hooks.h 2.75 KB
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// Copyright (C) 2013-2020 Internet Systems Consortium, Inc. ("ISC")
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//
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// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at http://mozilla.org/MPL/2.0/.
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#ifndef HOOKS_H
#define HOOKS_H

#include <hooks/callout_handle.h>
#include <hooks/library_handle.h>

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namespace {

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// Version 20 of the hooks framework, set for Kea 1.7.10
const int KEA_HOOKS_VERSION = 20;
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// Names of the framework functions.
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const char* const LOAD_FUNCTION_NAME = "load";
const char* const UNLOAD_FUNCTION_NAME = "unload";
const char* const VERSION_FUNCTION_NAME = "version";
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const char* const MULTI_THREADING_COMPATIBLE_FUNCTION_NAME =
    "multi_threading_compatible";
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// Typedefs for pointers to the framework functions.
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typedef int (*version_function_ptr)();
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typedef int (*load_function_ptr)(isc::hooks::LibraryHandle&);
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typedef int (*unload_function_ptr)();
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typedef int (*multi_threading_compatible_function_ptr)();
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} // Anonymous namespace

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namespace isc {
namespace hooks {

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/// @brief User-Library Initialization for Statically-Linked Kea
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///
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/// If Kea is statically-linked, a user-created hooks library will not be
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/// able to access symbols in it.  In particular, it will not be able to access
/// singleton objects.
///
/// The hooks framework handles some of this.  For example, although there is
/// a singleton ServerHooks object, hooks framework objects store a reference
/// to it when they are created.  When the user library needs to register a
/// callout (which requires access to the ServerHooks information), it accesses
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/// the ServerHooks object through a pointer passed from the Kea image.
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///
/// The logging framework is more problematical. Here the code is partly
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/// statically linked (the Kea logging library) and partly shared (the
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/// log4cplus).  The state of the former is not accessible to the user library,
/// but the state of the latter is.  So within the user library, we need to
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/// initialize the Kea logging library but not initialize the log4cplus
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/// code.  Some of the initialization is done when the library is loaded, but
/// other parts are done at run-time.
///
/// This function - to be called by the user library code in its load() function
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/// when running against a statically linked Kea - initializes the Kea
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/// logging library.  In particular, it loads the message dictionary with the
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/// text of the Kea messages.
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///
/// @note This means that the virtual address space is loaded with two copies
/// of the message dictionary.  Depending on how the user libraries are linked,
/// loading multiple user libraries may involve loading one message dictionary
/// per library.

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void hooksStaticLinkInit();
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} // namespace hooks
} // namespace isc

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#endif  // HOOKS_H