用户空间辅助程序---热插拔

原文地址：http://blog.chinaunix.net/uid-20786208-id-4158792.html

对于热插拔，当然网上有很多资料，包括刚开始我也简单的讲过usb 热插拔. 当时说道2.6以后的内核都用uevent机制来代替老的机制.(具体从那个版本改变的可以看linux官网开发记录)

由于在看《深入理解linux网络内幕》中网络设备初始化一节中又提到了，而看《深入linux设备驱动程序内核机制》中详细讲解.当然这里我也自己分析了一把^^,我们就接着usb热插拔事件继续说事： 当有usb插板事件的时候，会触发到drivers/usb/core/hub.c 中  
/* Handle physical or logical connection change events.
 * This routine is called when:
 * a port connection-change occurs;
 * a port enable-change occurs (often caused by EMI);
 * usb_reset_and_verify_device() encounters changed descriptors (as from
 * a firmware download)
 * caller already locked the hub
 */
static void hub_port_connect_change(struct usb_hub *hub, int port1,
u16 portstatus, u16 portchange)
{

...
/* Run it through the hoops (find a driver, etc) */
if (!status) {
status = usb_new_device(udev);
if (status) {
spin_lock_irq(&device_state_lock);
hdev->children[port1-1] = NULL;
spin_unlock_irq(&device_state_lock);
}
}

...
}
这里我们只是做一个简单回忆 ，重点是 usb_new_device函数:

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1. /**
   
2.  * usb_new_device - perform initial device setup (usbcore-internal)
   
3.  * @udev: newly addressed device (in ADDRESS state)
   
4.  *
   
5.  * This is called with devices which have been detected but not fully
   
6.  * enumerated. The device descriptor is available, but not descriptors
   
7.  * for any device configuration. The caller must have locked either
   
8.  * the parent hub (if udev is a normal device) or else the
   
9.  * usb_bus_list_lock (if udev is a root hub). The parent's pointer to
   
10.  * udev has already been installed, but udev is not yet visible through
    
11.  * sysfs or other filesystem code.
    
12.  *
    
13.  * It will return if the device is configured properly or not. Zero if
    
14.  * the interface was registered with the driver core; else a negative
    
15.  * errno value.
    
16.  *
    
17.  * This call is synchronous, and may not be used in an interrupt context.
    
18.  *
    
19.  * Only the hub driver or root-hub registrar should ever call this.
    
20.  */
    
21. int usb_new_device(struct usb_device *udev)
    
22. {
    
23.     int err;
    
24. 
    
25.     if (udev->parent) {
    
26.         /* Increment the parent's count of unsuspended children */
    
27.         usb_autoresume_device(udev->parent);
    
28. 
    
29.         /* Initialize non-root-hub device wakeup to disabled;
    
30.          * device (un)configuration controls wakeup capable
    
31.          * sysfs power/wakeup controls wakeup enabled/disabled
    
32.          */
    
33.         device_init_wakeup(&udev->dev, 0);
    
34.     }
    
35. 
    
36.     err = usb_enumerate_device(udev);    /* Read descriptors */
    
37.     if (err < 0)
    
38.         goto fail;
    
39.     dev_dbg(&udev->dev, "udev %d, busnum %d, minor = %d\n",
    
40.             udev->devnum, udev->bus->busnum,
    
41.             (((udev->bus->busnum-1) * 128) + (udev->devnum-1)));
    
42.     /* export the usbdev device-node for libusb */
    
43.     udev->dev.devt = MKDEV(USB_DEVICE_MAJOR,
    
44.             (((udev->bus->busnum-1) * 128) + (udev->devnum-1)));
    
45. 
    
46.     /* Tell the */
    
47.     announce_device(udev);
    
48. 
    
49.     if (udev->serial)
    
50.         add_device_randomness(udev->serial, strlen(udev->serial));
    
51.     if (udev->product)
    
52.         add_device_randomness(udev->product, strlen(udev->product));
    
53.     if (udev->manufacturer)
    
54.         add_device_randomness(udev->manufacturer,
    
55.                  strlen(udev->manufacturer));
    
56. 
    
57.     /* Register the device. The device driver is responsible
    
58.      * for configuring the device and invoking the add-device
    
59.      * notifier chain (used by usbfs and possibly others).
    
60.      */
    
61.     err = device_add(&udev->dev);
    
62.     if (err) {
    
63.         dev_err(&udev->dev, "can't device_add, error %d\n", err);
    
64.         goto fail;
    
65.     }
    
66. 
    
67.     (void) usb_create_ep_devs(&udev->dev, &udev->ep0, udev);
    
68.     return err;
    
69. 
    
70. fail:
    
71.     usb_set_device_state(udev, USB_STATE_NOTATTACHED);
    
72.     usb_stop_pm(udev);
    
73.     return err;
    
74. }

里面的具体的一些初始化这里不在一一说明，我们只看device_add函数：

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1. /**
   
2.  * device_add - add device to device hierarchy.
   
3.  * @dev: device.
   
4.  *
   
5.  * This is part 2 of device_register(), though may be called
   
6.  * separately _iff_ device_initialize() has been called separately.
   
7.  *
   
8.  * This adds @dev to the kobject hierarchy via kobject_add(), adds it
   
9.  * to the global and sibling lists for the device, then
   
10.  * adds it to the other relevant subsystems of the driver model.
    
11.  *
    
12.  * NOTE: _Never_ directly free @dev after calling this function, even
    
13.  * if it returned an Always use put_device() to give up your
    
14.  * reference instead.
    
15.  */
    
16. int device_add(struct device *dev)
    
17. {
    
18.     struct device *parent = NULL;
    
19.     struct class_interface *class_intf;
    
20.     int error = -EINVAL;
    
21. 
    
22.     dev = get_device(dev);
    
23.     if (!dev)
    
24.         goto done;
    
25. 
    
26.     if (!dev->p) {
    
27.         error = device_private_init(dev);
    
28.         if (error)
    
29.             goto done;
    
30.     }
    
31. 
    
32.     /*
    
33.      * for statically allocated devices, which should all be converted
    
34.      * some day, we need to initialize the name. We prevent reading back
    
35.      * the name, and force the use of dev_name()
    
36.      */
    
37.     if (dev->init_name) {
    
38.         dev_set_name(dev, "%s", dev->init_name);
    
39.         dev->init_name = NULL;
    
40.     }
    
41. 
    
42.     if (!dev_name(dev))
    
43.         goto name_error;
    
44. 
    
45.     pr_debug("device: '%s': %s\n", dev_name(dev), __func__);
    
46. 
    
47.     parent = get_device(dev->parent);
    
48.     setup_parent(dev, parent);
    
49. 
    
50.     /* use parent numa_node */
    
51.     if (parent)
    
52.         set_dev_node(dev, dev_to_node(parent));
    
53. 
    
54.     /* first, register with generic layer. */
    
55.     /* we require the name to be set before, and pass NULL */
    
56.     error = kobject_add(&dev->kobj, dev->kobj.parent, NULL);
    
57.     if (error)
    
58.         goto Error;
    
59. 
    
60.     /* notify platform of device entry */
    
61.     if (platform_notify)
    
62.         platform_notify(dev);
    
63. 
    
64.     error = device_create_file(dev, &uevent_attr);
    
65.     if (error)
    
66.         goto attrError;
    
67. 
    
68.     if (MAJOR(dev->devt)) {
    
69.         error = device_create_file(dev, &devt_attr);
    
70.         if (error)
    
71.             goto ueventattrError;
    
72. 
    
73.         error = device_create_sys_dev_entry(dev);
    
74.         if (error)
    
75.             goto devtattrError;
    
76. 
    
