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Cache system zone ID when fetched from the file-system

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Record the device and inode numbers when found and assume we can
safely re-use the name if those have not changed.

Tidy up some preprocessor trivia in the process and moved
zone-availability check functions to before the system name lookup.

Pick-to: 5.15
Task-number: QTBUG-75585
Change-Id: I3660922ef3c94b553a20f887a676e8921693b30f
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
This commit is contained in:
Edward Welbourne 2020-04-03 12:01:01 +02:00
parent bd877e76a8
commit f20f0b03d5
1 changed files with 148 additions and 71 deletions
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219
src/corelib/time/qtimezoneprivate_tz.cpp
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@ -1,5 +1,6 @@
/****************************************************************************
**
** Copyright (C) 2020 The Qt Company Ltd.
** Copyright (C) 2019 Crimson AS <info@crimson.no>
** Copyright (C) 2013 John Layt <jlayt@kde.org>
** Contact: https://www.qt.io/licensing/
@ -42,18 +43,19 @@
#include "qtimezoneprivate_p.h"
#include "private/qlocale_tools_p.h"
#include <QtCore/QFile>
#include <QtCore/QMutex>
#include <QtCore/QHash>
#include <QtCore/QDataStream>
#include <QtCore/QDateTime>
#include <QtCore/QFile>
#include <QtCore/QHash>
#include <QtCore/QMutex>
#include <qdebug.h>
#include <qplatformdefs.h>
#include <algorithm>
#include <errno.h>
#include <limits.h>
#if !defined(Q_OS_INTEGRITY)
#ifndef Q_OS_INTEGRITY
#include <sys/param.h> // to use MAXSYMLINKS constant
#endif
#include <unistd.h> // to use _SC_SYMLOOP_MAX constant
@ -1100,73 +1102,6 @@ QTimeZonePrivate::Data QTzTimeZonePrivate::previousTransition(qint64 beforeMSecs
return last > tranCache().cbegin() ? dataForTzTransition(*--last) : invalidData();
}
static long getSymloopMax()
{
#if defined(SYMLOOP_MAX)
return SYMLOOP_MAX; // if defined, at runtime it can only be greater than this, so this is a safe bet
#else
errno = 0;
long result = sysconf(_SC_SYMLOOP_MAX);
if (result >= 0)
return result;
// result is -1, meaning either error or no limit
Q_ASSERT(!errno); // ... but it can't be an error, POSIX mandates _SC_SYMLOOP_MAX
// therefore we can make up our own limit
# if defined(MAXSYMLINKS)
return MAXSYMLINKS;
# else
return 8;
# endif
#endif
}
// TODO Could cache the value and monitor the required files for any changes
QByteArray QTzTimeZonePrivate::systemTimeZoneId() const
{
// Check TZ env var first, if not populated try find it
QByteArray ianaId = qgetenv("TZ");
// The TZ value can be ":/etc/localtime" which libc considers
// to be a "default timezone", in which case it will be read
// by one of the blocks below, so unset it here so it is not
// considered as a valid/found ianaId
if (ianaId == ":/etc/localtime")
ianaId.clear();
else if (ianaId.startsWith(':'))
ianaId = ianaId.mid(1);
// On most distros /etc/localtime is a symlink to a real file so extract name from the path
if (ianaId.isEmpty()) {
const QLatin1String zoneinfo("/zoneinfo/");
QString path = QFile::symLinkTarget(QStringLiteral("/etc/localtime"));
int index = -1;
long iteration = getSymloopMax();
// Symlink may point to another symlink etc. before being under zoneinfo/
// We stop on the first path under /zoneinfo/, even if it is itself a
// symlink, like America/Montreal pointing to America/Toronto
while (iteration-- > 0 && !path.isEmpty() && (index = path.indexOf(zoneinfo)) < 0)
path = QFile::symLinkTarget(path);
if (index >= 0) {
// /etc/localtime is a symlink to the current TZ file, so extract from path
ianaId = path.midRef(index + zoneinfo.size()).toUtf8();
}
}
// Some systems (e.g. uClibc) have a default value for $TZ in /etc/TZ:
if (ianaId.isEmpty()) {
QFile zone(QStringLiteral("/etc/TZ"));
if (zone.open(QIODevice::ReadOnly))
ianaId = zone.readAll().trimmed();
}
// Give up for now and return UTC
if (ianaId.isEmpty())
ianaId = utcQByteArray();
return ianaId;
}
