Hello Karim,
Here is the kernel dmesg and source code of the driver and a test .c file:
DMESG:
/ # chmod 777 testn ebbchar1.ko
/ # insmod ebbchar1.ko
EBBChar: Initializing the EBBChar LKM
EBBChar: registered correctly with major number 254
EBBChar: device class registered correctly
EBBChar: device class created correctly
/ #
/ # cd dev
/dev # mknod ebbchar c 254 0
/dev # chmod 777 ebbchar
/dev # cd ../
/ # ./testn
Starting device test code example...
EBBChar: Device has been opened 1 time(s)
Type in a short string to send to the kernel module:
test
Writing message to the device [test].
Non-resolvable page fault at bfaedc21, ip 21e8c54.
Page fault (non-resolved): pfa=bfaedc21 pc=21e8c54
Non-resolvable page fault at bfaedc21, ip 21e8c54.
.... (too many exact lines here)
Page fault (non-resolved): pfa=bfaedc21 pc=21e8c54
Non-resolvable page fault at 3, ip 200b9d8.
Page fault (non-resolved): pfa=3 pc=200b9d8
^[[5~^[[5~^[[5~^[[6~^[[6~^[[6~^[[6~INFO: task testn:85 blocked for more than 120 seconds.
Tainted: G O 4.3.0-l4 #4
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
testn D 023492a0 0 85 72 0x00000000
[<023492a0>] (__schedule) from [<023496f4>] (schedule+0x34/0x98)
[<023496f4>] (schedule) from [<0234ca70>] (rwsem_down_read_failed+0xec/0x128)
[<0234ca70>] (rwsem_down_read_failed) from [<02013914>] (do_page_fault+0x134/0x288)
[<02013914>] (do_page_fault) from [<0200b844>] (l4x_vcpu_entry_kern+0x240/0xdb4)
[<0200b844>] (l4x_vcpu_entry_kern) from [<0200da60>] (l4x_vcpu_entry_c+0x16a8/0x2668)
[<0200da60>] (l4x_vcpu_entry_c) from [<020138c0>] (do_page_fault+0xe0/0x288)
[<020138c0>] (do_page_fault) from [<00000000>] ( (null))
TEST.C:
/**
* @file testebbchar.c
* @author Derek Molloy
* @date 7 April 2015
* @version 0.1
* @brief A Linux user space program that communicates with the ebbchar.c LKM. It passes a
* string to the LKM and reads the response from the LKM. For this example to work the device
* must be called /dev/ebbchar.
* @see http://www.derekmolloy.ie/ for a full description and follow-up descriptions.
*/
#include<stdio.h>
#include<stdlib.h>
#include<errno.h>
#include<fcntl.h>
#include<string.h>
#define BUFFER_LENGTH 256 ///< The buffer length (crude but fine)
static char receive[BUFFER_LENGTH]; ///< The receive buffer from the LKM
int main(){
int ret, fd;
char stringToSend[BUFFER_LENGTH];
printf("Starting device test code example...\n");
fd = open("/dev/ebbchar", O_RDWR); // Open the device with read/write access
if (fd < 0){
perror("Failed to open the device...");
return errno;
}
printf("Type in a short string to send to the kernel module:\n");
scanf("%[^\n]%*c", stringToSend); // Read in a string (with spaces)
printf("Writing message to the device [%s].\n", stringToSend);
ret = write(fd, stringToSend, strlen(stringToSend)); // Send the string to the LKM
if (ret < 0){
perror("Failed to write the message to the device.");
return errno;
}
printf("Press ENTER to read back from the device...\n");
getchar();
printf("Reading from the device...\n");
ret = read(fd, receive, BUFFER_LENGTH); // Read the response from the LKM
if (ret < 0){
perror("Failed to read the message from the device.");
return errno;
}
printf("The received message is: [%s]\n", receive);
printf("End of the program\n");
return 0;
}
MODULE: EBBCHAR.C:
/**
* @file ebbchar.c
* @author Derek Molloy
* @date 7 April 2015
* @version 0.1
* @brief An introductory character driver to support the second article of my series on
* Linux loadable kernel module (LKM) development. This module maps to /dev/ebbchar and
* comes with a helper C program that can be run in Linux user space to communicate with
* this the LKM.
* @see http://www.derekmolloy.ie/ for a full description and follow-up descriptions.
