kernel_objects.html

ADI 公司blackfin系列的用户使用文挡。

<p>
 A Kset belongs to a subsystem, it has a type, a list of members and
</p>
<pre class="code"> also contains a kobject of its own.</pre>

<p>
 Ksets also participate in helping with hotplug operations by
</p>
<pre class="code"> specifying a hotplug name and adding items to the hotplug helper's
  environment.</pre>
<pre class="code c">&nbsp;
   <span class="kw4">struct</span> kset <span class="br0">&#123;</span>
        <span class="kw4">struct</span> subsystem        * subsys;
        <span class="kw4">struct</span> kobj_type        * ktype;
        <span class="kw4">struct</span> list_head        list;
        <span class="kw4">struct</span> kobject          kobj;
        <span class="kw4">struct</span> kset_hotplug_ops * hotplug_ops;
   <span class="br0">&#125;</span>;
&nbsp;</pre>
</div>
<!-- SECTION [5640-6170] -->
<h3><a name="ktype_overview" id="ktype_overview">Ktype Overview</a></h3>
<div class="level3">

<p>
 A Ktype defines the show and store operations that can be performed on the objectit also sets up the default attributes for the object.
</p>
<pre class="code c">&nbsp;
   <span class="kw4">struct</span> kobj_type <span class="br0">&#123;</span>
        <span class="kw4">void</span> <span class="br0">&#40;</span>*release<span class="br0">&#41;</span><span class="br0">&#40;</span><span class="kw4">struct</span> kobject *<span class="br0">&#41;</span>;
        <span class="kw4">struct</span> sysfs_ops        * sysfs_ops; <span class="co1">// just show and store</span>
        <span class="kw4">struct</span> attribute        ** default_attrs;
   <span class="br0">&#125;</span>;
&nbsp;</pre>
</div>
<!-- SECTION [6171-6542] -->
<h3><a name="subsystem_overview" id="subsystem_overview">Subsystem Overview</a></h3>
<div class="level3">

<p>
 This is a base level system it has a kset whose kobject allows the subsystem to be placed in the system hierarchy properly.
</p>
<pre class="code">

   struct subsystem {
        struct kset             kset;
        struct rw_semaphore     rwsem;
   };

</pre>

</div>
<!-- SECTION [6543-6821] -->
<h3><a name="confused" id="confused">Confused ??</a></h3>
<div class="level3">

<p>
An example will show the basic mechanics of setting up a small subsystem. 
</p>
<ul>
<li class="level1"><div class="li"> Remember Kobjects determine the position in the file system</div>
</li>
<li class="level1"><div class="li"> The KSET glues a kset to a subsystem</div>
</li>
</ul>

</div>
<!-- SECTION [6822-7032] -->
<h2><a name="kernel_object_sysfs_example" id="kernel_object_sysfs_example">Kernel Object / Sysfs Example</a></h2>
<div class="level2">

<p>
The example discussed will show the basics of setting up a subsystem of a single type of object with attributes.
</p>

</div>

<h4><a name="the_computer_object" id="the_computer_object">The Computer Object</a></h4>
<div class="level4">

<p>
The important kernel entity here is the kobject, the attributes are
</p>
<pre class="code"> defined by the use of the object.</pre>
<pre class="code c"><span class="co1">//</span>
<span class="co1">// Step 1 define an object</span>
<span class="co1">//</span>
   <span class="kw4">struct</span> computer <span class="br0">&#123;</span>
       <span class="kw4">struct</span> kobject kobj;  <span class="co1">// contains the name is also the directory entry</span>
&nbsp;
       <span class="co1">// user defined attributes follow</span>
       <span class="kw4">char</span> make<span class="br0">&#91;</span><span class="nu0">16</span><span class="br0">&#93;</span>;
       <span class="kw4">char</span> ip<span class="br0">&#91;</span><span class="nu0">16</span><span class="br0">&#93;</span>;
       <span class="kw4">int</span> speed;
       <span class="kw4">int</span> capacity;
       <span class="kw4">int</span> used;
   <span class="br0">&#125;</span>;
&nbsp;</pre>
</div>

<h4><a name="define_the_attributes" id="define_the_attributes">Define the attributes</a></h4>
<div class="level4">

