Button-hotplug驱动分析--openwrt下驱动模块

Button-hotplug驱动并不是按键的设备驱动，而是按键的input输入子系统层驱动：按键被按下时按键的设备驱动将对应的按键编号（对应该按键的GPIO号）等数据传递给input core，input core再调用本驱动的button_hotplug_handler来将数据输出到usrspace（环境变量通过sk_buff被广播出去后，所有的工作就成了应用层对某一类事件的处理内核已经做好无需关心了）。

#include
#include
#include
#include

#include
#include
#include
#include

#define DRV_NAME "button-hotplug"
#define DRV_VERSION "0.4.1"
#define DRV_DESC "Button Hotplug driver"

#define BH_SKB_SIZE 2048

#define PFX DRV_NAME ": "

#undef BH_DEBUG

#ifdef BH_DEBUG
#define BH_DBG(fmt, args...) printk(KERN_DEBUG "%s: " fmt, DRV_NAME, ##args )
#else
#define BH_DBG(fmt, args...) do {} while (0)
#endif

#define BH_ERR(fmt, args...) printk(KERN_ERR "%s: " fmt, DRV_NAME, ##args )

#ifndef BIT_MASK
#define BIT_MASK(nr)            (1UL << ((nr) % BITS_PER_LONG))
#endif

struct bh_priv {
unsigned long *seen;
struct input_handle handle;
};

struct bh_event {
const char *name;
char *action;
unsigned long seen;

struct sk_buff *skb;
struct work_struct work;
};

struct bh_map {
unsigned int code;
const char *name;
};

extern u64 uevent_next_seqnum(void);

#define BH_MAP(_code, _name) \
{ \
.code = (_code), \
.name = (_name), \
}

static struct bh_map button_map[] = {
BH_MAP(BTN_0, "BTN_0"),
BH_MAP(BTN_1, "BTN_1"),
BH_MAP(BTN_2, "BTN_2"),
BH_MAP(BTN_3, "BTN_3"),
BH_MAP(BTN_4, "BTN_4"),
BH_MAP(BTN_5, "BTN_5"),
BH_MAP(BTN_6, "BTN_6"),
BH_MAP(BTN_7, "BTN_7"),
BH_MAP(BTN_8, "BTN_8"),
BH_MAP(BTN_9, "BTN_9"),
BH_MAP(KEY_RESTART, "reset"),
BH_MAP(KEY_POWER, "power"),
BH_MAP(KEY_RFKILL, "rfkill"),
BH_MAP(KEY_WPS_BUTTON, "wps"),
BH_MAP(KEY_WIMAX, "wwan"),
};

/* -------------------------------------------------------------------------*/

static int bh_event_add_var(struct bh_event *event, int argv,
const char *format, ...)
{
static char buf[128];
char *s;
va_list args;
int len;

if (argv)
return 0;

va_start(args, format);
len = vsnprintf(buf, sizeof(buf), format, args);//将要添加的环境变量临时放在buf中，并获取环境变量的长度len
va_end(args);

if (len >= sizeof(buf)) {
BH_ERR("buffer size too small\n");
WARN_ON(1);
return -ENOMEM;
}

s = skb_put(event->skb, len + 1);//往sk_buff缓冲区中继续添加长度len的数据
strcpy(s, buf);//拷贝实际的数据内容到sk_buff缓冲区。

BH_DBG("added variable '%s'\n", s);

return 0;
}

static int button_hotplug_fill_event(struct bh_event *event)
{
int ret;

ret = bh_event_add_var(event, 0, "HOME=%s", "/");//往sk_buff缓冲区中添加环境变量HOME=/.
if (ret)
return ret;

ret = bh_event_add_var(event, 0, "PATH=%s",//往sk_buff缓冲区中添加环境变量PATH=/sbin:/bin:/usr/sbin:/usr/bin.
"/sbin:/bin:/usr/sbin:/usr/bin");
if (ret)
return ret;

ret = bh_event_add_var(event, 0, "SUBSYSTEM=%s", "button");
if (ret)//往sk_buff缓冲区中添加环境变量SUBSYSTEM=button.
return ret;

ret = bh_event_add_var(event, 0, "ACTION=%s", event->action);
if (ret)//往sk_buff缓冲区中添加环境变量ACTION=pressed(released?)--->详见201行。
return ret;

ret = bh_event_add_var(event, 0, "BUTTON=%s", event->name);
if (ret)
return ret;

ret = bh_event_add_var(event, 0, "SEEN=%ld", event->seen);
if (ret)
return ret;

ret = bh_event_add_var(event, 0, "SEQNUM=%llu", uevent_next_seqnum());

return ret;
}

static void button_hotplug_work(struct work_struct *work)
{
struct bh_event *event = container_of(work, struct bh_event, work);
int ret = 0;

event->skb = alloc_skb(BH_SKB_SIZE, GFP_KERNEL);
if (!event->skb)
goto out_free_event;

ret = bh_event_add_var(event, 0, "%s@", event->action);
if (ret)
goto out_free_skb;

ret = button_hotplug_fill_event(event);//先将硬件设备发生过的各种事件添加到环境变量缓冲区SK_BUFF中。
if (ret)
goto out_free_skb;