77.         devtmpfs_create_node(dev);
    
78.     }
    
79. 
    
80.     error = device_add_class_symlinks(dev);
    
81.     if (error)
    
82.         goto SymlinkError;
    
83.     error = device_add_attrs(dev);
    
84.     if (error)
    
85.         goto AttrsError;
    
86.     error = bus_add_device(dev);
    
87.     if (error)
    
88.         goto BusError;
    
89.     error = dpm_sysfs_add(dev);
    
90.     if (error)
    
91.         goto DPMError;
    
92.     device_pm_add(dev);
    
93. 
    
94.     /* Notify clients of device addition. This call must come
    
95.      * after dpm_sysf_add() and before kobject_uevent().
    
96.      */
    
97.     if (dev->bus)
    
98.         blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
    
99.                      BUS_NOTIFY_ADD_DEVICE, dev);
    
100. 
     
101.     kobject_uevent(&dev->kobj, KOBJ_ADD);
     
102.     bus_probe_device(dev);
     
103.     if (parent)
     
104.         klist_add_tail(&dev->p->knode_parent,
     
105.              &parent->p->klist_children);
     
106. 
     
107.     if (dev->class) {
     
108.         mutex_lock(&dev->class->p->class_mutex);
     
109.         /* tie the class to the device */
     
110.         klist_add_tail(&dev->knode_class,
     
111.              &dev->class->p->class_devices);
     
112. 
     
113.         /* notify any interfaces that the device is here */
     
114.         list_for_each_entry(class_intf,
     
115.                  &dev->class->p->class_interfaces, node)
     
116.             if (class_intf->add_dev)
     
117.                 class_intf->add_dev(dev, class_intf);
     
118.         mutex_unlock(&dev->class->p->class_mutex);
     
119.     }
     
120. done:
     
121.     put_device(dev);
     
122.     return error;
     
123.  DPMError:
     
124.     bus_remove_device(dev);
     
125.  BusError:
     
126.     device_remove_attrs(dev);
     
127.  AttrsError:
     
128.     device_remove_class_symlinks(dev);
     
129.  SymlinkError:
     
130.     if (MAJOR(dev->devt))
     
131.         device_remove_sys_dev_entry(dev);
     
132.  devtattrError:
     
133.     if (MAJOR(dev->devt))
     
134.         device_remove_file(dev, &devt_attr);
     
135.  ueventattrError:
     
136.     device_remove_file(dev, &uevent_attr);
     
137.  attrError:
     
138.     kobject_uevent(&dev->kobj, KOBJ_REMOVE);
     
139.     kobject_del(&dev->kobj);
     
140.  Error:
     
141.     cleanup_device_parent(dev);
     
142.     if (parent)
     
143.         put_device(parent);
     
144. name_error:
     
145.     kfree(dev->p);
     
146.     dev->p = NULL;
     
147.     goto done;
     
148. }

这个函数除了对设备模型做了些工作，还通知了一些事件. kobject_uevent(&dev->kobj, KOBJ_ADD);忘了说上边的代码已经到了drivers/base/core.c中. 我们看到KOBJ_ADD操作。而具体支持的操作看头文件include/linux/kobject.h
/*
 * The actions here must match the index to the string array
 * in lib/kobject_uevent.c
 *
 * Do not add new actions here without checking with the driver-core
 * maintainers. Action strings are not meant to express subsystem
 * or device specific properties. In most cases you want to send a
 * kobject_uevent_env(kobj, KOBJ_CHANGE, env) with additional event
 * specific variables added to the event environment.
 */
enum kobject_action {
KOBJ_ADD,
KOBJ_REMOVE,
KOBJ_CHANGE,
KOBJ_MOVE,
KOBJ_ONLINE,
KOBJ_OFFLINE,
KOBJ_MAX
};
那么kobject_uevent做了什么工作呢，我们知道，新内核机制已经变成uevent模式.
lib/kobject_uevent.c 

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1. /**
   
2.  * kobject_uevent - notify userspace by ending an uevent
   
3.  *
   
4.  * @action: action that is happening
   
5.  * @kobj: struct kobject that the action is happening to
   
6.  *
   
7.  * Returns 0 if kobject_uevent() is completed with success or the
   
8.  * corresponding error when it fails.
   
9.  */
   
10. int kobject_uevent(struct kobject *kobj, enum kobject_action action)
    
11. {
    
12.     return kobject_uevent_env(kobj, action, NULL);
    
13. }
    
14. EXPORT_SYMBOL_GPL(kobject_uevent);

好吧，调用了 kobject_uevent_env函数.

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1. /**
   
2.  * kobject_uevent_env - send an uevent with environmental data
   
3.  *
   
4.  * @action: action that is happening
   
5.  * @kobj: struct kobject that the action is happening to
   
6.  * @envp_ext: pointer to environmental data
   
7.  *
   
8.  * Returns 0 if kobject_uevent() is completed with success or the
   
9.  * corresponding error when it fails.
   
10.  */
    
11. int kobject_uevent_env(struct kobject *kobj, enum kobject_action action,
    
12.          char *envp_ext[])
    
13. {
    
14.     struct kobj_uevent_env *env;
    
15.     const char *action_string = kobject_actions[action];
    
16.     const char *devpath = NULL;
    
17.     const char *subsystem;
    
18.     struct kobject *top_kobj;
    
19.     struct kset *kset;
    
20.     struct kset_uevent_ops *uevent_ops;
    
21.     u64 seq;
    
22.     int i = 0;
    
23.     int retval = 0;
    
24. 
    
25.     pr_debug("kobject: '%s' (%p): %s\n",
    
26.          kobject_name(kobj), kobj, __func__);
    
27. 
    
28.     /* search the kset we belong to */
    
29.     top_kobj = kobj;
    
30.     while (!top_kobj->kset && top_kobj->parent)
    
31.         top_kobj = top_kobj->parent;
    
32. 
    
33.     if (!top_kobj->kset) {
    
34.         pr_debug("kobject: '%s' (%p): %s: attempted to send uevent "
    
35.              "without kset!\n", kobject_name(kobj), kobj,
    
36.              __func__);
    
37.         return -EINVAL;
    
38.     }
    
39. 
    
40.     kset = top_kobj->kset;
    
41.     uevent_ops = kset->uevent_ops;
    
42. 
    
43.     /* skip the event, if uevent_suppress is set*/
    
44.     if (kobj->uevent_suppress) {
    
45.         pr_debug("kobject: '%s' (%p): %s: uevent_suppress "
    
46.                  "caused the event to drop!\n",
    
47.                  kobject_name(kobj), kobj, __func__);
    
48.         return 0;
    
49.     }
    
50.     /* skip the event, if the filter returns zero. */
    
51.     if (uevent_ops && uevent_ops->filter)
    
52.         if (!uevent_ops->filter(kset, kobj)) {
    
53.             pr_debug("kobject: '%s' (%p): %s: filter function "
    
54.                  "caused the event to drop!\n",
    
55.                  kobject_name(kobj), kobj, __func__);
    
56.             return 0;
    
57.         }
    
58. 
    
59.     /* originating subsystem */
    
60.     if (uevent_ops && uevent_ops->name)
    
61.         subsystem = uevent_ops->name(kset, kobj);
    
62.     else
    
63.         subsystem = kobject_name(&kset->kobj);
    
64.     if (!subsystem) {
    
65.         pr_debug("kobject: '%s' (%p): %s: unset subsystem caused the "
    
66.              "event to drop!\n", kobject_name(kobj), kobj,
    
67.              __func__);
    
68.         return 0;
    
69.     }
    
70. 
    
