| DoubleHead |
06-24-2015 08:14 AM |
Problem with block device filter (make_request_fn)
Hello!
Im new in kernel modules development, and try to make simple block device filter. And have a two little questions :)
I've changed make_request_fn() with my own function (see my code below). I've digged source codes of read() etc and now I expect, my function must be called for all request (read and write) . But in my virtualbox with Centos7(3.10), I see my function work only for writes and not for reads. Could anyone say where I was wrong? :)
And next one - I can get request data from bio_data, but how I can determine the size of this data buffer? Is b->bi_size correct field to get this size?
Code:
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/blkdev.h>
#include <linux/buffer_head.h>
#define PARTITION_NAME "/dev/sdb"
char *ptr;
int i;
struct block_device *bd;
make_request_fn *orig_mrqfn;
static void filter_mrqfn(struct request_queue *rq, struct bio *b)
{
printk(KERN_INFO "filter: Sector=lu Size=%d bi_rw=%lu\n", b->bi_sector, b->bi_size, b->bi_rw);
ptr=(char *)bio_data(b);
for(i=0;i<b->bi_size;i++) //4096 as bio is going to be in 4kb chunk?????
{
printk("%c",*ptr);
ptr++;
}
orig_mrqfn(rq, b); /* calling the original make_request_fn() */
}
/*
* set_mrqfn() - Change the original make_request_fn() to our
* modules request function
*/
static void set_mrqfn(void)
{
struct super_block *sb;
printk(KERN_DEBUG "filter: %s\n", __FUNCTION__);
/* lock filesystem to prevent any further changes */
fsync_bdev(bd);
sb = freeze_bdev(bd);
if (bd->bd_disk->queue->make_request_fn == filter_mrqfn) {
printk(KERN_INFO "filter: modules request function is already active\n");
} else {
/* save the pointer to the original make_request_fn() */
orig_mrqfn = bd->bd_disk->queue->make_request_fn;
/* replace the original with our modules request function */
bd->bd_disk->queue->make_request_fn = filter_mrqfn;
}
/* unlock filesystem */
thaw_bdev(bd, sb);
}
/*
* restore_mrqfn() - Restore the original make_request_fn()
*/
static void restore_mrqfn(void)
{
struct super_block *sb = bd->bd_super;
printk(KERN_DEBUG "filter: %s\n", __FUNCTION__);
if (orig_mrqfn) {
/* lock filesystem to prevent any further changes */
fsync_bdev(bd);
sb = freeze_bdev(bd);
/* restore the original request function */
bd->bd_disk->queue->make_request_fn = orig_mrqfn;
/* unlock filesystem */
thaw_bdev(bd, sb);
}
orig_mrqfn = NULL;
}
static int __init filter_init(void)
{
printk(KERN_DEBUG "filter: %s\n", __FUNCTION__);
orig_mrqfn = NULL;
// Read block device from path
bd = blkdev_get_by_path(PARTITION_NAME, FMODE_READ, NULL);
if (IS_ERR(bd)) {
printk(KERN_ERR "filter: failed to get block device\n");
return 0;
}
printk(KERN_INFO "filter: found block device with major number %d\n", bd->bd_disk->major);
printk(KERN_INFO "filter: file system block size %d\n", bd->bd_block_size);
printk(KERN_INFO "filter: start sector %lu\n", (unsigned long)bd->bd_part->start_sect);
printk(KERN_INFO "filter: number of sectors %lu\n", (unsigned long)bd->bd_part->nr_sects);
printk(KERN_INFO "filter: logical block size %d\n", bdev_logical_block_size(bd));
printk(KERN_INFO "filter: physical block size %d\n", bdev_physical_block_size(bd));
set_mrqfn();
return 0;
}
static void __exit filter_exit(void)
{
printk(KERN_DEBUG "filter: %s\n", __FUNCTION__);
restore_mrqfn();
if (!IS_ERR(bd)) {
blkdev_put(bd, FMODE_READ);
}
}
module_init(filter_init);
module_exit(filter_exit);
MODULE_LICENSE("Dual MIT/GPL");
MODULE_AUTHOR("Me");
With best regards,
Vasily |
