hi kernel'ers :
i have a kernel module in which i am trying to implement a simple device driver
following the LDD3 book.
currently i am only trying to open and close the device node. the module
compiles fine and when insmod'ed it sets up the hooks using cdev_init() and
cdev_add().
then i create the device node in the /dev directory as per the major and minor
number.
but when i try to open() the device node i get the following Oops message :
(/var/log/messages)
====================================================================================================================
Aug 9 19:30:05 linux-ujq3 kernel: BUG: unable to handle kernel NULL pointer
dereference at virtual address 00000005
Aug 9 19:30:05 linux-ujq3 kernel: printing eip:
Aug 9 19:30:05 linux-ujq3 kernel: c017340a
Aug 9 19:30:05 linux-ujq3 kernel: *pde = 00000000
Aug 9 19:30:05 linux-ujq3 kernel: Oops: 0002 [#1]
Aug 9 19:30:05 linux-ujq3 kernel: SMP
Aug 9 19:30:05 linux-ujq3 kernel: last sysfs file:
/devices/system/cpu/cpu1/online
Aug 9 19:30:05 linux-ujq3 kernel: Modules linked in: skull snd_pcm_oss
snd_mixer_oss snd_seq snd_seq_device iptable_filter ip_tables ip6table_filter
ip6_tables x_tables ipv6 micr
ocode firmware_class apparmor nls_iso8859_1 nls_cp437 vfat fat fuse loop dm_mod
snd_hda_intel snd_pcm ohci1394 8139cp snd_timer ieee1394 8139too snd parport_pc
ati_agp rtc_cmos mi
i agpgart i2c_piix4 button rtc_core usb_storage soundcore sr_mod cdrom
snd_page_alloc i2c_core ide_core rtc_lib parport sg sd_mod ohci_hcd ehci_hcd
usbcore edd ext3 mbcache jbd fa
n pata_atiixp sata_sil libata scsi_mod thermal processor
Aug 9 19:30:05 linux-ujq3 kernel: CPU: 1
Aug 9 19:30:05 linux-ujq3 kernel: EIP: 0060:[<c017340a>] Tainted: G
N VLI
Aug 9 19:30:05 linux-ujq3 kernel: EFLAGS: 00210246 (2.6.22.17-0.1-default #1)
Aug 9 19:30:05 linux-ujq3 kernel: EIP is at chrdev_open+0x79/0x133
Aug 9 19:30:05 linux-ujq3 kernel: eax: 00000001 ebx: f3f6de44 ecx:
f3f6de44 edx: f3d51f64
Aug 9 19:30:05 linux-ujq3 kernel: esi: f3f6de44 edi: 00000000 ebp:
f3d51e60 esp: f3f99ee0
Aug 9 19:30:05 linux-ujq3 kernel: ds: 007b es: 007b fs: 00d8 gs: 0033
ss: 0068
Aug 9 19:30:05 linux-ujq3 kernel: Process a.out (pid: 4364, ti=f3f98000
task=dff8b570 task.ti=f3f98000)
Aug 9 19:30:05 linux-ujq3 kernel: Stack: f421a3c0 00000000 f421a3c0 f3d51e60
f3f99f30 c0173391 c016f8b7 dfbf13c0
Aug 9 19:30:05 linux-ujq3 kernel: f3e8dc6c f421a3c0 ffffff9c f3f99f30
00000003 c016f9e8 f421a3c0 00000000
Aug 9 19:30:05 linux-ujq3 kernel: 0804855b c016fa2e bfa9f9d8 f3f99f30
f3e8dc6c dfbf13c0 13645c10 00000005
Aug 9 19:30:05 linux-ujq3 kernel: Call Trace:
Aug 9 19:30:05 linux-ujq3 kernel: [<c0173391>] chrdev_open+0x0/0x133
Aug 9 19:30:05 linux-ujq3 kernel: [<c016f8b7>] __dentry_open+0xc1/0x178
Aug 9 19:30:05 linux-ujq3 kernel: [<c016f9e8>] nameidata_to_filp+0x24/0x33
Aug 9 19:30:05 linux-ujq3 kernel: [<c016fa2e>] do_filp_open+0x37/0x3e
Aug 9 19:30:05 linux-ujq3 kernel: [<c016f79b>] get_unused_fd+0x57/0xb2
Aug 9 19:30:05 linux-ujq3 kernel: [<c016fa77>] do_sys_open+0x42/0xc8
Aug 9 19:30:05 linux-ujq3 kernel: [<c016fb36>] sys_open+0x1c/0x1e
Aug 9 19:30:05 linux-ujq3 kernel: [<c0104e22>] sysenter_past_esp+0x6b/0xa9
Aug 9 19:30:05 linux-ujq3 kernel: [<c02c0000>] unix_find_other+0x75/0x161
Aug 9 19:30:05 linux-ujq3 kernel: =======================
Aug 9 19:30:05 linux-ujq3 kernel: Code: c3 2d 15 00 8b b5 0c 01 00 00 85 f6 75
36 89 9d 0c 01 00 00 8b 44 24 04 8d 95 04 01 00 00 89 de 31 ff 89 85 10 01 00
00 8b 43 48 <89> 50 0
4 89 85 04 01 00 00 8d 43 48 89 53 48 31 db 89 85 08 01
Aug 9 19:30:05 linux-ujq3 kernel: EIP: [<c017340a>] chrdev_open+0x79/0x133
SS:ESP 0068:f3f99ee0
========================================================================================================================
the line : "Aug 9 19:30:05 linux-ujq3 kernel: BUG: unable to handle kernel
NULL pointer dereference at virtual address 00000005" comes from mm/fault.c
(do_page_fault()), but i am unable to find what is causing the problem (may be
a very very silly one :)).
