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

[randy_dunlap <rdunlap@xenotime.net>]

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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