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251 lines
7.4 KiB
C++
251 lines
7.4 KiB
C++
/*
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* \brief Generic root component implementation
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* \author Norman Feske
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* \date 2006-05-22
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*
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* This class is there for your convenience. It performs the common actions
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* that must always be taken when creating a new session.
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*/
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/*
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* Copyright (C) 2006-2012 Genode Labs GmbH
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*
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* This file is part of the Genode OS framework, which is distributed
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* under the terms of the GNU General Public License version 2.
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*/
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#ifndef _INCLUDE__ROOT__COMPONENT_H_
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#define _INCLUDE__ROOT__COMPONENT_H_
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#include <root/root.h>
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#include <base/rpc_server.h>
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#include <base/heap.h>
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#include <ram_session/ram_session.h>
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#include <util/arg_string.h>
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#include <base/printf.h>
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namespace Genode {
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/**
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* Session creation policy for a single-client service
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*/
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class Single_client
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{
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private:
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bool _used;
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public:
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Single_client() : _used(0) { }
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void aquire(const char *args)
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{
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if (_used)
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throw Root::Unavailable();
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_used = true;
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}
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void release() { _used = false; }
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};
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/**
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* Session-creation policy for a multi-client service
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*/
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struct Multiple_clients
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{
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void aquire(const char *args) { }
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void release() { }
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};
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/**
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* Template for implementing the root interface
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*
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* \param SESSION_TYPE session-component type to manage,
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* derived from 'Rpc_object'
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* \param POLICY session-creation policy
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*
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* The 'POLICY' template parameter allows for constraining the session
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* creation to only one instance at a time (using the 'Single_session'
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* policy) or multiple instances (using the 'Multiple_sessions' policy).
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*
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* The 'POLICY' class must provide the following two functions:
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*
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* :'aquire(const char *args)': is called with the session arguments
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* at creation time of each new session. It can therefore implement
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* a session-creation policy taking session arguments into account.
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* If the policy denies the creation of a new session, it throws
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* one of the exceptions defined in the 'Root' interface.
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*
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* :'release': is called at the destruction time of a session. It enables
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* the policy to keep track of and impose restrictions on the number
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* of existing sessions.
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*
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* The default policy 'Multiple_clients' imposes no restrictions on the
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* creation of new sessions.
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*/
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template <typename SESSION_TYPE, typename POLICY = Multiple_clients>
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class Root_component : public Rpc_object<Typed_root<SESSION_TYPE> >, private POLICY
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{
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private:
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/*
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* Entry point that manages the session objects
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* created by this root interface
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*/
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Rpc_entrypoint *_ep;
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/*
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* Allocator for allocating session objects.
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* This allocator must be used by the derived
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* class when calling the 'new' operator for
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* creating a new session.
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*/
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Allocator *_md_alloc;
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protected:
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/**
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* Create new session (to be implemented by a derived class)
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*
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* Only a derived class knows the constructor arguments of
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* a specific session. Therefore, we cannot unify the call
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* of its 'new' operator and must implement the session
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* creation at a place, where the required knowledge exist.
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*
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* In the implementation of this function, the heap, provided
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* by 'Root_component' must be used for allocating the session
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* object.
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*
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* \throw Allocator::Out_of_memory typically caused by the
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* meta-data allocator
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* \throw Root::Invalid_args typically caused by the
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* session-component constructor
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*/
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virtual SESSION_TYPE *_create_session(const char *args) = 0;
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/**
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* Inform session about a quota upgrade
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*
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* Once a session is created, its client can successively extend
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* its quota donation via the 'Parent::transfer_quota' function.
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* This will result in the invokation of 'Root::upgrade' at the
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* root interface the session was created with. The root interface,
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* in turn, informs the session about the new resources via the
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* '_upgrade_session' function. The default implementation is
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* suited for sessions that use a static amount of resources
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* accounted for at session-creation time. For such sessions, an
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* upgrade is not useful. However, sessions that dynamically
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* allocate resources on behalf of its client, should respond to
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* quota upgrades by implementing this function.
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*
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* \param session session to upgrade
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* \param args description of additional resources in the
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* same format as used at session creation
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*/
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virtual void _upgrade_session(SESSION_TYPE *session, const char *args) { }
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virtual void _destroy_session(SESSION_TYPE *session) {
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destroy(_md_alloc, session); }
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/**
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* Return allocator to allocate server object in '_create_session()'
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*/
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Allocator *md_alloc() { return _md_alloc; }
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Rpc_entrypoint *ep() { return _ep; }
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public:
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/**
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* Constructor
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*
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* \param ep entry point that manages the sessions of this
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* root interface.
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* \param ram_session provider of dataspaces for the backing store
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* of session objects and session data
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*/
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Root_component(Rpc_entrypoint *ep, Allocator *metadata_alloc)
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: _ep(ep), _md_alloc(metadata_alloc) { }
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/********************
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** Root interface **
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********************/
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Session_capability session(Root::Session_args const &args)
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{
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if (!args.is_valid_string()) throw Root::Invalid_args();
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POLICY::aquire(args.string());
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/*
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* We need to decrease 'ram_quota' by
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* the size of the session object.
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*/
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size_t ram_quota = Arg_string::find_arg(args.string(), "ram_quota").long_value(0);
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size_t const remaining_ram_quota = ram_quota - sizeof(SESSION_TYPE) -
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md_alloc()->overhead(sizeof(SESSION_TYPE));
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if (remaining_ram_quota < 0) {
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PERR("Insufficient ram quota, provided=%zd, required=%zd",
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ram_quota, sizeof(SESSION_TYPE) + md_alloc()->overhead(sizeof(SESSION_TYPE)));
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throw Root::Quota_exceeded();
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}
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/*
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* Deduce ram quota needed for allocating the session object from the
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* donated ram quota.
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*
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* XXX the size of the 'adjusted_args' buffer should dependent
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* on the message-buffer size and stack size.
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*/
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enum { MAX_ARGS_LEN = 256 };
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char adjusted_args[MAX_ARGS_LEN];
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strncpy(adjusted_args, args.string(), sizeof(adjusted_args));
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char ram_quota_buf[64];
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snprintf(ram_quota_buf, sizeof(ram_quota_buf), "%zd",
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remaining_ram_quota);
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Arg_string::set_arg(adjusted_args, sizeof(adjusted_args),
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"ram_quota", ram_quota_buf);
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SESSION_TYPE *s = 0;
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try { s = _create_session(adjusted_args); }
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catch (Allocator::Out_of_memory) { throw Root::Quota_exceeded(); }
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return _ep->manage(s);
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}
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void upgrade(Session_capability session, Root::Upgrade_args const &args)
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{
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if (!args.is_valid_string()) throw Root::Invalid_args();
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SESSION_TYPE *s =
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dynamic_cast<SESSION_TYPE *>(_ep->obj_by_cap(session));
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if (!s) return;
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_upgrade_session(s, args.string());
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}
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void close(Session_capability session)
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{
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SESSION_TYPE *s =
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dynamic_cast<SESSION_TYPE *>(_ep->obj_by_cap(session));
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if (!s) return;
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/* let the entry point forget the session object */
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_ep->dissolve(s);
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_destroy_session(s);
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POLICY::release();
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return;
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}
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};
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}
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#endif /* _INCLUDE__ROOT__COMPONENT_H_ */
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