os: make 'terminal_crosslink' buffer size configurable

Fixes #5135

repos/os/recipes/pkg/test-terminal_crosslink/runtime

@@ -30,6 +30,7 @@
 		<start name="terminal_crosslink">
 			<resource name="RAM" quantum="1M"/>
 			<provides> <service name="Terminal"/> </provides>
+			<config buffer="4K"/>
 		</start>
 		<start name="test-terminal_crosslink">
 			<resource name="RAM" quantum="1M"/>

repos/os/src/server/terminal_crosslink/README

@@ -1,14 +1,11 @@
 The 'terminal_crosslink' server allows exactly two clients to communicate with
 each other using the 'Terminal' interface. Data sent to the server gets stored
-in a buffer of 4096 bytes (one buffer per client). As long as the data to be
-written fits into the buffer, the 'write()' call returns immediately. If no
-more data fits into the buffer, the 'write()' call blocks until the other
-client has consumed some of the data from the buffer via the 'read()' call. The
-'read()' call never blocks. A signal receiver can be used to block until new
-data is ready for reading.
+in a buffer of configurable size (one buffer per client, 4K by default). The
+'read()' and 'write()' calls never block. A signal receiver can be used to
+block until new data is ready for reading.
 
 Example
 -------
 
-An example run script 'terminal_crosslink.run' can be found in the 'os/run'
-directory.
+An example depot package 'test-terminal_crosslink' can be found in the
+'os/recipes/pkg' directory.

repos/os/src/server/terminal_crosslink/main.cc

@@ -5,13 +5,14 @@
  */
 
 /*
- * Copyright (C) 2012-2017 Genode Labs GmbH
+ * Copyright (C) 2012-2024 Genode Labs GmbH
  *
  * This file is part of the Genode OS framework, which is distributed
  * under the terms of the GNU Affero General Public License version 3.
  */
 
 /* Genode includes */
+#include <base/attached_rom_dataspace.h>
 #include <base/component.h>
 #include <base/heap.h>
 
@@ -27,10 +28,18 @@ namespace Terminal_crosslink {
 
 struct Terminal_crosslink::Main
 {
-	Env  &_env;
-	Heap  _heap { _env.ram(), _env.rm() };
+	Env &_env;
 
-	Root  _terminal_root { _env, _heap };
+	Sliced_heap _heap { _env.ram(), _env.rm() };
+
+	Attached_rom_dataspace _config { _env, "config" };
+
+	Number_of_bytes const DEFAULT_BUFFER_SIZE { 4096 };
+
+	size_t const _buffer_size {
+		_config.xml().attribute_value("buffer", DEFAULT_BUFFER_SIZE) };
+
+	Root _terminal_root { _env, _heap, _buffer_size };
 
 	Main(Env &env) : _env(env)
 	{

repos/os/src/server/terminal_crosslink/terminal_root.h

@@ -5,7 +5,7 @@
  */
 
 /*
- * Copyright (C) 2012-2017 Genode Labs GmbH
+ * Copyright (C) 2012-2024 Genode Labs GmbH
  *
  * This file is part of the Genode OS framework, which is distributed
  * under the terms of the GNU Affero General Public License version 3.
@@ -67,10 +67,10 @@ namespace Terminal_crosslink {
 			/**
 			 * Constructor
 			 */
-			Root(Env &env, Allocator &alloc)
+			Root(Env &env, Allocator &alloc, size_t buffer_size)
 			: Root_component(&env.ep().rpc_ep(), &alloc),
-			  _session_component1(env, _session_component2),
-			  _session_component2(env, _session_component1),
+			  _session_component1(env, _session_component2, buffer_size),
+			  _session_component2(env, _session_component1, buffer_size),
 			  _session_state(0)
 			{ }
 	};

repos/os/src/server/terminal_crosslink/terminal_session_component.cc

@@ -5,7 +5,7 @@
  */
 
 /*
- * Copyright (C) 2012-2017 Genode Labs GmbH
+ * Copyright (C) 2012-2024 Genode Labs GmbH
  *
  * This file is part of the Genode OS framework, which is distributed
  * under the terms of the GNU Affero General Public License version 3.
@@ -23,11 +23,13 @@
 using namespace Genode;
 
 Terminal_crosslink::Session_component::Session_component(Env &env,
-                                                         Session_component &partner)
+                                                         Session_component &partner,
+                                                         size_t buffer_size)
 : _env(env),
   _partner(partner),
+  _buffer_size(buffer_size),
   _session_cap(_env.ep().rpc_ep().manage(this)),
-  _io_buffer(env.ram(), env.rm(), BUFFER_SIZE),
+  _io_buffer(env.ram(), env.rm(), IO_BUFFER_SIZE),
   _cross_num_bytes_avail(0)
 {
 }
@@ -85,22 +87,25 @@ bool Terminal_crosslink::Session_component::avail()
 
 size_t Terminal_crosslink::Session_component::_read(size_t dst_len)
 {
-	return _partner.cross_read(_io_buffer.local_addr<unsigned char>(), dst_len);
+	return _partner.cross_read(_io_buffer.local_addr<unsigned char>(),
+	                           min(dst_len, _io_buffer.size()));
 }
 
 
 size_t Terminal_crosslink::Session_component::_write(size_t num_bytes)
 {
+	num_bytes = min(num_bytes, _io_buffer.size());
+
 	unsigned char *src = _io_buffer.local_addr<unsigned char>();
 
 	size_t num_bytes_written = 0;
-	while (num_bytes_written < num_bytes)
-		try {
-			_buffer.add(src[num_bytes_written]);
-			++num_bytes_written;
-		} catch(Local_buffer::Overflow) {
-			break;
-		}
+	bool error = false;
+
+	while ((num_bytes_written < num_bytes) && !error)
+		_buffer.add(src[num_bytes_written]).with_result(
+			[&] (Ring_buffer::Add_ok)    { ++num_bytes_written; },
+			[&] (Ring_buffer::Add_error) { error = true; }
+		);
 