<p>
The attributes of the object will appear as regular files
</p>
<pre class="code">  permissions and names need to be set at this stage.
  The only other element in the attribute structure is the
  module owner.</pre>

<p>
Note that no show / store access functions are defined in basic attributes.
</p>
<pre class="code c"><span class="co1">//</span>
<span class="co1">// Step 2 define its attributes</span>
<span class="co1">//</span>
<span class="co2">#define COM_MODE ( S_IRUGO | S_IWUGO )</span>
<span class="kw4">static</span> <span class="kw4">struct</span> attribute computer_attr_make =<span class="br0">&#123;</span>.<span class="me1">name</span>=<span class="st0">"make"</span>,.<span class="me1">mode</span>=COM_MODE <span class="br0">&#125;</span>;
<span class="kw4">static</span> <span class="kw4">struct</span> attribute computer_attr_ip   =<span class="br0">&#123;</span>.<span class="me1">name</span>=<span class="st0">"ip"</span>,  .<span class="me1">mode</span>=COM_MODE <span class="br0">&#125;</span>;
<span class="kw4">static</span> <span class="kw4">struct</span> attribute computer_attr_speed=<span class="br0">&#123;</span>.<span class="me1">name</span>=<span class="st0">"speed"</span>,.<span class="me1">mode</span>=COM_MODE <span class="br0">&#125;</span>;
<span class="kw4">static</span> <span class="kw4">struct</span> attribute computer_attr_capacity=<span class="br0">&#123;</span>.<span class="me1">name</span>=<span class="st0">"capacity"</span>,.<span class="me1">mode</span>=COM_MODE<span class="br0">&#125;</span>;
<span class="kw4">static</span> <span class="kw4">struct</span> attribute computer_attr_used = <span class="br0">&#123;</span>.<span class="me1">name</span>=<span class="st0">"used"</span>,.<span class="me1">mode</span>=COM__MODE <span class="br0">&#125;</span>;
<span class="co1">//</span>
<span class="co1">//</span>
<span class="co1">// Now build an attribute structure as a null terminated list</span>
<span class="co1">//</span>
<span class="kw4">static</span> <span class="kw4">struct</span> attribute* computer_default_attrs<span class="br0">&#91;</span><span class="br0">&#93;</span> = <span class="br0">&#123;</span>
    &amp;computer_attr_make,
    &amp;computer_attr_ip,
    &amp;computer_attr_speed,
    &amp;computer_attr_capacity,
    &amp;computer_attr_used,
    <span class="kw2">NULL</span>
<span class="br0">&#125;</span>;
&nbsp;</pre>
</div>

<h4><a name="define_the_object_type" id="define_the_object_type">Define the object type</a></h4>
<div class="level4">

<p>
 The sysfs_ops table will contain the show and store routines
</p>

<p>
The release routine will tell the system how to remove the object.
</p>

<p>
The type also defines the default attributes for the object.
</p>
<pre class="code c">&nbsp;
<span class="co1">//</span>
<span class="co1">// Now we can define the type</span>
<span class="co1">//</span>
<span class="kw4">static</span> <span class="kw4">struct</span> kobj_type computer_ktype = <span class="br0">&#123;</span>
    .<span class="me1">release</span> = computer_release,
    .<span class="me1">sysfs_ops</span> = &amp;computer_sysfs_ops,
    .<span class="me1">default_attrs</span> = computer_default_attrs
<span class="br0">&#125;</span>;
&nbsp;</pre>
</div>

<h4><a name="define_the_subsystem_type" id="define_the_subsystem_type">Define the subsystem  type</a></h4>
<div class="level4">

<p>
 The subsystem type simply contains the notifier and clean up routine used when the system is deleted.
</p>

<p>
Again the sysfs_ops table will contain the show and store routines
</p>

<p>
The release routine will tell the system how to remove the object.
</p>

<p>
The type also defines the default attributes for th object.
</p>
<pre class="code c">&nbsp;
<span class="kw4">static</span> <span class="kw4">struct</span> kobj_type sysfs_computer_ktype = <span class="br0">&#123;</span>
    .<span class="me1">release</span> = sysfs_computer_release,
    .<span class="me1">sysfs_ops</span> = <span class="kw2">NULL</span>,
    .<span class="me1">default_attrs</span> = <span class="kw2">NULL</span>
<span class="br0">&#125;</span>;
&nbsp;</pre>
</div>

