block_session: extend interface with sync() call

To support components, which implement the block session's server side
rpc object, and which doesn't write data to their device backend immediately,
an additional synchronization call is needed. Thereby, clients like for
instance a file system can tell these components, when a synchronization is
required.

Ref #113

os/include/block_session/block_session.h

@@ -129,6 +129,11 @@ namespace Block {
 		                  Genode::size_t *blk_size,
 		                  Operations     *ops) = 0;
 
+		/**
+		 * Synchronize with block device, like ensuring data to be written
+		 */
+		virtual void sync() = 0;
+
 		/**
 		 * Request packet-transmission channel
 		 */
@@ -146,7 +151,8 @@ namespace Block {
 
 		GENODE_RPC(Rpc_info, void, info, Genode::size_t *, Genode::size_t *, Operations *);
 		GENODE_RPC(Rpc_tx_cap, Genode::Capability<Tx>, _tx_cap);
-		GENODE_RPC_INTERFACE(Rpc_info, Rpc_tx_cap);
+		GENODE_RPC(Rpc_sync, void, sync);
+		GENODE_RPC_INTERFACE(Rpc_info, Rpc_tx_cap, Rpc_sync);
 	};
 }
 

os/include/block_session/client.h

@@ -55,6 +55,7 @@ namespace Block {
 
 			Tx *tx_channel() { return &_tx; }
 			Tx::Source *tx() { return _tx.source(); }
+			void sync()      { call<Rpc_sync>(); }
 
 			/*
 			 * Wrapper for alloc_packet, allocates 2KB aligned packets