[rados] Asynchronous operations

[Rutger ter Borg <rutger@terborg.net>]

Dear list,

I'm currently writing a Boost.Asio-like interface to librados.hpp. Most 
things are working like expected, and some things I couldn't figure out 
from the available docs and code. I have itemized a couple of questions 
below.

* to avoid allocations done by rados, I'm currently using 
buffer::create_static() for both reads and writes. I suppose this is ok?

* suppose you have the following code example

boost::asio::io_service ios;
pool pool( "some pool", ios );

std::string some_data( "this is an example string of data" );
pool.async_write_object_at( "hello", 0, boost::asio::buffer( some_data 
), &done );

ios.run();

with respect to this interface, I have the following questions:

a) the IoCtx's synchronous read() and write() functions return the 
number of bytes read and written; is there a way to get to this number 
from AioCompletion? I would like to define the function signature for 
the callback handler (see 'done' in the example above) something like

void( const boost::system::error_code&, std::size_t )

where the second argument would be the number of bytes transferred.

b) is it possible to cancel outstanding asynchronous operations? I.e., 
have the possibility to implement something like

pool.cancel();

?

TIA,
Regards,

Rutger