[RFC]Something wrong with my module

[harryxiyou]

On Thu, Apr 12, 2012 at 10:33 PM, Jonathan Neuschäfer
<j.neuschaefer at gmx.net> wrote:

Hi Jonathan

> On Thu, Apr 12, 2012 at 09:52:02PM +0800, harryxiyou wrote:
>> On Thu, Apr 12, 2012 at 9:03 PM, Jonathan Neuschäfer
>> <j.neuschaefer at gmx.net> wrote:
>>
>> Hi Jonathan,
>>
[...]
>>
>> I give the pid 8, state 8, and comm "jiawei" in my module. But it can
>> not print correctly. Maybe kernel can tell my bogus one,right?
>
> This has to do with the way accessing struct fields works in C:
> For each struct each field name is translated by the compiler into an
> offset which is used to compute the address of a field given the struct's
> address. When you access the pid field of a struct task_struct the offset
> will be at least around 20 * sizeof(int), which is an invalid offset to
> your struct pcb, where the offsets are (most of the time):
>        pid: 0
>        state: sizeof(int)
>        flag: 2 * sizeof(int)
>        comm: 3 * sizeof(int)
>        tasks: 3 * sizeof(int) + sizeof(char *)
> (You get (an approximation of) the offset of a field by adding the size
>  of the previous field (the compiler also adds some padding - see
>  Documentation/unaligned-memory-access.txt in the kernel tree and
>  http://en.wikipedia.org/wiki/Data_padding#Data_structure_padding))
>

It sounds well. I will test it, which delare a structure named 'pcb'
but including
all the fileds as task_struct structure.

Thanks
Harry Wei