文件系统小册（Fuse&Posix&K8s csi）【2 Posix标准】

文件系统小册（Fuse&Posix&K8s csi）【2 Posix】

POSIX：可移植操作系统接口（标准）

1 概念

拓展：GNU、Linux、Unix关系

三者联系与区别：

参考文章：https://www.gnu.org/gnu/linux-and-gnu.html

2 POSIX的标准文件接口(常用部分)

open：打开文件

close：关闭文件

creat：创建文件

read：读文件内容

write：写内容到文件

lseek：改变文件指针的位置（文件定位）

fsync：将文件数据从系统缓存区写到磁盘

flock：文件锁，用于进程间同步

stat：获取文件的统计信息

truncate：截断文件

symlink：创建符号链接（如：软链，类比快捷方式）

readlink：读取符号链接的内容

opendir：打开目录

readdir：读取目录内容

mkdir：创建目录

rmdir： 删除目录

telldir：定位目录的当前位置

seekdir：定位目录

rename：重命名

chmod：动态修改文件访问权限

chown：动态修改文件所有者和组别

3 与FUSE的关系：FUSE实现了POSIX

fuse_operations 结构体定义了一系列的回调函数，这些函数对应于POSIX文件操作，例如：

• getattr: 实现stat操作。
• read: 实现read操作。
• write: 实现write操作。
• open: 实现open操作。
• create: 实现creat操作。
• unlink: 实现unlink操作。
• rename: 实现rename操作。
• mkdir: 实现mkdir操作。
• symlink: 实现symlink操作。
• readlink: 实现readlink操作。
• chmod: 实现chmod操作。
• chown: 实现chown操作。
• truncate: 实现truncate操作。
  flush: 实现文件关闭前的清理操作。
  …

源码：

• https://github.com/libfuse/libfuse/中的fuse.h文件

/** Get file attributes.
	 *
	 * Similar to stat().  The 'st_dev' and 'st_blksize' fields are
	 * ignored. The 'st_ino' field is ignored except if the 'use_ino'
	 * mount option is given. In that case it is passed to userspace,
	 * but libfuse and the kernel will still assign a different
	 * inode for internal use (called the "nodeid").
	 *
	 * `fi` will always be NULL if the file is not currently open, but
	 * may also be NULL if the file is open.
	 */
	int (*getattr) (const char *, struct stat *, struct fuse_file_info *fi);

	/** Read the target of a symbolic link
	 *
	 * The buffer should be filled with a null terminated string.  The
	 * buffer size argument includes the space for the terminating
	 * null character.	If the linkname is too long to fit in the
	 * buffer, it should be truncated.	The return value should be 0
	 * for success.
	 */
	int (*readlink) (const char *, char *, size_t);

	/** Create a file node
	 *
	 * This is called for creation of all non-directory, non-symlink
	 * nodes.  If the filesystem defines a create() method, then for
	 * regular files that will be called instead.
	 */
	int (*mknod) (const char *, mode_t, dev_t);

	/** Create a directory
	 *
	 * Note that the mode argument may not have the type specification
	 * bits set, i.e. S_ISDIR(mode) can be false.  To obtain the
	 * correct directory type bits use  mode|S_IFDIR
	 * */
	int (*mkdir) (const char *, mode_t);

	/** Remove a file */
	int (*unlink) (const char *);

	/** Remove a directory */
	int (*rmdir) (const char *);

	/** Create a symbolic link */
	int (*symlink) (const char *, const char *);

	/** Rename a file
	 *
	 * *flags* may be `RENAME_EXCHANGE` or `RENAME_NOREPLACE`. If
	 * RENAME_NOREPLACE is specified, the filesystem must not
	 * overwrite *newname* if it exists and return an error
	 * instead. If `RENAME_EXCHANGE` is specified, the filesystem
	 * must atomically exchange the two files, i.e. both must
	 * exist and neither may be deleted.
	 */
	int (*rename) (const char *, const char *, unsigned int flags);

	/** Create a hard link to a file */
	int (*link) (const char *, const char *);

	/** Change the permission bits of a file
	 *
	 * `fi` will always be NULL if the file is not currently open, but
	 * may also be NULL if the file is open.
	 */
	int (*chmod) (const char *, mode_t, struct fuse_file_info *fi);

	/** Change the owner and group of a file
	 *
	 * `fi` will always be NULL if the file is not currently open, but
	 * may also be NULL if the file is open.
	 *
	 * Unless FUSE_CAP_HANDLE_KILLPRIV is disabled, this method is
	 * expected to reset the setuid and setgid bits.
	 */
	int (*chown) (const char *, uid_t, gid_t, struct fuse_file_info *fi);

	/** Change the size of a file
	 *
	 * `fi` will always be NULL if the file is not currently open, but
	 * may also be NULL if the file is open.
	 *
	 * Unless FUSE_CAP_HANDLE_KILLPRIV is disabled, this method is
	 * expected to reset the setuid and setgid bits.
	 */
	int (*truncate) (const char *, off_t, struct fuse_file_info *fi);
	...

4 测试系统是否满足POSIX语义 （pjdfstest）

#git clone源码
git clone https://github.com/pjd/pjdfstest.git
cd pjdfstest

# 编译源码
autoreconf -ifs   
 ./configure   
make pjdfstest
# 查看版本
prove --version

## 进入目标目录，执行pjdfstest脚本
cd /root/test （文件系统的挂载目录）
# 测试所有用例(-v显示进度)
prove -rv /root/pjdfstest/tests（pjdfstest里的tests目录）
# 测试单个语义
prove -r /root/pjdfstest/tests/open

参考：https://www.gnu.org/software/libc/manual/html_node/POSIX.html