71.     /* environment buffer */
    
72.     env = kzalloc(sizeof(struct kobj_uevent_env), GFP_KERNEL);
    
73.     if (!env)
    
74.         return -ENOMEM;
    
75. 
    
76.     /* complete object path */
    
77.     devpath = kobject_get_path(kobj, GFP_KERNEL);
    
78.     if (!devpath) {
    
79.         retval = -ENOENT;
    
80.         goto exit;
    
81.     }
    
82. 
    
83.     /* default keys */
    
84.     retval = add_uevent_var(env, "ACTION=%s", action_string);
    
85.     if (retval)
    
86.         goto exit;
    
87.     retval = add_uevent_var(env, "DEVPATH=%s", devpath);
    
88.     if (retval)
    
89.         goto exit;
    
90.     retval = add_uevent_var(env, "SUBSYSTEM=%s", subsystem);
    
91.     if (retval)
    
92.         goto exit;
    
93. 
    
94.     /* keys passed in from the caller */
    
95.     if (envp_ext) {
    
96.         for (i = 0; envp_ext[i]; i++) {
    
97.             retval = add_uevent_var(env, "%s", envp_ext[i]);
    
98.             if (retval)
    
99.                 goto exit;
    
100.         }
     
101.     }
     
102. 
     
103.     /* let the kset specific function add its stuff */
     
104.     if (uevent_ops && uevent_ops->uevent) {
     
105.         retval = uevent_ops->uevent(kset, kobj, env);
     
106.         if (retval) {
     
107.             pr_debug("kobject: '%s' (%p): %s: uevent() returned "
     
108.                  "%d\n", kobject_name(kobj), kobj,
     
109.                  __func__, retval);
     
110.             goto exit;
     
111.         }
     
112.     }
     
113. 
     
114.     /*
     
115.      * Mark "add" and "remove" events in the object to ensure proper
     
116.      * events to userspace during automatic cleanup. If the object did
     
117.      * send an "add" event, "remove" will automatically generated by
     
118.      * the core, if not already done by the caller.
     
119.      */
     
120.     if (action == KOBJ_ADD)
     
121.         kobj->state_add_uevent_sent = 1;
     
122.     else if (action == KOBJ_REMOVE)
     
123.         kobj->state_remove_uevent_sent = 1;
     
124. 
     
125.     /* we will send an event, so request a new sequence number */
     
126.     spin_lock(&sequence_lock);
     
127.     seq = ++uevent_seqnum;
     
128.     spin_unlock(&sequence_lock);
     
129.     retval = add_uevent_var(env, "SEQNUM=%llu", (unsigned long long)seq);
     
130.     if (retval)
     
131.         goto exit;
     
132. 
     
133. #if defined(CONFIG_NET)
     
134.     /* send netlink message */
     
135.     if (uevent_sock) {
     
136.         struct sk_buff *skb;
     
137.         size_t len;
     
138. 
     
139.         /* allocate message with the maximum possible size */
     
140.         len = strlen(action_string) + strlen(devpath) + 2;
     
141.         skb = alloc_skb(len + env->buflen, GFP_KERNEL);
     
142.         if (skb) {
     
143.             char *scratch;
     
144. 
     
145.             /* add header */
     
146.             scratch = skb_put(skb, len);
     
147.             sprintf(scratch, "%s@%s", action_string, devpath);
     
148. 
     
149.             /* copy keys to our continuous event payload buffer */
     
150.             for (i = 0; i < env->envp_idx; i++) {
     
151.                 len = strlen(env->envp[i]) + 1;
     
152.                 scratch = skb_put(skb, len);
     
153.                 strcpy(scratch, env->envp[i]);
     
154.             }
     
155. 
     
156.             NETLINK_CB(skb).dst_group = 1;
     
157.             retval = netlink_broadcast(uevent_sock, skb, 0, 1,
     
158.                          GFP_KERNEL);
     
159.             /* ENOBUFS should be handled in userspace */
     
160.             if (retval == -ENOBUFS || retval == -ESRCH)
     
161.                 retval = 0;
     
162.         } else
     
163.             retval = -ENOMEM;
     
164.     }
     
165. #endif
     
166. 
     
167.     /* call uevent_helper, usually only enabled during early boot */
     
168.     if (uevent_helper[0]) {
     
169.         char *argv [3];
     
170. 
     
171.         argv [0] = uevent_helper;
     
172.         argv [1] = (char *)subsystem;
     
173.         argv [2] = NULL;
     
174.         retval = add_uevent_var(env, "HOME=/");
     
175.         if (retval)
     
176.             goto exit;
     
177.         retval = add_uevent_var(env,
     
178.                     "PATH=/sbin:/bin:/usr/sbin:/usr/bin");
     
179.         if (retval)
     
180.             goto exit;
     
181. 
     
182.         retval = call_usermodehelper(argv[0], argv,
     
183.                      env->envp, UMH_WAIT_EXEC);
     
184.     }
     
185. 
     
186. exit:
     
187.     kfree(devpath);
     
188.     kfree(env);
     
189.     return retval;
     
190. }

这个函数里做了最重要的工作. 第一发送一个netlink组播；第二调用了call_usermodehelper执行用户空间的应用程序.
这里面不得不说uevent_helper变量.由它指定具体调用哪个应用程序.add_uevent_var只是传递一些变量.
char uevent_helper[UEVENT_HELPER_PATH_LEN] = CONFIG_UEVENT_HELPER_PATH;  //系统默认的值
而CONFIG_UEVENT_HELPER_PATH，可以查看arch/XXX/configs/  里。一般是/sbin/XXX  。
当然从用户空间也可以修改这个值：
#cat  /proc/sys/kernel/hotplug 
or
#cat /sys/kernel/uevent_helper
可以查看当前系统设定的值，由于我做的是嵌入式系统，默认是/sbin/mdev (这里说明一下mdev只是udev缩减版，具体资料可以查一查就明白，它会检测设备模型下面一些变量值的变化并作出相应动作)
而对于为什么这两个变量的值是一样的，我做了简单分析：
第一个是procfs，我们看kernel/sysctl.c :
kernel_table :

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1. static struct ctl_table kern_table[] = {
   
