vfs,libc: introduce Vfs::Env::User interface

The new interface is meant to replace the 'Vfs::Io_response_handler'.
In contrast to the 'Io_response_handler', which had to be called
on a 'Vfs_handle', the new interface does not require any specific
'Vfs_handle'. It is merely meant to prompt the VFS user (like the libc)
to re-attempt stalled I/O operations but it does not provide any
immediate hint, about which of the handles have become ready for
reading/writing.

Issue #4697

repos/libports/src/lib/libc/internal/env.h

@@ -64,8 +64,11 @@ class Libc::Env_implementation : public Libc::Env, public Config_accessor
 
 	public:
 
-		Env_implementation(Genode::Env &env, Genode::Allocator &alloc)
-		: _env(env), _vfs_env(_env, alloc, _vfs_config()) { }
+		Env_implementation(Genode::Env &env, Genode::Allocator &alloc,
+		                   Vfs::Env::User &vfs_user)
+		:
+			_env(env), _vfs_env(_env, alloc, _vfs_config(), vfs_user)
+		{ }
 
 		Vfs::File_system &vfs() { return _vfs_env.root_dir(); }
 

repos/libports/src/lib/libc/internal/kernel.h

@@ -151,7 +151,24 @@ struct Libc::Kernel final : Vfs::Io_response_handler,
 		 */
 		void reset_malloc_heap() override;
 
-		Env_implementation _libc_env { _env, _heap };
+		/* io_progress_handler marker */
+		bool _io_progressed = false;
+
+		struct Vfs_user : Vfs::Env::User
+		{
+			bool &_io_progressed;
+
+			Vfs_user(bool &io_progressed) : _io_progressed(io_progressed) { }
+
+			void wakeup_vfs_user() override
+			{
+				_io_progressed = true;
+			}
+		};
+
+		Vfs_user _vfs_user { _io_progressed };
+
+		Env_implementation _libc_env { _env, _heap, _vfs_user };
 
 		bool const _update_mtime = _libc_env.libc_config().attribute_value("update_mtime", true);
 
@@ -205,9 +222,6 @@ struct Libc::Kernel final : Vfs::Io_response_handler,
 		jmp_buf _user_context;
 		bool    _valid_user_context          = false;
 
-		/* io_progress_handler marker */
-		bool _io_progressed { false };
-
 		Thread &_myself { *Thread::myself() };
 
 		addr_t _kernel_stack = Thread::mystack().top;

repos/os/include/vfs/env.h

@@ -60,6 +60,20 @@ struct Vfs::Env : Interface
 	};
 
 	virtual Io &io() = 0;
+
+	/**
+	 * Interface for notifying the VFS user about possible progress
+	 *
+	 * This interface allows VFS plugins to prompt the potential unblocking of
+	 * the VFS user, e.g., continuing a write operation that was stalled
+	 * because of a saturated I/O buffer.
+	 */
+	struct User : Interface, Genode::Noncopyable
+	{
+		virtual void wakeup_vfs_user() = 0;
+	};
+
+	virtual User &user() = 0;
 };
 
 #endif /* _INCLUDE__VFS__ENV_H_ */

repos/os/include/vfs/simple_env.h

@@ -22,12 +22,13 @@
 namespace Vfs { struct Simple_env; }
 
 
-class Vfs::Simple_env : public Vfs::Env, private Vfs::Env::Io
+class Vfs::Simple_env : public Vfs::Env, private Vfs::Env::Io, private Vfs::Env::User
 {
 	private:
 
 		Genode::Env       &_env;
 		Genode::Allocator &_alloc;
+		Vfs::Env::User    &_user;
 
 		Global_file_system_factory _fs_factory { _alloc };
 
@@ -41,9 +42,15 @@ class Vfs::Simple_env : public Vfs::Env, private Vfs::Env::Io
 
 		Simple_env(Genode::Env       &env,
 		           Genode::Allocator &alloc,
-		           Genode::Xml_node   config)
+		           Genode::Xml_node   config,
+		           Vfs::Env::User    &user)
 		:
-			_env(env), _alloc(alloc), _root_dir(*this, config, _fs_factory)
+			_env(env), _alloc(alloc), _user(user), _root_dir(*this, config, _fs_factory)
+		{ }
+
+		Simple_env(Genode::Env &env, Genode::Allocator &alloc, Genode::Xml_node config)
+		:
+			Simple_env(env, alloc, config, *this)
 		{ }
 
 		void apply_config(Genode::Xml_node const &config)
@@ -56,6 +63,7 @@ class Vfs::Simple_env : public Vfs::Env, private Vfs::Env::Io
 		Vfs::File_system  &root_dir()         override { return _root_dir; }
 		Deferred_wakeups  &deferred_wakeups() override { return _deferred_wakeups; }
 		Vfs::Env::Io      &io()               override { return *this; }
+		Vfs::Env::User    &user()             override { return _user; }
 
 		/**
 		 * Vfs::Env::Io interface
@@ -70,6 +78,14 @@ class Vfs::Simple_env : public Vfs::Env, private Vfs::Env::Io
 			_deferred_wakeups.trigger();
 			_env.ep().wait_and_dispatch_one_io_signal();
 		}
+
+		/**
+		 * Vfs::Env::User interface
+		 *
+		 * Fallback implementation used if no 'user' is specified at
+		 * construction time.
+		 */
+		void wakeup_vfs_user() override { };
 };
 
 #endif /* _INCLUDE__VFS__SIMPLE_ENV_H_ */