Listing 5. Entire FUSE Shim C++ Class

#include <fuselagefs/fuselagefs.hh>
using namespace Fuselage;
using namespace Fuselage::Helpers;

#include <aio.h>
#include <errno.h>

#include <string>
#include <iostream>
using namespace std;
...
class CustomFilesystem
 :
 public Delegatefs
{
 typedef Delegatefs _Base;
 off_t m_oldOffset;
 off_t m_startNextAIOOffset;
 enum
 {
   aio_buffer_sz = 8 * 1024 * 1024,
   aio_consume_window = aio_buffer_sz / 2,
   debug_readahread_aio = false
 };
 char aio_buffer[ aio_buffer_sz ];

 void schedule_readahread_aio( int fd,
     off_t offset, bool forceNewReadAHead )
 {
   if( m_startNextAIOOffset <= offset
        || forceNewReadAHead )
   {
     cerr << "Starting an async read request"
          << " at offset:" << offset << endl;

     ssize_t retval; ssize_t nbytes;
     struct aiocb arg;
     bzero( &arg, sizeof (struct aiocb));
     arg.aio_fildes = fd;
     arg.aio_offset = offset;
     arg.aio_buf = (void *) aio_buffer;
     arg.aio_nbytes = aio_buffer_sz;
     arg.aio_sigevent.sigev_notify = SIGEV_NONE;

     retval = aio_read( &arg );
     if( retval < 0 )
       cerr << "error starting aio request!"
            << endl;

     m_startNextAIOOffset = offset
        + aio_consume_window;

     if( debug_readahread_aio )
     {
       while ( (retval = aio_error( &arg ) )
           == EINPROGRESS )
       {}
       cerr << "aio_return():"
            << aio_return( &arg )
             << endl;
      }
    }
 }

public:

 CustomFilesystem()
 :
 _Base(),
 m_startNextAIOOffset( 0 ),
 m_oldOffset( -1 )
 {
 }

 virtual int fs_read( const char *path,
    char *buf, size_t size,
    off_t offset, struct fuse_file_info *fi)
 {
   cerr << "fs_read() offset:" << offset
      << " sz:" << size << endl;
   int fd = fi->fh;

   bool forceNewReadAHead = false;
   if( (offset - size) != m_oldOffset )
   {
     cerr << "possible seek() between read()s!"
          << endl;
     forceNewReadAHead = true;
     aio_cancel( fd, 0 );
   }
   schedule_readahread_aio( fd, offset,
                            forceNewReadAHead );
   m_oldOffset = offset;
   return _Base::fs_read( path, buf,
                          size, offset, fi );
 }
};