acl.h:
/*
File: fs/ext2/acl.h
(C) 2001 Andreas Gruenbacher, <a .gruenbacher@computer.org>
*/
#include <linux /posix_acl_xattr.h>
//简单说一下acl(访问控制表)，比传统的Linux具有更灵活的文件权限设定，ext2文件系统的扩展属性支持acl，这一点在编译的时候可以指定。
#define EXT2_ACL_VERSION 0x0001
//定义acl的版本；
typedef struct {
__le16 e_tag;
__le16 e_perm;
__le32 e_id;
} ext2_acl_entry;
//__le16类型的定义：
//typedef __u16 __bitwise __le16;
//看起来比较复杂，其实（在x86平台下）只是一个unsigned short，__bitwise这个只是通过gcc的扩展使用sparse这个工具来进行代码检查。
//ext2_acl_entry定义访问控制项的结构体
//__le16 e_tag; 自身的使用者或組
//__le16 e_perm; 允许访问的
//__le32 e_id;
typedef struct {
__le16 e_tag;
__le16 e_perm;
} ext2_acl_entry_short;
//定义访问控制项的简单结构；
typedef struct {
__le32 a_version;
} ext2_acl_header;
//接下来两个函数分别用到了size_t与ssize_t对应在x86平台下分别是unsigned int与int
static inline size_t ext2_acl_size(int count)
{
if (count < = 4) {
return sizeof(ext2_acl_header) +
count * sizeof(ext2_acl_entry_short);
} else {
return sizeof(ext2_acl_header) +
4 * sizeof(ext2_acl_entry_short) +
(count - 4) * sizeof(ext2_acl_entry);
}
}
//该函数用来计算acl的占用空间大小，当使用的acl多于4后剩余的acl使用完整的ext2_acl_entry来记录。
static inline int ext2_acl_count(size_t size)
{
ssize_t s;
size -= sizeof(ext2_acl_header);
s = size - 4 * sizeof(ext2_acl_entry_short);
if (s < 0) {
if (size % sizeof(ext2_acl_entry_short))
return -1;
return size / sizeof(ext2_acl_entry_short);
} else {
if (s % sizeof(ext2_acl_entry))
return -1;
return s / sizeof(ext2_acl_entry) + 4;
}
}
//该函数与上面的函数刚好相反
#ifdef CONFIG_EXT2_FS_POSIX_ACL
//当内核编译时指定使用ext2的acl属性时这里ext2_permission等函数被申明，否则这些函数被定义为空。
/* Value for inode->u.ext2_i.i_acl and inode->u.ext2_i.i_default_acl
if the ACL has not been cached */
#define EXT2_ACL_NOT_CACHED ((void *)-1)
/* acl.c */
extern int ext2_permission (struct inode *, int, struct nameidata *);
extern int ext2_acl_chmod (struct inode *);
extern int ext2_init_acl (struct inode *, struct inode *);
#else
#include </linux><linux /sched.h>
#define ext2_permission NULL
#define ext2_get_acl NULL
#define ext2_set_acl NULL
static inline int
ext2_acl_chmod (struct inode *inode)
{
return 0;
}
static inline int ext2_init_acl (struct inode *inode, struct inode *dir)
{
return 0;
}
#endif
file.c:
/*
* linux/fs/ext2/file.c
*
* Copyright (C) 1992, 1993, 1994, 1995
* Remy Card (card@masi.ibp.fr)
* Laboratoire MASI - Institut Blaise Pascal
* Universite Pierre et Marie Curie (Paris VI)
*
* from
*
* linux/fs/minix/file.c
*
* Copyright (C) 1991, 1992 Linus Torvalds
*
* ext2 fs regular file handling primitives
*
* 64-bit file support on 64-bit platforms by Jakub Jelinek
* (jj@sunsite.ms.mff.cuni.cz)
*/
#include </linux><linux /time.h>
#include "ext2.h"
#include "xattr.h"
#include "acl.h"
/*
* Called when filp is released. This happens when all file descriptors
* for a single struct file are closed. Note that different open() calls
* for the same file yield different struct file structures.
*/
static int ext2_release_file (struct inode * inode, struct file * filp)
{
if (filp->f_mode & FMODE_WRITE) {
mutex_lock(&EXT2_I(inode)->truncate_mutex);
ext2_discard_reservation(inode);
mutex_unlock(&EXT2_I(inode)->truncate_mutex);
}
return 0;
}
//该函数释放文件所使用的block，前提是该文件以"写"的模式被打开。
/*
* We have mostly NULL's here: the current defaults are ok for
* the ext2 filesystem.
*/
const struct file_operations ext2_file_operations = {
.llseek = generic_file_llseek,
.read = do_sync_read,
.write = do_sync_write,
.aio_read = generic_file_aio_read,
.aio_write = generic_file_aio_write,
.ioctl = ext2_ioctl,
#ifdef CONFIG_COMPAT
.compat_ioctl = ext2_compat_ioctl,
#endif
.mmap = generic_file_mmap,
.open = generic_file_open,
.release = ext2_release_file,
.fsync = ext2_sync_file,
.splice_read = generic_file_splice_read,
.splice_write = generic_file_splice_write,
};
//ext2_file_operations这个结构体定义了上层（VFS）文件操作函数在ext2文件系统这一层中的具体实现函数。
//这里又用到了gcc的扩展使用.[index]这样的方式来初始化结构体，这样结构体中的成员就不会受到顺序的限制。
#ifdef CONFIG_EXT2_FS_XIP
const struct file_operations ext2_xip_file_operations = {
.llseek = generic_file_llseek,
.read = xip_file_read,
.write = xip_file_write,
.ioctl = ext2_ioctl,
#ifdef CONFIG_COMPAT
.compat_ioctl = ext2_compat_ioctl,
#endif
.mmap = xip_file_mmap,
.open = generic_file_open,
.release = ext2_release_file,
.fsync = ext2_sync_file,
};
#endif
//ext2_xip_file_operations定义了使用xip(eXecute In Place)的文件操作函数
const struct inode_operations ext2_file_inode_operations = {
.truncate = ext2_truncate,
#ifdef CONFIG_EXT2_FS_XATTR
.setxattr = generic_setxattr,
.getxattr = generic_getxattr,
.listxattr = ext2_listxattr,
.removexattr = generic_removexattr,
#endif
.setattr = ext2_setattr,
.permission = ext2_permission,
};
//ext2_file_inode_operations定义了ext2中inode的文件操作函数。
