read actor

Hi,

When one uses do_generic_file_read to (in-kernel) read a file from the 
page cache one has to give a read_actor as parameter. Suppose different 
do_generic_file_read instances occur simultaneously, then how can a 
shared file_read_actor differentiate between the different 
do_generic_file_read instances that made a call to it?
Shouldn't read_descriptor_t contain something like
	void *this_data;
to make this possible?

I also very much could use a this_data field so my read_actor can put the 
data into a structure pointed to by this_data.
If something for this already is present somewhere... please point me to 
that place in the code tree.

Please CC me; I'm not on the list.

Frank.