标签：各字段含义 读取 lseek keep hooks read linux fifo mode
linux下一切皆文件，大致可分为以下几类：目录、普通文件、硬连接、软连接、字符设备、块设备、FIFO、Socket，其在物理存储体内存储按inode和数据块存储，inode代表元数据，是除实际数据外的所有（属性）数据。根据不同的文件类型有以下几种情况：
》对于常规文件，文件的数据存储在数据块中，其他数据（即属性）存储在inode中。
》对于目录，该目录下的所有文件名和目录名存储在数据块中，注意文件名保存在它所在目录的数据块中，除文件名之外，ls -l命令看到的其它信息都保存在该文件的inode中。注意这个概念：目录也是一种文件，是一种特殊类型的文件。
》对于硬链接，其只是在硬链接所在目录的数据块中增加或修改文件名，并修改硬链接目标inode的链接数（ls显示属性的第二项），并不会增加inode或数据块。
》对于符号链接，如果目标路径名较短则直接保存在inode中以便更快地查找，如果目标路径名较长则分配一个数据块来保存。
》设备文件、FIFO和socket等特殊文件没有数据块，设备文件的主设备号和次设备号保存在inode中。
inode结构体定义在linux/fs.h中：
/* * Keep mostly read-only and often accessed (especially for * the RCU path lookup and ‘stat‘ data) fields at the beginning * of the ‘struct inode‘ */ struct inode { umode_t i_mode; unsigned short i_opflags; uid_t i_uid; gid_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; 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; blkcnt_t i_blocks; loff_t i_size; #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 */ struct hlist_node i_hash; struct list_head i_wb_list; /* backing dev IO list */ struct list_head i_lru; /* inode LRU list */ struct list_head i_sb_list; union { struct list_head i_dentry; struct rcu_head i_rcu; }; atomic_t i_count; unsigned int i_blkbits; u64 i_version; atomic_t i_dio_count; atomic_t i_writecount; const struct file_operations *i_fop; /* former ->i_op->default_file_ops */ struct file_lock *i_flock; 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; }; __u32 i_generation; #ifdef CONFIG_FSNOTIFY __u32 i_fsnotify_mask; /* all events this inode cares about */ struct hlist_head i_fsnotify_marks; #endif #ifdef CONFIG_IMA atomic_t i_readcount; /* struct files open RO */ #endif void *i_private; /* fs or device private pointer */ };
stat函数读取文件的inode，然后把inode中的各种文件属性填入一个struct stat结构体传出给调用者。ls或stat可查看inode属性。
struct stat { dev_t st_dev; /* ID of device containing file */ ino_t st_ino; /* inode number */ mode_t st_mode; /* protection */ nlink_t st_nlink; /* number of hard links */ uid_t st_uid; /* user ID of owner */ gid_t st_gid; /* group ID of owner */ dev_t st_rdev; /* device ID (if special file) */ off_t st_size; /* total size, in bytes */ blksize_t st_blksize; /* blocksize for file system I/O */ blkcnt_t st_blocks; /* number of 512B blocks allocated */ time_t st_atime; /* time of last access */ time_t st_mtime; /* time of last modification */ time_t st_ctime; /* time of last status change */ };
普通文件
~$ls -li wang
588946 -rw-rw-r-- 1 yuxi yuxi 9045 Feb 12 18:37 wang
st_ino file_type st_mode st_nlink st_uid st_gid st_size st_mtime file_name
目录
712708 drwxrwxr-x 2 yuxi yuxi 4096 Oct 6 15:52 file
st_ino file_type st_mode st_nlink st_uid st_gid st_size st_mtime dir_name
硬链接
~$ln wang hard_wang
~$ls -li wang hard_wang
588946 -rwxrwxr-x 2 yuxi yuxi 9045 Feb 12 18:37 hard_wang
588946 -rwxrwxr-x 2 yuxi yuxi 9045 Feb 12 18:37 wang
st_ino file_type st_mode st_nlink st_uid st_gid st_size st_mtime file_name
符号链接
2011 lrwxrwxrwx 1 root root 15 Mar 19 10:01 stdout -> /proc/self/fd/1
st_ino file_type st_mode st_nlink st_uid st_gid st_size（软链接文件名大小） st_mtime file_name
字符设备
1904 crw-rw-rw- 1 root tty 5, 0 Mar 19 10:01 tty
st_ino file_type st_mode st_nlink st_uid st_gid st_rdev st_mtime dev_name
块设备
7502 brw-rw---- 1 root disk 8, 0 Mar 19 10:01 sda
st_ino file_type st_mode st_nlink st_uid st_gid st_rdev st_mtime dev_name
socket
9252 srw-rw-rw- 1 root root 0 Mar 19 10:01 log
st_ino file_type st_mode st_nlink st_uid st_gid st_size st_mtime file_name
所有文件都是通过open或类open函数将inode与file建立联系，release将file结构体的修改更新inode。用inode填充file结构体（file为RAM结构体），实现了物理结构体与RAM结构体的分离，之后的read、write等file_operations函数直接操作file结构体即可完成对文件的所有更改。
int (*open) (struct inode *, struct file *);
extern struct file * dentry_open(struct dentry *, struct vfsmount *, int, const struct cred *);
extern int dcache_dir_open(struct inode *, struct file *);
int (*release) (struct inode *, struct file *);
file结构体定义于linux/fs.h，如下：
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; /* * Protects f_ep_links, f_flags, f_pos vs i_size in lseek SEEK_CUR. * Must not be taken from IRQ context. */ spinlock_t f_lock; #ifdef CONFIG_SMP int f_sb_list_cpu; #endif atomic_long_t f_count; unsigned int f_flags; fmode_t f_mode; 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; #endif /* #ifdef CONFIG_EPOLL */ struct address_space *f_mapping; #ifdef CONFIG_DEBUG_WRITECOUNT unsigned long f_mnt_write_state; #endif };
字符文件open函数调用过程记录：
参考：
2. ext2文件系统了解
标签：各字段含义 读取 lseek keep hooks read linux fifo mode
原文地址：http://www.cnblogs.com/embedded-linux/p/6579679.html
