Here is a suggestion:
buf shuld be a pointer to an *user land* memory region which has to be
passed to the kernel. That is the prototype of copy_to_user:
copy_to_user(to, from, sizeof(from));
So , buf in your program is not in user land.
I dont know if there is a way of passing an argument to init_module so
that u can do a copy_to_user there. Generally , u wuld define another
fn/.., in ur case that is called when u do a read :
struct file_operations{
read: foo_read;
};
and in foo_read:
int foo_read(unsigned long arg)
{
char *cptr = (char *)arg;
int ret;
ret = copy_to_user(cptr,data,sizeof(data);
/* check ret value for error */
return ret;
}
User land:
int main()
{
char buf[20];
/* open*/
read(fd, buf, /*whatever*/);
printf("%s\n",buf);
}
Pointers from user land are suppossed to be used in kernel as unsigned
longs
Narasimhamurthy Giri, Clemson University Computer Science Dept.
-------------------------------------------------------------------------------
Judge not lest ye be judged yourself.
-------------------------------------------------------------------------------
On Wed, 27 Mar 2002, shahnavaz wrote:
> Hi,
> I have written a small code to understand copy_to/from_user.
>
> I know there are lots of mistake in the code.Can someone correct
> me..*Please*.I have searched a lot in this context but in vain.I cannot find
> any suitable example in "Linux Device Driver "Book in this context.
>
> TIA
> shan
>
>
> #include ...
> int test_major=0,major;
> char *data="copy_to_user",*buf;
>
> struct file_operations test_fops={
> ...
> };
>
> int init_module()
> {
> int count;
> major=register_chrdev(test_major,"Test",&test_fops);
> if(major < 0)
> {
> printk(KERN_WARNING"cant get major %d\n",test_major);
> return -1;
> }
> else
> printk(KERN_WARNING"major number is %d\n",major);
> count=copy_to_user(buf,data,13);
> if(count < 0){
> printk(KERN_WARNING"data could not be copied\n");
> }
> else
> printk(KERN_WARNING"data copied\n");
> return 0;
> }
> void cleanup_module()
> {
> unregister_chrdev(major,"Test");
> }
>
> After compiling i have done #mknode Test c 254 0
>
> Userland program:
>
> int main()
> {
> char buff[13];
>
> int fd=open("/dev/Test",O_RDONLY);
>
> read(fd,&buff,13);
> printf("%s\n",buff);
> return 0;
> }
>
>
> When i run the userland program it prints garbage.
> --
> Kernelnewbies: Help each other learn about the Linux kernel.
> Archive: http://mail.nl.linux.org/kernelnewbies/
> FAQ: http://kernelnewbies.org/faq/
>
>
--
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Archive: http://mail.nl.linux.org/kernelnewbies/
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