我們已經知道了kset內嵌了kobject來表示自身的節點，創建kset就要完成其內嵌kobject，註冊kset時會產生一個事件，事件而最終會調用uevent_ops字段指向結構中的函數，這個事件是通過用戶空間的hotplug程序處理。下面我們一步一步分析。
內核同樣提供了創建和註冊kset的函數kset_create_and_add()
struct kset *kset_create_and_add(const char *name,
struct kset_uevent_ops *uevent_ops,
struct kobject *parent_kobj)
{
struct kset *kset;
int error;
kset = kset_create (name, uevent_ops, parent_kobj);
if (!kset)
return NULL;
error = kset_register(kset);
if (error) {
kfree(kset);
return NULL;
}
return kset;
}
輸入參數有一個kset_uevent_ops類型的結構變量，其結構包含三個函數指針，我們在後面的分析到這三個函數在什麼時候被調用，kset_uevent_ops結構定義如下：
struct kset_uevent_ops {
int (*filter)(struct kset *kset, struct kobject *kobj);
const char *(*name)(struct kset *kset, struct kobject *kobj);
int (*uevent)(struct kset *kset, struct kobject *kobj,
struct kobj_uevent_env *env);
};
繼續看上面的函數，先調用kset_create ()創建一個kset，接着調用kset_register()註冊它。
static struct kset *kset_create(const char *name,
struct kset_uevent_ops *uevent_ops,
struct kobject *parent_kobj)
{
struct kset *kset;
int retval;
kset = kzalloc(sizeof(*kset), GFP_KERNEL);
if (!kset)
return NULL;
retval = kobject_set_name(&kset->kobj, name);
if (retval) {
kfree(kset);
return NULL;
}
kset->uevent_ops = uevent_ops;
kset->kobj.parent = parent_kobj;
/*
* The kobject of this kset will have a type of kset_ktype and belong to
* no kset itself. That way we can properly free it when it is
* finished being used.
*/
kset->kobj.ktype = &kset_ktype;
kset->kobj.kset = NULL;
return kset;
}
爲kset分配內存，如我們上面分析，初始化了kset內嵌的kobject（這裏還未將kobject註冊到文件系統），另外用輸入參數初始化kset的uevent_ops字段。
接着看kset的註冊函數kset_register()：
int kset_register(struct kset *k)
{
int err;
if (!k)
return -EINVAL;
kset_init(k);
err = kobject_add_internal(&k->kobj);
if (err)
return err;
kobject_uevent(&k->kobj, KOBJ_ADD);
return 0;
}
在這裏終於看到調用kobject_add_internal（）將kset內嵌的kobject註冊到文件系統，這個函數我們在上面已經分析。
我們上面說到註冊kset會產生一個事件，就是在這裏調用了kobject_uevent(&k->kobj, KOBJ_ADD)
kobject_uevent()在\lib\ kobject_uevent.c中：
int kobject_uevent(struct kobject *kobj, enum kobject_action action)
{
return kobject_uevent_env(kobj, action, NULL);
}
轉入kobject_uevent_env()：
這個函數比較長，我們分段分析
int kobject_uevent_env(struct kobject *kobj, enum kobject_action action,
char *envp_ext[])
{
struct kobj_uevent_env *env;
const char *action_string = kobject_actions[action];
const char *devpath = NULL;
const char *subsystem;
struct kobject *top_kobj;
struct kset *kset;
struct kset_uevent_ops *uevent_ops;
u64 seq;
int i = 0;
int retval = 0;
pr_debug("kobject: '%s' (%p): %s\n",
kobject_name(kobj), kobj, __func__);
/* search the kset we belong to */
top_kobj = kobj;
while (!top_kobj->kset && top_kobj-> parent)
top_kobj = top_kobj->parent;
if (!top_kobj->kset) {
pr_debug("kobject: '%s' (%p): %s: attempted to send uevent "
"without kset!\n", kobject_name(kobj), kobj,
__func__);
return -EINVAL;
}
kset = top_kobj->kset;
uevent_ops = kset-> uevent_ops;
如果如果kobj的kset和parent字段都不存在，說明找不到所屬kset，也就沒有uevent_ops，不能產生事件，返回錯誤信息；相反則找到了存在kset的kobj或父kobject（依次往上找），並賦值給uevent_ops。
/* skip the event, if uevent_suppress is set*/
if (kobj-> uevent_suppress) {
pr_debug("kobject: '%s' (%p): %s: uevent_suppress "
"caused the event to drop!\n",
kobject_name(kobj), kobj, __func__);
return 0;
}
如果設置了uevent_suppress字段，說明不希望產生事件，忽略事件正確返回。注意驅動程序將在適當的地方產生改事件。
/* skip the event, if the filter returns zero. */
if (uevent_ops && uevent_ops->filter)
if (!uevent_ops->filter(kset, kobj)) {
pr_debug("kobject: '%s' (%p): %s: filter function "
"caused the event to drop!\n",
kobject_name(kobj), kobj, __func__);
return 0;
}
