Linux设备模型分析之kobject
作者:刘昊昱 博客:http://blog.csdn.net/liuhaoyutz内核版本:2.6.36 一、kobject应用举例Linux设备模型最基本的组成元素是kobject,我们先来看一个kobject的应用例子,该程序在Ubuntu 10.10, 2.6.32-38-generic-pae内核上调试通过。#include#include#inc
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作者:刘昊昱
博客:http://blog.csdn.net/liuhaoyutz
内核版本:2.6.36
一、kobject应用举例
Linux设备模型最基本的组成元素是kobject,我们先来看一个kobject的应用例子,该程序在Ubuntu 10.10, 2.6.32-38-generic-pae内核上调试通过。
#include <linux/device.h> #include <linux/module.h> #include <linux/kernel.h> #include <linux/init.h> #include <linux/string.h> #include <linux/sysfs.h> #include <linux/stat.h> MODULE_AUTHOR("haoyu"); MODULE_LICENSE("Dual BSD/GPL"); struct my_kobject { int value; struct kobject kobj; }; struct my_kobject my_kobj; void kobject_release(struct kobject *kobject); ssize_t kobject_attr_show(struct kobject *kobject, struct attribute *attr,char *buf); ssize_t kobject_attr_store(struct kobject *kobject,struct attribute *attr,const char *buf, size_t count); struct attribute kobject_attr1 = { .name = "name", .mode = S_IRWXUGO, }; struct attribute kobject_attr2 = { .name = "value", .mode = S_IRWXUGO, }; static struct attribute *kobject_def_attrs[] = { &kobject_attr1, &kobject_attr2, NULL, }; struct sysfs_ops kobject_sysfs_ops = { .show = kobject_attr_show, .store = kobject_attr_store, }; struct kobj_type ktype = { .release = kobject_release, .sysfs_ops = &kobject_sysfs_ops, .default_attrs = kobject_def_attrs, }; void kobject_release(struct kobject *kobject) { printk("kobject release.\n"); } ssize_t kobject_attr_show(struct kobject *kobject, struct attribute *attr,char *buf) { int count = 0; struct my_kobject *my_kobj = container_of(kobject, struct my_kobject, kobj); printk("kobject attribute show.\n"); if(strcmp(attr->name, "name") == 0) count = sprintf(buf, "%s\n", kobject->name); else if(strcmp(attr->name, "value") == 0) count = sprintf(buf, "%d\n", my_kobj->value); else printk("no this attribute.\n"); return count; } ssize_t kobject_attr_store(struct kobject *kobject,struct attribute *attr,const char *buf, size_t count) { int val; struct my_kobject *my_kobj = container_of(kobject, struct my_kobject, kobj); printk("kobject attribute store.\n"); if(strcmp(attr->name, "name") == 0) printk("Can not change name.\n"); else if(strcmp(attr->name, "value") == 0) { val = buf[0] - '0'; if(val == 0 || val == 1) my_kobj->value = val; else printk("value is '0' or '1'\n"); } else printk("no this attribute.\n"); return count; } static int kobject_test_init(void) { printk("kboject test init.\n"); kobject_init_and_add(&my_kobj.kobj,&ktype,NULL,"kobject_test"); return 0; } static void kobject_test_exit(void) { printk("kobject test exit.\n"); kobject_del(&my_kobj.kobj); } module_init(kobject_test_init); module_exit(kobject_test_exit);
该模块执行过程如下图所示:
二、相关数据结构:
kobject是Linux设备模型中最基本的数据结构,代表设备模式的一个基本对象。
kobj_type是kobject的类型,包括kobject的属性以及属性的操作接口,不同的kobject可以具有相同的kobj_type。
kset是几个kobject的集合,这些kobject可以具有相同的kobj_type,也可以具有不同的kobj_type。
struct kobject { const char *name; struct list_head entry; struct kobject *parent; struct kset *kset; struct kobj_type *ktype; struct sysfs_dirent *sd; struct kref kref; unsigned int state_initialized:1; unsigned int state_in_sysfs:1; unsigned int state_add_uevent_sent:1; unsigned int state_remove_uevent_sent:1; unsigned int uevent_suppress:1; }; /** * struct kset - a set of kobjects of a specific type, belonging to a specific subsystem. * * A kset defines a group of kobjects. They can be individually * different "types" but overall these kobjects all want to be grouped * together and operated on in the same manner. ksets are used to * define the attribute callbacks and other common events that happen to * a kobject. * * @list: the list of all kobjects for this kset * @list_lock: a lock for iterating over the kobjects * @kobj: the embedded kobject for this kset (recursion, isn't it fun...) * @uevent_ops: the set of uevent operations for this kset. These are * called whenever a kobject has something happen to it so that the kset * can add new environment variables, or