Re: cdev_init() problems in char device driver (kernel 2.6.4-52)(newbie ques)

From: randy_dunlap
Date: Wed Jun 22 2005 - 13:57:20 EST

On Wed, 15 Jun 2005 19:31:10 -0400 Hemant Mohapatra wrote:

| Hello all,
|
| I am writing a simple char driver on Linux (Suse 9.1, kernel 2.6.4.52,
| gcc 3.3.3) and having the following problems (code is cut-pasted at
| the end):
|
| 1) MODULE_LICENSE gives the following on make -
|
| error: parse error before string constant
| warning: type defaults to `int' in declaration of `MODULE_LICENCE'
| warning: data definition has no type or storage class

Spell it "MODULE_LICENSE" and it will work.

You need to use a 2.6 kbuild Makefile...

Add near top of source file:
#include <linux/config.h>

Source file #includes <linux/cdev.h> 2 times.

Don't use MOD_INC_USE_COUNT/MOD_DEC_USE_COUNT in 2.6.x.

I didn't try to load the module (yet).

| Btw, it works fine in another program which simply does module_init()
| and module_exit().
|
| 2) insmod faults (SIGSEGV) with strace ending at the line:
|
| init_module("^?ELF^A^A^A", 0xc529 <unfinished ...>
| 4299 +++ killed by SIGSEGV +++
|
| dmesg output:
|
| MAJOR(dev)=253
| Before cdev_init
| Unable to handle kernel NULL pointer dereference at virtual address 00000018
| printing eip:
| c01da533
| *pde = 00000000
| Oops: 0002 [#2]
| CPU: 0
| EIP: 0060:[<c01da533>] Tainted: PF
| EFLAGS: 00010292 (2.6.4-52-default)
| EIP is at kobject_init+0x3/0x40
| eax: 00000000 ebx: 00000000 ecx: 00000000 edx: 00000000
| esi: d9126880 edi: d912684c ebp: d059de48 esp: d059de28
| ds: 007b es: 007b ss: 0068
| Process insmod (pid: 3877, threadinfo=d059c000 task=d6494d70)
| Stack: c0341da8 d91280cc d9126800 000000fd 00000001 d9126232 0fd00000 c0341d98
| c0341d98 c0132305 00000000 d9142e54 d9142e54 00000500 00000500 d05dc9a0
| d059de8c c0138db0 0000304c 00000282 00000000 d05dc980 00000001 d059deb4
| Call Trace:
| [<d91280cc>] scull_init+0xcc/0x15f [cd]
| [<c0132305>] sys_init_module+0x105/0x15b0
| [<c0138db0>] file_read_actor+0x0/0xe0
| [<c01da3e0>] kobject_put+0x0/0x20
| [<d9128000>] scull_init+0x0/0x15f [cd]
| [<c01c8d96>] selinux_file_alloc_security+0x26/0x80
| [<c01ca1e0>] selinux_file_permission+0x160/0x170
| [<c0155b5e>] __fput+0x9e/0xf0
| [<c0107dc9>] sysenter_past_esp+0x52/0x79
|
| Code: c7 40 18 01 00 00 00 8d 40 1c 89 43 1c 89 43 20 8b 43 28 31
|
|
| Analysis done:
|
| I was getting the same erorr on cdev_init() so to find out where
| exactly the inmod was crashing, I manually did whatever was being done
| inside cdev_init and figured out that it was crashing at
| kobject_init().
|
| I have gone through /proc/ksyms to figure out exactly which
| instruction causes the fault but have not been successful.
|
| relevant ksymoops info:
|
| Code; c01da533 <kobject_init+3/40>
| 00000000 <_EIP>:
| Code; c01da533 <kobject_init+3/40> <=====
| 0: c7 40 18 01 00 00 00 movl $0x1,0x18(%eax) <=====
| Code; c01da53a <kobject_init+a/40>
| 7: 8d 40 1c lea 0x1c(%eax),%eax
| Code; c01da53d <kobject_init+d/40>
| a: 89 43 1c mov %eax,0x1c(%ebx)
| Code; c01da540 <kobject_init+10/40>
| d: 89 43 20 mov %eax,0x20(%ebx)
| Code; c01da543 <kobject_init+13/40>
| 10: 8b 43 28 mov 0x28(%ebx),%eax
| Code; c01da546 <kobject_init+16/40>
| 13: 31 00 xor %eax,(%eax)
|
|
| Any help extended would be highly appreciated.
|
| Thanks,
| Hemant R Mohapatra
|
|
|
| ------------------------------------------------------------------------
|
| Code:
|
| #if defined( CONFIG_MODVERSIONS ) && ! defined( MODVERSIONS )
| #define MODVERSIONS
| #endif
|
| #include <linux/module.h>
