Re: Netlink socket returns NULL in vmx.c kernel file

["Irfan Ullah (울라 이르판)" <irfan@dke.khu.ac.kr>]

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Thank you very much. I am trying to rewrite the code. and fix these issues.

On Tue, Nov 5, 2019 at 7:43 PM Valdis Klētnieks <valdis.kletnieks@vt.edu>
wrote:

> On Tue, 05 Nov 2019 17:59:43 +0900, Irfan Ullah said:
>
> > Thank you for the response.
> > Attached are the files for kernel-user spaces communication.
>
> >               //when I remove this wait the code does not work
> >               msleep(3000);
>
> If your code doesn't work, but sticking in random delays makes
> it start working, you almost certainly have a race condition or
> synchronization issue that should be fixed using proper locking.
>
> > void hello_exit(void)
> > {
> >       //netlink_kernel_release(nl_sk);
>
> Congratulations. You just leaked a socket here, which is going to
> make it difficult to use that socket until you either reboot or find a
> way to close it properly before trying to create it again.
>
> > (code generates some warnings, but it is not severe and could be ignored
> for the time being).
>
> You should do the following:
> 1) Understand your code well enough so you understand *why* the compiler
> issued the warning.
> 2) Correct your code so the compiler doesn't complain. It almost certainly
> understands C better than you do.
>
> gcc 9.2.1 emits one warning on the kernel module code at default warning
> levels.  And it's one you *really* need to fix, because it indicates that
> you
> and the compiler are not on the same page about what types your variables
> are.
> Since it's going to go ahead and generate code based on what types *it*
> thinks
> your variables are, you will have nothing but pain and anguish debugging if
> you thought they were some other type....
>
> In fact, you may want to compile the kernel module with 'make W=1' to get
> more
> warnings.  If your system has sparse, you should use 'make W=1 C=1'.
>
> And all the warnings this generates are things that shouldn't be seen in
> clean
> kernel code.
>
> I didn't bother looking closely at your userspace.  I gave up
> when I saw this:
>
>      14 int sock_fd;
> (...)
>      68 void user_space_receiver()
>      69 {
> (...)
>      96                 user_space_receiver(sock_fd);
>
> There's 2 basic ways to pass a variable to a function. You're trying
> to use both of them here.  Pick one and use it properly.
>
> Oh - and there's no possible way to reach the close(sock_fd); on line
> 77, because the rest of the function infinite loops without a break.  At
> the
> very least, you should be checking the return code from recvmsg() and
> exiting the while(1) loop if there's an issue.
>
> Bottom line:  You need to get a *lot* more experience writing proper
> C code in userspace before you try to write kernel code.
>


-- 
*Best Regards,*


*Mr. Irfan Ullah*
PhD Candidate
Data and Knowledge Engineering(DKE) Lab
Department of Computer Science and Engineering
Kyung Hee University, South Korea.
 +82-010-591-51651 <+82%2010-3877-8867>
  sahibzada.iu@gmail.com
 sahibzada_irfanullah

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