2.     {
   
3.         .ctl_name    = CTL_UNNUMBERED,
   
4.         .procname    = "sched_child_runs_first",
   
5.         .data        = &sysctl_sched_child_runs_first,
   
6.         .maxlen        = sizeof(unsigned int),
   
7.         .mode        = 0644,
   
8.         .proc_handler    = &proc_dointvec,
   
9.     },
   
10. #ifdef CONFIG_SCHED_DEBUG
    
11.     {
    
12.         .ctl_name    = CTL_UNNUMBERED,
    
13.         .procname    = "sched_min_granularity_ns",
    
14.         .data        = &sysctl_sched_min_granularity,
    
15.         .maxlen        = sizeof(unsigned int),
    
16.         .mode        = 0644,
    
17.         .proc_handler    = &sched_nr_latency_handler,
    
18.         .strategy    = &sysctl_intvec,
    
19.         .extra1        = &min_sched_granularity_ns,
    
20.         .extra2        = &max_sched_granularity_ns,
    
21.     },
    
22.     {
    
23.         .ctl_name    = CTL_UNNUMBERED,
    
24.         .procname    = "sched_latency_ns",
    
25.         .data        = &sysctl_sched_latency,
    
26.         .maxlen        = sizeof(unsigned int),
    
27.         .mode        = 0644,
    
28.         .proc_handler    = &sched_nr_latency_handler,
    
29.         .strategy    = &sysctl_intvec,
    
30.         .extra1        = &min_sched_granularity_ns,
    
31.         .extra2        = &max_sched_granularity_ns,
    
32.     },
    
33.     {
    
34.         .ctl_name    = CTL_UNNUMBERED,
    
35.         .procname    = "sched_wakeup_granularity_ns",
    
36.         .data        = &sysctl_sched_wakeup_granularity,
    
37.         .maxlen        = sizeof(unsigned int),
    
38.         .mode        = 0644,
    
39.         .proc_handler    = &proc_dointvec_minmax,
    
40.         .strategy    = &sysctl_intvec,
    
41.         .extra1        = &min_wakeup_granularity_ns,
    
42.         .extra2        = &max_wakeup_granularity_ns,
    
43.     },
    
44.     {
    
45.         .ctl_name    = CTL_UNNUMBERED,
    
46.         .procname    = "sched_shares_ratelimit",
    
47.         .data        = &sysctl_sched_shares_ratelimit,
    
48.         .maxlen        = sizeof(unsigned int),
    
49.         .mode        = 0644,
    
50.         .proc_handler    = &proc_dointvec,
    
51.     },
    
52.     {
    
53.         .ctl_name    = CTL_UNNUMBERED,
    
54.         .procname    = "sched_shares_thresh",
    
55.         .data        = &sysctl_sched_shares_thresh,
    
56.         .maxlen        = sizeof(unsigned int),
    
57.         .mode        = 0644,
    
58.         .proc_handler    = &proc_dointvec_minmax,
    
59.         .strategy    = &sysctl_intvec,
    
60.         .extra1        = &zero,
    
61.     },
    
62.     {
    
63.         .ctl_name    = CTL_UNNUMBERED,
    
64.         .procname    = "sched_features",
    
65.         .data        = &sysctl_sched_features,
    
66.         .maxlen        = sizeof(unsigned int),
    
67.         .mode        = 0644,
    
68.         .proc_handler    = &proc_dointvec,
    
69.     },
    
70.     {
    
71.         .ctl_name    = CTL_UNNUMBERED,
    
72.         .procname    = "sched_migration_cost",
    
73.         .data        = &sysctl_sched_migration_cost,
    
74.         .maxlen        = sizeof(unsigned int),
    
75.         .mode        = 0644,
    
76.         .proc_handler    = &proc_dointvec,
    
77.     },
    
78.     {
    
79.         .ctl_name    = CTL_UNNUMBERED,
    
80.         .procname    = "sched_nr_migrate",
    
81.         .data        = &sysctl_sched_nr_migrate,
    
82.         .maxlen        = sizeof(unsigned int),
    
83.         .mode        = 0644,
    
84.         .proc_handler    = &proc_dointvec,
    
85.     },
    
86.     {
    
87.         .ctl_name    = CTL_UNNUMBERED,
    
88.         .procname    = "sched_time_avg",
    
89.         .data        = &sysctl_sched_time_avg,
    
90.         .maxlen        = sizeof(unsigned int),
    
91.         .mode        = 0644,
    
92.         .proc_handler    = &proc_dointvec,
    
93.     },
    
94.     {
    
95.         .ctl_name    = CTL_UNNUMBERED,
    
96.         .procname    = "timer_migration",
    
97.         .data        = &sysctl_timer_migration,
    
98.         .maxlen        = sizeof(unsigned int),
    
99.         .mode        = 0644,
    
100.         .proc_handler    = &proc_dointvec_minmax,
     
101.         .strategy    = &sysctl_intvec,
     
102.         .extra1        = &zero,
     
103.         .extra2        = &one,
     
104.     },
     
105. #endif
     
106.     {
     
107.         .ctl_name    = CTL_UNNUMBERED,
     
108.         .procname    = "sched_rt_period_us",
     
109.         .data        = &sysctl_sched_rt_period,
     
110.         .maxlen        = sizeof(unsigned int),
     
111.         .mode        = 0644,
     
112.         .proc_handler    = &sched_rt_handler,
     
113.     },
     
114.     {
     
115.         .ctl_name    = CTL_UNNUMBERED,
     
116.         .procname    = "sched_rt_runtime_us",
     
117.         .data        = &sysctl_sched_rt_runtime,
     
118.         .maxlen        = sizeof(int),
     
119.         .mode        = 0644,
     
120.         .proc_handler    = &sched_rt_handler,
     
121.     },
     
122.     {
     
123.         .ctl_name    = CTL_UNNUMBERED,
     
124.         .procname    = "sched_compat_yield",
     
125.         .data        = &sysctl_sched_compat_yield,
     
126.         .maxlen        = sizeof(unsigned int),
     
127.         .mode        = 0644,
     
128.         .proc_handler    = &proc_dointvec,
     
129.     },
     
130. #ifdef CONFIG_PROVE_LOCKING
     
131.     {
     
132.         .ctl_name    = CTL_UNNUMBERED,
     
133.         .procname    = "prove_locking",
     
134.         .data        = &prove_locking,
     
135.         .maxlen        = sizeof(int),
     
136.         .mode        = 0644,
     
137.         .proc_handler    = &proc_dointvec,
     
138.     },
     
139. #endif
     
140. #ifdef CONFIG_LOCK_STAT
     
141.     {
     
142.         .ctl_name    = CTL_UNNUMBERED,
     
143.         .procname    = "lock_stat",
     
144.         .data        = &lock_stat,
     
145.         .maxlen        = sizeof(int),
     
146.         .mode        = 0644,
     
147.         .proc_handler    = &proc_dointvec,
     
148.     },
     
149. #endif
     
150.     {
     
151.         .ctl_name    = KERN_PANIC,
     
152.         .procname    = "panic",
     
153.         .data        = &panic_timeout,
     
154.         .maxlen        = sizeof(int),
     
155.         .mode        = 0644,
     
156.         .proc_handler    = &proc_dointvec,
     
157.     },
     
158.     {
     
159.         .ctl_name    = KERN_CORE_USES_PID,
     
160.         .procname    = "core_uses_pid",
     
161.         .data        = &core_uses_pid,
     
