Ho avuto lo stesso problema e l'ho risolto creando un modulo del kernel che si blocca nello stato D.
Dato che non ho alcuna esperienza nei moduli, ho preso il codice da questo tutorial con alcune modifiche trovate da qualche parte .
Il risultato è un dispositivo su / dev / memory che si blocca in lettura ma può essere risvegliato scrivendo su di esso (ha bisogno di due scritture, non so perché ma non mi interessa).
Per usarlo solo:
# make
# make mknod
# make install
# cat /dev/memory # this gets blocked
Per sbloccare, da un altro terminale:
# 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
Codice per 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;
}