dbus+policykit初级hello world应用
因为Ylmf os要做的好用，操作习惯上更像windows。所以，跟其他发行版不一样。很多时候需要root权限的时候。我们的程序就自动的提升权限进行操作。以免用户输入密码。这样做也用弊端。如果一个恶意的程序获得了这个权限。就会造成很严重的后果。
我们用dbus来进行这个权限的提升操作。其实dbus是一个消息总线。具体不展开来说。要了解请自行google。我们写了一个叫ylmfdbus的一个dbus服务。这个服务设计成可插拔的。如果我有一个新的程序中某一个模块需要在root权限下执行。就需要把这个功能抽象的写成一个GObject类。然后注册到ylmfdbus里面。我们就可以通过调用dbus的方法来在root下执行这个函数，或者模块。在执行这个被提权的函数时候，为了防止被恶意操作，我们加入policykit验证，在每次GObject方法调用的时候现调用policykit。
接下来，我们开始进行打怪升级。
我们现看看已有装备：
[Dbus相关]
ylmf-dbus-global-defines.h
com.ylmf.DBusGlib.conf
com.ylmf.DBusGlib.service
service-main.c
[PolicyKit相关]
policykit-ylmf.c
policykit-ylmf.h
com.ylmf.PolicyKit.policy
[Makefile]
Makefile
com.ylmf.DBusGlib.service这个文件很简单。就配置了一下我们服务的路径。这里已经配置好了，不用去管它。这件装备已经是顶级了。
com.ylmf.DBusGlib.conf这个文件是dbus服务的配置文件。如果我们需要添加了新的对象。要在里面配置一个新的路径。这个路径的作用是跟namespace的作用一样的。这里约定用com.ylmf.dbus.xxxx来命名。也就是说，如果你只是添加了一个对象。这个文件只用添加一行。说明路径就好了。
ylmf-dbus-global-defines.h用来宏定义的公共文件，每一个对象要定义两个东西。一个是object path,一个是object interface。也只有一个地方用到在main函数里面注册。注意，这里的object path要跟com.ylmf.DBusGlib.conf里面的path一样哦。
service-main.c就是我们ylmfdbus的main。很简单，自身只带了一个注册函数。
Makefile。每当我们新写了一个object。要相应的想里面添加内容。后面会详细说明。
文件policykit-ylmf.c是验证函数的实现，在我们注册的GOboject类里面，我们只用在开头#include policykit-ylmf.h调用里面的check_auth()方法就ok了。
com.ylmf.PolicyKit.policy这个文件是公共的权限说明文件。在它里面定义了你每一个动作(action)的id，说明，消息，权限等等信息。本来可以都用一个。但是为了代码的易懂。希望每一个函数都对应一个动作（action）。
以上是我们ylmfdbus已经有的装备。现在，我们来看怎么要写一个自己的object并且注册进去。
普通的gobject一般只用头文件和c文件。我们要写一个能注册到ylmfdbus里面的gobject需要多一些的内容。多出两个文件。一个xml用来描述方法然后通过dbus-binding-tool转换成一个xxx-glue.h约定的头文件。一个list文件通过glib-genmarshal来生成一个xxx-marshal.c文件，用来连接gobject的信号类型的c文件。
接下来说说gobject文件里面多的东西。
一个完整最小的类（hello world）应该包含以下东西：
/* helloworld.h */
#ifndef __HELLO_WORLD_H_
#define __HELLO_WORLD_H_
#include <glib-object.h>
G_BEGIN_DECLS
#define HELLO_WORLD_TYPE (hello_world_get_type())
#define HELLO_WORLD(o) (G_TYPE_CHECK_INSTANCE_CAST((o),HELLO_WORLD_TYPE,HelloWorld))
#define HELLO_WORLD_CLASS(o) (G_TYPE_CHECK_CLASS_CAST((o),HELLO_WORLD_TYPE,HelloWorldClass))
#define HELLO_WORLD_GET_CLASS(o) (G_TYPE_INSTANCE_GET_CLASS ((o), HELLO_WORLD_TYPE, HelloWorldClass))
#define IS_HELLO_WORLD(o) (G_TYPE_CHECK_INSTANCE_TYPE ((o), HELLO_WORLD_TYPE))
#define IS_HELLO_WORLD_CLASS(o) (G_TYPE_CHECK_CLASS_TYPE ((o), HELLO_WORLD_TYPE))
typedef struct _HelloWorld HelloWorld;
typedef struct _HelloWorldClass HelloWorldClass;
struct _HelloWorld
{
GObject parent;
};
struct _HelloWorldClass
{
GObjectClass parent_class;
};
GType
hello_world_get_type(void);
G_END_DECLS
#endif //__HELLO_WORLD_H_
/* helloworld.c */
#ifdef HAVE_CONFIG_H
# include <config.h>
#endif
#include <glib.h>
#include "helloworld.h"
static void