 	_cross_num_bytes_avail += num_bytes_written;
 	_partner.cross_write();

repos/os/src/server/terminal_crosslink/terminal_session_component.h

@@ -5,7 +5,7 @@
  */
 
 /*
- * Copyright (C) 2012-2017 Genode Labs GmbH
+ * Copyright (C) 2012-2024 Genode Labs GmbH
  *
  * This file is part of the Genode OS framework, which is distributed
  * under the terms of the GNU Affero General Public License version 3.
@@ -15,17 +15,113 @@
 #define _TERMINAL_SESSION_COMPONENT_H_
 
 /* Genode includes */
+#include <base/heap.h>
 #include <base/rpc_server.h>
 #include <base/attached_ram_dataspace.h>
-#include <os/ring_buffer.h>
 #include <terminal_session/terminal_session.h>
 
 namespace Terminal_crosslink {
 
 	using namespace Genode;
 
-	enum { STACK_SIZE = sizeof(addr_t)*1024 };
-	enum { BUFFER_SIZE = 4096 };
+	static constexpr size_t IO_BUFFER_SIZE = 4096;
+
+	class Ring_buffer
+	{
+		private:
+
+			size_t _head = 0;
+			size_t _tail = 0;
+
+			char *_queue { };
+
+			size_t _queue_size;
+
+			/*
+			 * Noncopyable
+			 */
+			Ring_buffer(Ring_buffer const &);
+			Ring_buffer &operator = (Ring_buffer const &);
+
+		public:
+
+			/**
+			 * Constructor
+			 */
+			Ring_buffer(Byte_range_ptr const &buffer)
+			: _queue(buffer.start), _queue_size(buffer.num_bytes) { }
+
+			struct     Add_ok    { };
+			enum class Add_error { OVERFLOW };
+
+			using Add_result = Attempt<Add_ok, Add_error>;
+
+			/**
+			 * Place element into ring buffer
+			 */
+			Add_result add(char ev)
+			{
+				if ((_head + 1)%_queue_size != _tail) {
+					_queue[_head] = ev;
+					_head = (_head + 1)%_queue_size;
+					return Add_ok();
+				} else
+					return Add_error::OVERFLOW;
+			}
+
+			/**
+			 * Take element from ring buffer
+			 *
+			 * \return  element
+			 */
+			char get()
+			{
+				unsigned char e = _queue[_tail];
+				_tail = (_tail + 1)%_queue_size;
+				return e;
+			}
+
+			/**
+			 * Return true if ring buffer is empty
+			 */
+			bool empty() const { return _tail == _head; }
+	};
+
+
+	class Allocated_ring_buffer : public Ring_buffer
+	{
+		private:
+
+			Genode::Allocator &_alloc;
+
+			char *_buffer { };
+
+			char *_init_buffer(Genode::Allocator &alloc, size_t size)
+			{
+				_buffer = static_cast<char*>(alloc.alloc(size));
+				return _buffer;
+			};
+
+			/*
+			 * Noncopyable
+			 */
+			Allocated_ring_buffer(Allocated_ring_buffer const &);
+			Allocated_ring_buffer &operator = (Allocated_ring_buffer const &);
+
+		public:
+
+			Allocated_ring_buffer(Genode::Allocator &alloc, size_t queue_size)
+			: Ring_buffer(Byte_range_ptr(_init_buffer(alloc, queue_size),
+			                             queue_size)),
+			  _alloc(alloc)
+			{ }
+
+			~Allocated_ring_buffer()
+			{
+				destroy(_alloc, _buffer);
+			}
+	};
+
 
 	class Session_component : public Rpc_object<Terminal::Session,
 	                                            Session_component>
@@ -33,15 +129,17 @@ namespace Terminal_crosslink {
 		private:
 
 			Env                        &_env;
+			Heap                        _alloc { _env.ram(), _env.rm() };
 
 			Session_component          &_partner;
+
+			size_t                      _buffer_size;
+
 			Genode::Session_capability  _session_cap;
 
 			Attached_ram_dataspace      _io_buffer;
 
-			typedef Genode::Ring_buffer<unsigned char, BUFFER_SIZE+1> Local_buffer;
-
-			Local_buffer                _buffer { };
+			Allocated_ring_buffer       _buffer { _alloc, _buffer_size + 1 };
 			size_t                      _cross_num_bytes_avail;
 			Signal_context_capability   _read_avail_sigh { };
 
@@ -50,7 +148,8 @@ namespace Terminal_crosslink {
 			/**
 			 * Constructor
 			 */
-			Session_component(Env &env, Session_component &partner);
+			Session_component(Env &env, Session_component &partner,
+			                  size_t buffer_size);
 
 			Session_capability cap();