Stop using readdir_r: glibc deprecated it and it's not a good idea

POSIX does not require that readdir() be reentrant even for operations
on different dirent objects, but all implementations (according to the
glibc documentation) already do that. Moreover, it's not a good idea to
use readdir_r since the buffer space is limited by the caller, so
certain file names may be too long (ENAMETOOLONG) -- we had a workaround
for QNX, but for no other OS. According to the glibc documentation, it
is expected that POSIX will mark readdir_r obsolete and instead require
some form of reentrancy for readdir.

This commit makes everyone use readdir instead. The macros in
qplatformdefs.h are left behind in case someone else is using them.

With glibc 2.24, we started getting:

 qplatformdefs.h:150:35: warning: ‘int readdir_r(DIR*, dirent*, dirent**)’ is deprecated [-Wdeprecated-declarations]
 qfilesystemiterator_unix.cpp:112:17: note: in expansion of macro ‘QT_READDIR_R’

Task-number: QTBUG-56088
Change-Id: I33dc971f005a4848bb8ffffd14749b4082f62e69
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
Reviewed-by: James McDonnell <jmcdonnell@blackberry.com>

3 files changed, 2 insertions, 48 deletions

diff --git a/src/corelib/io/qfilesystemengine.cpp b/src/corelib/io/qfilesystemengine.cpp
index 02aa2ff4b7..055ff3600b 100644
--- a/src/corelib/io/qfilesystemengine.cpp
+++ b/src/corelib/io/qfilesystemengine.cpp
@@ -216,7 +216,7 @@ bool QFileSystemEngine::fillMetaData(int fd, QFileSystemMetaData &data)
     return false;
 }
 
-#if defined(QT_EXT_QNX_READDIR_R)
+#if defined(_DEXTRA_FIRST)
 static void fillStat64fromStat32(struct stat64 *statBuf64, const struct stat &statBuf32)
 {
     statBuf64->st_mode = statBuf32.st_mode;
@@ -281,7 +281,7 @@ void QFileSystemMetaData::fillFromStatBuf(const QT_STATBUF &statBuffer)
 
 void QFileSystemMetaData::fillFromDirEnt(const QT_DIRENT &entry)
 {
-#if defined(QT_EXT_QNX_READDIR_R)
+#if defined(_DEXTRA_FIRST)
     knownFlagsMask = 0;
     entryFlags = 0;
     for (dirent_extra *extra = _DEXTRA_FIRST(&entry); _DEXTRA_VALID(extra, &entry);
diff --git a/src/corelib/io/qfilesystemiterator_p.h b/src/corelib/io/qfilesystemiterator_p.h
index 119068a648..51dfe65f57 100644
--- a/src/corelib/io/qfilesystemiterator_p.h
+++ b/src/corelib/io/qfilesystemiterator_p.h
@@ -87,14 +87,6 @@ private:
 #else
     QT_DIR *dir;
     QT_DIRENT *dirEntry;
-#if defined(_POSIX_THREAD_SAFE_FUNCTIONS) && !defined(Q_OS_CYGWIN) || defined(QT_EXT_QNX_READDIR_R)
-    // for readdir_r
-    QScopedPointer<QT_DIRENT, QScopedPointerPodDeleter> mt_file;
-#if defined(QT_EXT_QNX_READDIR_R)
-    // for _readdir_r
-    size_t direntSize;
-#endif
-#endif
     int lastError;
 #endif
 
diff --git a/src/corelib/io/qfilesystemiterator_unix.cpp b/src/corelib/io/qfilesystemiterator_unix.cpp
index 6f094bd3b2..7d0e910188 100644
--- a/src/corelib/io/qfilesystemiterator_unix.cpp
+++ b/src/corelib/io/qfilesystemiterator_unix.cpp
@@ -46,9 +46,6 @@ QFileSystemIterator::QFileSystemIterator(const QFileSystemEntry &entry, QDir::Fi
     : nativePath(entry.nativeFilePath())
     , dir(0)
     , dirEntry(0)
-#if defined(Q_OS_QNX) && defined(__EXT_QNX__READDIR_R)
-    , direntSize(0)
-#endif
     , lastError(0)
 {
     Q_UNUSED(filters)
@@ -58,32 +55,8 @@ QFileSystemIterator::QFileSystemIterator(const QFileSystemEntry &entry, QDir::Fi
     if ((dir = QT_OPENDIR(nativePath.constData())) == 0) {
         lastError = errno;
     } else {
-
         if (!nativePath.endsWith('/'))
             nativePath.append('/');
-
-#if defined(_POSIX_THREAD_SAFE_FUNCTIONS) && !defined(Q_OS_CYGWIN) || defined(QT_EXT_QNX_READDIR_R)
-        // ### Race condition; we should use fpathconf and dirfd().
-        size_t maxPathName = ::pathconf(nativePath.constData(), _PC_NAME_MAX);
-        if (maxPathName == size_t(-1))
-            maxPathName = FILENAME_MAX;
-        maxPathName += sizeof(QT_DIRENT) + 1;
-
-        QT_DIRENT *p = reinterpret_cast<QT_DIRENT*>(::malloc(maxPathName));
-        Q_CHECK_PTR(p);
-
-        mt_file.reset(p);
-#if defined(QT_EXT_QNX_READDIR_R)
-        direntSize = maxPathName;
-
-        // Include extra stat information in the readdir() call (d_stat member of
-        // dirent_extra_stat). This is used in QFileSystemMetaData::fillFromDirEnt() to
-        // avoid extra stat() calls when iterating over directories
-        int flags = dircntl(dir, D_GETFLAG) |  D_FLAG_STAT | D_FLAG_FILTER;
-        if (dircntl(dir, D_SETFLAG, flags) == -1)
-            lastError = errno;
-#endif
-#endif
     }
 }
 
@@ -98,18 +71,7 @@ bool QFileSystemIterator::advance(QFileSystemEntry &fileEntry, QFileSystemMetaDa
     if (!dir)
         return false;
 
-#if defined(QT_EXT_QNX_READDIR_R)
-    lastError = QT_EXT_QNX_READDIR_R(dir, mt_file.data(), &dirEntry, direntSize);
-    if (lastError)
-        return false;
-#elif defined(_POSIX_THREAD_SAFE_FUNCTIONS) && !defined(Q_OS_CYGWIN)
-    lastError = QT_READDIR_R(dir, mt_file.data(), &dirEntry);
-    if (lastError)
-        return false;
-#else
-    // ### add local lock to prevent breaking reentrancy
     dirEntry = QT_READDIR(dir);
-#endif // _POSIX_THREAD_SAFE_FUNCTIONS
 
     if (dirEntry) {
         fileEntry = QFileSystemEntry(nativePath + QByteArray(dirEntry->d_name), QFileSystemEntry::FromNativePath());