On Unix, the memory allocated by QFile::map() is not always dealocated by QFile::unmap().

The extra memory required by the offset is not taken into account when munmap() is called.

Here is an example to reproduce the bug:
#include <QCoreApplication>
#include <QFile>
#include <QString>
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <unistd.h>
void maps(QString label)

{ puts(label.toAscii().data()); system(QString("grep /bigfile$ /proc/%2/maps") .arg(getpid()).toAscii().data()); } int main(int argc, char** argv) { unsigned char* addr; QCoreApplication app(argc, argv); QFile file("bigfile"); file.open(QIODevice::WriteOnly); file.resize(4097); file.close(); maps("Initial state:"); file.open(QIODevice::ReadOnly); maps("After open():"); addr = file.map(1, file.size() - 1); maps("After map():"); file.unmap(addr); maps("After unmap():"); addr = file.map(1, file.size() - 1); maps("After second map():"); file.unmap(addr); maps("After second unmap():"); addr = file.map(1, file.size() - 1); maps("After third map():"); file.unmap(addr); maps("After third unmap():"); file.close(); maps("After close():"); return 0; } Here is a patch by Andy Goth to solve the issue: diff --git a/src/corelib/io/qfsfileengine_unix.cpp b/src/corelib/io/qfsfileengine_unix.cpp index bb64773..1788470 100644 --- a/src/corelib/io/qfsfileengine_unix.cpp +++ b/src/corelib/io/qfsfileengine_unix.cpp @@ -988,8 +988,9 @@ bool QFSFileEnginePrivate::unmap(uchar *ptr) return false; }

• uchar *start = ptr - maps[ptr].first;
• int len = maps[ptr].second;
  + const int extra = maps[ptr].first;
  + uchar *start = ptr - extra;
  + int len = maps[ptr].second + extra;
  if (-1 == munmap(start, len)) {
  q->setError(QFile::UnspecifiedError, qt_error_string(errno));
  return false;