On Fri, Sep 24, 2010 at 5:41 PM, sri <bskmohan@xxxxxxxxx> wrote:
what part is not able to understand?
Here is a program I wrote
but it is dropping characters though I gave 14 bytes to kmalloc and buffer but still the program is unable to read and write as I expect it to do.
I did an strace on the program and have posted the log at the end
#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/system.h> /* cli(), *_flags */
#include <asm/uaccess.h> /* copy_from/to_user */
MODULE_LICENSE("Dual BSD/GPL");
int bond_open(struct inode *inode, struct file *filp);
int bond_release(struct inode *inode, struct file *filp);
ssize_t bond_read(struct file *filp, char *buf, size_t count, loff_t *f_pos);
ssize_t bond_write(struct file *filp, char *buf, size_t count, loff_t *f_pos);
void bond_exit(void);
int bond_init(void);
struct file_operations bond_fops = {
read: bond_read,
write: bond_write,
open: bond_open,
release: bond_release
};
module_init(bond_init);
module_exit(bond_exit);
int bond_major = 60;
char *bond_buffer;
int bond_init(void) {
int result;
result = register_chrdev(bond_major, "bond", &bond_fops);
if (result < 0) {
printk(KERN_ALERT "memory: cannot obtain major number %d\n", bond_major);
return result;
}
bond_buffer = kmalloc(14, GFP_KERNEL);
if (!bond_buffer) {
result = -ENOMEM;
goto fail;
}
memset(bond_buffer, 0, 14);
printk(KERN_ALERT "Inserting bond module\n");
return 0;
fail:
bond_exit();
return result;
}
void bond_exit(void) {
unregister_chrdev(bond_major, "bond");
if (bond_buffer) {
kfree(bond_buffer);
}
printk( KERN_ALERT "Removing bond module\n");
}
int bond_open(struct inode *inode, struct file *filp) {
return 0;
}
int bond_release(struct inode *inode, struct file *filp) {
return 0;
}
ssize_t bond_read(struct file *filp, char *buf,
size_t count, loff_t *f_pos) {
copy_to_user(buf,bond_buffer,count<14 ? count:14);
/* if (*f_pos == 0) {
*f_pos+=1;
return 1;
} else {
return 0;
}*/
}
ssize_t bond_write( struct file *filp, char *buf,
size_t count, loff_t *f_pos) {
// char *tmp;
//tmp=buf+count-1;
copy_from_user(bond_buffer,buf,count<14 ? count : 14);
return 1;
}
Here is the Makefile
ifeq ($(KERNELRELEASE),)
KERNELDIR ?= /lib/modules/$(shell uname -r)/build
PWD := $(shell pwd)
.PHONY: build clean
build:
$(MAKE) -C $(KERNELDIR) M=$(PWD) modules
clean:
rm -rf *.o *~ core .depend .*.cmd *.ko *.mod.c
rm -rf modules.order Module.symvers
else
$(info Building with KERNELRELEASE =${KERNELRELEASE})
obj-m := bond.o
endif
and here is the strace
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f2a2f03b000
write(1, "abcde", 5) = 1
write(1, "bcde", 4) = 1
write(1, "cde", 3) = 1
write(1, "de", 2) = 1
write(1, "e", 1) = 1
close(1) = 0
munmap(0x7f2a2f03b000, 4096) = 0
close(2) = 0
exit_group(0) = ?
so copy_from_user and copy_to_write are not doing what I expect them to do this is not clear to me.
