Hello all !!!
I am trying to make a simple tty driver to illustrate the tty driver
interface. I have made this the module and the application listed below. When
I run the application I get a kernel segmentation fault.
My "call trace" shows that the error is in function write_chan from n_tty.c
and I did not find the reason for the fault.
Could anyone help me ?
Thanks in advance
---
Henrique Gobbi
[email protected]
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* This module make nothing. It is just to illustrate
* some aspects of tty driver interface
*/
#include <linux/config.h>
#include <linux/module.h>
#include <linux/errno.h>
#include <linux/signal.h>
#include <linux/sched.h>
#include <linux/timer.h>
#include <linux/interrupt.h>
#include <linux/tty.h>
#include <linux/serial.h>
#include <linux/major.h>
#include <linux/string.h>
#include <linux/fcntl.h>
#include <linux/ptrace.h>
#include <linux/mm.h>
#include <linux/ioport.h>
#include <linux/init.h>
#include <linux/delay.h>
#include <linux/spinlock.h>
#include <linux/proc_fs.h>
#include <linux/slab.h>
#include <asm/system.h>
#include <asm/io.h>
#include <asm/irq.h>
#include <asm/uaccess.h>
#include <asm/bitops.h>
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/pci.h>
#include <linux/version.h>
#include <linux/stat.h>
static struct tty_driver cy_serial_driver;
static int serial_refcount;
static struct tty_struct *serial_table;
static struct termios *serial_termios;
static struct termios *serial_termios_locked;
static unsigned char * tmp_buf;
void cy_cleanup_module(void) {
printk("Driver - GoodBye, cruel world\n");
}
static int cy_open (struct tty_struct *tty, struct file *filp) {
unsigned long page;
MOD_INC_USE_COUNT;
printk("Driver - open. Minor: %d\n", MINOR(tty->device) );
if ( !tmp_buf ) {
page = get_free_page(GFP_KERNEL);
if ( !page ) {
return -ENOMEM;
}
if ( tmp_buf ) {
free_page(page);
} else {
tmp_buf = (unsigned char *) page;
}
}
return 0;
}
static void cy_close (struct tty_struct * tty, struct file *filp) {
printk("Driver - close\n");
MOD_DEC_USE_COUNT;
if (tmp_buf) {
free_page( (unsigned long) tmp_buf );
tmp_buf = NULL;
}
return;
}
static int cy_write ( struct tty_struct * tty, int from_user, const unsigned
char *buf, int count) {
printk("Driver - Trying to write %d bytes\n", count);
return 0;
}
int __init cy_init(void)
{
printk("Driver - init\n");
/* Initialize the tty_driver structure */
memset(&cy_serial_driver, 0, sizeof(struct tty_driver));
cy_serial_driver.magic = TTY_DRIVER_MAGIC;
cy_serial_driver.driver_name = "curso";
#ifdef CONFIG_DEVFS_FS
cy_serial_driver.name = "tts/curso%d";
#else
cy_serial_driver.name = "ttycurso%d";
#endif
cy_serial_driver.major = 87;
cy_serial_driver.minor_start = 0;
cy_serial_driver.num = 1;
cy_serial_driver.type = TTY_DRIVER_TYPE_SERIAL;
cy_serial_driver.subtype = SERIAL_TYPE_NORMAL;
cy_serial_driver.init_termios = tty_std_termios;
cy_serial_driver.init_termios.c_cflag =
B9600 | CS8 | CREAD | HUPCL | CLOCAL;
cy_serial_driver.init_termios.c_oflag |= OPOST;
cy_serial_driver.flags = TTY_DRIVER_REAL_RAW;
cy_serial_driver.refcount = &serial_refcount;
cy_serial_driver.table = & serial_table;
cy_serial_driver.termios = & serial_termios;
cy_serial_driver.termios_locked = & serial_termios_locked;
cy_serial_driver.open = cy_open;
cy_serial_driver.close = cy_close;
cy_serial_driver.write = cy_write;
if (tty_register_driver(&cy_serial_driver))
panic("Couldn't register Cyclades serial driver\n");
return 0;
}
module_init(cy_init);
module_exit(cy_cleanup_module);
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// Application
# include <stdio.h>
# include <sys/types.h>
# include <sys/stat.h>
# include <fcntl.h>
# include <errno.h>
# include <unistd.h>
int main (void) {
int fd;
int aux;
char buf[100];
printf("User - Opening the device\n");
fd = open ("/dev/ttycurso0", O_RDWR | O_NONBLOCK);
if ( fd == -1) {
perror("User - Error opening the device, exiting");
return 1;
}
strcpy(buf, "Espero 13");
printf("User - Writing 10 bytes to device");
aux = write(fd, buf, 10);
printf("User - Writing return: %d", aux);
printf("User - Closing the device\n");
aux = close(fd);
if ( aux == -1) {
perror("User - Error closing the device, exiting");
return 1;
}
return 0;
}
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