Linux 2.6.36以后file_operations…

今天尝试在2.6.39内核上编译一个驱动,
在编译驱动时发现从2.6.36的内核开始，include/linux/semaphore.h
和 include/linux/fs.h中有了两处变化与驱动相关：

1， 在include/linux/semaphore.h 中

在编译阶段初始化的变化：

将#define DECLARE_MUTEX(name)
改成了 #define DEFINE_SEMAPHORE(name)

#if LINUX_VERSION_CODE
< KERNEL_VERSION(2,6,36)

DECLARE_MUTEX(led_sem);

#else

DEFINE_SEMAPHORE(led_sem);

#endif

在运行时初始化得变化（动态分配）：

以去除：

void init_MUTEX(struct
semaphore *sem);

void init_MUTEX_LOCKED(struct
semaphore *sem);

可通过以下初始：

void sema_init(struct semaphore
*sem, int val);

2，后备缓存：include/linux/slab.h

kmem_cache_t 类型已改为：

struct kmem_cache

创建缓存对象函数

kmem_cache_t *kmem_cache_create(const
char *name, size_t size,

size_t offset,

unsigned long flags,

void (*constructor)(void *, kmem_cache_t *,

unsigned long flags), void (*destructor)(void *, kmem_cache_t *,
unsigned long flags));

已改为(参数少了一个，返回值内型变化)：

struct kmem_cache *kmem_cache_create(const
char *name, size_t size,

size_t offset,

unsigned long flags,

void (*)(void ));

2， file_operations结构体有了一些变化，它去掉了：

int
(*ioctl) (struct inode *, struct file *, unsigned int, unsigned
long);

另外添加了：

long (*fallocate)(struct file *file, int mode,
loff_t offset,loff_t len);

这是2.6.36的内核里的定义include/linux/fs.h：

struct file_operations {

struct
module *owner;

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
(*aio_read) (struct kiocb *, const struct iovec *, unsigned long,
loff_t);

ssize_t
(*aio_write) (struct kiocb *, const struct iovec *, unsigned long,
loff_t);

int
(*readdir) (struct file *, void *, filldir_t);

unsigned int
(*poll) (struct file *, struct poll_table_struct *);

//从2.6.36开始删除ioctl(),
2.6.35中有

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 *);

int (*open)
(struct inode *, struct file *);

int (*flush)
(struct file *, fl_owner_t id);

int
(*release) (struct inode *, struct file *);

int (*fsync)
(struct file *, int datasync);

int
(*aio_fsync) (struct kiocb *, 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 **);

// long (*fallocate)(struct
file *file, int mode, loff_t
offset, loff_t
len); 从2.6.38内核开始添加该项，2.6.37以下无

};

下面是Linux-2.6.35里的file_operations

struct file_operations {

struct
module *owner;

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
(*aio_read) (struct kiocb *, const struct iovec *, unsigned long,
loff_t);

ssize_t
(*aio_write) (struct kiocb *, const struct iovec *, unsigned long,
loff_t);

int
(*readdir) (struct file *, void *, filldir_t);

unsigned int
(*poll) (struct file *, struct poll_table_struct *);

int (*ioctl)
(struct inode *, struct file *, unsigned int, unsigned
long);

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 *);

int (*open)
(struct inode *, struct file *);

int (*flush)
(struct file *, fl_owner_t id);

int
(*release) (struct inode *, struct file *);

int (*fsync)
(struct file *, struct dentry *, int datasync);

int
(*aio_fsync) (struct kiocb *, 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 **);

};

[guowenxue@localhost at91sam9260]$ make

make[1]: Entering directory
`/usr/.devices_group/guowenxue/l350-dev06/src/kernel/linux-2.6.38'

CC [M]
/usr/.devices_group/guowenxue/embedded_project/drivers/at91sam9260/dev_skeleton.o

/usr/.devices_group/guowenxue/embedded_project/drivers/at91sam9260/dev_skeleton.c:93:
error: unknown field 'ioctl' specified in initializer

/usr/.devices_group/guowenxue/embedded_project/drivers/at91sam9260/dev_skeleton.c:93:
warning: initialization from incompatible pointer type

make[2]: ***
[/usr/.devices_group/guowenxue/embedded_project/drivers/at91sam9260/dev_skeleton.o]
Error 1

make[1]: ***
[_module_/usr/.devices_group/guowenxue/embedded_project/drivers/at91sam9260]
Error 2

make[1]: Leaving directory
`/usr/.devices_group/guowenxue/l350-dev06/src/kernel/linux-2.6.38'

make: *** [modules] Error 2

参考别的字符设备的驱动drivers/char/ppdev.c：

static const struct file_operations pp_fops = {

.owner
=
THIS_MODULE,

.llseek
= no_llseek,

.read
=
pp_read,

.write
=
pp_write,

.poll
=
pp_poll,

.unlocked_ioctl = pp_ioctl,

.open
=
pp_open,

.release
= pp_release,

};