<h4><a name="define_the_set" id="define_the_set">Define the Set</a></h4>
<div class="level4">

<p>
 In this example a static definition is used for a set.
</p>

<p>
All the generated objects will be added to this set which will also be used  by the subsystem to find its components.
</p>
<pre class="code c">&nbsp;
   <span class="kw4">static</span> <span class="kw4">struct</span> kset computer_set;
&nbsp;</pre>
</div>

<h4><a name="declare_the_subsystem" id="declare_the_subsystem">Declare the Subsystem</a></h4>
<div class="level4">

<p>
 The decl_subsystem helper function can be used here
</p>
<pre class="code c">&nbsp;
<span class="co1">// The following macro completes the definition of the subsystem</span>
decl_subsys<span class="br0">&#40;</span>sysfs_computer, &amp;sysfs_computer_ktype, <span class="nu0">0</span> <span class="br0">&#41;</span>;
&nbsp;
<span class="co1">//or by hand ..</span>
&nbsp;
<span class="kw4">struct</span> subsystem sysfs_computer_subsys = <span class="br0">&#123;</span>
        .<span class="me1">kset</span> = <span class="br0">&#123;</span>
                .<span class="me1">kobj</span> = <span class="br0">&#123;</span> .<span class="me1">name</span> = __stringify<span class="br0">&#40;</span>sysfs_computer<span class="br0">&#41;</span> <span class="br0">&#125;</span>,
                .<span class="me1">ktype</span> = &amp;sysfs_computer_ktype,
                .<span class="me1">hotplug_ops</span> =<span class="nu0">0</span>
        <span class="br0">&#125;</span>
<span class="br0">&#125;</span>;</pre>
</div>
<!-- SECTION [7033-10334] -->
<h3><a name="define_the_kset" id="define_the_kset">Define the KSET</a></h3>
<div class="level3">

<p>
 <strong></strong> The KOBJECT SET is the key to the whole system <strong></strong>
</p>
<pre class="code c">&nbsp;
    <span class="kw4">char</span> * name = <span class="st0">"computers"</span>;
    kobject_set_name<span class="br0">&#40;</span>&amp;computer_set-&gt;kobj, <span class="st0">"%s"</span>, name<span class="br0">&#41;</span>;
&nbsp;
    <span class="co1">// associate the set with a subsystem</span>
    computer_set-&gt;subsys = &amp;sysfs_computer_subsys;
&nbsp;
    <span class="co1">// define the type of the set</span>
    computer_set-&gt;kobj.<span class="me1">ktype</span> = &amp;sysfs_computer_ktype;
&nbsp;
    <span class="co1">// define the type of objects contained in the set</span>
    computer_set-&gt;ktype = &amp;computer_ktype;
&nbsp;
    <span class="co1">// No hotplug for this object</span>
    computer_set-&gt;hotplug_ops = <span class="kw2">NULL</span>;
&nbsp;
   <span class="co1">// register the set to make it appear</span>
   kset_register<span class="br0">&#40;</span>computer_set<span class="br0">&#41;</span>;
&nbsp;</pre>
</div>

<h4><a name="register_the_subsystem" id="register_the_subsystem">Register the Subsystem</a></h4>
<div class="level4">

<p>
This will make sysfs aware of the subsystem.
</p>
<pre class="code c">&nbsp;
        subsystem_register<span class="br0">&#40;</span>&amp;sysfs_computer_subsys<span class="br0">&#41;</span>;
&nbsp;</pre>
</div>

<h4><a name="initialize_each_object_s_system_components" id="initialize_each_object_s_system_components">Initialize each object's system components</a></h4>
<div class="level4">

