genode/repos/os/include/audio_in_session/connection.h
Norman Feske 9cba459958 base: remove Child::heap
This patch improves the accounting for the backing store of
session-state meta data. Originally, the session state used to be
allocated by a child-local heap partition fed from the child's RAM
session. However, whereas this approach was somehow practical from a
runtime's (parent's) point of view, the child component could not count
on the quota in its own RAM session. I.e., if the Child::heap grew at
the parent side, the child's RAM session would magically diminish. This
caused two problems. First, it violates assumptions of components like
init that carefully manage their RAM resources (and giving most of them
away their children). Second, if a child transfers most of its RAM
session quota to another RAM session (like init does), the child's RAM
session may actually not allow the parent's heap to grow, which is a
very difficult error condition to deal with.

In the new version, there is no Child::heap anymore. Instead, session
states are allocated from the runtime's RAM session. In order to let
children pay for these costs, the parent withdraws the local session
costs from the session quota donated from the child when the child
initiates a new session. Hence, in principle, all components on the
route of the session request take a small bite from the session quota to
pay for their local book keeping

Consequently, the session quota that ends up at the server may become
depleted more or less, depending on the route. In the case where the
remaining quota is insufficient for the server, the server responds with
'QUOTA_EXCEEDED'. Since this behavior must generally be expected, this
patch equips the client-side 'Env::session' implementation with the
ability to re-issue session requests with successively growing quota
donations.

For several of core's services (ROM, IO_MEM, IRQ), the default session
quota has now increased by 2 KiB, which should suffice for session
requests to up to 3 hops as is the common case for most run scripts. For
longer routes, the retry mechanism as described above comes into effect.
For the time being, we give a warning whenever the server-side quota
check triggers the retry mechanism. The warning may eventually be
removed at a later stage.
2017-02-28 12:59:23 +01:00

52 lines
1.3 KiB
C++

/*
* \brief Connection to Audio_in service
* \author Josef Soentgen
* \date 2015-05-08
*/
/*
* Copyright (C) 2015 Genode Labs GmbH
*
* This file is part of the Genode OS framework, which is distributed
* under the terms of the GNU General Public License version 2.
*/
#ifndef _INCLUDE__AUDIO_IN_SESSION__CONNECTION_H_
#define _INCLUDE__AUDIO_IN_SESSION__CONNECTION_H_
#include <audio_in_session/client.h>
#include <base/connection.h>
#include <base/allocator.h>
namespace Audio_in { struct Connection; }
struct Audio_in::Connection : Genode::Connection<Session>, Audio_in::Session_client
{
/**
* Issue session request
*
* \noapi
*/
Capability<Audio_in::Session> _session(Genode::Parent &parent, char const *channel)
{
return session(parent, "ram_quota=%ld, channel=\"%s\"",
10*1024 + sizeof(Stream), channel);
}
/**
* Constructor
*
* \param progress_signal install progress signal, the client may then
* call 'wait_for_progress', which is sent when the
* server processed one or more packets
*/
Connection(Genode::Env &env, char const *channel, bool progress_signal = false)
:
Genode::Connection<Session>(env, _session(env.parent(), channel)),
Session_client(env.rm(), cap(), progress_signal)
{ }
};
#endif /* _INCLUDE__AUDIO_IN_SESSION__CONNECTION_H_ */