Becoz if u r trying to copy this strucher to user -
struct myStruct
{
char* name;
int value1;
}data1,data2;
data.name="hello";
data.value1=20;
--
copy_to_user(arg,&data,sizeof(data) //this will fail
--
becoz it think it will just copy the pointer not the value. This pointer is bad address for user.
Also make sure u allocate space for variable name in user space.
----
__copy_from_user(&data2, (void*)arg, sizeof(data2)) ;
__copy_to_user(data2.name,data1.name,.....);
data2.value1= data1.value1;
__copy_to_user((void*)arg, &data2, sizeof(data2));
---
I think it should work.Correct me if i am wrong.
-manisha
On 8/20/06, John Que <qwejohn@xxxxxxxxx> wrote:
Hello,
I am trying to copy a table (an array of structs) from
kernel to user space in a kernel module ioctl method.
I do it thus;
...
...
struct myStruct
{
char* name;
int value1;
int value2;
struct myStruct *next;
};
static struct myStruct* myTable = NULL;
there is allocation of memOry for myTable in the module init() thus:
myTable = kmalloc( MAXELEM* sizeof(struct MYStruct), GFP_KERNEL);
and it is filled with values.
(MAXENTIRES is 1000 - maybe it is too big ??)
...
...
...
static int my_ioctl(struct inode* inode,
struct file* file,
unsigned int cmd,
unsigned long data)
{
switch (cmd)
{
case MYIOCTL:
{
int res;
res = copy_to_user((void __user*)data,
relayTable,
numberOfPorts* sizeof(struct relayStruct));
printk("res is %d\n",res);
}
...
...
}
copy_to_user() should return 0 in case of success;
I keep getting positive number after calling copy_to_user();
(it is 240 or 160 or 80, depends on which trial I made)
I also tried to copy only one element (numberOfPorts=1) , and
I had also tried : copy_to_user((struct relayStruct*)data,
and also copy_to_user() returned error.
When I try to use this IOCTL from user space I get garbage
for the table entries.
Any ideas what is wrong here?
Regards,
John
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