162.         .maxlen        = sizeof(int),
     
163.         .mode        = 0644,
     
164.         .proc_handler    = &proc_dointvec,
     
165.     },
     
166.     {
     
167.         .ctl_name    = KERN_CORE_PATTERN,
     
168.         .procname    = "core_pattern",
     
169.         .data        = core_pattern,
     
170.         .maxlen        = CORENAME_MAX_SIZE,
     
171.         .mode        = 0644,
     
172.         .proc_handler    = &proc_dostring,
     
173.         .strategy    = &sysctl_string,
     
174.     },
     
175.     {
     
176.         .ctl_name    = CTL_UNNUMBERED,
     
177.         .procname    = "core_pipe_limit",
     
178.         .data        = &core_pipe_limit,
     
179.         .maxlen        = sizeof(unsigned int),
     
180.         .mode        = 0644,
     
181.         .proc_handler    = &proc_dointvec,
     
182.     },
     
183. #ifdef CONFIG_PROC_SYSCTL
     
184.     {
     
185.         .procname    = "tainted",
     
186.         .maxlen     = sizeof(long),
     
187.         .mode        = 0644,
     
188.         .proc_handler    = &proc_taint,
     
189.     },
     
190. #endif
     
191. #ifdef CONFIG_LATENCYTOP
     
192.     {
     
193.         .procname    = "latencytop",
     
194.         .data        = &latencytop_enabled,
     
195.         .maxlen        = sizeof(int),
     
196.         .mode        = 0644,
     
197.         .proc_handler    = &proc_dointvec,
     
198.     },
     
199. #endif
     
200. #ifdef CONFIG_BLK_DEV_INITRD
     
201.     {
     
202.         .ctl_name    = KERN_REALROOTDEV,
     
203.         .procname    = "real-root-dev",
     
204.         .data        = &real_root_dev,
     
205.         .maxlen        = sizeof(int),
     
206.         .mode        = 0644,
     
207.         .proc_handler    = &proc_dointvec,
     
208.     },
     
209. #endif
     
210.     {
     
211.         .ctl_name    = CTL_UNNUMBERED,
     
212.         .procname    = "print-fatal-signals",
     
213.         .data        = &print_fatal_signals,
     
214.         .maxlen        = sizeof(int),
     
215.         .mode        = 0644,
     
216.         .proc_handler    = &proc_dointvec,
     
217.     },
     
218. #ifdef CONFIG_SPARC
     
219.     {
     
220.         .ctl_name    = KERN_SPARC_REBOOT,
     
221.         .procname    = "reboot-cmd",
     
222.         .data        = reboot_command,
     
223.         .maxlen        = 256,
     
224.         .mode        = 0644,
     
225.         .proc_handler    = &proc_dostring,
     
226.         .strategy    = &sysctl_string,
     
227.     },
     
228.     {
     
229.         .ctl_name    = KERN_SPARC_STOP_A,
     
230.         .procname    = "stop-a",
     
231.         .data        = &stop_a_enabled,
     
232.         .maxlen        = sizeof (int),
     
233.         .mode        = 0644,
     
234.         .proc_handler    = &proc_dointvec,
     
235.     },
     
236.     {
     
237.         .ctl_name    = KERN_SPARC_SCONS_PWROFF,
     
238.         .procname    = "scons-poweroff",
     
239.         .data        = &scons_pwroff,
     
240.         .maxlen        = sizeof (int),
     
241.         .mode        = 0644,
     
242.         .proc_handler    = &proc_dointvec,
     
243.     },
     
244. #endif
     
245. #ifdef CONFIG_SPARC64
     
246.     {
     
247.         .ctl_name    = CTL_UNNUMBERED,
     
248.         .procname    = "tsb-ratio",
     
249.         .data        = &sysctl_tsb_ratio,
     
250.         .maxlen        = sizeof (int),
     
251.         .mode        = 0644,
     
252.         .proc_handler    = &proc_dointvec,
     
253.     },
     
254. #endif
     
255. #ifdef __hppa__
     
256.     {
     
257.         .ctl_name    = KERN_HPPA_PWRSW,
     
258.         .procname    = "soft-power",
     
259.         .data        = &pwrsw_enabled,
     
260.         .maxlen        = sizeof (int),
     
261.          .mode        = 0644,
     
262.         .proc_handler    = &proc_dointvec,
     
263.     },
     
264.     {
     
265.         .ctl_name    = KERN_HPPA_UNALIGNED,
     
266.         .procname    = "unaligned-trap",
     
267.         .data        = &unaligned_enabled,
     
268.         .maxlen        = sizeof (int),
     
269.         .mode        = 0644,
     
270.         .proc_handler    = &proc_dointvec,
     
271.     },
     
272. #endif
     
273.     {
     
274.         .ctl_name    = KERN_CTLALTDEL,
     
275.         .procname    = "ctrl-alt-del",
     
276.         .data        = &C_A_D,
     
277.         .maxlen        = sizeof(int),
     
278.         .mode        = 0644,
     
279.         .proc_handler    = &proc_dointvec,
     
280.     },
     
281. #ifdef CONFIG_FUNCTION_TRACER
     
282.     {
     
283.         .ctl_name    = CTL_UNNUMBERED,
     
284.         .procname    = "ftrace_enabled",
     
285.         .data        = &ftrace_enabled,
     
286.         .maxlen        = sizeof(int),
     
287.         .mode        = 0644,
     
288.         .proc_handler    = &ftrace_enable_sysctl,
     
289.     },
     
290. #endif
     
291. #ifdef CONFIG_STACK_TRACER
     
292.     {
     
293.         .ctl_name    = CTL_UNNUMBERED,
     
294.         .procname    = "stack_tracer_enabled",
     
295.         .data        = &stack_tracer_enabled,
     
296.         .maxlen        = sizeof(int),
     
297.         .mode        = 0644,
     
298.         .proc_handler    = &stack_trace_sysctl,
     
299.     },
     
300. #endif
     
301. #ifdef CONFIG_TRACING
     
302.     {
     
303.         .ctl_name    = CTL_UNNUMBERED,
     
304.         .procname    = "ftrace_dump_on_oops",
     
305.         .data        = &ftrace_dump_on_oops,
     
306.         .maxlen        = sizeof(int),
     
307.         .mode        = 0644,
     
308.         .proc_handler    = &proc_dointvec,
     
309.     },
     
310. #endif
     
311. #ifdef CONFIG_MODULES
     
312.     {
     
313.         .ctl_name    = KERN_MODPROBE,
     
314.         .procname    = "modprobe",
     
315.         .data        = &modprobe_path,
     
316.         .maxlen        = KMOD_PATH_LEN,
     
317.         .mode        = 0644,
     
318.         .proc_handler    = &proc_dostring,
     
319.         .strategy    = &sysctl_string,
     
320.     },
     
321.     {
     
322.         .ctl_name    = CTL_UNNUMBERED,
     
323.         .procname    = "modules_disabled",
     
324.         .data        = &modules_disabled,
     
325.         .maxlen        = sizeof(int),
     
326.         .mode        = 0644,
     
327.         /* only handle a transition from default "0" to "1" */
     
328.         .proc_handler    = &proc_dointvec_minmax,
     
329.         .extra1        = &one,
     
330.         .extra2        = &one,
     
331.     },
     
332. #endif
     
333. #if defined(CONFIG_HOTPLUG) && defined(CONFIG_NET)
     