如果uevent_ops->filter返回0，同樣忽略事件正確返回。
if (uevent_ops && uevent_ops->name)
subsystem = uevent_ops->name(kset, kobj);
else
subsystem = kobject_name(&kset->kobj);
if (!subsystem) {
pr_debug("kobject: '%s' (%p): %s: unset subsystem caused the "
"event to drop!\n", kobject_name(kobj), kobj,
__func__);
return 0;
}
獲得子系統的名稱，不存在則返回。
/* environment buffer */
env = kzalloc(sizeof(struct kobj_uevent_env), GFP_KERNEL);
if (!env)
return -ENOMEM;
分配一個kobj_uevent_env結構內存，用於存放環境變量的值。
/* complete object path */
devpath = kobject_get_path(kobj, GFP_KERNEL);
if (!devpath) {
retval = -ENOENT;
goto exit;
}
獲得引發事件的kobject在sysfs中的路徑。
/* default keys */
retval = add_uevent_var(env, "ACTION=%s", action_string);
if (retval)
goto exit;
retval = add_uevent_var(env, "DEVPATH=%s", devpath);
if (retval)
goto exit;
retval = add_uevent_var(env, "SUBSYSTEM=%s", subsystem);
if (retval)
goto exit;
/* keys passed in from the caller */
if (envp_ext) {
for (i = 0; envp_ext[i]; i++) {
retval = add_uevent_var(env, "%s", envp_ext[i]);
if (retval)
goto exit;
}
}
調用add_uevent_var()kobj_uevent_env填充action_string,kobject路徑,子系統名稱以及其他指定環境變量。
/* let the kset specific function add its stuff */
if (uevent_ops && uevent_ops->uevent) {
retval = uevent_ops->uevent(kset, kobj, env);
if (retval) {
pr_debug("kobject: '%s' (%p): %s: uevent() returned "
"%d\n", kobject_name(kobj), kobj,
__FUNCTION__, retval);
goto exit;
}
}
調用uevent_ops的uevent函數，編程人員可在此函數中實現自定義的功能。
/*
* Mark "add" and "remove" events in the object to ensure proper
* events to userspace during automatic cleanup. If the object did
* send an "add" event, "remove" will automatically generated by
* the core, if not already done by the caller.
*/
if (action == KOBJ_ADD)
kobj->state_add_uevent_sent = 1;
else if (action == KOBJ_REMOVE)
kobj->state_remove_uevent_sent = 1;
設置KOBJ_ADD和KOBJ_REMOVE的標誌。
/* we will send an event, so request a new sequence number */
spin_lock(&sequence_lock);
seq = ++uevent_seqnum;
spin_unlock(&sequence_lock);
retval = add_uevent_var(env, "SEQNUM=%llu", (unsigned long long)seq);
if (retval)
goto exit;
#if defined(CONFIG_NET)
/* send netlink message */
if (uevent_sock) {
struct sk_buff *skb;
size_t len;
/* allocate message with the maximum possible size */
len = strlen(action_string) + strlen(devpath) + 2;
skb = alloc_skb(len + env->buflen, GFP_KERNEL);
if (skb) {
char *scratch;
/* add header */
scratch = skb_put(skb, len);
sprintf(scratch, "%s@%s", action_string, devpath);
/* copy keys to our continuous event payload buffer */
for (i = 0; i < env->envp_idx; i++) {
len = strlen(env->envp[i]) + 1;
scratch = skb_put(skb, len);
strcpy(scratch, env->envp[i]);
}
NETLINK_CB(skb).dst_group = 1;
retval = netlink_broadcast(uevent_sock, skb, 0, 1,
GFP_KERNEL);
/* ENOBUFS should be handled in userspace */
if (retval == -ENOBUFS)
retval = 0;
} else
retval = -ENOMEM;
}
#endif
/* call uevent_helper, usually only enabled during early boot */
if (uevent_helper[0]) {
char *argv [3];
argv [0] = uevent_helper;
argv [1] = (char *)subsystem;
argv [2] = NULL;
retval = add_uevent_var(env, "HOME=/");
if (retval)
goto exit;
retval = add_uevent_var(env,
"PATH=/sbin:/bin:/usr/sbin:/usr/bin");
if (retval)
goto exit;
添加HOME和PATH環境變量。
retval = call_usermodehelper(argv[0], argv,
env->envp, UMH_WAIT_EXEC);
}
exit:
kfree(devpath);
kfree(env);
return retval;
}
調用hotplug函數。
看一下kset_unregister（）
void kset_unregister (struct kset *k)
{
if (!k)
return;
kobject_put(&k-> kobj);
}
減少其內嵌的kobj計數，爲0則釋放其內存空間。
已經分析完kobject和kset，linux的設備模型就是基於這兩個數據結構的，在此基礎上，後續將分析設備模型中的device、driver、和bus。