Linux内核当中关于设备的管理

在linux内核当中，主要就是字符设备和块设备，对应的结构体就是struct cdev和struct gendisk，在内核当中是通过如下结构的两个变量bdev_map和cdev_map来进行管理的：

struct kobj_map {
    struct probe {
        struct probe *next;
        dev_t dev;
        unsigned long range;
        struct module *owner;
        kobj_probe_t *get;
        int (*lock)(dev_t, void *);
        void *data;
    } *probes[255];
    struct mutex *lock;
};

它本质上就是一个带互斥量的哈希表，根据设备的主设备号%255来找到对应的槽，槽冲突使用链表的形式进行解决

• dev表示设备的设备号
• range表示辅设备号的范围
• owner表示拥有这个设备的模块
• get和kobject相关
• lock与设备锁定相关
• data则根据不同的map类型（字符或者块）分别指向不同的结构（cdev或者gendisk）

其中两个通用的设备结构的定义如下，其中gendisk稍微复杂一点，会涉及到分区等信息：

struct cdev {
    struct kobject kobj;
    struct module *owner;
    const struct file_operations *ops;
    struct list_head list;
    dev_t dev;
    unsigned int count;
} __randomize_layout;

struct gendisk {
    /* major, first_minor and minors are input parameters only,
     * don't use directly. Use disk_devt() and disk_max_parts().
     */
    int major;            /* major number of driver */
    int first_minor;
    int minors; /* maximum number of minors, =1 for
                                         * disks that can't be partitioned. */

    char disk_name[DISK_NAME_LEN];    /* name of major driver */
    char *(*devnode)(struct gendisk *gd, umode_t *mode);

    unsigned int events;        /* supported events */
    unsigned int async_events;    /* async events, subset of all */

    /* Array of pointers to partitions indexed by partno.
     * Protected with matching bdev lock but stat and other
     * non-critical accesses use RCU. Always access through
     * helpers.
     */
    struct disk_part_tbl __rcu *part_tbl;// 分区表
    struct hd_struct part0;

    const struct block_device_operations *fops;
    struct request_queue *queue;
    void *private_data;

    int flags;
    struct kobject *slave_dir;

    struct timer_rand_state *random;
    atomic_t sync_io;        /* RAID */
    struct disk_events *ev;
#ifdef  CONFIG_BLK_DEV_INTEGRITY
    struct kobject integrity_kobj;
#endif    /* CONFIG_BLK_DEV_INTEGRITY */
    int node_id;
    struct badblocks *bb;
};

struct kobj_map {
    struct probe {
        struct probe *next;
        dev_t dev;
        unsigned long range;
        struct module *owner;
        kobj_probe_t *get;
        int (*lock)(dev_t, void *);
        void *data;
    } *probes[255];
    struct mutex *lock;
};

struct kobj_map {
    struct probe {
        struct probe *next;
        dev_t dev;
        unsigned long range;
        struct module *owner;
        kobj_probe_t *get;
        int (*lock)(dev_t, void *);
        void *data;
    } *probes[255];
    struct mutex *lock;
};