334.     {
     
335.         .ctl_name    = KERN_HOTPLUG,
     
336.         .procname    = "hotplug",
     
337.         .data        = &uevent_helper,
     
338.         .maxlen        = UEVENT_HELPER_PATH_LEN,
     
339.         .mode        = 0644,
     
340.         .proc_handler    = &proc_dostring,
     
341.         .strategy    = &sysctl_string,
     
342.     },
     
343. #endif
     
344. #ifdef CONFIG_CHR_DEV_SG
     
345.     {
     
346.         .ctl_name    = KERN_SG_BIG_BUFF,
     
347.         .procname    = "sg-big-buff",
     
348.         .data        = &sg_big_buff,
     
349.         .maxlen        = sizeof (int),
     
350.         .mode        = 0444,
     
351.         .proc_handler    = &proc_dointvec,
     
352.     },
     
353. #endif
     
354. #ifdef CONFIG_BSD_PROCESS_ACCT
     
355.     {
     
356.         .ctl_name    = KERN_ACCT,
     
357.         .procname    = "acct",
     
358.         .data        = &acct_parm,
     
359.         .maxlen        = 3*sizeof(int),
     
360.         .mode        = 0644,
     
361.         .proc_handler    = &proc_dointvec,
     
362.     },
     
363. #endif
     
364. #ifdef CONFIG_MAGIC_SYSRQ
     
365.     {
     
366.         .ctl_name    = KERN_SYSRQ,
     
367.         .procname    = "sysrq",
     
368.         .data        = &__sysrq_enabled,
     
369.         .maxlen        = sizeof (int),
     
370.         .mode        = 0644,
     
371.         .proc_handler    = &proc_dointvec,
     
372.     },
     
373. #endif
     
374. #ifdef CONFIG_PROC_SYSCTL
     
375.     {
     
376.         .procname    = "cad_pid",
     
377.         .data        = NULL,
     
378.         .maxlen        = sizeof (int),
     
379.         .mode        = 0600,
     
380.         .proc_handler    = &proc_do_cad_pid,
     
381.     },
     
382. #endif
     
383.     {
     
384.         .ctl_name    = KERN_MAX_THREADS,
     
385.         .procname    = "threads-max",
     
386.         .data        = &max_threads,
     
387.         .maxlen        = sizeof(int),
     
388.         .mode        = 0644,
     
389.         .proc_handler    = &proc_dointvec,
     
390.     },
     
391.     {
     
392.         .ctl_name    = KERN_RANDOM,
     
393.         .procname    = "random",
     
394.         .mode        = 0555,
     
395.         .child        = random_table,
     
396.     },
     
397.     {
     
398.         .ctl_name    = KERN_OVERFLOWUID,
     
399.         .procname    = "overflowuid",
     
400.         .data        = &overflowuid,
     
401.         .maxlen        = sizeof(int),
     
402.         .mode        = 0644,
     
403.         .proc_handler    = &proc_dointvec_minmax,
     
404.         .strategy    = &sysctl_intvec,
     
405.         .extra1        = &minolduid,
     
406.         .extra2        = &maxolduid,
     
407.     },
     
408.     {
     
409.         .ctl_name    = KERN_OVERFLOWGID,
     
410.         .procname    = "overflowgid",
     
411.         .data        = &overflowgid,
     
412.         .maxlen        = sizeof(int),
     
413.         .mode        = 0644,
     
414.         .proc_handler    = &proc_dointvec_minmax,
     
415.         .strategy    = &sysctl_intvec,
     
416.         .extra1        = &minolduid,
     
417.         .extra2        = &maxolduid,
     
418.     },
     
419. #ifdef CONFIG_S390
     
420. #ifdef CONFIG_MATHEMU
     
421.     {
     
422.         .ctl_name    = KERN_IEEE_EMULATION_WARNINGS,
     
423.         .procname    = "ieee_emulation_warnings",
     
424.         .data        = &sysctl_ieee_emulation_warnings,
     
425.         .maxlen        = sizeof(int),
     
426.         .mode        = 0644,
     
427.         .proc_handler    = &proc_dointvec,
     
428.     },
     
429. #endif
     
430.     {
     
431.         .ctl_name    = KERN_S390_USER_DEBUG_LOGGING,
     
432.         .procname    = "userprocess_debug",
     
433.         .data        = &sysctl_userprocess_debug,
     
434.         .maxlen        = sizeof(int),
     
435.         .mode        = 0644,
     
436.         .proc_handler    = &proc_dointvec,
     
437.     },
     
438. #endif
     
439.     {
     
440.         .ctl_name    = KERN_PIDMAX,
     
441.         .procname    = "pid_max",
     
442.         .data        = &pid_max,
     
443.         .maxlen        = sizeof (int),
     
444.         .mode        = 0644,
     
445.         .proc_handler    = &proc_dointvec_minmax,
     
446.         .strategy    = sysctl_intvec,
     
447.         .extra1        = &pid_max_min,
     
448.         .extra2        = &pid_max_max,
     
449.     },
     
450.     {
     
451.         .ctl_name    = KERN_PANIC_ON_OOPS,
     
452.         .procname    = "panic_on_oops",
     
453.         .data        = &panic_on_oops,
     
454.         .maxlen        = sizeof(int),
     
455.         .mode        = 0644,
     
456.         .proc_handler    = &proc_dointvec,
     
457.     },
     
458. #if defined CONFIG_PRINTK
     
459.     {
     
460.         .ctl_name    = KERN_PRINTK,
     
461.         .procname    = "printk",
     
462.         .data        = &console_loglevel,
     
463.         .maxlen        = 4*sizeof(int),
     
464.         .mode        = 0644,
     
465.         .proc_handler    = &proc_dointvec,
     
466.     },
     
467.     {
     
468.         .ctl_name    = KERN_PRINTK_RATELIMIT,
     
469.         .procname    = "printk_ratelimit",
     
470.         .data        = &printk_ratelimit_state.interval,
     
471.         .maxlen        = sizeof(int),
     
472.         .mode        = 0644,
     
473.         .proc_handler    = &proc_dointvec_jiffies,
     
474.         .strategy    = &sysctl_jiffies,
     
475.     },
     
476.     {
     
477.         .ctl_name    = KERN_PRINTK_RATELIMIT_BURST,
     
478.         .procname    = "printk_ratelimit_burst",
     
479.         .data        = &printk_ratelimit_state.burst,
     
480.         .maxlen        = sizeof(int),
     
481.         .mode        = 0644,
     
482.         .proc_handler    = &proc_dointvec,
     
483.     },
     
484.     {
     
485.         .ctl_name    = CTL_UNNUMBERED,
     
486.         .procname    = "printk_delay",
     
487.         .data        = &printk_delay_msec,
     
488.         .maxlen        = sizeof(int),
     
489.         .mode        = 0644,
     
490.         .proc_handler    = &proc_dointvec_minmax,
     
491.         .strategy    = &sysctl_intvec,
     
492.         .extra1        = &zero,
     
493.         .extra2        = &ten_thousand,
     
494.     },
     
495. #endif
     
496.     {
     
497.         .ctl_name    = KERN_NGROUPS_MAX,
     
498.         .procname    = "ngroups_max",
     
499.         .data        = &ngroups_max,
     
500.         .maxlen        = sizeof (int),
     
501.         .mode        = 0444,
     
502.         .proc_handler    = &proc_dointvec,
     
503.     },
     
504. #if defined(CONFIG_X86_LOCAL_APIC) && defined(CONFIG_X86)
     
505.     {
     
506.         .ctl_name = KERN_UNKNOWN_NMI_PANIC,
     
507.         .procname = "unknown_nmi_panic",
     
508.         .data = &unknown_nmi_panic,
     
509.         .maxlen = sizeof (int),
     
510.         .mode = 0644,
     
511.         .proc_handler = &proc_dointvec,
     
512.     },
     
513.     {
     
514.         .procname = "nmi_watchdog",
     
515.         .data = &nmi_watchdog_enabled,
     
516.         .maxlen = sizeof (int),
     
517.         .mode = 0644,
     
518.         .proc_handler = &proc_nmi_enabled,
     
519.     },
     
520. #endif
     
521. #if defined(CONFIG_X86)
     
522.     {
     
523.         .ctl_name    = KERN_PANIC_ON_NMI,
     
524.         .procname    = "panic_on_unrecovered_nmi",
     
525.         .data        = &panic_on_unrecovered_nmi,
     
526.         .maxlen        = sizeof(int),
     
527.         .mode        = 0644,
     
528.         .proc_handler    = &proc_dointvec,
     
529.     },
     
530.     {
     
531.         .ctl_name    = CTL_UNNUMBERED,
     
532.         .procname    = "panic_on_io_nmi",
     
533.         .data        = &panic_on_io_nmi,
     
534.         .maxlen        = sizeof(int),
     
535.         .mode        = 0644,
     
536.         .proc_handler    = &proc_dointvec,
     
537.     },
     
538.     {
     
539.         .ctl_name    = KERN_BOOTLOADER_TYPE,
     
540.         .procname    = "bootloader_type",
     
541.         .data        = &bootloader_type,
     
542.         .maxlen        = sizeof (int),
     
543.         .mode        = 0444,
     
544.         .proc_handler    = &proc_dointvec,
     
545.     },
     
546.     {
     
547.         .ctl_name    = CTL_UNNUMBERED,
     
548.         .procname    = "bootloader_version",
     
549.         .data        = &bootloader_version,
     
550.         .maxlen        = sizeof (int),
     
551.         .mode        = 0444,
     
552.         .proc_handler    = &proc_dointvec,
     
553.     },
     
554.     {
     
555.         .ctl_name    = CTL_UNNUMBERED,
     
556.         .procname    = "kstack_depth_to_print",
     
557.         .data        = &kstack_depth_to_print,
     
558.         .maxlen        = sizeof(int),
     
559.         .mode        = 0644,
     
560.         .proc_handler    = &proc_dointvec,
     
561.     },
     
562.     {
     
563.         .ctl_name    = CTL_UNNUMBERED,
     
564.         .procname    = "io_delay_type",
     
565.         .data        = &io_delay_type,
     
566.         .maxlen        = sizeof(int),
     
567.         .mode        = 0644,
     
568.         .proc_handler    = &proc_dointvec,
     
569.     },
     
570. #endif
     
571. #if defined(CONFIG_MMU)
     
