socket-wrapper fd-passing

[Anoop C S]

On Tue, 2020-06-30 at 07:33 +0200, Stefan Metzmacher via samba-
technical wrote:
> Hi Anoop,
> 
> > > In short, I could successfully run `make test` with changes to
> > > work out
> > > of a common shared file. Still there is one
> > > test(test_thread_echo_tcp_sendmsg_recvmsg, which I added) failing
> > > almost consistently on my local system and not on GitLab CI. I
> > > have
> > > been trying to root cause this failure for quite sometime now(as
> > > and
> > > when time allows me) without any luck in fixing it. I would love
> > > to see
> > > another pair of eyes reviewing the changes.
> > 
> > I guess the problem I described above and the code that tries to
> > construct the updated SCM_RIGHTS fd array, seems wrong, as far as I
> > can
> > see it only tries to pass the tmp pipe read end, but not the actual
> > fd
> > array passed from the caller.
> > 
> > I tried to get the SCM_RIGHTS passing working here:
> > https://gitlab.com/metze/socket_wrapper/-/tree/fd-passing-unix
> > 
> > Once I got this working I'll try to integrate this with the rest of
> > your
> > patches.
> 
> I got the basics working. I took your shared space patches on top,
> but
> that just fails immediately in Samba's make test.

Ok. I think I haven't tried it yet. I will check locally on my system.

> > > > An additional idea would be using temporary anonymous files
> > > > (maybe
> > > > memfd_create() or an similation for it) for shared structures
> > > > for
> > > > passed
> > > > sockets. In sendmsg() the sender would move the
> > > > socket_info[_container]
> > > > structures from malloc'ed memory to an temporary memory file.
> > > > This will replace the pipe fd of the original design.
> > > > If multiple fd's are passed, the memory file contains an array
> > > > of
> > > > socket_info[_container] structures.
> > > > int *socket_fds_idx would be changed to an array of structures
> > > > or we have an additional array to store possible fd for the
> > > > temporary
> > > > files and have the destructing code lock at it and select
> > > > between
> > > > free() and munmap()/close().
> > > > This design would not require a named file, like the one
> > > > specified
> > > > by SOCKET_WRAPPER_FD_PASSING_DB.
> > > 
> > > Hm.. this is new to me. I will think about it.
> > 
> > I guess it means we would need to undo some of the changes we made
> > to one array of socket_info structures.
> > 
> > I'll let you know if I get the basic passing of information via the
> > tmp
> > pipe working...
> 
> As Samba does not require that the socket is usable from two
> processes
> at the same time, I guess we can take a short cut and just pass
> the socket_info structure (an array of them) through the pipe.
> That would allow us to have multichannel tested in gitlab/autobuild.

I am looking through your changes and will let you know in case I need
more clarifications.

> I'll see if I can get this to work. Once we have these basics,
> we can try to improve the design to be more generic with shared
> structures, when we really need it.

Fine.