ioctl ～～unlocked_ioctl和compat_ioctl

kernel 2.6.36 中已经完全删除了struct file_operations 中的ioctl 函数指针，取而代之的是unlocked_ioctl ，上网查了一些资料，说在应用程序中ioctl是兼容的，不必变化。而在驱动程序中这个指针函数变了之后最大的影响是参数中少了inode ，所以应用程序ioctl是兼容的，但驱动程序中我们的ioctl函数必须变化,否则就会发生cmd参数的变化：

原来的驱动程序

static const struct file_operations globalmem_fops=
{
.owner=THIS_MODULE,
.llseek=globalmem_llseek,
.open=globalmem_open,
.read=globalmem_read,
.write=globalmem_write,
.ioctl=globalmem_ioctl,
.release=globalmem_release,
};

int globalmem_ioctl(struct inode* inode,struct file* filp, unsigned int cmd,unsigned long arg)

{

switch (cmd)

  {

   case:XXX:   ...

    ……

  }

}

改变后的

static const struct file_operations globalmem_fops=
{
.owner=THIS_MODULE,
.llseek=globalmem_llseek,
.open=globalmem_open,
.read=globalmem_read,
.write=globalmem_write,
.unlocked_ioctl=globalmem_ioctl,
.release=globalmem_release,
};

int globalmem_ioctl(struct file* filp, unsigned int cmd,unsigned long arg)//没有inode参数！

{

switch (cmd)

  {

   case:XXX:   ...

    ……

  }

}

The ioctl() system call has long been out of favor among the kernel developers, who see it as a completely uncontrolled entry point into the kernel. Given the vast number of applications which expect ioctl() to be present, however, it will not go away anytime soon. So it is worth the trouble to ensure that ioctl() calls are performed quickly and correctly - and that they do not unnecessarily impact the rest of the system.

ioctl() is one of the remaining parts of the kernel which runs under the Big Kernel Lock (BKL). In the past, the usage of the BKL has made it possible for long-running ioctl() methods to create long latencies for unrelated processes. Recent changes, which have made BKL-covered code preemptible, have mitigated that problem somewhat. Even so, the desire to eventually get rid of the BKL altogether suggests that ioctl() should move out from under its protection.

Simply removing the lock_kernel() call before calling ioctl() methods is not an option, however. Each one of those methods must first be audited to see what other locking may be necessary for it to run safely outside of the BKL. That is a huge job, one which would be hard to do in a single "flag day" operation. So a migration path must be provided. As of 2.6.11, that path will exist.

The (by Michael s. Tsirkin) adds a new member to the file_operations structure:

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

If a driver or filesystem provides an unlocked_ioctl() method, it will be called in preference to the older ioctl(). The differences are that the inode argument is not provided (it's available asfilp->f_dentry->d_inode) and the BKL is not taken prior to the call. All new code should be written with its own locking, and should use unlocked_ioctl(). Old code should be converted as time allows. For code which must run on multiple kernels, there is a new HAVE_UNLOCKED_IOCTL macro which can be tested to see if the newer method is available or not.

Michael's patch adds one other operation:

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

If this method exists, it will be called (without the BKL) whenever a 32-bit process callsioctl() on a 64-bit system. It should then do whatever is required to convert the argument to native data types and carry out the request. If compat_ioctl() is not provided, the older conversion mechanism will be used, as before. The HAVE_COMPAT_IOCTL macro can be tested to see if this mechanism is available on any given kernel.

The compat_ioctl() method will probably filter down into a few subsystems. Andi Kleen has posted patches adding new compat_ioctl() methods to the block_device_operations and scsi_host_templatestructures, for example, though those patches have not been merged as of this writing.




参考：http://blog.csdn.net/cbl709/article/details/7295772