Re: [Openslp-users] slpd seems to hijack the port I'm using in my application

[Nick W. <ne...@wi...>]

Someone on the devel list with more experience working with linux daemons
will need to make this fix.  And they should patch the debian start-stop
script as well as earlier explained in this email chain.  We should do this
before the code freeze.

Robert, thanks for finding these issues!

--Nick

On Wed, Oct 17, 2012 at 10:30 AM, Robert Hegner <rh...@hs...> wrote:

> Ok I found out what's wrong. And I would consider this as a bug in OpenSLP.
>
> I'm a Linux newbie but The Linux Programming Interface by Michael
> Kerrisk (a great book, by the way) helped me understand what's going on.
>
> You can see in my first post that when slpd listens to the same port as
> my application, it also uses the same file descriptor.
>
> As I wrote earlier, I use system() to run the start/stop script of slpd.
> According to Kerrisk's book, system() is typically implemented using a
> combination of fork() (which copies all open file descriptors) and
> exec() (which does not close any file descriptors). So slpd inherits my
> open file descriptors when I start it from within my application.
>
> In chapter 37 of his book, Kerrisk also describes the seven steps for
> daemonizing a program. Step 6 is:
> "Close all open file descriptors that the daemon has inherited from its
> parent. (A daemon may need to keep certain inherited file descriptors
> open, [...]"
>
> And he also provides some example code showing how to accomplish this:
>
> maxfd = sysconf(_SC_OPEN_MAX);
> if (maxfd == -1)
>     maxfd = BD_MAX_CLOSE; // 8192 in his example
> for (fd = 0; fd < maxfd; fd++)
>     close(fd);
>
> I had a look at the OpenSLP source code and I found that Daemonize() (in
> slpd_main.c) does not close all open file descriptors (it only closes
> descriptors 0 to 2 under some condition).
>
> I tried to close all file descriptors in Daemonize() but it seemed to
> cause some problems. I guess that slpd has already opened some of its
> own sockets at that time, which are then being closed again.
>
> But adding
>
> for (i = 3; i < 8192; i++)
>     close(i);
>
> at the beginning of main() solves all my problems :)
>
> Something like this should be in Daemonize() and not at the beginning of
> main(), but I guess someone who is familiar with the initialization code
> of slpd should have a look at this.
>
> I hope this change will make it into Release of version 2.0
>
> Robert
>
>