Linux 2.6.36以后file_operations和DECLARE_MUTEX 的变化-优快云博客

本文介绍从2.6.36到2.6.38内核的驱动移植过程中遇到的问题，主要关注include/linux/semaphore.h和include/linux/fs.h的变化，特别是mutex定义和file_operations结构体的更新。

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今天尝试移植了2.6.38的内核到AT91SAM9260上，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

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

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); /*Which LED*/

.....

}

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

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。