[virtual system file] sget函数解析

struct super_block *sget(struct file_system_type *type,int (*test)(struct super_block *,void *),int (*set)(struct super_block *,void *),int flags,void *data) /* find or create a superblock */{struct super_block *s = NULL;struct super_block *old;int err;retry:spin_lock(&sb_lock);if (test) {/* 该if语句，用于搜索type->fs_supers链表是否有需求的super_block实例，如果有则返回该实例，如果没有退出该if */hlist_for_each_entry(old, &type->fs_supers, s_instances) {if (!test(old, data))continue;if (!grab_super(old))goto retry;if (s) {up_write(&s->s_umount);destroy_super(s);s = NULL;}return old;}}if (!s) {spin_unlock(&sb_lock);s = alloc_super(type, flags);/* 分配一个super_block的实例，并对其成员初始化 */if (!s)return ERR_PTR(-ENOMEM);goto retry;}err = set(s, data);/* 关联super_block与data */if (err) {spin_unlock(&sb_lock);up_write(&s->s_umount);destroy_super(s);return ERR_PTR(err);}s->s_type = type;strlcpy(s->s_id, type->name, sizeof(s->s_id));list_add_tail(&s->s_list, &super_blocks);hlist_add_head(&s->s_instances, &type->fs_supers); /* 将super_block添加到type->fs_supers的hash链表 */spin_unlock(&sb_lock);get_filesystem(type);register_shrinker(&s->s_shrink);return s;}EXPORT_SYMBOL(sget);

总结：sget是在@type的fs_supers链表中找是否与@data相匹配的super_block实例，通过@test方法，如果找到直接返回该实例；如果没有找到则通过alloc_super方法申请一个新的super_block实例，并将该实例用@set方法与@data关联起来与进一步的初始化，并将该实例添加到super_blocks链表和@type->fs_supers链表中，然后返回该实例。