator!=(const QT_STATBUF &st_buf1,
                        const QT_STATBUF &st_buf2)
 {
     return !(st_buf1 == st_buf2);
 }
 
 static bool testLinkCountSupport(const QByteArray &fileName)
 {
     QT_STATBUF st_buf;
     int result = -1;
     // Check if hardlinks raise the link count at all?
     if (!::link(fileName.data(), QByteArray(fileName + ".test").data())) {
         result = QT_LSTAT(fileName.data(), &st_buf);
         ::unlink(QByteArray(fileName + ".test").data());
     }
     return (result < 0 || ((result == 0) && (st_buf.st_nlink == 2)));
 }
 
 void KLockFile::Private::writeIntoLockFile(QFile &file)
 {
     file.setPermissions(QFile::ReadUser | QFile::WriteUser | QFile::ReadGroup | QFile::ReadOther);
 
     char hostname[256];
     hostname[0] = 0;
     gethostname(hostname, 255);
     hostname[255] = 0;
     m_hostname = QString::fromLocal8Bit(hostname);
     if (m_componentName.isEmpty() && QCoreApplication::instance()) { // TODO Qt5: should be fixed by new Q_GLOBAL_STATIC: qcoreappdata() was dangling, in kconfigtest testSyncOnExit.
         m_componentName = QCoreApplication::applicationName();
     }
 
     m_pid = getpid();
 
     file.write(QByteArray::number(m_pid) + '\n');
     file.write(m_componentName.toUtf8() + '\n');
     file.write(hostname);
     file.flush();
 }
 
 void KLockFile::Private::readLockFile()
 {
     m_pid = -1;
     m_hostname.clear();
     m_componentNameFromFile.clear();
 
     QFile file(m_fileName);
     if (file.open(QIODevice::ReadOnly)) {
         QTextStream ts(&file);
         if (!ts.atEnd()) {
             m_pid = ts.readLine().toInt();
         }
         if (!ts.atEnd()) {
             m_componentNameFromFile = ts.readLine();
         }
         if (!ts.atEnd()) {
             m_hostname = ts.readLine();
         }
     }
 }
 
 KLockFile::LockResult KLockFile::Private::lockFileWithLink(QT_STATBUF &st_buf)
 {
     const QByteArray lockFileName = QFile::encodeName(m_fileName);
     int result = QT_LSTAT(lockFileName.data(), &st_buf);
     if (result == 0) {
         return KLockFile::LockFail;
     }
 
     QTemporaryFile uniqueFile;
     uniqueFile.setFileTemplate(m_fileName);
     if (!uniqueFile.open()) {
         return KLockFile::LockError;
     }
 
     writeIntoLockFile(uniqueFile);
 
     QByteArray uniqueName = QFile::encodeName(uniqueFile.fileName());
 
     // Create lock file
     result = ::link(uniqueName.data(), lockFileName.data());
     if (result != 0) {
         return KLockFile::LockError;
     }
 
     if (!linkCountSupport) {
         return KLockFile::LockOK;
     }
 
     QT_STATBUF st_buf2;
     result = QT_LSTAT(uniqueName.data(), &st_buf2);
     if (result != 0) {
         return KLockFile::LockError;
     }
 
     result = QT_LSTAT(lockFileName.data(), &st_buf);
     if (result != 0) {
         return KLockFile::LockError;
     }
 
     if (st_buf != st_buf2 || S_ISLNK(st_buf.st_mode) || S_ISLNK(st_buf2.st_mode)) {
         // SMBFS supports hardlinks by copying the file, as a result the above test will always fail
         // cifs increases link count artifically but the inodes are still different
         if ((st_buf2.st_nlink > 1 ||
                 ((st_buf.st_nlink == 1) && (st_buf2.st_nlink == 1))) && (st_buf.st_ino != st_buf2.st_ino)) {
             linkCountSupport = testLinkCountSupport(uniqueName);
             if (!linkCountSupport) {
                 return KLockFile::LockOK;    // Link count support is missing... assume everything is OK.
             }
         }
         return KLockFile::LockFail;
     }
 
     return KLockFile::LockOK;
 }
 
 bool KLockFile::Private::isNfs() const
 {
     const KFileSystemType::Type fsType = KFileSystemType::fileSystemType(m_fileName);
     return fsType == KFileSystemType::Nfs;
 }
 
