Case closed.

It is a Qt bug to use opendir (src/corelib/io/qfsfileengine_iterator_unix.cpp) trying to access directory in large filesystem.

scandir64 fixes the problem

Qt Code: 
  1. static QStringList getFileList( const char* dirname, const QRegExp& filter )
  2. {
  3.   QStringList fileList;
  4.  
  5.   struct dirent64 **namelist=NULL;
  6.   int sz = scandir64( dirname, &namelist, 0 , alphasort );
  7.   for ( int idx=0; idx < sz; idx++ ) {
  8.     if ( QString( namelist[idx]->d_name ).contains( filter ) ) {
  9.       QString fullpath( dirname );
  10.       fullpath += "/";
  11.       fullpath += namelist[idx]->d_name;
  12.       fileList << fullpath;
  13.     }
  14.   }
  15.  
  16.   if ( sz > 0 ) {
  17.     while( sz-- ) {
  18.       free( namelist[sz] );
  19.     }
  20.     free( namelist );
  21.   }
  22.  
  23.   return fileList;
  24.  
  25. } // getFileList
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