hello_world_finalize(GObject *object);
static GObject*
hello_world_constructor(GType type,
guint n_construct_properties,
GObjectConstructParam *construct_properties);
G_DEFINE_TYPE(HelloWorld,hello_world,G_TYPE_OBJECT)
static void
hello_world_class_init(HelloWorldClass *klass)
{
GObjectClass *object_class= G_OBJECT_CLASS(klass);
object_class->constructor = hello_world_constructor;
object_class->finalize = hello_world_finalize;
}
static void
hello_world_init(HelloWorld *objname)
{
}
static GObject*
hello_world_constructor(GType type,
guint n_construct_properties,
GObjectConstructParam *construct_properties)
{
GObject *object;
HelloWorld *objname;
object = G_OBJECT_CLASS(hello_world_parent_class)->constructor(
type,
n_construct_properties,
construct_properties);
objname = HELLO_WORLD(object);
return object;
}
static void
hello_world_finalize(GObject *object)
{
HelloWorld *objname;
objname = HELLO_WORLD(object);
if(G_OBJECT_CLASS(hello_world_parent_class)->finalize){
G_OBJECT_CLASS(hello_world_parent_class)->finalize(object);
}
}
HelloWorld*
hello_world_new(void)
{
return HELLO_WORLD(g_object_new(HELLO_WORLD_TYPE,NULL));
}
我们应该注意到我们的helloworld类的有一个统一的前缀"hello_world"这个很重要。在我们用dbus-binding-tool和glib-genmarshal工具来自动生成代码的时候加参数的时候要是一样的。其次是描述接口的xml文件中标签<method name="">这里填写的是方法名的后缀。开头用大写。然后自己要在类里面实现这个方法。这个是基本的一个GObject对象，我们可以在后面写其他的方法了。在写其他方法的时候，我们必需要注意每一个方法有两个参数是固定的。第一个参数是这个对象本身的指针，最后一个参数是DBusGMethodInvocation类型的指针，这两个参数必须有。如果有其他的输入输出函数则需要在描述接口的xml文件中进行描述，描述接口的xml文件中每一个方法必须添加 <annotation name="org.freedesktop.DBus.GLib.Async" value=""/>
例子：在xml里面写的是HelloWorld 然后前缀是ylmf_xxxx 生成的xxx-glue.h文件里面的方法名就是ylmf_xxxx_hello_world。
dbus-binding-tool --prefix= --mode=glib-server --output=xxx-glue.h xxx.xml
dbus-binding-tool --prefix=auto_login --mode-glib-server --output=auto-login-glue.h login.xml
然后在我们的类的c文件里面需要include xxxx-glue.h文件的时候。注意不要写到文件开头。要写到函数定义完实现具体函数前.
最后需要注意的地方 是我们在xxxx__class_init方法里面需要添加 dbus_g_object_type_install_info函数用来在注册的时候使得dbus认识这个object
如果每一个方法中有首先第一个传入参数必须是这个类本身，然后后面跟入需要传入的参数，并且在xml文件里面描述。如果需要返回，最好传入DBusGMethodInvocation这个类型。然后调用dbus_g_method_return来进行函数的调用
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2011年9月01日 23:12
弱弱一个建议，以后注意通用性而不要局限于某distro（特定程序除外），像这个，我们似乎可以直接用 org.FreeDesktop.PolicyKit1 这个接口。
2011年9月02日 11:52
@Mike Manilone:
愿闻其详。。我对dbus不是很了解。
2011年9月03日 23:01
@Yu: 也只是对dbus摸了一下而已。。。不过限定某单一发行版确实令人反感。
最佳方法也许是直接用 polkit 的 C 接口？
2011年9月03日 23:53
@Mike Manilone: ^_^ 这个 你其实 没看懂。。就是写了一个通用的。。可插拔的（xe了。。。）。 只是 前面 我说了 背景。 org.FreeDesktop.PolicyKit1 我看了 貌似可以实现 我想要的功能。 懒了。。没有去深入的看。
2011年9月03日 23:54
@Mike Manilone: ylmf这个关键字 在里面 只是一个名称而已 可以随便改的。
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