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Linux 驱动程序 简单字符驱动设备

scull 字符设备驱动程序的设备描述

字符设备驱动程序是分配一段内存,然后提供对这个设备的管理方式,我们通过它提供的操作来操纵字符驱动设备,本质上是一个我们分配的模拟内存来模拟驱动设备。

 

结构如下:

 

scull

几个重要方法,我们最初只提供几个简单的接口函数。

 

read : 拷贝数据到应用程序空间。

write: 拷贝数据到内核空间,在这里就是我们的字符驱动设备。

open : 打开并且初始化设备。

字符设备驱动程序几个重要的数据结构:

 

struct scull_dev {

struct scull_qset *data;  /* Pointer to first quantum set */

int quantum;              /* the current quantum size */

int qset;                 /* the current array size */

unsigned long size;       /* amount of data stored here */

unsigned int access_key;  /* used by sculluid and scullpriv */

struct semaphore sem;     /* mutual exclusion semaphore     */

struct cdev cdev;   /* Char device structure */

};

 

struct cdev {

struct kobject kobj;

struct module *owner;

const struct file_operations *ops;

struct list_head list;

dev_t dev;

unsigned int count;

};

 

struct inode {

umode_t i_mode;

unsigned short i_opflags;

kuid_t i_uid;

kgid_t i_gid;

unsigned int i_flags;

 

#ifdef CONFIG_FS_POSIX_ACL

struct posix_acl *i_acl;

struct posix_acl *i_default_acl;

#endif

 

const struct inode_operations *i_op;

struct super_block *i_sb;

struct address_space *i_mapping;

 

#ifdef CONFIG_SECURITY

void *i_security;

#endif

 

/* Stat data, not accessed from path walking */

unsigned long i_ino;

/*

* Filesystems may only read i_nlink directly.  They shall use the

* following functions for modification:

*

*    (set|clear|inc|drop)_nlink

*    inode_(inc|dec)_link_count

*/

union {

const unsigned int i_nlink;

unsigned int __i_nlink;

};

dev_t i_rdev;

loff_t i_size;

struct timespec i_atime;

struct timespec i_mtime;

struct timespec i_ctime;

spinlock_t i_lock; /* i_blocks, i_bytes, maybe i_size */

unsigned short          i_bytes;

unsigned int i_blkbits;

blkcnt_t i_blocks;

 

#ifdef __NEED_I_SIZE_ORDERED

seqcount_t i_size_seqcount;

#endif

 

/* Misc */

unsigned long i_state;

struct mutex i_mutex;

 

unsigned long dirtied_when; /* jiffies of first dirtying */

unsigned long dirtied_time_when;

 

struct hlist_node i_hash;

struct list_head i_io_list; /* backing dev IO list */

#ifdef CONFIG_CGROUP_WRITEBACK

struct bdi_writeback *i_wb; /* the associated cgroup wb */

 

/* foreign inode detection, see wbc_detach_inode() */

int i_wb_frn_winner;

u16 i_wb_frn_avg_time;

u16 i_wb_frn_history;

#endif

struct list_head i_lru; /* inode LRU list */

struct list_head i_sb_list;

union {

struct hlist_head i_dentry;

struct rcu_head i_rcu;

};

u64 i_version;

atomic_t i_count;

atomic_t i_dio_count;

atomic_t i_writecount;

#ifdef CONFIG_IMA

atomic_t i_readcount; /* struct files open RO */

#endif

const struct file_operations *i_fop; /* former ->i_op->default_file_ops */

struct file_lock_context *i_flctx;

struct address_space i_data;

struct list_head i_devices;

union {

struct pipe_inode_info *i_pipe;

struct block_device *i_bdev;

struct cdev *i_cdev;

char *i_link;

};

 

__u32 i_generation;

 

#ifdef CONFIG_FSNOTIFY

__u32 i_fsnotify_mask; /* all events this inode cares about */

struct hlist_head i_fsnotify_marks;

#endif

 

void *i_private; /* fs or device private pointer */

};

 

struct file {

union {

struct llist_node fu_llist;

struct rcu_head fu_rcuhead;

} f_u;

struct path f_path;

struct inode *f_inode; /* cached value */

const struct file_operations *f_op;

 

/*

* Protects f_ep_links, f_flags.

* Must not be taken from IRQ context.