filter out the uevents if so * desired. */ struct kset { struct list_head list; spinlock_t list_lock; struct kobject kobj; const struct kset_uevent_ops *uevent_ops; }; struct kset_uevent_ops { int (* const filter)(struct kset *kset, struct kobject *kobj); const char *(* const name)(struct kset *kset, struct kobject *kobj); int (* const uevent)(struct kset *kset, struct kobject *kobj, struct kobj_uevent_env *env); }; struct kobj_type { void (*release)(struct kobject *kobj); const struct sysfs_ops *sysfs_ops; struct attribute **default_attrs; const struct kobj_ns_type_operations *(*child_ns_type)(struct kobject *kobj); const void *(*namespace)(struct kobject *kobj); }; struct sysfs_ops { ssize_t (*show)(struct kobject *, struct attribute *,char *); ssize_t (*store)(struct kobject *,struct attribute *,const char *, size_t); }; struct attribute { const char *name; mode_t mode; #ifdef CONFIG_DEBUG_LOCK_ALLOC struct lock_class_key *key; struct lock_class_key skey; #endif }; /* * Callbacks so sysfs can determine namespaces * @current_ns: return calling task's namespace * @netlink_ns: return namespace to which a sock belongs (right?) * @initial_ns: return the initial namespace (i.e. init_net_ns) */ struct kobj_ns_type_operations { enum kobj_ns_type type; const void *(*current_ns)(void); const void *(*netlink_ns)(struct sock *sk); const void *(*initial_ns)(void); }; struct kref { atomic_t refcount; };
三、kobject注册和注销过程分析
kobject的注册是通过调用kobject_init_and_add函数,该函数定义如下:
/** * kobject_init_and_add - initialize a kobject structure and add it to the kobject hierarchy * @kobj: pointer to the kobject to initialize * @ktype: pointer to the ktype for this kobject. * @parent: pointer to the parent of this kobject. * @fmt: the name of the kobject. * * This function combines the call to kobject_init() and * kobject_add(). The same type of error handling after a call to * kobject_add() and kobject lifetime rules are the same here. */ int kobject_init_and_add(struct kobject *kobj, struct kobj_type *ktype, struct kobject *parent, const char *fmt, ...) { va_list args; int retval; kobject_init(kobj, ktype); va_start(args, fmt); retval = kobject_add_varg(kobj, parent, fmt, args); va_end(args); return retval; }
这个函数分为两部分,首先调用kobject_init函数对kobject对象进行基本的初始化。然后,调用kobject_add_varg函数将kobject注册到系统中。va_start和va_end是处理可变参数的固定语法。先来看kobject_init,该函数定义如下:
/** * kobject_init - initialize a kobject structure * @kobj: pointer to the kobject to initialize * @ktype: pointer to the ktype for this kobject. * * This function will properly initialize a kobject such that it can then * be passed to the kobject_add() call. * * After this function is called, the kobject MUST be cleaned up by a call * to kobject_put(), not by a call to kfree directly to ensure that all of * the memory is cleaned up properly. */ void kobject_init(struct kobject *kobj, struct kobj_type *ktype) { char *err_str; if (!kobj) { err_str = "invalid kobject pointer!"; goto error; } if (!ktype) { err_str = "must have a ktype to be initialized properly!\n"; goto error; } if (kobj->state_initialized) { /* do not error out as sometimes we can recover */ printk(KERN_ERR "kobject (%p): tried to init an initialized " "object, something is seriously wrong.\n", kobj); dump_stack(); } kobject_init_internal(kobj); kobj->ktype = ktype; return; error: printk(KERN_ERR "kobject (%p): %s\n", kobj, err_str); dump_stack(); }
该函数首先确保kobj和ktype都存在,否则直接退出。如果该kobj进行过初始化,则打印警告信息。然后调用kobject_init_internal真正开始初始化kobj,最后把kobj->ktype设置为ktype。kobject_init_internal函数定义如下:
static void kobject_init_internal(struct kobject *kobj) { if (!kobj) return; kref_init(&kobj->kref); INIT_LIST_HEAD(&kobj->entry); kobj->state_in_sysfs = 0; kobj->state_add_uevent_sent = 0; kobj->state_remove_uevent_sent = 0; kobj->state_initialized = 1; }
首先初始化kobj->kref,实际上kobj->kref就是一个原子变量(atomic_t)。接着初始化链表项kobj->entry,并设置其他kobject成员。至此,kobject_init函数就分析完了,我们返回到kobject_init_and_add函数,下面该分析kobject_add_varg函数了:
