[Interest] QFileInfo not working inside non privileged docker container

[Manner Róbert]

Hi,

We have an issue at our company where Qt gets crosscompiled inside a
docker. Suddenly it stopped building after trying to upgrade to Qt 5.10.0
(5.9.2 worked for sure). It fails at the last step of configure: running
qmake with a dummy qt.conf to generate the makefile. Same build goes fine
outside of docker.

I have tracked down the issue until that the root cause seems to be that
QFileInfo is not working, it is not giving back any meaningful data for
files or directories.

I have created an example to demonstrate the problem: it runs fine outside
docker (on a real host) or inside docker in privileged mode. But without
privileged mode (which is not possible during a docker image build), it
does not work.

----------------------------------- EXAMPLE STARTS
#include <QFileInfo>
#include <QDebug>

int main (int argc, char* argv[])
{
    Q_UNUSED(argc);
    Q_UNUSED(argv);
    QFileInfo fi(__FILE__);
    qDebug() << "Filesize:" << fi.size() << "Is file?" << fi.isFile() <<
"Exists?" << fi.exists();
    // Output is: Filesize: 0 Is file? false Exists? false

    QFileInfo di(".");
    qDebug() << "Is directory?" << di.isDir() << "Is file?" << di.isFile()
<< "Exists?" << di.exists();
    // Output is: Is directory? false Is file? false Exists? false

    return 0;
}
------------------------------------- EXAMPLE ENDS

(The host and guest is a pretty recent archlinux with qt 5.10.)

Do you have any idea what happened with QFileInfo between 5.9 and 5.10
which could cause such problem? Any idea what I should patch out?

Thanks in advance,

Robert
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