对c有点生锈，如何打印此结构的有用信息？

Question

So I'm trying to debug a linux module someone else wrote and it's a while since I wrote anything in c/c++

I get an error here (this question is indirectly related to the error):

video_register_device(usbMightex->vdev, VFL_TYPE_GRABBER, video_nr)

so I wanted to try and find out what usbMightex->vdev is.

This it's structure:

http://www.linuxtv.org/downloads/legacy/video4linux/v4l2dwgNew.html

struct video_device

char name[32]                              :Canonical name for this device.
int type                                   :Type of V4L2 device
(use type2 as well, look at videodev2.h for details on type2)
int minor                                  :The device's minor number
struct file_operations *fops;              :File operations used, which are displayed below
void (*release)(struct video_device *vfd); :Release function used by the driver to release
void *priv:                                :Can be used by the driver

I already have a pr_err statement that is used to print information but not sure how to use it. Not sure where it's defined. I think I'll be happy with a simple printf statement or smth similar so I can then pick up the output with dmesg

Thank you.

UPDATE

A commenter asked for some more information with regards to the error:

I have posted a different question about the problem generally here:

https://askubuntu.com/questions/565700/how-do-i-load-a-module-that-has-no-signature-in-ubuntu-12-04

This question is NOT about the error, it was merely about how to print some information that would potentially be useful in solving the error. Thank you to all that responded.

Answer 1

The most obvious answer is, use a debugger and put a breakpoint where you want to see the variables.

To print out in code then, assuming your linked page is correct (you should verify this by checking the header file, otherwise nonsense output may ensue):

printf("%31s\n", v->name);
printf("%d\n", v->type);
printf("%d\n", v->minor);
printf("%p\n", (void *)v->fops);
printf(PRIxMAX "\n", (uintmax_t)v->release);
printf("%p\n", priv);

where v is the pointer to the instance of the structure.

Answer 2

If it is compiled as kernel module (*.ko), you could probably insert and remove it multiple times without reboot

lsmod , modprobe , insmod etc

And you might find useful printk() functions, they output to syslog which goes into dmesg IIRC