 KLockFile::LockResult KLockFile::Private::lockFile(QT_STATBUF &st_buf)
 {
     if (isNfs()) {
         return lockFileWithLink(st_buf);
     }
 
     return lockFileOExcl(st_buf);
 }
 
 KLockFile::LockResult KLockFile::Private::lockFileOExcl(QT_STATBUF &st_buf)
 {
     const QByteArray lockFileName = QFile::encodeName(m_fileName);
 
     int fd = QT_OPEN(lockFileName.constData(), O_WRONLY | O_CREAT | O_EXCL, 0644);
     if (fd < 0) {
         if (errno == EEXIST) {
             // File already exists
             if (QT_LSTAT(lockFileName.constData(), &st_buf) != 0) { // caller wants stat buf details
                 // File got deleted meanwhile! Clear struct rather than leaving it unset.
                 st_buf.st_dev = 0;
                 st_buf.st_ino = 0;
                 st_buf.st_uid = 0;
                 st_buf.st_gid = 0;
                 st_buf.st_nlink = 0;
             }
             return LockFail;
         } else {
             return LockError;
         }
     }
     // We hold the lock, continue.
     if (!m_file.open(fd, QIODevice::WriteOnly)) {
         close(fd);
         return LockError;
     }
     writeIntoLockFile(m_file);
 
     // stat to get the modification time
     const int result = QT_LSTAT(QFile::encodeName(m_fileName).data(), &st_buf);
     if (result != 0) {
         close(fd);
         return KLockFile::LockError;
     }
     mustCloseFd = true;
     return KLockFile::LockOK;
 }
 
 KLockFile::LockResult KLockFile::Private::deleteStaleLock()
 {
     if (isNfs()) {
         return deleteStaleLockWithLink();
     }
 
     // I see no way to prevent the race condition here, where we could
     // delete a new lock file that another process just got after we
     // decided the old one was too stale for us too.
     qWarning("WARNING: deleting stale lockfile %s", qPrintable(m_fileName));
     QFile::remove(m_fileName);
     return LockOK;
 }
 
 KLockFile::LockResult KLockFile::Private::deleteStaleLockWithLink()
 {
     // This is dangerous, we could be deleting a new lock instead of
     // the old stale one, let's be very careful
 
     // Create temp file
     QTemporaryFile *ktmpFile = new QTemporaryFile;
     ktmpFile->setFileTemplate(m_fileName);
     if (!ktmpFile->open()) {
         delete ktmpFile;
         return KLockFile::LockError;
     }
 
     const QByteArray lckFile = QFile::encodeName(m_fileName);
     const QByteArray tmpFile = QFile::encodeName(ktmpFile->fileName());
     delete ktmpFile;
 
     // link to lock file
     if (::link(lckFile.data(), tmpFile.data()) != 0) {
         return KLockFile::LockFail;    // Try again later
     }
 
     // check if link count increased with exactly one
     // and if the lock file still matches
     QT_STATBUF st_buf1;
     QT_STATBUF st_buf2;
     memcpy(&st_buf1, &statBuf, sizeof(QT_STATBUF));
     st_buf1.st_nlink++;
     if ((QT_LSTAT(tmpFile.data(), &st_buf2) == 0) && st_buf1 == st_buf2) {
         if ((QT_LSTAT(lckFile.data(), &st_buf2) == 0) && st_buf1 == st_buf2) {
             // - - if yes, delete lock file, delete temp file, retry lock
             qWarning("WARNING: deleting stale lockfile %s", lckFile.data());
             ::unlink(lckFile.data());
             ::unlink(tmpFile.data());
             return KLockFile::LockOK;
         }
     }
 
