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Detect system time zone from linked symlinks 

[ChangeLog][QtCore][QTimeZone] The IANA timezone database backend
now properly follows symlinks even when they point to variable
locations like /run or /var (useful when /etc is mounted read-only).

Fixes: QTBUG-75936
Fixes: QTBUG-75527
Change-Id: If0dc2bfa20659e76c3bd062c75597a9ad01ad954
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Damien Caliste 2019-05-20 15:44:18 +02:00
parent 5f30fd6426
commit 4ebac33644
1 changed files with 38 additions and 5 deletions
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43
src/corelib/tools/qtimezoneprivate_tz.cpp
View File

@ -51,6 +51,12 @@
#include "qlocale_tools_p.h"
#include <algorithm>
#include <errno.h>
#include <limits.h>
#if !defined(Q_OS_INTEGRITY)
#include <sys/param.h> // to use MAXSYMLINKS constant
#endif
#include <unistd.h> // to use _SC_SYMLOOP_MAX constant
QT_BEGIN_NAMESPACE
@ -1045,6 +1051,27 @@ QTimeZonePrivate::Data QTzTimeZonePrivate::previousTransition(qint64 beforeMSecs
return last > m_tranTimes.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
{
@ -1062,12 +1089,18 @@ QByteArray QTzTimeZonePrivate::systemTimeZoneId() const
// On most distros /etc/localtime is a symlink to a real file so extract name from the path
if (ianaId.isEmpty()) {
const QString path = QFile::symLinkTarget(QStringLiteral("/etc/localtime"));
if (!path.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
int index = path.indexOf(QLatin1String("/zoneinfo/"));
if (index != -1)
ianaId = path.mid(index + 10).toUtf8();
ianaId = path.mid(index + zoneinfo.size()).toUtf8();
}
}