这里ioctl()已使用unlocked_ioctl代替。

但这里不是一个简单的替换，要注意unlocked_ioctl和ioctl的函数原型并不一致。

unlocked_ioctl:
long
(*unlocked_ioctl) (struct file *, unsigned int, unsigned
long);

ioctl: int(*ioctl)
(struct inode
*,struct file *, unsigned int, unsigned long);

The 'inode'
value that was passed to 'ioctl' function is available for use with
the 'unlocked_ioctl' function by way of
filp->d_entry->d_inode:

long
(*unlocked_ioctl) (struct file *filp, unsigned int
cmd, unsigned long arg);

...

struct inode
*inode =
filp->f_path.dentry->d_inode

There is a nice explanation of this at http://lwn.net/Articles/119652/

如：

static long
dev_ioctl(struct file *file, unsigned int cmd, unsigned long
arg)

{

int index =
NUM(file->f_path.dentry->d_inode->i_rdev);

.....

}

--------------------------------------

在file_operations 结构体中，会看到许多函数指针所指向的函数都必须传进struct
file 结构体指针struct file
* 作为参数。struct
file 结构体定义在<linux/fs.h> 中，完整如下：

引用

struct file {

union {

struct list_head fu_list;

struct rcu_head fu_rcuhead;

} f_u;

struct path f_path;

#definef_dentry
f_path.dentry
#definef_vfsmnt
f_path.mnt

const struct file_operations *f_op;

spinlock_t f_lock;

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

void *private_data;

#ifdef
CONFIG_EPOLL

struct list_head f_ep_links;

#endif

struct address_space *f_mapping;

#ifdef
CONFIG_DEBUG_WRITECOUNT

unsigned long f_mnt_write_state;

#endif

};

在设备驱动中，struct
file 结构体也是一个非常重要的数据结构。注意的是，这里的file 和应用程序中的FILE 流指针没有什么关系，FILE 定义在C 库中，它永远不会出现在内核代码中。

file structure 结构代表一个打开的文件(open
file).(打开的文件并没有确切的指定到哪个设备驱动，实际上每个打开的文件都与内核空间中的struct
file 结构相关联)。

file
structure 结构在调用open 打开一个文件时由内核创建，并会被传递给任一个对这个打开文件进行操作的函数；当所有事情都做完后，会调用close() 关闭掉文件，此时内核释放这个数据结构。

一般地，在内核源码中，struct
file 结构体的指针往往写成filp 。

struct
file 中的几个重要成员：

mode_t
f_mode;
文件模式根据FMMODE_READ 和FMODE_WRITE 位来识别文件是否可读或可写，或是可读可写。在read() 和write() 系统调用中，没有必要对此权限进行检查，因为内核已经在你的系统调用之前已经做了检查。如果文件没有相应的读或写权限，那么如果尝试读写都将被拒绝，驱动程序甚至对此情况毫无知觉。

loff_t
f_pos;
此变量表示当前的文件读写位置。loff_t 在所有的平台上都是64 位的变量(
long long 型,
gcc 专用术语)。驱动程序如果想知道当前在文件中所处位置，那么可以通过读取此变量得知，但是一般地不应直接对此进行更改。通过llseek() 方法可以改变文件位置。

unsigned int
f_flags;
这是表示如O_RDONLY,
O_NONBLOCK与O_SYNC 这样的标志。一个驱动程序应该检查O_NONBLOCK 标志，以查看是否有非阻塞操作的请求。其它的标志用得比较少。需要注意的是，检查read/write 权限应该是通过检查f_mode 得到而不是f_flags 。所有的标志定义在头文件linux/fcntl.h 中可以看到。

struct
file_operations*f_op;
内核安排这个指针作为它的open 实现的一部分，当需要分派什么操作时，会读取它。filp->f_op 因为不会被内核保存起来以在其后之用，所以我们可以改变我们对相关文件的操作，在对文件使用新的操作方法时，我们就会转移到相应调用上。

void
*private_data;
在对驱动调用open 方法之前，open() 系统调用会这个指针设置为NULL 。用户可以自由使用这个域，或者对其忽略。可以使用这个域之想分配的数据空间，但必须记得在内核销毁file
structure 之前在release 方法里释放掉原来分配的内存。private_data 对于系统调用之间信息的保存会显得非常有用。

struct
dentry*f_dentry;
目录入口(dentry) 结构与文件相关。一般的，除了在以filp->f_dentry->d_inode 来访问inode 结构时，我们不太关心dentry 这个结构。