5.1.2. sysfs源码分析
源码文件 fs/sysfs
5.1.2.1. sysfs的初始化和挂载
sysfs文件系统的初始化是在sysfs_init中完成的
static struct file_system_type sysfs_fs_type = {
.name = "sysfs",
.init_fs_context = sysfs_init_fs_context,
.kill_sb = sysfs_kill_sb,
.fs_flags = FS_USERNS_MOUNT,
};
int __init sysfs_init(void)
{
int err;
sysfs_root = kernfs_create_root(NULL, KERNFS_ROOT_EXTRA_OPEN_PERM_CHECK,
NULL);
if (IS_ERR(sysfs_root))
return PTR_ERR(sysfs_root);
sysfs_root_kn = sysfs_root->kn;
//注册sysfs文件系统
err = register_filesystem(&sysfs_fs_type);
if (err) {
kernfs_destroy_root(sysfs_root);
return err;
}
return 0;
}
5.1.2.2. 在sysfs文件系统中创建目录
在linux设备模型中，每注册一个kobjcet就会为之创建一个目录，创建目录的接口为 sysfs_create_dir_ns ,代码如下
/**
* sysfs_create_dir_ns - create a directory for an object with a namespace tag
* @kobj: object we're creating directory for
* @ns: the namespace tag to use
*/
int sysfs_create_dir_ns(struct kobject *kobj, const void *ns)
{
struct kernfs_node *parent, *kn;
kuid_t uid;
kgid_t gid;
if (WARN_ON(!kobj))
return -EINVAL;
//如果kobject没有指定父节点，则将其父节点指定为sysfs的根目录
if (kobj->parent)
parent = kobj->parent->sd;
else
parent = sysfs_root_kn;
if (!parent)
return -ENOENT;
kobject_get_ownership(kobj, &uid, &gid);
//创建目录
kn = kernfs_create_dir_ns(parent, kobject_name(kobj),
S_IRWXU | S_IRUGO | S_IXUGO, uid, gid,
kobj, ns);
if (IS_ERR(kn)) {
if (PTR_ERR(kn) == -EEXIST)
sysfs_warn_dup(parent, kobject_name(kobj));
return PTR_ERR(kn);
}
kobj->sd = kn;
return 0;
}
5.1.2.3. 在sysfs文件系统中创建一般属性文件
kobject的每一项属性都对应在sysfs文件系统中的一个文件，文件名称与属性名称相同。 创建一般属性的接口为 sysfs_create_file_ns ,代码如下
/**
* sysfs_create_file_ns - create an attribute file for an object with custom ns
* @kobj: object we're creating for
* @attr: attribute descriptor
* @ns: namespace the new file should belong to
*/
int sysfs_create_file_ns(struct kobject *kobj, const struct attribute *attr,
const void *ns)
{
kuid_t uid;
kgid_t gid;
if (WARN_ON(!kobj || !kobj->sd || !attr))
return -EINVAL;
kobject_get_ownership(kobj, &uid, &gid);
return sysfs_add_file_mode_ns(kobj->sd, attr, false, attr->mode,
uid, gid, ns);
}
EXPORT_SYMBOL_GPL(sysfs_create_file_ns);
int sysfs_add_file_mode_ns(struct kernfs_node *parent,
const struct attribute *attr, bool is_bin,
umode_t mode, kuid_t uid, kgid_t gid, const void *ns)
{
struct lock_class_key *key = NULL;
const struct kernfs_ops *ops;
struct kernfs_node *kn;
loff_t size;
if (!is_bin) {
struct kobject *kobj = parent->priv;
const struct sysfs_ops *sysfs_ops = kobj->ktype->sysfs_ops;
/* every kobject with an attribute needs a ktype assigned */
if (WARN(!sysfs_ops, KERN_ERR
"missing sysfs attribute operations for kobject: %s\n",
kobject_name(kobj)))
return -EINVAL;
if (sysfs_ops->show && sysfs_ops->store) {
if (mode & SYSFS_PREALLOC)
ops = &sysfs_prealloc_kfops_rw;
else
ops = &sysfs_file_kfops_rw;
} else if (sysfs_ops->show) {
if (mode & SYSFS_PREALLOC)
ops = &sysfs_prealloc_kfops_ro;
else
ops = &sysfs_file_kfops_ro;
} else if (sysfs_ops->store) {
if (mode & SYSFS_PREALLOC)
ops = &sysfs_prealloc_kfops_wo;
else
ops = &sysfs_file_kfops_wo;
} else
ops = &sysfs_file_kfops_empty;
size = PAGE_SIZE;
} else {
struct bin_attribute *battr = (void *)attr;
if (battr->mmap)
ops = &sysfs_bin_kfops_mmap;
else if (battr->read && battr->write)
ops = &sysfs_bin_kfops_rw;
else if (battr->read)
ops = &sysfs_bin_kfops_ro;
else if (battr->write)
ops = &sysfs_bin_kfops_wo;
else
ops = &sysfs_file_kfops_empty;
size = battr->size;
}
#ifdef CONFIG_DEBUG_LOCK_ALLOC
if (!attr->ignore_lockdep)
key = attr->key ?: (struct lock_class_key *)&attr->skey;
#endif
kn = __kernfs_create_file(parent, attr->name, mode & 0777, uid, gid,
size, ops, (void *)attr, ns, key);
if (IS_ERR(kn)) {
if (PTR_ERR(kn) == -EEXIST)
sysfs_warn_dup(parent, attr->name);
return PTR_ERR(kn);
}
return 0;
}