Getting a reference to an input device from a kernel module

Question

I am writing a kernel module that needs to perform the equivalent of an ioctl on another device (the "target" device). The target device is an input device which is mounted at dev/something.

I know that one way to do this would be to open the target device from my module and then just call ioctl as described in this SO question. However I understand that this is a hack and that there is probably a better way.

Is it possible to retrieve to a struct *input_dev from my kernel module, given either the target module name or the mount point of the target device?

Would it help if it was built into the kernel instead? I see the same problem. — Grodriguez, Jul 22 '14 at 11:37
Because it is using kernel timers. But this is not relevant to the actual question. — Grodriguez, Jul 22 '14 at 11:39
Not the timers I want to use. But as I said this is not relevant to the actual question. — Grodriguez, Jul 22 '14 at 11:58
Let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/57754/discussion-between-grodriguez-and-cl). — Grodriguez, Jul 22 '14 at 12:04
If you develope such test kind of module for userspace then It will require some porting effort for every new OS. If your test suite is minimum and more regarding unit testing of kernel driver's features then you can keep that in Kernel space. — Jeegar Patel, Jul 22 '14 at 12:24
If this is just not testing then also if any driver/module wants to use any functanility of another driver or module then also it would be in kernel space. — Jeegar Patel, Jul 22 '14 at 12:26

Jeegar Patel · Accepted Answer · 2014-07-22T11:40:49.593

1

Option1: 1st option of opening your target device node is the better option. I have done same 2-3 times in past. But here it works only after file system get mounted and then your test module can open that module.

struct file* test;
test = filp_open("/dev/targetDevice",O_RDWR,0);

Now in call ioctl

test->f_op->unlocked_ioctl(test,IOCTL_MACRO,params);

Option2:

Another solution i am thinking is, If target module is under your control then from that target module make that pointer as EXPORT_SYMBOL() and access that in your test module.

Option3:

Another option is instead of exporting pointer of that struct just export any function of target module and perform your required from that task.

edited Jul 22 '14 at 11:40

answered Jul 22 '14 at 10:24

Jeegar Patel

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Can you show some example code? (btw the target module is not under my control) – Grodriguez Jul 22 '14 at 11:15
@Grodriguez if can not do changes in target module then my both suggestion are not useful. – Jeegar Patel Jul 22 '14 at 11:19
Why would I need to have control over the target module in order to open the device node? – Grodriguez Jul 22 '14 at 11:19
For opening target device node you do not need to change anything in target device driver but for option2 and option3 i suggested in that you need to change some code in target device driver file. – Jeegar Patel Jul 22 '14 at 11:28
Do you have any example code showing how to open the device node and perform a ioctl call? I found that ioctl needs an fd, sys_open which returns an fd is no longer exported, and filp_open returns a file* instead. – Grodriguez Jul 22 '14 at 11:29

Getting a reference to an input device from a kernel module

1 Answers1