Eu tive o mesmo problema e resolvi criando um módulo do kernel que fica preso no estado D.
Como não tenho experiência em módulos, peguei o código desse histórico com algumas modificações encontradas em algum lugar .
O resultado é um dispositivo em / dev / memory que fica preso na leitura, mas pode ser acordado gravando nele (ele precisa de duas gravações, não sei por que, mas não me importo).
Para usá-lo apenas:
# make
# make mknod
# make install
# cat /dev/memory # this gets blocked
Para desbloquear, de outro terminal:
# echo -n a > /dev/memory
# echo -n a > /dev/memory
Makefile:
obj-m += memory.o
all:
make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules
clean:
make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean
install:
sudo insmod memory.ko
uninstall:
sudo rmmod memory
mknod:
sudo mknod /dev/memory c 60 0
sudo chmod 666 /dev/memory
Código para memory.c:
/* Necessary includes for device drivers */
#include <linux/init.h>
#include <linux/module.h>
#include <linux/kernel.h> /* printk() */
#include <linux/slab.h> /* kmalloc() */
#include <linux/fs.h> /* everything... */
#include <linux/errno.h> /* error codes */
#include <linux/types.h> /* size_t */
#include <linux/proc_fs.h>
#include <linux/fcntl.h> /* O_ACCMODE */
#include <asm/uaccess.h> /* copy_from/to_user */
#include <linux/sched.h>
MODULE_LICENSE("Dual BSD/GPL");
/* Declaration of memory.c functions */
int memory_open(struct inode *inode, struct file *filp);
int memory_release(struct inode *inode, struct file *filp);
ssize_t memory_read(struct file *filp, char *buf, size_t count, loff_t *f_pos);
ssize_t memory_write(struct file *filp, char *buf, size_t count, loff_t *f_pos);
void memory_exit(void);
int memory_init(void);
/* Structure that declares the usual file */
/* access functions */
ssize_t memory_write( struct file *filp, char *buf, size_t count, loff_t *f_pos);
ssize_t memory_read(struct file *filp, char *buf, size_t count, loff_t *f_pos);
int memory_open(struct inode *inode, struct file *filp);
int memory_release(struct inode *inode, struct file *filp);
struct file_operations memory_fops = {
.read = memory_read,
.write = memory_write,
.open = memory_open,
.release = memory_release
};
/* Declaration of the init and exit functions */
module_init(memory_init);
module_exit(memory_exit);
/* Global variables of the driver */
/* Major number */
int memory_major = 60;
/* Buffer to store data */
char *memory_buffer;
int memory_init(void) {
int result;
/* Registering device */
result = register_chrdev(memory_major, "memory", &memory_fops);
if (result < 0) {
printk(
"<1>memory: cannot obtain major number %d\n", memory_major);
return result;
}
/* Allocating memory for the buffer */
memory_buffer = kmalloc(1, GFP_KERNEL);
if (!memory_buffer) {
result = -ENOMEM;
goto fail;
}
memset(memory_buffer, 0, 1);
printk("<1>Inserting memory module\n");
return 0;
fail:
memory_exit();
return result;
}
void memory_exit(void) {
/* Freeing the major number */
unregister_chrdev(memory_major, "memory");
/* Freeing buffer memory */
if (memory_buffer) {
kfree(memory_buffer);
}
printk("<1>Removing memory module\n");
}
int memory_open(struct inode *inode, struct file *filp) {
/* Success */
return 0;
}
int memory_release(struct inode *inode, struct file *filp) {
/* Success */
return 0;
}
static DECLARE_WAIT_QUEUE_HEAD(wq);
static volatile int flag = 0;
ssize_t memory_read(struct file *filp, char *buf,
size_t count, loff_t *f_pos) {
printk("<1>going to sleep\n");
flag = 0;
//wait_event_interruptible(wq, flag != 0);
wait_event(wq, flag != 0);
printk("<1>Reading from memory module\n");
/* Transfering data to user space */
copy_to_user(buf,memory_buffer,1);
/* Changing reading position as best suits */
if (*f_pos == 0) {
*f_pos+=1;
return 1;
} else {
return 0;
}
}
ssize_t memory_write( struct file *filp, char *buf,
size_t count, loff_t *f_pos) {
char *tmp;
printk("<1>wake someone up\n");
flag = 1;
//wake_up_interruptible(&wq);
wake_up(&wq);
printk("<1>Writting to memory module\n");
tmp=buf+count-1;
copy_from_user(memory_buffer,tmp,1);
return 1;
}