NETLINK_CB(event->skb).dst_group = 1;
broadcast_uevent(event->skb, 0, 1, GFP_KERNEL);//将sk_buff中的环境变量广播出去(上层应用可通过socket监听到)--->此处属于传递数据给应用层

 out_free_skb:
if (ret) {
BH_ERR("work error %d\n", ret);
kfree_skb(event->skb);
}
 out_free_event:
kfree(event);
}

static int button_hotplug_create_event(const char *name, unsigned long seen,
int pressed)
{
struct bh_event *event;

BH_DBG("create event, name=%s, seen=%lu, pressed=%d\n",
name, seen, pressed);

event = kzalloc(sizeof(*event), GFP_KERNEL);
if (!event)
return -ENOMEM;

event->name = name;
event->seen = seen;
event->action = pressed ? "pressed" : "released";

INIT_WORK(&event->work, (void *)(void *)button_hotplug_work);
schedule_work(&event->work);//将任务添加到工作队列，并请求调度新任务以执行。

return 0;
}

/* -------------------------------------------------------------------------*/
static int button_get_index(unsigned int code)
{
int i;

for (i = 0; i < ARRAY_SIZE(button_map); i++)
if (button_map[i].code == code)
return i;

return -1;
}
static void button_hotplug_event(struct input_handle *handle,
  unsigned int type, unsigned int code, int value)
{
struct bh_priv *priv = handle->private;//handle为input的总线，该结构体保存了各种输入设备
//在上次产生事件时系统的节拍数。
unsigned long seen = jiffies;//系统本次启动至今的节拍数(即systick总数)
int btn;

BH_DBG("event type=%u, code=%u, value=%d\n", type, code, value);

if (type != EV_KEY)
return;

btn = button_get_index(code);
if (btn < 0)
return;

button_hotplug_create_event(button_map[btn].name,
(seen - priv->seen[btn]) / HZ, value);//事件为案件pressed，seen为上次按键松开到此次pressed的时间。
//事件为realsed，seen才为用户按住按键所持续的时间。
priv->seen[btn] = seen;//将该输入设备产生此次事件时的系统节拍数重新保存在handle总线的结构体中。
}

static int button_hotplug_connect(struct input_handler *handler,
struct input_dev *dev, const struct input_device_id *id)
{
struct bh_priv *priv;
int ret;
int i;

for (i = 0; i < ARRAY_SIZE(button_map); i++)
if (test_bit(button_map[i].code, dev->keybit))
break;

if (i == ARRAY_SIZE(button_map))
return -ENODEV;

priv = kzalloc(sizeof(*priv) +
      (sizeof(unsigned long) * ARRAY_SIZE(button_map)),
      GFP_KERNEL);
if (!priv)
return -ENOMEM;

priv->seen = (unsigned long *) &priv[1];
priv->handle.private = priv;
priv->handle.dev = dev;
priv->handle.handler = handler;
priv->handle.name = DRV_NAME;

ret = input_register_handle(&priv->handle);
if (ret)
goto err_free_priv;

ret = input_open_device(&priv->handle);
if (ret)
goto err_unregister_handle;

BH_DBG("connected to %s\n", dev->name);

return 0;

 err_unregister_handle:
input_unregister_handle(&priv->handle);

 err_free_priv:
kfree(priv);
return ret;
}

static void button_hotplug_disconnect(struct input_handle *handle)
{
struct bh_priv *priv = handle->private;

input_close_device(handle);
input_unregister_handle(handle);

kfree(priv);
}

static const struct input_device_id button_hotplug_ids[] = {
{
                .flags = INPUT_DEVICE_ID_MATCH_EVBIT,
                .evbit = { BIT_MASK(EV_KEY) },
        },
{
/* Terminating entry */
},
};


MODULE_DEVICE_TABLE(input, button_hotplug_ids);


static struct input_handler button_hotplug_handler = {
.event = button_hotplug_event,
.connect = button_hotplug_connect,
.disconnect = button_hotplug_disconnect,
.name = DRV_NAME,
.id_table = button_hotplug_ids,
};


/* -------------------------------------------------------------------------*/


static int __init button_hotplug_init(void)
{
int ret;


printk(KERN_INFO DRV_DESC " version " DRV_VERSION "\n");
ret = input_register_handler(&button_hotplug_handler);
if (ret)
BH_ERR("unable to register input handler\n");


return ret;
}
module_init(button_hotplug_init);


static void __exit button_hotplug_exit(void)
{
input_unregister_handler(&button_hotplug_handler);
}
module_exit(button_hotplug_exit);


MODULE_DESCRIPTION(DRV_DESC);
MODULE_VERSION(DRV_VERSION);
MODULE_AUTHOR("Gabor Juhos ");
MODULE_LICENSE("GPL v2");