From: Corinna Vinschen <corinna-cygwin@cygwin.com>
To: cygwin-developers@cygwin.com
Subject: Re: The unreliability of AF_UNIX datagram sockets
Date: Thu, 29 Apr 2021 19:39:26 +0200 [thread overview]
Message-ID: <YIrvTiytEebHIBPc@calimero.vinschen.de> (raw)
In-Reply-To: <16e1d55e-15ea-6c0e-04e4-aa6cb2c0c1bd@cornell.edu>
On Apr 29 12:44, Ken Brown wrote:
> On 4/29/2021 11:05 AM, Corinna Vinschen wrote:
> > So maybe we should really think hard about the alternative
> > implementation using POSIX message queues, I guess. And *if* we do
> > that, this should be used likewise for STREAM as for DGRAM sockets, so
> > the code is easier to maintain. Obvious advantage: No problem with
> > older OS versions. And maybe it's even dirt easy to implement in
> > comparison with using other methods, because the transport mechanism
> > is already in place.
>
> Yes, I don't think it should be too hard. The one thing I can think of
> that's missing is a facility for doing a partial read of a message on the
> message queue. (This would be needed for a recv call on a STREAM socket, in
> which the buffer is smaller than the payload of the next message on the
> queue.) But this should be straightforward to implement.
>
> Alternatively, I guess we could read the whole message and store the excess
> in a readahead buffer.
Alternatively, we could introduce a new, internal-only method into the
POSIX msq code, one that reads a partial message, reduces the message
to the remainder and keeps it on the queue head...
> On 4/29/2021 11:18 AM, Corinna Vinschen wrote:
> > While searching the net I found this additional gem of information:
> >
> > Native AF_UNIX sockets don't support abstract sockets. You must bind to
> > a valid path, so you always have a visible file in the filesystem.
> > Discussed here: https://github.com/microsoft/WSL/issues/4240
> >
> > We could workaround that with our POSIX unlink semantics, probably,
> > but it's YA downside
>
> Agreed. The more features that are missing from native AF_UNIX sockets, the
> less appealing they become.
>
> Concerning abstract sockets, would we still have an issue if we used message
> queues? Wouldn't there be a visible file under /dev/mqueue? Or is there a
> way around that?
Good point! There's no way around that yet. In theory that shouldn't
matter because /dev/mqueue is kind of a "virtual" path, even if Cygwin
implements the queues as real files. But that's setting the perspective
straight, we're in fact no better than the native AF_UNIX here ¯\_(ツ)_/¯
Probably we should actually add an internal-only way of creating
non-file backed mqueues for the purpose of adding abstract sockets.
Corinna
next prev parent reply other threads:[~2021-04-29 17:39 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-27 15:47 Ken Brown
2021-04-29 11:05 ` Corinna Vinschen
2021-04-29 11:16 ` Corinna Vinschen
2021-04-29 14:38 ` Ken Brown
2021-04-29 15:05 ` Corinna Vinschen
2021-04-29 15:18 ` Corinna Vinschen
2021-04-29 16:44 ` Ken Brown
2021-04-29 17:39 ` Corinna Vinschen [this message]
2021-05-01 21:41 ` Ken Brown
2021-05-03 10:30 ` Corinna Vinschen
2021-05-03 15:45 ` Corinna Vinschen
2021-05-03 16:56 ` Ken Brown
2021-05-03 18:40 ` Corinna Vinschen
2021-05-03 19:48 ` Ken Brown
2021-05-03 20:50 ` Ken Brown
2021-05-04 11:06 ` Corinna Vinschen
2021-05-13 14:30 ` Ken Brown
2021-05-17 10:26 ` Corinna Vinschen
2021-05-17 13:02 ` Ken Brown
2021-05-17 13:02 ` Ken Brown
2021-05-20 13:46 ` Ken Brown
2021-05-20 19:25 ` Corinna Vinschen
2021-05-21 21:54 ` Ken Brown
2021-05-22 15:49 ` Corinna Vinschen
2021-05-22 16:50 ` Ken Brown
2021-05-22 18:21 ` Ken Brown
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