Linux文件系统数据结构

下面是Linux fs 相关数据结构的一些笔记，列出的是我开发中经常用到的一些结构成员，以linux 3.12为例。

#dentry

  struct dentry{
  	struct dentry 	*d_parent;	      /* parent directory */
  	struct qstr 	d_name;		
  	struct inode 	*d_inode;	      /* Where the name belongs to */
  	unsigned char d_iname[DNAME_INLINE_LEN];        /* small names */
  	...
  };

dentry: directory entry

detail: http://goo.gl/Lisgeg

#inode

  struct inode{
  	unsigned long           		i_ino;
  	umode_t                 		i_mode;
  	struct super_block              *i_sb;
  	const struct file_operations    *i_fop;
  	void                   			*i_security;
  	...
  };

detail: http://goo.gl/TphYHp

inode->i_mode 是 16位整数，下面是8进制表示

  #define S_IFMT  00170000
  #define S_IFSOCK 0140000
  #define S_IFLNK	 0120000
  #define S_IFREG  0100000
  #define S_IFBLK  0060000
  #define S_IFDIR  0040000
  #define S_IFCHR  0020000
  #define S_IFIFO  0010000
  #define S_ISUID  0004000
  #define S_ISGID  0002000
  #define S_ISVTX  0001000
  
  #define S_ISLNK(m)	(((m) & S_IFMT) == S_IFLNK)
  #define S_ISREG(m)	(((m) & S_IFMT) == S_IFREG)
  #define S_ISDIR(m)	(((m) & S_IFMT) == S_IFDIR)
  #define S_ISCHR(m)	(((m) & S_IFMT) == S_IFCHR)
  #define S_ISBLK(m)	(((m) & S_IFMT) == S_IFBLK)
  #define S_ISFIFO(m)	(((m) & S_IFMT) == S_IFIFO)
  #define S_ISSOCK(m)	(((m) & S_IFMT) == S_IFSOCK)
  
  #define S_IRWXU 00700
  #define S_IRUSR 00400
  #define S_IWUSR 00200
  #define S_IXUSR 00100
  
  #define S_IRWXG 00070
  #define S_IRGRP 00040
  #define S_IWGRP 00020
  #define S_IXGRP 00010
  
  #define S_IRWXO 00007
  #define S_IROTH 00004
  #define S_IWOTH 00002
  #define S_IXOTH 00001

举例

root@ubuntu:~# ls -il temp.txt 
681278 -rw-r--r-- 1 root root 56844 Jul  9 08:46 temp.txt

i_ino = 681278
i_imode = 00644

#super_block

  struct super_block {
        unsigned long               s_magic;
        void                        *s_security;
        const struct xattr_handler  **s_xattr;
  };

s_magic: http://goo.gl/jOhHRM

s_xattr 文件扩展属性

struct xattr_handler{
    size_t (*list)(...);
    int (*get)(...);
    int (*set)(...);
};
struct xattr {
    const char *name;
    void *value;
    size_t value_len;
};

用户空间使用attr示例

      root@ubuntu:~# apt-get install attr
      root@ubuntu:~# touch hello.c
      root@ubuntu:~# setfattr -n user.author -v geeksword -h hello.c 
      root@ubuntu:~# getfattr -n user.author hello.c 
      # file: hello.c
      user.author="geeksword"
      root@ubuntu:~# 

涉及的系统调用是

    setxattr()
    getxattr()

#file

  struct file{
  	struct path             		f_path;
  	unsigned int            		f_flags;	/* 文件属性 */
  	fmode_t                 		f_mode;	/* 文件打开模式 */
  	struct inode            	    *f_inode;	
  	const struct file_operations    *f_op;
  	const struct cred       		*f_cred;
  	void                    		*f_security;
  };

detail: http://goo.gl/56ouH4

位于源码/include/linux/fs.h头部

file->f_flags: http://goo.gl/YCkhZq

#define O_ACCMODE	00000003
#define O_RDONLY	00000000
#define O_WRONLY	00000001
#define O_RDWR		00000002
#define O_CREAT		00000100	/* not fcntl */
#define O_EXCL		00000200	/* not fcntl */
#define O_NOCTTY	00000400	/* not fcntl */
#define O_TRUNC		00001000	/* not fcntl */
#define O_APPEND	00002000
#define O_NONBLOCK	00004000
#define O_DSYNC		00010000	/* used to be O_SYNC, see below */
#define FASYNC		00020000	/* fcntl, for BSD compatibility */
#define O_DIRECT	00040000	/* direct disk access hint */
#define O_LARGEFILE	00100000
#define O_DIRECTORY	00200000	/* must be a directory */
#define O_NOFOLLOW	00400000	/* don't follow links */
#define O_NOATIME	01000000
#define O_CLOEXEC	02000000	/* set close_on_exec */

file->f_mode

   /*
   * flags in file.f_mode.  Note that FMODE_READ and FMODE_WRITE must correspond
   * to O_WRONLY and O_RDWR via the strange trick in __dentry_open()
   */
  
  /* file is open for reading */
  #define FMODE_READ		((__force fmode_t)0x1)
  /* file is open for writing */
  #define FMODE_WRITE		((__force fmode_t)0x2)
  /* file is seekable */
  #define FMODE_LSEEK		((__force fmode_t)0x4)
  /* file can be accessed using pread */
  #define FMODE_PREAD		((__force fmode_t)0x8)
  /* file can be accessed using pwrite */
  #define FMODE_PWRITE		((__force fmode_t)0x10)
  /* File is opened for execution with sys_execve / sys_uselib */
  #define FMODE_EXEC		((__force fmode_t)0x20)
  /* File is opened with O_NDELAY (only set for block devices) */
  #define FMODE_NDELAY		((__force fmode_t)0x40)
  /* File is opened with O_EXCL (only set for block devices) */
  #define FMODE_EXCL		((__force fmode_t)0x80)

一些文件操作相关函数参数mask的掩码，标识访问文件的方式

  #define MAY_EXEC		0x00000001
  #define MAY_WRITE		0x00000002
  #define MAY_READ		0x00000004
  #define MAY_APPEND	0x00000008
  #define MAY_ACCESS	0x00000010
  #define MAY_OPEN		0x00000020
  #define MAY_CHDIR		0x00000040

#file_operations

  struct file_operations{
  	int (*open) (struct inode *, struct file *);
  	ssize_t (*read) (struct file *, char __user *, size_t, loff_t *);
  	ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);
  	...
  };

details: http://goo.gl/oMQuKj

#path

  struct path {
  	struct vfsmount *mnt;
  	struct dentry *dentry;
  };

#more

• open系统调用入口
• linux 2.x read 系统调用分析