static int kobject_add_varg(struct kobject *kobj, struct kobject *parent, const char *fmt, va_list vargs) { int retval; retval = kobject_set_name_vargs(kobj, fmt, vargs); if (retval) { printk(KERN_ERR "kobject: can not set name properly!\n"); return retval; } kobj->parent = parent; return kobject_add_internal(kobj); }
首先调用kobject_set_name_vargs设置kob->name。然后初始化kobj->parent为parent参数指定的kobject。最后,调用kobject_add_internal将kobject注册到系统中,该函数定义如下:static int kobject_add_internal(struct kobject *kobj) { int error = 0; struct kobject *parent; if (!kobj) return -ENOENT; if (!kobj->name || !kobj->name[0]) { WARN(1, "kobject: (%p): attempted to be registered with empty " "name!\n", kobj); return -EINVAL; } parent = kobject_get(kobj->parent); /* join kset if set, use it as parent if we do not already have one */ if (kobj->kset) { if (!parent) parent = kobject_get(&kobj->kset->kobj); kobj_kset_join(kobj); kobj->parent = parent; } pr_debug("kobject: '%s' (%p): %s: parent: '%s', set: '%s'\n", kobject_name(kobj), kobj, __func__, parent ? kobject_name(parent) : "<NULL>", kobj->kset ? kobject_name(&kobj->kset->kobj) : "<NULL>"); error = create_dir(kobj); if (error) { kobj_kset_leave(kobj); kobject_put(parent); kobj->parent = NULL; /* be noisy on error issues */ if (error == -EEXIST) printk(KERN_ERR "%s failed for %s with " "-EEXIST, don't try to register things with " "the same name in the same directory.\n", __func__, kobject_name(kobj)); else printk(KERN_ERR "%s failed for %s (%d)\n", __func__, kobject_name(kobj), error); dump_stack(); } else kobj->state_in_sysfs = 1; return error; }
首先确保kobj->name已经被赋值,即kobject必须有名字。如果指定了kobj->kset,则调用kobj_kset_join将kobj加入到kobj->kset中。同时,如果kobj->parent仍为NULL,则将kobj->parent设置为kobj->kset->kobj。然后,调用create_dir(kobj)在/sys目录下建立kobject相关目录结构。
kobj_kset_join函数定义如下:
/* add the kobject to its kset's list */ static void kobj_kset_join(struct kobject *kobj) { if (!kobj->kset) return; kset_get(kobj->kset); spin_lock(&kobj->kset->list_lock); list_add_tail(&kobj->entry, &kobj->kset->list); spin_unlock(&kobj->kset->list_lock); }
create_dir函数定义如下:static int create_dir(struct kobject *kobj) { int error = 0; if (kobject_name(kobj)) { error = sysfs_create_dir(kobj); if (!error) { error = populate_dir(kobj); if (error) sysfs_remove_dir(kobj); } } return error; }
首先调用sysfs_create_dir在/sys下建立目录,然后再调用populate_dir在新建目录下生成属性文件。sysfs_create_dir函数定义如下:
/** * sysfs_create_dir - create a directory for an object. * @kobj: object we're creating directory for. */ int sysfs_create_dir(struct kobject * kobj) { enum kobj_ns_type type; struct sysfs_dirent *parent_sd, *sd; const void *ns = NULL; int error = 0; BUG_ON(!kobj); if (kobj->parent) parent_sd = kobj->parent->sd; else parent_sd = &sysfs_root; if (sysfs_ns_type(parent_sd)) ns = kobj->ktype->namespace(kobj); type = sysfs_read_ns_type(kobj); error = create_dir(kobj, parent_sd, type, ns, kobject_name(kobj), &sd); if (!error) kobj->sd = sd; return error; }
这里主要是通过调用create_dir函数建立kobject对应的目录。这个函数我们就不继续向下跟踪了。下面来看populate_dir函数,其定义如下:
/* * populate_dir - populate directory with attributes. * @kobj: object we're working on. * * Most subsystems have a set of default attributes that are associated * with an object that registers with them. This is a helper called during * object registration that loops through the default attributes of the * subsystem and creates attributes files for them in sysfs. */ static int populate_dir(struct kobject *kobj) { struct kobj_type *t = get_ktype(kobj); struct attribute *attr; int error = 0; int i; if (t && t->default_attrs) { for (i = 0; (attr = t->default_attrs[i]) != NULL; i++) { error = sysfs_create_file(kobj, attr); if (error) break; } } return error; }
该函数循环遍历kobject的所有属性,并调用sysfs_create_file函数在/sys系统对应目录下建立属性文件。至此,kobject的注册过程我们就分析完了。
kobject的注销过程是调用kobject_del函数,该函数定义如下:
/** * kobject_del - unlink kobject from hierarchy. * @kobj: object. */ void kobject_del(struct kobject *kobj) { if (!kobj) return; sysfs_remove_dir(kobj); kobj->state_in_sysfs = 0; kobj_kset_leave(kobj); kobject_put(kobj->parent); kobj->parent = NULL; }
这里需要注意的是,只要把目录删除,目录下的属性文件自动就删除了。
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