Done with passing file descriptors

[Conrad Scott]

"David E Euresti" <davie@MIT.EDU> wrote:
> So should I send my patch now or wait until I get a confirmation
> from somebody?

David, I've been following the discussion of the file descriptor
passing (without following all the ins&outs and perhaps I too should
go read up on it now in Stevens).

I've been doing quite a bit of hacking in the cygserver code over the
last week. What I've done so far is on the cygwin_daemon branch, which
I will be submitting as a patch into HEAD in another few days. It
would be good if we could synchronize this otherwise there's going to
be some well-hairy merging going on. I'm about to commit another big
dollop of changes into the branch (a gentle re-working of the
client_request class). After that I'm unlikely to touch the non-shm
parts of the cygserver code so I shouldn't disturb you after that. Of
course, I could try to get my changes to this point back into HEAD
now? I might send a message to cygwin-patches later on.

I realise what I'm effectively doing is asking you to merge your code
against my changes (rather than making me do it) and also asking you
to depend on my non-HEAD changes. So, I wouldn't be offended if you in
reply you sought to get your changes into HEAD before me. That's the
fun of branches.

Of course, others will have their views on this, to which mine are
pretty subsidiary.

Oh, and BTW, I'm interested in seeing your code once you've submit it.
I assume you've not got much in the way of security issues to worry
about with what you're doing as long as the receiver can proof to
cygserver that it is indeed the receiver of the file descriptors.

You'll also have a handle leakage problem with your current design.
That is, if a client makes the initial request to cygserver in
preparation for sending a file descriptor and then that process dies,
cygserver has already duplicated the handles and can't know whether it
should keep them or not since the message may or may not have been
sent to the receiving client via the socket. The same is true if the
receiver dies between receiving the message from the socket and asking
cygserver to duplicate the handle for it.

I'm unclear what can be done about this, short of a horrendously
complicated protocol, but it makes the system rather fragile, since
there could be handles held onto indefinitely by cygserver, and thus
objects can't be deleted etc. Any thoughts? or have I missed
something?

Looking forward to thinking some more about this :-)

// Conrad




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