after this the system hangs and the only solution is a hard reboot.
where am i going wrong or am i missing something.
i am running : Linux linux-ujq3 2.6.22.17-0.1-default #1 SMP 2008/02/10
20:01:04 UTC i686 i686 i386 GNU/Linux
source is attached : skull.c and skull.h
thanks in advance.
-Venky
# include "skull.h"
#include <linux/cdev.h>
MODULE_LICENSE("Dual BSD/GPL");
static char *device_name = "skull";
static dev_t device_number;
static int no_of_device_nodes = 1;
/*
This is the device structure that skull uses to store data structures.
currently only 2 members for testing.
*/
struct skull_dev {
unsigned long amt; /* amount of data */
struct cdev cdev; /* the actual cdev structure */
};
/*
These are the actual fops functions, open, release, read and write.
*/
/*
Open the device.
Get the acutal skull_dev structure from the cdev structure and save it in file->private_data.
Print the device number for debug.
*/
int skull_open(struct inode *inode, struct file *filp) {
/*
struct skull_dev *dev;
dev = container_of(inode->i_cdev, struct skull_dev, cdev);
filp->private_data = dev;
printk(KERN_ALERT "Device number : %d.%d calling skull_open\n", imajor(inode), iminor(inode));
*/
printk(KERN_ALERT "Opening skull device\n");
return 0;
}
/*
Remove the device.
*/
int skull_release(struct inode *inode, struct file *filp) {
return 0;
}
/*
This is skull's file operations structure.
*/
struct file_operations skull_fops = {
.owner = THIS_MODULE,
.open = skull_open,
.read = NULL,
.write = NULL,
.release = skull_release,
};
/*
Now we actually hand over the driver to the kernel.
index - now 0, will be used when we have more than 1 device nodes.
*/
static int setup_skull_and_hand_over(struct skull_dev *sk_dev, int index) {
int error;
cdev_init(&sk_dev->cdev, &skull_fops);
sk_dev->cdev.owner = THIS_MODULE;
sk_dev->cdev.ops = &skull_fops;
error = cdev_add(&sk_dev->cdev, device_number, 1);
if(error) {
printk(KERN_ALERT "blah, something is wrong, no entry\n");
return 0;
}
printk(KERN_ALERT "skull_fops added to cdev list\n");
return 1;
}
/*
initializaton function
*/
static int skull_init(void) {
int skull_registered;
struct skull_dev skull_devel;
if(skull_major) {
device_number = MKDEV(skull_major, skull_minor);
skull_registered = register_chrdev_region(device_number, no_of_device_nodes, device_name);
}
else {
skull_registered = alloc_chrdev_region(&device_number, skull_minor, no_of_device_nodes, device_name);
}
if(skull_registered < 0)
return 1;
/*
else continue here with the adding of the driver into the kernel
*/
memset(&skull_devel, 0, sizeof(skull_devel));
if (!setup_skull_and_hand_over(&skull_devel, 0))
return 1;
printk(KERN_ALERT "skull driver installed successfully with dev no : %d.%d\n", MAJOR(device_number), MINOR(device_number));
return 0;
}
/*
dtor function
*/
static void skull_exit(void) {
printk(KERN_ALERT "Skull removedn\n");
unregister_chrdev_region(device_number, no_of_device_nodes);
}
module_init(skull_init);
module_exit(skull_exit);
/*
This ths is skull header file to choose
between dynamic/static device no.
*/
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/kdev_t.h>
#include <linux/sched.h>
#include <linux/moduleparam.h>
/*
non zero major means static device number allocation
*/
static dev_t skull_major = 0;
static dev_t skull_minor = 0;
