Linux内核大讲堂 (一) 设备驱动的基石驱动模型(2)

上节我们分析到int kset_register(struct kset *k)函数中的kobject_add_internal(&k->kobj),我们接着分析,先唤起来一下大家的记忆，给出kset_register的函数定义：

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;

}

我们接着需要分析kobject_uevent(&k->kobj, KOBJ_ADD),这个东西是用来告诉用户空间有新朋友来啦，他叫什么什么名字。我们来看看它具体是怎么干活的。

int kobject_uevent(struct kobject *kobj, enum kobject_action action)

{

return kobject_uevent_env(kobj, action, NULL);

}

里面就一个函数：

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;

/* 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;

}

/* 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;

}

/* originating subsystem */

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;

}

/* environment buffer */

env = kzalloc(sizeof(struct kobj_uevent_env), GFP_KERNEL);

if (!env)

return -ENOMEM;

/* complete object path */

devpath = kobject_get_path(kobj, GFP_KERNEL);

if (!devpath) {

retval = -ENOENT;

goto exit;

}

/* 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;

}

}

/* 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,

__func__, retval);

goto exit;

}

}

/*

* 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;

/* 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;

retval = call_usermodehelper(argv[0], argv,

env->envp, UMH_WAIT_EXEC);

}

exit:

kfree(devpath);

kfree(env);

return retval;

}

我们经过前面那些初始化等之后，最后调用了call_usermodehelper函数。

static inline int

call_usermodehelper(char *path, char **argv, char **envp, enum umh_wait wait)

{

struct subprocess_info *info;

gfp_t gfp_mask = (wait == UMH_NO_WAIT) ? GFP_ATOMIC : GFP_KERNEL;

info = call_usermodehelper_setup(path, argv, envp, gfp_mask);

if (info == NULL)

return -ENOMEM;

return call_usermodehelper_exec(info, wait);

}

凭着在linux上的编程经验我们都知道，这个东西按照传入的参数执行了一个程序。

没错，这个就是用于与用户空间交互的重要角色。后们将会在后续合适的章节中详细讲述。

转载自：/article/1887169.html