bool QTzTimeZonePrivate::isTimeZoneIdAvailable(const QByteArray &ianaId) const
{
return tzZones->contains(ianaId);
@ -1191,4 +1126,146 @@ QList<QByteArray> QTzTimeZonePrivate::availableTimeZoneIds(QLocale::Country coun
return result;
}
// Getting the system zone's ID:
namespace {
class ZoneNameReader : public QObject
{
public:
QByteArray name()
{
/* Assumptions:
a) Systems don't change which of localtime and TZ they use without a
reboot.
b) When they change, they use atomic renames, hence a new device and
inode for the new file.
c) If we change which *name* is used for a zone, while referencing
the same final zoneinfo file, we don't care about the change of
name (e.g. if Europe/Oslo and Europe/Berlin are both symlinks to
the same CET file, continuing to use the old name, after
/etc/localtime changes which of the two it points to, is
harmless).
The alternative would be to use a file-system watcher, but they are a
scarce resource.
*/
const StatIdent local = identify("/etc/localtime");
const StatIdent tz = identify("/etc/TZ");
if (!m_name.isEmpty() && m_last.isValid() && (m_last == local || m_last == tz))
return m_name;
m_name = etcLocalTime();
if (!m_name.isEmpty()) {
m_last = local;
return m_name;
}
m_name = etcTZ();
m_last = m_name.isEmpty() ? StatIdent() : tz;
return m_name;
}
private:
QByteArray m_name;
struct StatIdent
{
static constexpr unsigned long bad = ~0ul;
unsigned long m_dev, m_ino;
StatIdent() : m_dev(bad), m_ino(bad) {}
StatIdent(const QT_STATBUF &data) : m_dev(data.st_dev), m_ino(data.st_ino) {}
bool isValid() { return m_dev != bad || m_ino != bad; }
bool operator==(const StatIdent &other)
{ return other.m_dev == m_dev && other.m_ino == m_ino; }
};
StatIdent m_last;
static StatIdent identify(const char *path)
{
QT_STATBUF data;
return QT_STAT(path, &data) == -1 ? StatIdent() : StatIdent(data);
}
static QByteArray etcLocalTime()
{
// On most distros /etc/localtime is a symlink to a real file so extract
// name from the path
const QLatin1String zoneinfo("/zoneinfo/");
QString path = QStringLiteral("/etc/localtime");
long iteration = getSymloopMax();
// Symlink may point to another symlink etc. before being under zoneinfo/
// We stop on the first path under /zoneinfo/, even if it is itself a
// symlink, like America/Montreal pointing to America/Toronto
do {
path = QFile::symLinkTarget(path);
int index = path.indexOf(zoneinfo);
if (index >= 0) // Found zoneinfo file; extract zone name from path:
return path.midRef(index + zoneinfo.size()).toUtf8();
} while (!path.isEmpty() && --iteration > 0);
return QByteArray();
}
static QByteArray etcTZ()
{
// Some systems (e.g. uClibc) have a default value for $TZ in /etc/TZ:
const QString path = QStringLiteral("/etc/TZ");
QFile zone(path);
if (zone.open(QIODevice::ReadOnly))
return zone.readAll().trimmed();
return QByteArray();
}
// Any chain of symlinks longer than this is assumed to be a loop:
static long getSymloopMax()
{
#ifdef SYMLOOP_MAX
// If defined, at runtime it can only be greater than this, so this is a safe bet:
return SYMLOOP_MAX;
#else
errno = 0;
long result = sysconf(_SC_SYMLOOP_MAX);
if (result >= 0)
return result;
// result is -1, meaning either error or no limit
Q_ASSERT(!errno); // ... but it can't be an error, POSIX mandates _SC_SYMLOOP_MAX
// therefore we can make up our own limit
# ifdef MAXSYMLINKS
return MAXSYMLINKS;
# else
return 8;
# endif
#endif
}
};
}
QByteArray QTzTimeZonePrivate::systemTimeZoneId() const
{
// Check TZ env var first, if not populated try find it
QByteArray ianaId = qgetenv("TZ");
// The TZ value can be ":/etc/localtime" which libc considers
// to be a "default timezone", in which case it will be read
// by one of the blocks below, so unset it here so it is not
// considered as a valid/found ianaId
if (ianaId == ":/etc/localtime")
ianaId.clear();
else if (ianaId.startsWith(':'))
ianaId = ianaId.mid(1);
if (ianaId.isEmpty()) {
thread_local static ZoneNameReader reader;
ianaId = reader.name();
}
// Give up for now and return UTC
if (ianaId.isEmpty())
ianaId = utcQByteArray();
return ianaId;
}
QT_END_NAMESPACE