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 OPENSOLARIS

kvm_uread

kvm_kread(3KVM) 					    Kernel VM Library Functions 					   kvm_kread(3KVM)

NAME

       kvm_kread, kvm_kwrite, kvm_uread, kvm_uwrite - copy data to or from a kernel image or running system

SYNOPSIS

       cc [ flag... ] file... -lkvm [ library...]
       #include <kvm.h>

       ssize_t kvm_kread(kvm_t *kd, uintptr_t addr, void *buf, size_t nbytes);

       ssize_t kvm_kwrite(kvm_t *kd, uintptr_t addr, void *buf, size_t nbytes);

       ssize_t kvm_uread(kvm_t *kd, uintptr_t addr, void *buf, size_t nbytes);

       ssize_t kvm_uwrite(kvm_t *kd, uintptr_t addr, void *buf, size_t nbytes);

DESCRIPTION

       The  kvm_kread() function transfers data from the kernel address space to the address space of the process. nbytes bytes of data are copied
       from the kernel virtual address given by addr to the buffer pointed to by buf.

       The kvm_kwrite() function is like kvm_kread(), except that  the	direction  of  the  transfer  is  reversed.  To  use  this  function,  the
       kvm_open(3KVM) call that returned  kd must have specified write access.

       The  kvm_uread()  function transfers data from the address space of the processes specified in the most recent  kvm_getu(3KVM) call. nbytes
       bytes of data are copied from the user virtual address given by addr to the buffer pointed to by buf.

       The kvm_uwrite() function is like kvm_uread(), except that  the	direction  of  the  transfer  is  reversed.  To  use  this  function,  the
       kvm_open(3KVM)  call  that returned kd must have specified write access. The address is resolved in the address space of the process speci-
       fied in the most recent kvm_getu(3KVM) call.

RETURN VALUES

       On success, these functions return the number of bytes actually transferred. On failure, they return -1.

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Stable			   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |Unsafe			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       kvm_getu(3KVM), kvm_nlist(3KVM), kvm_open(3KVM), attributes(5)

SunOS 5.11							    2 May 2002							   kvm_kread(3KVM)