linux 内核数据结构 file_operations、file、inode

文件操作结构

将驱动程序操作连接到设备编号，结构定义在<linux/fs.h>，其中包含一组函数指针，每个打开的文件（在内部由一个file结构表示）和一组函数关联（通过包含指向一个file_operations结构的f_op字段）。

struct file_operations {//指向拥有该结构的模块的指针struct module *owner;//修改当前文件的读写位置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 *);int (*iterate_shared) (struct file *, struct dir_context *);__poll_t (*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 *);unsigned long mmap_supported_flags;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 (*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_MMUunsigned (*mmap_capabilities)(struct file *);
#endifssize_t (*copy_file_range)(struct file *, loff_t, struct file *,loff_t, size_t, unsigned int);int (*clone_file_range)(struct file *, loff_t, struct file *, loff_t,u64);ssize_t (*dedupe_file_range)(struct file *, u64, u64, struct file *,u64);
} __randomize_layout;

file结构

file结构与用户空间的FILE没有任何关联。file结构代表一个打开的文件，由内核在open时创建，并传递给在该文件上进行操作的所有函数。

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 *///与文件相关的操作const struct file_operations    *f_op;/** Protects f_ep_links, f_flags.* Must not be taken from IRQ context.*/spinlock_t        f_lock;enum rw_hint     f_write_hint;atomic_long_t      f_count;//文件标志，检查用户请求是否是非阻塞的操作unsigned int       f_flags;//文件模式，表示文件可读或可写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_SECURITYvoid          *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;errseq_t     f_wb_err;
} __randomize_layout

inode结构

内核用inode结构在内部表示文件，它和file不同，后者表示打开的文件描述符，对于单个文件，可能会有许多表示打开的文件描述符的file结构，但它们都指向单个inode结构。

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_ACLstruct posix_acl  *i_acl;struct posix_acl *i_default_acl;
#endifconst struct inode_operations *i_op;struct super_block    *i_sb;struct address_space  *i_mapping;#ifdef CONFIG_SECURITYvoid           *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 timespec64    i_atime;struct timespec64   i_mtime;struct timespec64   i_ctime;spinlock_t      i_lock; /* i_blocks, i_bytes, maybe i_size */unsigned short          i_bytes;unsigned int       i_blkbits;enum rw_hint      i_write_hint;blkcnt_t       i_blocks;#ifdef __NEED_I_SIZE_ORDEREDseqcount_t     i_size_seqcount;
#endif/* Misc */unsigned long       i_state;struct rw_semaphore i_rwsem;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_WRITEBACKstruct 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;
#endifstruct list_head  i_lru;      /* inode LRU list */struct list_head    i_sb_list;struct list_head  i_wb_list;  /* backing dev writeback list */union {struct hlist_head    i_dentry;struct rcu_head        i_rcu;};atomic64_t      i_version;atomic_t      i_count;atomic_t        i_dio_count;atomic_t        i_writecount;
#ifdef CONFIG_IMAatomic_t       i_readcount; /* struct files open RO */
#endifconst 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;unsigned        i_dir_seq;};__u32           i_generation;#ifdef CONFIG_FSNOTIFY__u32            i_fsnotify_mask; /* all events this inode cares about */struct fsnotify_mark_connector __rcu    *i_fsnotify_marks;
#endif#if IS_ENABLED(CONFIG_FS_ENCRYPTION)struct fscrypt_info   *i_crypt_info;
#endifvoid          *i_private; /* fs or device private pointer */
} __randomize_layout;

作为常规，只有下面两个字段对驱动程序有用：
dev_t i_rdev;
对表示设备文件的inode结构，包含了真正的设备编号。
struct cdev *i_cdev;
struct cdev表示字符设备的内核内部数据结构，当inode指向一个字符设备文件，该字段包含指向struct cdev结构的指针

下面两个宏可用来从inode中获得主设备号和次设备号：
unsigned int iminor(struct inode *inode);
unsigned int imajor(struct inode *inode);