| #include <linux/init.h>
| #include <asm/current.h>
| #include <asm/uaccess.h>
| #include <linux/sched.h>
| #include <linux/fs.h>
| #include <linux/kernel.h>
| #include <linux/kobject.h>
| #include <linux/kobj_map.h>
| #include <linux/cdev.h>
| #ifdef CONFIG_KMOD
| #include <linux/kmod.h>
| #endif
| #include <linux/cdev.h>
|
| #define DEVICE_NAME "scull"
| #define SUCCESS 0
| #define FAIL -1
| #define SIZE 10
| #define TYPE(dev) (MINOR(dev) >> 4) //highers 4 bits refer to type
| of device (char, in this case)
| //lower 4 bits refer to NUM for the device
| #define NUM(dev) (MINOR(dev) & 0xf)
|
|
| static int Major, Minor;
| static int device_opened = 0;
|
| static char MSGBUF[SIZE];
| static char *msg_ptr;
| static int device_open (struct inode *in, struct file *filp);
| static int device_release (struct inode *in, struct file *filp);
| /* static ssize_t device_read (struct file *, char *, size_t, loff_t *);
| static ssize_t device_write (struct file *, char *, size_t, loff_t *);
| * */
|
| static int
| device_open (struct inode *in, struct file *filp)
| {
|
| /* int type=TYPE(in->i_rdev); */// Old way of getting the driver's
| // major/minor number.
| /* int num=NUM(in->i_rdev); */
| int counter = 0;
| int type = TYPE (iminor (in));
| int num = NUM (iminor (in));
|
| if (device_opened)
| {
| return -EBUSY;
| }
| device_opened++;
| msg_ptr = MSGBUF; //this is the pointer used in reading from
| the device in the device_read func
|
| sprintf (MSGBUF, "This is call to open() device number: %d\n", ++counter);
|
| //return some info about the driver
| printk ("<1> TYPE of device = %d\n and NUM of device = %d\n", type, num);
| MOD_INC_USE_COUNT;
| return SUCCESS;
| }
|
|
| static int
| device_release (struct inode *in, struct file *filp)
| {
|
| device_opened--;
| MOD_DEC_USE_COUNT;
| return SUCCESS;
| }
|
| static struct file_operations scull_fops = {
| .open = device_open,
| .release = device_release,
| .owner = THIS_MODULE,
| // .read = device_read,
| // .write = device_write,
| };
|
| static struct cdev scull_cdev = {
| .kobj = {.name = "scull", },
| .owner = THIS_MODULE,
| };
|
| static int __init scull_init (void)
| {
| /* dev_t dev=MKDEV(63,0); */
| dev_t dev;
| int retval;
|
| retval=alloc_chrdev_region(&dev, 0, 1, DEVICE_NAME);
| if(!retval)
| {
| Major=MAJOR(dev);
| Minor=MINOR(dev);
| }
| else {
| return FAIL;
| }
| printk("MAJOR(dev)=%d\n", MAJOR(dev));
|
| printk("<1> Before cdev_init\n");
|
|
| memset(&scull_cdev, 0, sizeof(scull_cdev));
| INIT_LIST_HEAD(&scull_cdev.list);
| //scull_cdev.kobj.ktype = &ktype_cdev_default; -- not working, why?
| kobject_init(&scull_cdev.kobj);
| scull_cdev.ops = &scull_fops;
| //kobject_set_name(&scull_cdev.kobj,"scull");
|
| //cdev_init(&scull_cdev, &scull_fops); -- was not working, so the above
| //simplification
|
| printk("<1> after cdev_init:\n");
|
| retval=cdev_add(&scull_cdev, dev, 1);
| if(retval)
| {
| cdev_del(&scull_cdev);
| kobject_put(&scull_cdev.kobj);
| unregister_chrdev_region(dev, 1);
| printk("<1> Error in cdev_add:");
| goto error;
| }
| printk ("<1> scull_init was a Success and the major device number is
| %d \n", Major);
| return 0;
|
| error:
| printk(KERN_ERR "error register raw device\n");
| return FAIL;
|
| }
|
| static void scull_exit (void)
| {
| printk ("<1> Removing scull drivers from /proc/devices\n");
| unregister_chrdev_region (MKDEV(Major,0), 1);
| }
|
|
| module_init (scull_init);
| module_exit (scull_exit);
| //MODULE_LICENCE("GPL"); - doesn't work.
| -


---
~Randy
-
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