Re: AF_UNIX status report

[Corinna Vinschen <corinna-cygwin@cygwin.com>]

On Nov  3 10:43, Ken Brown via Cygwin-developers wrote:
> On 10/30/2020 5:20 AM, Corinna Vinschen wrote:
> > On Oct 29 14:53, Joe Lowe wrote:
> > > On 2020-10-29 13:19, Ken Brown via Cygwin-developers wrote:
> > > > On 10/27/2020 5:43 AM, Corinna Vinschen wrote:
> > > > > On Oct 26 18:04, Ken Brown via Cygwin-developers wrote:
> > > > > > 2. I haven't given any thought at all as to how to implement SCM_RIGHTS
> > > > > > ancillary data.  I could definitely use suggestions on that
> > > > > > before I start
> > > > > > thrashing around.
> > > > > 
> > > > > I have only vague ideas at that point.  Assuming we can replace the
> > > > > socket implemantation with the pipe implementation, what we have is a
> > > > > pipe which can impersonate the peer at least from the server side, and
> > > > > it knows the client process.  This in turn can be used to duplicate
> > > > > handles.  So what we could do is to define fhandler methods which create
> > > > > a matching serialization  and deserialization of the fhandler data, plus
> > > > > duplicating the handles for the other process, sent over the pipe as
> > > > > admin package.  This must work in either direction, regardless if the
> > > > > server or the client sends the SCM_RIGHTS block.
> > > > 
> > > > This sounds reasonable.
> > > > 
> > > > I have no experience with serialization.  Do you happen to know of a
> > > > good example that I could look at?
> > 
> > Unfortunately not.  Probably we can just send the entire fhandler and
> > the recipient fiddles the content in a per-class way, kind of like
> > fhandler::dup.
> 
> I'm working on implementing this, and I've bumped into an elementary C++
> question.  In order to send the fhandler in an admin packet, I need to
> determine its size dynamically, given an (fhandler_base *) pointer to it.
> AFAICS, this requires something like the following.
> 
> In the definition of class fhandler_base, put a virtual function
> 
>   virtual size_t size () const { return sizeof *this; }
> 
> and then repeat this essentially verbatim in every derived class:
> 
>   size_t size () const { return sizeof *this; }
> 
> Does this seem right?  I did an internet search and didn't find anything
> substantially different, although there were several suggestions to use
> templates in various ways.  I'm not convinced that using templates would
> actually improve the code, but I can do it if you think it's better.

Actually, I don't like templates that much.  You could do the above, or
just always send a block of size fhandler_union.


Corinna