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Subject: Re: [EXTERNAL] Re: mkfifo: cannot set permissions of 'x.fifo': Not a
 directory
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From: Martin Wege via Cygwin <cygwin AT cygwin DOT com>
Reply-To: Martin Wege <martin DOT l DOT wege AT gmail DOT com>
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On Wed, Aug 23, 2023 at 5:44 PM Jeffrey Altman via Cygwin
<cygwin AT cygwin DOT com> wrote:
>
> On 8/22/2023 10:52 AM, Lavrentiev, Anton (NIH/NLM/NCBI) [C] via Cygwin
> wrote:
> >> FIFOs which don't make *any* sense
> >> ... FWIW, a remote NFS fileystem.
> > I got an impression that the OP is trying to deploy something (maybe the entire Cygwin) onto an NFS share.  So the named FIFO "file" is also created in there.
> >
> > It's pointless to assume that the FIFO can be used as a communication device between the hosts that can mount the share, but it can be quite feasible to envision a scenario, in which the same host opens the FIFO located on the share from two processes and establish the communication using that special "file" (which is basically a special data-less i-node).
>
> I've been following this thread with quite a bit of curiosity. For those
> who do not know me, I'm the lead developer of the AFS filesystem on
> Windows. There have been requests for more than two decades for AFS
> clients to add support for locally created pipe files because AFS
> volumes are often used as home directories (even on Windows) and so many
> applications allocate a pipe in the home directory as a method of
> inter-process communication or a lock. The problem is that even if the
> intended usage of the file is entirely local, the directory object, the
> directory entry and the allocated inode (or equivalent) is network
> visible.

Who cares? It is up to the user, script or application author to do
'the right thing(tm)'.

>
> What happens when the user executes two copies of an
> application such as PyCharm on two separate machines sharing the same
> home directory? Does the directory entry and inode get reused on startup
> and/or deleted on exit? How does that impact the process instance on the
> other machine? The conclusion I came to long ago is that if pipes are to
> be implemented in a network file system namespace then the pipes must be
> fully functional network pipes. In just about all cases applications can
> be configured to use a non-default paths. In my opinion they should not
> be placed in a shared file system.

Oh my god. Please have this debate at the Austin Group. They do the
POSIX standard. We're here about implementing&using the POSIX
standard.

We only want that mkfifo() works with Cygwin on a NFS filesystem, as
specified in https://pubs.opengroup.org/onlinepubs/009696799/functions/mkfifo.html

My intention was not to invent something new. Just code using mkfifo,
and scripts using /usr/bin/mkfifo, should work on NFS. On UNIX&Linux
this works.

Have a look at https://cygwin.com/pipermail/cygwin/2023-August/254266.html,
sounds like there is a feasible way to implement this.

Thanks,
Martin

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