*/

spinlock_t f_lock;

atomic_long_t f_count;

unsigned int f_flags;

fmode_t f_mode;

struct mutex f_pos_lock;

loff_t f_pos;

struct fown_struct f_owner;

const struct cred *f_cred;

struct file_ra_state f_ra;

 

u64 f_version;

#ifdef CONFIG_SECURITY

void *f_security;

#endif

/* needed for tty driver, and maybe others */

void *private_data;

 

#ifdef CONFIG_EPOLL

/* Used by fs/eventpoll.c to link all the hooks to this file */

struct list_head f_ep_links;

struct list_head f_tfile_llink;

#endif /* #ifdef CONFIG_EPOLL */

struct address_space *f_mapping;

} __attribute__((aligned(4))); /* lest something weird decides that 2 is OK */

 

struct file_handle {

__u32 handle_bytes;

int handle_type;

/* file identifier */

unsigned char f_handle[0];

};

 

struct file_operations {

struct module *owner;

loff_t (*llseek) (struct file *, loff_t, int);

ssize_t (*read) (struct file *, char __user *, size_t, loff_t *);

ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);

ssize_t (*read_iter) (struct kiocb *, struct iov_iter *);

ssize_t (*write_iter) (struct kiocb *, struct iov_iter *);

int (*iterate) (struct file *, struct dir_context *);

unsigned int (*poll) (struct file *, struct poll_table_struct *);

long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);

long (*compat_ioctl) (struct file *, unsigned int, unsigned long);

int (*mmap) (struct file *, struct vm_area_struct *);

int (*open) (struct inode *, struct file *);

int (*flush) (struct file *, fl_owner_t id);

int (*release) (struct inode *, struct file *);

int (*fsync) (struct file *, loff_t, loff_t, int datasync);

int (*aio_fsync) (struct kiocb *, int datasync);

int (*fasync) (int, struct file *, int);

int (*lock) (struct file *, int, struct file_lock *);

ssize_t (*sendpage) (struct file *, struct page *, int, size_t, loff_t *, int);

unsigned long (*get_unmapped_area)(struct file *, unsigned long, unsigned long, unsigned long, unsigned long);

int (*check_flags)(int);

int (*flock) (struct file *, int, struct file_lock *);

ssize_t (*splice_write)(struct pipe_inode_info *, struct file *, loff_t *, size_t, unsigned int);

ssize_t (*splice_read)(struct file *, loff_t *, struct pipe_inode_info *, size_t, unsigned int);

int (*setlease)(struct file *, long, struct file_lock **, void **);

long (*fallocate)(struct file *file, int mode, loff_t offset,

loff_t len);

void (*show_fdinfo)(struct seq_file *m, struct file *f);

#ifndef CONFIG_MMU

unsigned (*mmap_capabilities)(struct file *);

#endif

};

 

 

设备驱动程序设计的基本框架

 

 

scull_mem

1.申请设备号,主,次设备号。

 

2.构建我们的设备结构。

 

3.编写fops的内核提供的操作方法,更新fops指针。

 

4.注册我们的设备。

 

 

测试结果

 

我们可以看到,当给我们的scull新设备写入数据的时候,使用free命令就可以看到内存被成功占用。

 

这里有一个重要问题:

 

如何安全的将数据在用户空间和逻辑空间之间拷贝?

 

解决方法:内核提供了安全的拷贝函数:

copy_to_user

copy_from_user

 

关于这两个函数有一篇博客描述的比较清楚:

 

http://blog.csdn.net/ce123_zhouwei/article/details/8454226

 

 

unsigned long copy_to_user(void __user *to, const void *from, unsigned long n);

 

如果数据拷贝成功,则返回零;否则,返回没有拷贝成功的数据字节数。

 

*to是用户空间的指针,

 

*from是内核空间指针,

 

n表示从内核空间向用户空间拷贝数据的字节数。

功能:用于将用户空间的数据传送到内核空间。

 

unsigned long copy_from_user(void * to, const void __user * from, unsigned long n)

 

第一个参数to是内核空间的数据目标地址指针,

 

第二个参数from是用户空间的数据源地址指针,

 

第三个参数n是数据的长度。

 

如果数据拷贝成功,则返回零;否则,返回没有拷贝成功的数据字节数。

 

此函数将from指针指向的用户空间地址开始的连续n个字节的数据产送到to指针指向的内核空间地址.

 

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