When a <gpu> node is present in the VFS, the plugin opens a
Gpu::Connection for each open call to the 'gpu' node and installs a
completion signal handler. A read only to the fd returned only comes
back if a completion signal has been received between two read
transctions to the fd.
For now the Gpu::Connections can be retrieved by calling the
'vfs_gpu_connection(unsigned long id)' function. The id can be obtained
using 'stat' on the 'gpu' device and is located in the inode (st_ino)
field of the stat buffer.
issue #4380
