Linux字元裝置驅動分析

Linux字元裝置驅動分析

1、字元裝置描述 struct cdev

struct cdev表示字元裝置的核心的內部結構。

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

2、三個重要的結構體：

struct file、struct inode、struct file_operations。

<1>、struct file代表一個開啟的檔案，每開啟一次就建立一次。它由核心在open時建立，並傳遞給在該檔案上進行操作的所有函數，直到最後的close函數。在檔案的所有執行個體都被關閉後，核心才會釋放這個資料結構。通常用filp表示指向這個結構的指標。

struct file {
 /*
  * fu_list becomes invalid after file_free is called and queued via
  * fu_rcuhead for RCU freeing
  */
 union {
  struct list_head fu_list;
  struct rcu_head  fu_rcuhead;
 } f_u;
 struct path  f_path;
#define f_dentry f_path.dentry
#define f_vfsmnt f_path.mnt
 const struct file_operations *f_op;   //與檔案相關的操作
 spinlock_t  f_lock;  /* f_ep_links, f_flags, no IRQ */
 atomic_long_t  f_count;
 unsigned int   f_flags;  //檔案標誌O_RDONLY、O_NONBLOCK、O_SYNC
 fmode_t   f_mode;
 loff_t   f_pos;   //當前的讀寫位置
 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;
#endif /* #ifdef CONFIG_EPOLL */
 struct address_space *f_mapping;
#ifdef CONFIG_DEBUG_WRITECOUNT
 unsigned long f_mnt_write_state;
#endif
};

 struct inode結構用來記錄檔案的物理上的資訊。核心用核心inode結構在內部表示檔案，它表示開啟的檔案描述符，

struct inode {
 struct hlist_node i_hash;
 struct list_head i_list;  /* backing dev IO list */
 struct list_head i_sb_list;
 struct list_head i_dentry;
 unsigned long  i_ino;
 atomic_t  i_count;
 unsigned int  i_nlink;
 uid_t   i_uid;
 gid_t   i_gid;
 dev_t   i_rdev;   //表示裝置檔案的inode結構、該欄位包含了真正的裝置編號。
 u64   i_version;
 loff_t   i_size;
#ifdef __NEED_I_SIZE_ORDERED
 seqcount_t  i_size_seqcount;
#endif
 struct timespec  i_atime;
 struct timespec  i_mtime;
 struct timespec  i_ctime;
 blkcnt_t  i_blocks;
 unsigned int  i_blkbits;
 unsigned short          i_bytes;
 umode_t   i_mode;
 spinlock_t  i_lock; /* i_blocks, i_bytes, maybe i_size */
 struct mutex  i_mutex;
 struct rw_semaphore i_alloc_sem;
 const struct inode_operations *i_op;
 const struct file_operations *i_fop; /* former ->i_op->default_file_ops */
 struct super_block *i_sb;
 struct file_lock *i_flock;
 struct address_space *i_mapping;
 struct address_space i_data;
#ifdef CONFIG_QUOTA
 struct dquot  *i_dquot[MAXQUOTAS];
#endif
 struct list_head i_devices;
 union {
  struct pipe_inode_info *i_pipe;
  struct block_device *i_bdev;
  struct cdev  *i_cdev;   //struct cdev表示字元裝置的核心的核心結構，當inode指向一個字元裝置檔案時，該欄位包括了指向struct cdev結構的指標。
 };

 __u32   i_generation;

#ifdef CONFIG_FSNOTIFY
 __u32   i_fsnotify_mask; /* all events this inode cares about */
 struct hlist_head i_fsnotify_mark_entries; /* fsnotify mark entries */
#endif

#ifdef CONFIG_INOTIFY
 struct list_head inotify_watches; /* watches on this inode */
 struct mutex  inotify_mutex; /* protects the watches list */
#endif

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

 unsigned int  i_flags;

 atomic_t  i_writecount;
#ifdef CONFIG_SECURITY
 void   *i_security;
#endif
#ifdef CONFIG_FS_POSIX_ACL
 struct posix_acl *i_acl;
 struct posix_acl *i_default_acl;
#endif
 void   *i_private; /* fs or device private pointer */
};

struct file_operations結構是一個函數指標的集合，定義能在裝置上進行的操作，對應關係表（把應用程式中相應的操作轉換為驅動程式中相應函數）。

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 (*aio_read) (struct kiocb *, const struct iovec *, unsigned long, loff_t);
 ssize_t (*aio_write) (struct kiocb *, const struct iovec *, unsigned long, loff_t);
 int (*readdir) (struct file *, void *, filldir_t);
 unsigned int (*poll) (struct file *, struct poll_table_struct *);
 int (*ioctl) (struct inode *, struct file *, unsigned int, unsigned long);
 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 *, struct dentry *, 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 **);
};

 核心中虛擬檔案系統中的read、write函數(read_write.c)

ssize_t vfs_read(struct file *file, char __user *buf, size_t count, loff_t *pos){ssize_t ret;if (!(file->f_mode & FMODE_READ))return -EBADF;if (!file->f_op || (!file->f_op->read && !file->f_op->aio_read))return -EINVAL;if (unlikely(!access_ok(VERIFY_WRITE, buf, count)))return -EFAULT;ret = rw_verify_area(READ, file, pos, count);if (ret >= 0) {count = ret;if (file->f_op->read)ret = file->f_op->read(file, buf, count, pos);elseret = do_sync_read(file, buf, count, pos);if (ret > 0) {fsnotify_access(file->f_path.dentry);add_rchar(current, ret);}inc_syscr(current);}return ret;}

 

 

ssize_t vfs_write(struct file *file, const char __user *buf, size_t count, loff_t *pos){ ssize_t ret; if (!(file->f_mode & FMODE_WRITE))  return -EBADF; if (!file->f_op || (!file->f_op->write && !file->f_op->aio_write))  return -EINVAL; if (unlikely(!access_ok(VERIFY_READ, buf, count)))  return -EFAULT; ret = rw_verify_area(WRITE, file, pos, count); if (ret >= 0) {  count = ret;  if (file->f_op->write)   ret = file->f_op->write(file, buf, count, pos);  else   ret = do_sync_write(file, buf, count, pos);  if (ret > 0) {   fsnotify_modify(file->f_path.dentry);   add_wchar(current, ret);  }  inc_syscw(current); } return ret;}