*/
#include <linux/init.h> // Macros used to mark up functions e.g. __init __exit
#include <linux/module.h> // Core header for loading LKMs into the kernel
#include <linux/device.h> // Header to support the kernel Driver Model
#include <linux/kernel.h> // Contains types, macros, functions for the kernel
#include <linux/fs.h> // Header for the Linux file system support
#include <asm/uaccess.h> // Required for the copy to user function
#define DEVICE_NAME "ebbchar" ///< The device will appear at /dev/ebbchar using this value
#define CLASS_NAME "ebb" ///< The device class -- this is a character device driver
MODULE_LICENSE("GPL"); ///< The license type -- this affects available functionality
MODULE_AUTHOR("Derek Molloy"); ///< The author -- visible when you use modinfo
MODULE_DESCRIPTION("A simple Linux char driver for the BBB"); ///< The description -- see modinfo
MODULE_VERSION("0.1"); ///< A version number to inform users
static int majorNumber; ///< Stores the device number -- determined automatically
static char message[256] = {0}; ///< Memory for the string that is passed from userspace
static short size_of_message; ///< Used to remember the size of the string stored
static int numberOpens = 0; ///< Counts the number of times the device is opened
static struct class* ebbcharClass = NULL; ///< The device-driver class struct pointer
static struct device* ebbcharDevice = NULL; ///< The device-driver device struct pointer
// The prototype functions for the character driver -- must come before the struct definition
static int dev_open(struct inode *, struct file *);
static int dev_release(struct inode *, struct file *);
static ssize_t dev_read(struct file *, char *, size_t, loff_t *);
static ssize_t dev_write(struct file *, const char *, size_t, loff_t *);
/** @brief Devices are represented as file structure in the kernel. The file_operations structure from
* /linux/fs.h lists the callback functions that you wish to associated with your file operations
* using a C99 syntax structure. char devices usually implement open, read, write and release calls
*/
static struct file_operations fops =
{
.open = dev_open,
.read = dev_read,
.write = dev_write,
.release = dev_release,
.owner = THIS_MODULE,
};
/** @brief The LKM initialization function
* The static keyword restricts the visibility of the function to within this C file. The __init
* macro means that for a built-in driver (not a LKM) the function is only used at initialization
* time and that it can be discarded and its memory freed up after that point.
* @return returns 0 if successful
*/
static int __init ebbchar_init(void){
printk(KERN_INFO "EBBChar: Initializing the EBBChar LKM\n");
// Try to dynamically allocate a major number for the device -- more difficult but worth it
majorNumber = register_chrdev(0, DEVICE_NAME, &fops);
if (majorNumber<0){
printk(KERN_ALERT "EBBChar failed to register a major number\n");
return majorNumber;
}
printk(KERN_INFO "EBBChar: registered correctly with major number %d\n", majorNumber);
// Register the device class
ebbcharClass = class_create(THIS_MODULE, CLASS_NAME);
if (IS_ERR(ebbcharClass)){ // Check for error and clean up if there is
unregister_chrdev(majorNumber, DEVICE_NAME);
printk(KERN_ALERT "Failed to register device class\n");
return PTR_ERR(ebbcharClass); // Correct way to return an error on a pointer
}
printk(KERN_INFO "EBBChar: device class registered correctly\n");
// Register the device driver
ebbcharDevice = device_create(ebbcharClass, NULL, MKDEV(majorNumber, 0), NULL, DEVICE_NAME);
if (IS_ERR(ebbcharDevice)){ // Clean up if there is an error
class_destroy(ebbcharClass); // Repeated code but the alternative is goto statements
unregister_chrdev(majorNumber, DEVICE_NAME);
printk(KERN_ALERT "Failed to create the device\n");
return PTR_ERR(ebbcharDevice);
}
printk(KERN_INFO "EBBChar: device class created correctly\n"); // Made it! device was initialized
return 0;
}
/** @brief The LKM cleanup function
* Similar to the initialization function, it is static. The __exit macro notifies that if this
* code is used for a built-in driver (not a LKM) that this function is not required.
*/
static void __exit ebbchar_exit(void){
device_destroy(ebbcharClass, MKDEV(majorNumber, 0)); // remove the device
class_unregister(ebbcharClass); // unregister the device class
class_destroy(ebbcharClass); // remove the device class
unregister_chrdev(majorNumber, DEVICE_NAME); // unregister the major number
printk(KERN_INFO "EBBChar: Goodbye from the LKM!\n");
}
/** @brief The device open function that is called each time the device is opened
* This will only increment the numberOpens counter in this case.