     // SMBFS supports hardlinks by copying the file, as a result the above test will always fail
     if (linkCountSupport) {
         linkCountSupport = testLinkCountSupport(tmpFile);
     }
 
     if (!linkCountSupport) {
         // Without support for link counts we will have a little race condition
         qWarning("WARNING: deleting stale lockfile %s", lckFile.data());
         ::unlink(tmpFile.data());
         if (::unlink(lckFile.data()) < 0) {
             qWarning("WARNING: Problem deleting stale lockfile %s: %s", lckFile.data(),
                      strerror(errno));
             return KLockFile::LockFail;
         }
         return KLockFile::LockOK;
     }
 
     // Failed to delete stale lock file
     qWarning("WARNING: Problem deleting stale lockfile %s", lckFile.data());
     ::unlink(tmpFile.data());
     return KLockFile::LockFail;
 }
 
 KLockFile::LockResult KLockFile::lock(LockFlags options)
 {
     if (d->isLocked) {
         return KLockFile::LockOK;
     }
 
     KLockFile::LockResult result;
     int hardErrors = 5;
     int n = 5;
     while (true) {
         QT_STATBUF st_buf;
         // Try to create the lock file
         result = d->lockFile(st_buf);
 
         if (result == KLockFile::LockOK) {
             d->staleTimer = QTime();
             break;
         } else if (result == KLockFile::LockError) {
             d->staleTimer = QTime();
             if (--hardErrors == 0) {
                 break;
             }
         } else { // KLockFile::Fail -- there is already such a file present (e.g. left by a crashed app)
             if (!d->staleTimer.isNull() && d->statBuf != st_buf) {
                 d->staleTimer = QTime();
             }
 
             if (d->staleTimer.isNull()) {
                 memcpy(&(d->statBuf), &st_buf, sizeof(QT_STATBUF));
                 d->staleTimer.start();
 
                 d->readLockFile();
             }
 
             bool isStale = false;
             if ((d->m_pid > 0) && !d->m_hostname.isEmpty()) {
                 // Check if hostname is us
                 char hostname[256];
                 hostname[0] = 0;
                 gethostname(hostname, 255);
                 hostname[255] = 0;
 
                 if (d->m_hostname == QString::fromLocal8Bit(hostname)) {
                     // Check if pid still exists
                     int res = ::kill(d->m_pid, 0);
                     if ((res == -1) && (errno == ESRCH)) {
                         isStale = true;    // pid does not exist
                     }
                 }
             }
             if (d->staleTimer.elapsed() > (d->staleTime * 1000)) {
                 isStale = true;
             }
 
             if (isStale) {
                 if ((options & ForceFlag) == 0) {
                     return KLockFile::LockStale;
                 }
 
                 result = d->deleteStaleLock();
 
                 if (result == KLockFile::LockOK) {
                     // Lock deletion successful
                     d->staleTimer = QTime();
                     continue; // Now try to get the new lock
                 } else if (result != KLockFile::LockFail) {
                     return result;
                 }
             }
         }
 
         if (options & NoBlockFlag) {
             break;
         }
 
         struct timeval tv;
         tv.tv_sec = 0;
         tv.tv_usec = n * ((KRandom::random() % 200) + 100);
         if (n < 2000) {
             n = n * 2;
         }
 
         select(0, nullptr, nullptr, nullptr, &tv);
     }
     if (result == LockOK) {
         d->isLocked = true;
     }
     return result;
 }
 
 bool KLockFile::isLocked() const
 {
     return d->isLocked;
 }
 
 void KLockFile::unlock()
 {
     if (d->isLocked) {
         ::unlink(QFile::encodeName(d->m_fileName).data());
         if (d->mustCloseFd) {
             close(d->m_file.handle());
             d->mustCloseFd = false;
         }
         d->m_file.close();
         d->m_pid = -1;
         d->isLocked = false;
     }
 }
 
 bool KLockFile::getLockInfo(int &pid, QString &hostname, QString &appname)
 {
     if (d->m_pid == -1) {
         return false;
     }
     pid = d->m_pid;
     hostname = d->m_hostname;
     appname = d->m_componentNameFromFile;
     return true;
 }