This patch removes the blocking Block::Session::sync RPC function and
adds the asynchronous operations SYNC and TRIM to the block session's
packet-stream interface.
Even though the patch adjusts all block components to the interface
change, the components keep the former blocking handling of sync
internally for now because of the design of the 'Block::Driver'
interface. This old interface is not worth changing. We should instead
migrate the block servers step by step to the new
'Block::Request_stream' API.
Fixes#3274
The new request tag allows a block-session client to uniquely correlate
acknowledgements with outstanding requests. Until now, this was possible
for read and write operations by taking the value of the request's
packet-stream offset. However, SYNC and TRIM requests do not carry any
packet-stream payload and thereby lack meaningful offset values. By
introducing the notion of a 'tag', we can support multiple outstanding
requests of any type and don't need to overload the meaning of the
'offset' value.
Issue #3274
This patch splits the 'Request' definition into smaller types that are
suitable for the client-side API too.
The new 'Operation' type comprises the block operation's type (opcode)
and the operation's arguments (block number, block count).
The former 'Request::operation_defined' is now 'Operation::valid'.
The 'Request' aggregates an 'Operation', which changes its object
layout.
Note that this commit relaxes the bit-precise definition of 'Request' to
facilitate the use of 'unsigned long' where appropriate, in particular
for the request tag (which should correspond to an 'Id_space::Id'). The
originally bit-precise definition was pursued to allow the sharing of
the 'Request' type between SPARK and C++ code. However, it turns out
that defining a native type in each language and a (set of) converting
constructors is a more natural approach.
Issue #3283
This patch renames 'wakeup_client' to 'wakeup_client_if_needed' to
clarify that the method triggers signals only when needed, not on every
call.
The name 'wakeup_client' is prone to misguide users to call the function
conditionally as an optimization, thereby complicating the code, but to
no effect.
Fixes#3279
This patch replaces the formerly fixed 2 KiB data alignment within the
packet-stream buffer by a server-defined alignment. This has two
benefits.
First, when using block servers that provide small block sizes like 512
bytes, we avoid fragmenting the packet-stream buffer, which occurs when
aligning 512-byte requests at 2 KiB boundaries. This reduces meta data
costs for the packet-stream allocator and also allows fitting more
requests into the buffer.
Second, block drivers with alignment constraints dictated by the
hardware can now pass those constraints to the client, thereby easing
the use of zero-copy DMA directly into the packet stream.
The alignment is determined by the Block::Session_client at construction
time and applied by the Block::Session_client::alloc_packet method.
Block-session clients should always use this method, not the 'alloc_packet'
method of the packet stream (tx source) directly. The latter merely
applies a default alignment of 2 KiB.
At the server side, the alignment is automatically checked by
block/component.h (old API) and block/request_stream.h (new API).
Issue #3274
This patch modernizes the 'Block::Session::info' interface. Instead of
using out parameters, the 'init' RPC function returns a compound 'Info'
object now. The rather complicated 'Operations' struct is replaced by
a 'writeable' attribute in the 'Info' object.
Fixes#3275
This is a safeguard against accidentally taking the 'Ack' interface as a
value instead of a reference.
The 'Payload' interface should also not be copied (and potentially
stored) because it contains a pointer.
