Move the readlink(2) wrapper to qcore_unix.cpp

This deduplicates the code between QFileSystemEngine and QLockFile.

Change-Id: I1eba2b016de74620bfc8fffd14cd005d5fd9beaa
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@qt.io>

5 files changed, 45 insertions, 34 deletions

diff --git a/src/corelib/io/qfilesystemengine_unix.cpp b/src/corelib/io/qfilesystemengine_unix.cpp
index 929db259ec..2c8c4e8f9e 100644
--- a/src/corelib/io/qfilesystemengine_unix.cpp
+++ b/src/corelib/io/qfilesystemengine_unix.cpp
@@ -44,6 +44,7 @@
 #include "qfile.h"
 
 #include <QtCore/qoperatingsystemversion.h>
+#include <QtCore/private/qcore_unix_p.h>
 #include <QtCore/qvarlengtharray.h>
 
 #include <stdlib.h> // for realpath()
@@ -150,30 +151,8 @@ static bool isPackage(const QFileSystemMetaData &data, const QFileSystemEntry &e
 //static
 QFileSystemEntry QFileSystemEngine::getLinkTarget(const QFileSystemEntry &link, QFileSystemMetaData &data)
 {
-#if defined(__GLIBC__) && !defined(PATH_MAX)
-#define PATH_CHUNK_SIZE 256
-    char *s = 0;
-    int len = -1;
-    int size = PATH_CHUNK_SIZE;
-
-    while (1) {
-        s = (char *) ::realloc(s, size);
-        Q_CHECK_PTR(s);
-        len = ::readlink(link.nativeFilePath().constData(), s, size);
-        if (len < 0) {
-            ::free(s);
-            break;
-        }
-        if (len < size) {
-            break;
-        }
-        size *= 2;
-    }
-#else
-    char s[PATH_MAX+1];
-    int len = readlink(link.nativeFilePath().constData(), s, PATH_MAX);
-#endif
-    if (len > 0) {
+    QByteArray s = qt_readlink(link.nativeFilePath().constData());
+    if (s.length() > 0) {
         QString ret;
         if (!data.hasFlags(QFileSystemMetaData::DirectoryType))
             fillMetaData(link, data, QFileSystemMetaData::DirectoryType);
@@ -184,11 +163,7 @@ QFileSystemEntry QFileSystemEngine::getLinkTarget(const QFileSystemEntry &link,
             if (!ret.isEmpty() && !ret.endsWith(QLatin1Char('/')))
                 ret += QLatin1Char('/');
         }
-        s[len] = '\0';
-        ret += QFile::decodeName(QByteArray(s));
-#if defined(__GLIBC__) && !defined(PATH_MAX)
-        ::free(s);
-#endif
+        ret += QFile::decodeName(s);
 
         if (!ret.startsWith(QLatin1Char('/'))) {
             const QString linkFilePath = link.filePath();
diff --git a/src/corelib/io/qlockfile_unix.cpp b/src/corelib/io/qlockfile_unix.cpp
index f21aced87c..1ee8ce889c 100644
--- a/src/corelib/io/qlockfile_unix.cpp
+++ b/src/corelib/io/qlockfile_unix.cpp
@@ -260,15 +260,15 @@ QString QLockFilePrivate::processNameByPid(qint64 pid)
 #elif defined(Q_OS_LINUX)
     if (!qt_haveLinuxProcfs())
         return QString();
+
     char exePath[64];
-    char buf[PATH_MAX + 1];
     sprintf(exePath, "/proc/%lld/exe", pid);
-    size_t len = (size_t)readlink(exePath, buf, sizeof(buf));
-    if (len >= sizeof(buf)) {
+
+    QByteArray buf = qt_readlink(exePath);
+    if (buf.isEmpty()) {
         // The pid is gone. Return some invalid process name to fail the test.
         return QStringLiteral("/ERROR/");
     }
-    buf[len] = 0;
     return QFileInfo(QFile::decodeName(buf)).fileName();
 #elif defined(Q_OS_HAIKU)
     thread_info info;
diff --git a/src/corelib/kernel/qcore_unix.cpp b/src/corelib/kernel/qcore_unix.cpp
index 686143f8c7..3b0da136ca 100644
--- a/src/corelib/kernel/qcore_unix.cpp
+++ b/src/corelib/kernel/qcore_unix.cpp
@@ -50,6 +50,37 @@
 
 QT_BEGIN_NAMESPACE
 
+QByteArray qt_readlink(const char *path)
+{
+#ifndef PATH_MAX
+    // suitably large value that won't consume too much memory
+#  define PATH_MAX  1024*1024
+#endif
+
+    QByteArray buf(256, Qt::Uninitialized);
+
+    ssize_t len = ::readlink(path, buf.data(), buf.size());
+    while (len == buf.size()) {
+        // readlink(2) will fill our buffer and not necessarily terminate with NUL;
+        if (buf.size() >= PATH_MAX) {
+            errno = ENAMETOOLONG;
+            return QByteArray();
+        }
+
+        // double the size and try again
+        buf.resize(buf.size() * 2);
+        len = ::readlink(path, buf.data(), buf.size());
+    }
+
+    if (len == -1)
+        return QByteArray();
+
+    buf.resize(len);
+    return buf;
+}
+
+#ifndef QT_BOOTSTRAPPED
+
 #if QT_CONFIG(poll_pollts)
 #  define ppoll pollts
 #endif
@@ -121,4 +152,6 @@ int qt_safe_poll(struct pollfd *fds, nfds_t nfds, const struct timespec *timeout
     }
 }
 
+#endif // QT_BOOTSTRAPPED
+
 QT_END_NAMESPACE
diff --git a/src/corelib/kernel/qcore_unix_p.h b/src/corelib/kernel/qcore_unix_p.h
index ea5d98cbf3..9d2c4f6c31 100644
--- a/src/corelib/kernel/qcore_unix_p.h
+++ b/src/corelib/kernel/qcore_unix_p.h
@@ -55,6 +55,7 @@
 #include <QtCore/private/qglobal_p.h>
 #include "qplatformdefs.h"
 #include "qatomic.h"
+#include "qbytearray.h"
 
 #ifndef Q_OS_UNIX
 # error "qcore_unix_p.h included on a non-Unix system"
@@ -339,6 +340,7 @@ static inline pid_t qt_safe_waitpid(pid_t pid, int *status, int options)
 // in qelapsedtimer_mac.cpp or qtimestamp_unix.cpp
 timespec qt_gettime() Q_DECL_NOTHROW;
 void qt_nanosleep(timespec amount);
+QByteArray qt_readlink(const char *path);
 
 /* non-static */
 inline bool qt_haveLinuxProcfs()
diff --git a/src/tools/bootstrap/bootstrap.pro b/src/tools/bootstrap/bootstrap.pro
index b92e5bb82b..8882df9fc5 100644
--- a/src/tools/bootstrap/bootstrap.pro
+++ b/src/tools/bootstrap/bootstrap.pro
@@ -94,7 +94,8 @@ SOURCES += \
            ../../xml/dom/qdom.cpp \
            ../../xml/sax/qxml.cpp
 
-unix:SOURCES += ../../corelib/io/qfilesystemengine_unix.cpp \
+unix:SOURCES += ../../corelib/kernel/qcore_unix.cpp \
+                ../../corelib/io/qfilesystemengine_unix.cpp \
                 ../../corelib/io/qfilesystemiterator_unix.cpp \
                 ../../corelib/io/qfsfileengine_unix.cpp