572.     {
     
573.         .ctl_name    = KERN_RANDOMIZE,
     
574.         .procname    = "randomize_va_space",
     
575.         .data        = &randomize_va_space,
     
576.         .maxlen        = sizeof(int),
     
577.         .mode        = 0644,
     
578.         .proc_handler    = &proc_dointvec,
     
579.     },
     
580. #endif
     
581. #if defined(CONFIG_S390) && defined(CONFIG_SMP)
     
582.     {
     
583.         .ctl_name    = KERN_SPIN_RETRY,
     
584.         .procname    = "spin_retry",
     
585.         .data        = &spin_retry,
     
586.         .maxlen        = sizeof (int),
     
587.         .mode        = 0644,
     
588.         .proc_handler    = &proc_dointvec,
     
589.     },
     
590. #endif
     
591. #if    defined(CONFIG_ACPI_SLEEP) && defined(CONFIG_X86)
     
592.     {
     
593.         .procname    = "acpi_video_flags",
     
594.         .data        = &acpi_realmode_flags,
     
595.         .maxlen        = sizeof (unsigned long),
     
596.         .mode        = 0644,
     
597.         .proc_handler    = &proc_doulongvec_minmax,
     
598.     },
     
599. #endif
     
600. #ifdef CONFIG_IA64
     
601.     {
     
602.         .ctl_name    = KERN_IA64_UNALIGNED,
     
603.         .procname    = "ignore-unaligned-usertrap",
     
604.         .data        = &no_unaligned_warning,
     
605.         .maxlen        = sizeof (int),
     
606.          .mode        = 0644,
     
607.         .proc_handler    = &proc_dointvec,
     
608.     },
     
609.     {
     
610.         .ctl_name    = CTL_UNNUMBERED,
     
611.         .procname    = "unaligned-dump-stack",
     
612.         .data        = &unaligned_dump_stack,
     
613.         .maxlen        = sizeof (int),
     
614.         .mode        = 0644,
     
615.         .proc_handler    = &proc_dointvec,
     
616.     },
     
617. #endif
     
618. #ifdef CONFIG_DETECT_SOFTLOCKUP
     
619.     {
     
620.         .ctl_name    = CTL_UNNUMBERED,
     
621.         .procname    = "softlockup_panic",
     
622.         .data        = &softlockup_panic,
     
623.         .maxlen        = sizeof(int),
     
624.         .mode        = 0644,
     
625.         .proc_handler    = &proc_dointvec_minmax,
     
626.         .strategy    = &sysctl_intvec,
     
627.         .extra1        = &zero,
     
628.         .extra2        = &one,
     
629.     },
     
630.     {
     
631.         .ctl_name    = CTL_UNNUMBERED,
     
632.         .procname    = "softlockup_thresh",
     
633.         .data        = &softlockup_thresh,
     
634.         .maxlen        = sizeof(int),
     
635.         .mode        = 0644,
     
636.         .proc_handler    = &proc_dosoftlockup_thresh,
     
637.         .strategy    = &sysctl_intvec,
     
638.         .extra1        = &neg_one,
     
639.         .extra2        = &sixty,
     
640.     },
     
641. #endif
     
642. #ifdef CONFIG_DETECT_HUNG_TASK
     
643.     {
     
644.         .ctl_name    = CTL_UNNUMBERED,
     
645.         .procname    = "hung_task_panic",
     
646.         .data        = &sysctl_hung_task_panic,
     
647.         .maxlen        = sizeof(int),
     
648.         .mode        = 0644,
     
649.         .proc_handler    = &proc_dointvec_minmax,
     
650.         .strategy    = &sysctl_intvec,
     
651.         .extra1        = &zero,
     
652.         .extra2        = &one,
     
653.     },
     
654.     {
     
655.         .ctl_name    = CTL_UNNUMBERED,
     
656.         .procname    = "hung_task_check_count",
     
657.         .data        = &sysctl_hung_task_check_count,
     
658.         .maxlen        = sizeof(unsigned long),
     
659.         .mode        = 0644,
     
660.         .proc_handler    = &proc_doulongvec_minmax,
     
661.         .strategy    = &sysctl_intvec,
     
662.     },
     
663.     {
     
664.         .ctl_name    = CTL_UNNUMBERED,
     
665.         .procname    = "hung_task_timeout_secs",
     
666.         .data        = &sysctl_hung_task_timeout_secs,
     
667.         .maxlen        = sizeof(unsigned long),
     
668.         .mode        = 0644,
     
669.         .proc_handler    = &proc_dohung_task_timeout_secs,
     
670.         .strategy    = &sysctl_intvec,
     
671.     },
     
672.     {
     
673.         .ctl_name    = CTL_UNNUMBERED,
     
674.         .procname    = "hung_task_warnings",
     
675.         .data        = &sysctl_hung_task_warnings,
     
676.         .maxlen        = sizeof(unsigned long),
     
677.         .mode        = 0644,
     
678.         .proc_handler    = &proc_doulongvec_minmax,
     
679.         .strategy    = &sysctl_intvec,
     
680.     },
     
681. #endif
     
682. #ifdef CONFIG_COMPAT
     
683.     {
     
684.         .ctl_name    = KERN_COMPAT_LOG,
     
685.         .procname    = "compat-log",
     
686.         .data        = &compat_log,
     
687.         .maxlen        = sizeof (int),
     
688.          .mode        = 0644,
     
689.         .proc_handler    = &proc_dointvec,
     
690.     },
     
691. #endif
     
692. #ifdef CONFIG_RT_MUTEXES
     
693.     {
     
694.         .ctl_name    = KERN_MAX_LOCK_DEPTH,
     
695.         .procname    = "max_lock_depth",
     
696.         .data        = &max_lock_depth,
     
697.         .maxlen        = sizeof(int),
     
698.         .mode        = 0644,
     
699.         .proc_handler    = &proc_dointvec,
     
700.     },
     
701. #endif
     
702.     {
     
703.         .ctl_name    = CTL_UNNUMBERED,
     
704.         .procname    = "poweroff_cmd",
     
705.         .data        = &poweroff_cmd,
     
706.         .maxlen        = POWEROFF_CMD_PATH_LEN,
     
707.         .mode        = 0644,
     
708.         .proc_handler    = &proc_dostring,
     
709.         .strategy    = &sysctl_string,
     
710.     },
     
711. #ifdef CONFIG_KEYS
     
712.     {
     
713.         .ctl_name    = CTL_UNNUMBERED,
     
714.         .procname    = "keys",
     
715.         .mode        = 0555,
     
716.         .child        = key_sysctls,
     
717.     },
     
718. #endif
     
719. #ifdef CONFIG_RCU_TORTURE_TEST
     
720.     {
     
721.         .ctl_name = CTL_UNNUMBERED,
     
722.         .procname = "rcutorture_runnable",
     
723.         .data = &rcutorture_runnable,
     
724.         .maxlen = sizeof(int),
     
