help with copy_to/from_user char device driver Post: 302468735

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Top Forums Programming help with copy_to/from_user char device driver Post 302468735 by dragonpoint on Wednesday 3rd of November 2010 05:11:30 PM

11-03-2010

Registered User

help with copy_to/from_user char device driver

hi,

I need to copy strings from kernel space to user space and vice versa.
Currently if I do the following on the shell

Write from user--> kernel :echo -n abcedef > /dev/stringdrvr
read from kernel-->user :cat /dev/stringdrvr

It only returns the last character 'f' and not entire string.

Also how do i copy 2 dimensional array data

Here is my code.

Code:

size_t count=99;

ssize_t stringdrvr_read(struct file *filp, char *buf, size_t count, loff_t *f_pos)
{
    copy_to_user(buf,stringdrvr_buffer,99);
    if (*f_pos == 0) { *f_pos+=1; return 1; }
    else { return 0; }
}

ssize_t stringdrvr_write( struct file *filp, char *buf, size_t count, loff_t *f_pos)
{
    char *tmp;
    tmp=buf+count-1;
    copy_from_user(stringdrvr_buffer,tmp,99);
    return 1;
}

---------- Post updated at 04:11 PM ---------- Previous update was at 03:32 PM ----------

oops...i knw what went wrong.... here is workin code

Code:

 read:
	int len, err;

	if( counter <= 0 )
		return 0;
	err = copy_to_user(buf,string,counter);
	if (err != 0)
		return -EFAULT;
	len  = counter;
	counter = 0;
	return len;

write:
  int err;
	err = copy_from_user(string,buf,count);
	if (err != 0)
		return -EFAULT;
	counter += count;
    //printk("<1>Counted = %d\n",count);
	return count;

Last edited by pludi; 11-03-2010 at 06:40 PM.. Reason: Please use code tags

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LEARN ABOUT OPENDARWIN

copy

COPY(9) 						   BSD Kernel Developer's Manual						   COPY(9)

NAME

     copy, copyin, copyout, copystr, copyinstr -- kernel copy functions

SYNOPSIS

     #include <sys/types.h>
     #include <sys/systm.h>

     int
     copyin(const void *uaddr, void *kaddr, size_t len);

     int
     copyout(const void *kaddr, void *uaddr, size_t len);

     int
     copystr(const void *kfaddr, void *kdaddr, size_t len, size_t *done);

     int
     copyinstr(const void *uaddr, void *kaddr, size_t len, size_t *done);

DESCRIPTION

     The copy functions are designed to copy contiguous data from one address to another.  All but copystr() copy data from user-space to kernel-
     space or vice-versa.

     The copy routines provide the following functionality:

     copyin()	   Copies len bytes of data from the user-space address uaddr to the kernel-space address kaddr.

     copyout()	   Copies len bytes of data from the kernel-space address kaddr to the user-space address uaddr.

     copystr()	   Copies a NUL-terminated string, at most len bytes long, from kernel-space address kfaddr to kernel-space address kdaddr.  The
		   number of bytes actually copied, including the terminating NUL, is returned in *done.

     copyinstr()   Copies a NUL-terminated string, at most len bytes long, from user-space address uaddr to kernel-space address kaddr.  The num-
		   ber of bytes actually copied, including the terminating NUL, is returned in *done.

RETURN VALUES

     The copy functions return 0 on success or EFAULT if a bad address is encountered.	In addition, the copystr(), and copyinstr() functions
     return ENAMETOOLONG if the string is longer than len bytes.

SEE ALSO

     fetch(9), store(9)

BSD
								  January 7, 1996							       BSD