<p>
This sets up the object in the sysfs hierarchy
</p>
<pre class="code c">&nbsp;
    <span class="co1">// create a new computer</span>
    <span class="kw4">struct</span> computer * computer = <span class="br0">&#40;</span><span class="kw4">struct</span> computer*<span class="br0">&#41;</span>kmalloc<span class="br0">&#40;</span>
        <span class="kw4">sizeof</span><span class="br0">&#40;</span><span class="kw4">struct</span> computer<span class="br0">&#41;</span>,GFP_KERNEL<span class="br0">&#41;</span>;
    <span class="kw1">if</span> <span class="br0">&#40;</span> <span class="kw2">NULL</span> == computer <span class="br0">&#41;</span> <span class="kw1">return</span> <span class="kw2">NULL</span>;
    memset<span class="br0">&#40;</span>computer, 0x00, <span class="kw4">sizeof</span><span class="br0">&#40;</span><span class="kw4">struct</span> computer<span class="br0">&#41;</span><span class="br0">&#41;</span>;
&nbsp;
    kobject_set_name<span class="br0">&#40;</span>&amp;computer-&gt;kobj, <span class="st0">"%s"</span> , name<span class="br0">&#41;</span>;
    computer-&gt;kobj.<span class="me1">parent</span> = &amp;computer_set.<span class="me1">kobj</span>;
    computer-&gt;kobj.<span class="me1">kset</span> = &amp;computer_set;
    computer-&gt;kobj.<span class="me1">ktype</span> = computer_set.<span class="me1">ktype</span>;
&nbsp;</pre>
</div>

<h4><a name="initialize_each_object_s_attributes" id="initialize_each_object_s_attributes">Initialize each object's attributes</a></h4>
<div class="level4">

<p>
Having established the object&rsquo;s place in the hierarchy now set its attributes.
</p>
<pre class="code c">&nbsp;
    strncpy<span class="br0">&#40;</span>computer-&gt;make,make,<span class="nu0">16</span><span class="br0">&#41;</span>;
    strncpy<span class="br0">&#40;</span>computer-&gt;ip,ip,<span class="nu0">16</span><span class="br0">&#41;</span>;
    computer-&gt;speed = speed;
    computer-&gt;capacity = capacity;
    computer-&gt;used = used;
&nbsp;</pre>
</div>

<h4><a name="register_the_object" id="register_the_object">Register the object</a></h4>
<div class="level4">

<p>
This step will expose the object to the sysfs system.
</p>
<pre class="code c">&nbsp;
    kobject_register<span class="br0">&#40;</span>&amp;computer-&gt;kobj<span class="br0">&#41;</span>;
&nbsp;</pre>
<p>
 &lt;h3&gt; Clean up &lt;/h3&gt;
</p>

<p>
&lt;p&gt; This step will remove  object from the sysfs system.
</p>
<pre class="code c">&nbsp;
        <span class="kw4">struct</span> kobject * kobj = <span class="kw2">NULL</span>;
        <span class="kw1">while</span><span class="br0">&#40;</span>!list_empty<span class="br0">&#40;</span>&amp;computer_set.<span class="me1">list</span><span class="br0">&#41;</span><span class="br0">&#41;</span> <span class="br0">&#123;</span>
            kobj = <span class="br0">&#40;</span><span class="kw4">struct</span> kobject *<span class="br0">&#41;</span> list_entry<span class="br0">&#40;</span>computer_set.<span class="me1">list</span>.<span class="me1">next</span>,
                                                 <span class="kw4">struct</span> kobject, entry<span class="br0">&#41;</span>;
            kobject_unregister<span class="br0">&#40;</span>kobj<span class="br0">&#41;</span>;
&nbsp;
        <span class="br0">&#125;</span>
        kset_unregister<span class="br0">&#40;</span>&amp;computer_set<span class="br0">&#41;</span>;
        subsystem_unregister<span class="br0">&#40;</span>&amp;sysfs_computer_subsys<span class="br0">&#41;</span>;
&nbsp;</pre>
</div>
<!-- SECTION [10335-12577] -->
<h3><a name="the_system_in_action" id="the_system_in_action">The system in action</a></h3>
<div class="level3">

<p>
 Here is an example of this system in action
</p>

<p>
&lt;code&gt;
</p>

<p>
/sys/sysfs_computer/ `&ndash; computers
</p>
<pre class="code">  |-- comp_node_0
  |   |-- capacity
  |   |-- ip
  |   |-- make
  |   |-- speed
  |   `-- used</pre>

<p>
[...] 
</p>
<pre class="code">  `-- comp_node_4
      |-- capacity
      |-- ip
      |-- make
      |-- speed
      `-- used</pre>

</div>
<!-- SECTION [12578-] --></body>
</html>