725.         .mode = 0644,
     
726.         .proc_handler = &proc_dointvec,
     
727.     },
     
728. #endif
     
729. #ifdef CONFIG_SLOW_WORK
     
730.     {
     
731.         .ctl_name    = CTL_UNNUMBERED,
     
732.         .procname    = "slow-work",
     
733.         .mode        = 0555,
     
734.         .child        = slow_work_sysctls,
     
735.     },
     
736. #endif
     
737. #ifdef CONFIG_PERF_EVENTS
     
738.     {
     
739.         .ctl_name    = CTL_UNNUMBERED,
     
740.         .procname    = "perf_event_paranoid",
     
741.         .data        = &sysctl_perf_event_paranoid,
     
742.         .maxlen        = sizeof(sysctl_perf_event_paranoid),
     
743.         .mode        = 0644,
     
744.         .proc_handler    = &proc_dointvec,
     
745.     },
     
746.     {
     
747.         .ctl_name    = CTL_UNNUMBERED,
     
748.         .procname    = "perf_event_mlock_kb",
     
749.         .data        = &sysctl_perf_event_mlock,
     
750.         .maxlen        = sizeof(sysctl_perf_event_mlock),
     
751.         .mode        = 0644,
     
752.         .proc_handler    = &proc_dointvec,
     
753.     },
     
754.     {
     
755.         .ctl_name    = CTL_UNNUMBERED,
     
756.         .procname    = "perf_event_max_sample_rate",
     
757.         .data        = &sysctl_perf_event_sample_rate,
     
758.         .maxlen        = sizeof(sysctl_perf_event_sample_rate),
     
759.         .mode        = 0644,
     
760.         .proc_handler    = &proc_dointvec,
     
761.     },
     
762. #endif
     
763. #ifdef CONFIG_KMEMCHECK
     
764.     {
     
765.         .ctl_name    = CTL_UNNUMBERED,
     
766.         .procname    = "kmemcheck",
     
767.         .data        = &kmemcheck_enabled,
     
768.         .maxlen        = sizeof(int),
     
769.         .mode        = 0644,
     
770.         .proc_handler    = &proc_dointvec,
     
771.     },
     
772. #endif
     
773. #ifdef CONFIG_BLOCK
     
774.     {
     
775.         .ctl_name    = CTL_UNNUMBERED,
     
776.         .procname    = "blk_iopoll",
     
777.         .data        = &blk_iopoll_enabled,
     
778.         .maxlen        = sizeof(int),
     
779.         .mode        = 0644,
     
780.         .proc_handler    = &proc_dointvec,
     
781.     },
     
782. #endif
     
783. /*
     
784.  * NOTE: do not add new entries to this table unless you have read
     
785.  * Documentation/sysctl/ctl_unnumbered.txt
     
786.  */
     
787.     { .ctl_name = 0 }
     
788. }

1. #if defined(CONFIG_HOTPLUG) && defined(CONFIG_NET)
   
2.     {
   
3.         .ctl_name    = KERN_HOTPLUG,
   
4.         .procname    = "hotplug",
   
5.         .data        = &uevent_helper,
   
6.         .maxlen        = UEVENT_HELPER_PATH_LEN,
   
7.         .mode        = 0644,
   
8.         .proc_handler    = &proc_dostring,
   
9.         .strategy    = &sysctl_string,
   
10.     },
    
11. #endif

我们看到hotplug的参数是uevent_helper
那么/sys/XXX 下面的是在哪里初始化的呢？
当然它涉及sysfs .  我们看文件kernel/ksysfs.c 

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1. static int __init ksysfs_init(void)
   
2. {
   
3.     int error;
   
4. 
   
5.     kernel_kobj = kobject_create_and_add("kernel", NULL);
   
6.     if (!kernel_kobj) {
   
7.         error = -ENOMEM;
   
8.         goto exit;
   
9.     }
   
10.     error = sysfs_create_group(kernel_kobj, &kernel_attr_group);
    
11.     if (error)
    
12.         goto kset_exit;
    
13. 
    
14.     if (notes_size > 0) {
    
15.         notes_attr.size = notes_size;
    
16.         error = sysfs_create_bin_file(kernel_kobj, &notes_attr);
    
17.         if (error)
    
18.             goto group_exit;
    
19.     }
    
20. 
    
21.     return 0;
    
22. 
    
23. group_exit:
    
24.     sysfs_remove_group(kernel_kobj, &kernel_attr_group);
    
25. kset_exit:
    
26.     kobject_put(kernel_kobj);
    
27. exit:
    
28.     return error;
    
29. }

它首先在/sys/目录下添加了kernel目录对象. 我们是否还记得uevent_helper变量？ 
我们看这段代码，似乎就会明白了

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1. #define KERNEL_ATTR_RO(_name) \
   
2. static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
   
3. 
   
4. #define KERNEL_ATTR_RW(_name) \
   
5. static struct kobj_attribute _name##_attr = \
   
6.     __ATTR(_name, 0644, _name##_show, _name##_store)
   
7. 
   
8. #if defined(CONFIG_HOTPLUG)
   
9. /* current uevent sequence number */
   
10. static ssize_t uevent_seqnum_show(struct kobject *kobj,
    
11.                  struct kobj_attribute *attr, char *buf)
    
12. {
    
13.     return sprintf(buf, "%llu\n", (unsigned long long)uevent_seqnum);
    
14. }
    
15. KERNEL_ATTR_RO(uevent_seqnum);
    
16. 
    
17. /* uevent helper program, used during early boo */
    
18. static ssize_t uevent_helper_show(struct kobject *kobj,
    
19.                  struct kobj_attribute *attr, char *buf)
    
20. {
    
21.     return sprintf(buf, "%s\n", uevent_helper);
    
22. }
    
23. static ssize_t uevent_helper_store(struct kobject *kobj,
    
24.                  struct kobj_attribute *attr,
    
25.                  const char *buf, size_t count)
    
26. {
    
27.     if (count+1 > UEVENT_HELPER_PATH_LEN)
    
28.         return -ENOENT;
    
29.     memcpy(uevent_helper, buf, count);
    
30.     uevent_helper[count] = '\0';
    
31.     if (count && uevent_helper[count-1] == '\n')
    
32.         uevent_helper[count-1] = '\0';
    
33.     return count;
    
34. }
    
35. KERNEL_ATTR_RW(uevent_helper);
    
36. #endif

KERNEL_ATTR_RW(uevent_helper);  对！就是它！我们在include/linux/sysfs.h中


#define __ATTR(_name,_mode,_show,_store) { \
.attr = {.name = __stringify(_name), .mode = _mode }, \
.show = _show, \
.store = _store, \
}
是否就和上边的代码联系起来了呢？ 
我们接着看ksysfs_init：
error = sysfs_create_group(kernel_kobj, &kernel_attr_group);
而kernel_attr_group是什么呢
static struct attribute_group kernel_attr_group = {
.attrs = kernel_attrs,
};

继续看kernel_attrs
static struct attribute * kernel_attrs[] = {
#if defined(CONFIG_HOTPLUG)
&uevent_seqnum_attr.attr,
&uevent_helper_attr.attr,
#endif
#ifdef CONFIG_PROFILING
&profiling_attr.attr,
#endif
#ifdef CONFIG_KEXEC
&kexec_loaded_attr.attr,
&kexec_crash_loaded_attr.attr,
&vmcoreinfo_attr.attr,
#endif
NULL
};

结合刚才看的一大堆宏定义.以及uevent_helper_store ，它用来写入uevent_helper。
既然我们知道了原理，就会少一些困惑^^. 而关于call_usermodehelper，有兴趣的可以自行分析学习.