* @param inodep A pointer to an inode object (defined in linux/fs.h)
* @param filep A pointer to a file object (defined in linux/fs.h)
*/
static int dev_open(struct inode *inodep, struct file *filep){
numberOpens++;
printk(KERN_INFO "EBBChar: Device has been opened %d time(s)\n", numberOpens);
return 0;
}
/** @brief This function is called whenever device is being read from user space i.e. data is
* being sent from the device to the user. In this case is uses the copy_to_user() function to
* send the buffer string to the user and captures any errors.
* @param filep A pointer to a file object (defined in linux/fs.h)
* @param buffer The pointer to the buffer to which this function writes the data
* @param len The length of the b
* @param offset The offset if required
*/
static ssize_t dev_read(struct file *filep, char *buffer, size_t len, loff_t *offset){
int error_count = 0;
// copy_to_user has the format ( * to, *from, size) and returns 0 on success
error_count = copy_to_user(buffer, message, size_of_message);
if (error_count==0){ // if true then have success
printk(KERN_INFO "EBBChar: Sent %d characters to the user\n", size_of_message);
return (size_of_message=0); // clear the position to the start and return 0
}
else {
printk(KERN_INFO "EBBChar: Failed to send %d characters to the user\n", error_count);
return -EFAULT; // Failed -- return a bad address message (i.e. -14)
}
}
/** @brief This function is called whenever the device is being written to from user space i.e.
* data is sent to the device from the user. The data is copied to the message[] array in this
* LKM using the sprintf() function along with the length of the string.
* @param filep A pointer to a file object
* @param buffer The buffer to that contains the string to write to the device
* @param len The length of the array of data that is being passed in the const char buffer
* @param offset The offset if required
*/
static ssize_t dev_write(struct file *filep, const char *buffer, size_t len, loff_t *offset){
sprintf(message, "%s(%d letters)", buffer, len); // appending received string with its length
size_of_message = strlen(message); // store the length of the stored message
printk(KERN_INFO "EBBChar: Received %d characters from the user\n", len);
return len;
}
/** @brief The device release function that is called whenever the device is closed/released by
* the userspace program
* @param inodep A pointer to an inode object (defined in linux/fs.h)
* @param filep A pointer to a file object (defined in linux/fs.h)
*/
static int dev_release(struct inode *inodep, struct file *filep){
printk(KERN_INFO "EBBChar: Device successfully closed\n");
return 0;
}
/** @brief A module must use the module_init() module_exit() macros from linux/init.h, which
* identify the initialization function at insertion time and the cleanup function (as
* listed above)
*/
module_init(ebbchar_init); module_exit(ebbchar_exit);
Thanks, Nourhan
On Wed, Feb 3, 2016 at 2:57 PM, karim.allah.ahmed@gmail.com < karim.allah.ahmed@gmail.com> wrote:
Hello Nourhan,
You have to post kernel dmesg + the character device source code.
Regards.
On Wed, Feb 3, 2016 at 2:24 PM, Nourhan Mohamed nourhan.abdeltawab@gmail.com wrote:
Hi Karim,
Worked really fine Thank you!
I can use "open" to open the device. However I get a page fault whenever
I
attempt to write to the device. The device works properly on my ubuntu machine so I can't guess what can be the problem. Would really help if
you
have any suggestions.
Thank you again BR, Nourhan
On Wed, Feb 3, 2016 at 12:00 PM, karim.allah.ahmed@gmail.com karim.allah.ahmed@gmail.com wrote:
Hello Nourhan,
On Wed, Feb 3, 2016 at 11:47 AM, Nourhan Mohamed nourhan.abdeltawab@gmail.com wrote:
Dear all,
I wanted to create a simple character device on L4Linux. I managed to cross-compile the module and run it on L4Linux on Versatile Express Realview Cortex-A15 ARM machine using the following command:
make -C ~/l4re/obj/l4linux/arm-mp/ M=$PWD CROSS_COMPILE=/usr/bin/arm-linux-gnueabi- L4ARCH=arm CONFIG_TCG_TPM=m modules V=1
When I try to insert the module using the insmod command I get the following printed out from the module: chardev: registered correctly with major number 254 chardev: device class registered correctly chardev: device class created correctly
With no failures in initializing the device printed at all. Also lsmod displays the device in the module list with status live.
However, the device doesn't appear in the /dev/ directory and hence I can not access it using the file operations. Any ideas where is the device located or how can it be accessed on L4Linux?
In linux systems, device nodes are not necessarily automatically generated under /dev/.
Use 'mknod' command-line to create a device node in user space that's connected to this character device.
Regards.
l4-hackers mailing list l4-hackers@os.inf.tu-dresden.de http://os.inf.tu-dresden.de/mailman/listinfo/l4-hackers
-- Karim Allah Ahmed.
-- Karim Allah Ahmed.