I've written a module that acts as a cache for fixed size objects but I
get a soft lockup trying to use the buffer cache.
I've attached the module that reproduces the error. You need to supply the
module with a block device, i.e.
insmod disk_cache.ko devname="/dev/hda2".
/*
* An object oriented disk cache.
*/
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/errno.h>
#include <linux/types.h>
#include <linux/vmalloc.h>
#include <linux/genhd.h>
#include <linux/blkdev.h>
#include <linux/hdreg.h>
#include <linux/workqueue.h>
#include <linux/bio.h>
#include <linux/buffer_head.h>
//#include "assert.h"
//#include "debug.h"
#define assert(s) if(!(s)) { printk(KERN_EMERG "assertion failed: %d: ", __LINE__); panic(#s);}
#define KERNEL_SECTOR_SIZE 512
MODULE_LICENSE("Dual BSD/GPL");
struct disk_cache {
int object_size; /* object size */
sector_t cache_size; /* number of objects to be held in cache */
sector_t disk_size; /* maximum number of objects */
int objects_per_sector; /* number of objects per sector */
sector_t start; /* start sector for data storage */
};
static int major_num = 0;
struct block_device *bdev = NULL;
sector_t start = 0;
static char *devname = NULL;
module_param(devname, charp, 0);
/*
* Create and initialize a disk cache.
* @disk_cache - an allocated disk_cache structure
* @object_size - the object size to use (in bytes)
* @cache_size - total memory size for cache (in objects)
* @disk_size - total disk size for objects (in objects)
*/
int disk_cache_create(struct disk_cache* const disk_cache, const int object_size, const sector_t disk_size) {
assert(disk_cache);
assert(disk_size > 0);
disk_cache->object_size = object_size;
disk_cache->disk_size = disk_size;
disk_cache->objects_per_sector = bdev_get_queue(bdev)->hardsect_size / object_size;
disk_cache->start = start;
start += ((unsigned long)disk_size / (unsigned long)disk_cache->objects_per_sector) + 1;
return 1;
}
EXPORT_SYMBOL(disk_cache_create);
/*
* Returns an address where the requested object is found.
*/
void * get_object(const struct disk_cache* disk_cache, const sector_t object_number) {
int offset = 0;
sector_t sector = 0;
struct buffer_head *bh = NULL;
assert(disk_cache);
assert(object_number < disk_cache->disk_size);
/*
* Compute page number in which requested object resides.
*/
sector = disk_cache->start + (unsigned long)object_number / (unsigned long)disk_cache->objects_per_sector;
//assert(sector < disk_cache->disk_size);
//assert(sector < get_capacity(bdev->bd_disk));
offset = ((unsigned long)object_number % (unsigned long)disk_cache->objects_per_sector) * disk_cache->object_size;
bh = __bread(bdev, sector, bdev_get_queue(bdev)->hardsect_size);
//return bh->b_data + offset;
return NULL;
}
EXPORT_SYMBOL(get_object);
/*
* Puts given object back to the buffer cache. Flag 'modified' must be set if the object was modified.
*/
void put_object(const struct disk_cache* const disk_cache, const sector_t object_number, const int modified) {
struct buffer_head *bh = NULL;
sector_t sector = disk_cache->start + (unsigned long)object_number / (unsigned long)disk_cache->objects_per_sector;
bh = __bread(bdev, sector, bdev_get_queue(bdev)->hardsect_size);
//if(modified) {
// lock_buffer(bh);
// set_buffer_uptodate(bh);
// mark_buffer_dirty(bh);
// unlock_buffer(bh);
//}
brelse(bh);
/*
* an additional release, we didn't released it in get_object
*/
brelse(bh);
}
EXPORT_SYMBOL(put_object);
static void test(void) {
struct disk_cache dk;
int i;
void *p;
if(!disk_cache_create(&dk, 6, 100)) {
printk(KERN_ERR "create cache error\n");
return;
}
for(i = 0; i < 100; i++) {
get_object(&dk, i);
put_object(&dk, i, 0);
}
}
static int __init disk_cache_init(void) {
major_num = register_blkdev(major_num, "disk_cache");
if (major_num <= 0) {
printk(KERN_ERR "disk_cache: unable to get major number\n");
return -EINVAL;
}
if(!devname) {
printk(KERN_ERR "disk_cache: must supply a valid block device\n");
return -EINVAL;
}
bdev = open_bdev_excl(devname, 0, NULL);
if(IS_ERR(bdev)) {
printk(KERN_ERR "disk_cache: cannot open device %s.\n", devname);
return -EINVAL;
}
printk(KERN_INFO "disk_cache: using device %s\n", devname);
printk(KERN_INFO "disk_cache: %llu sectors\n", get_capacity(bdev->bd_disk));
test();
return 0;
}
static void __exit disk_cache_exit(void) {
close_bdev_excl(bdev);
}
module_init(disk_cache_init);
module_exit(disk_cache_exit);
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
