[PATCH fifo 0/2] Add support for duplex FIFOs

[Corinna Vinschen]

On Apr 29 18:42, Ken Brown wrote:
> On 4/29/2019 2:29 PM, Ken Brown wrote:
> > On 3/25/2019 7:06 PM, Ken Brown wrote:
> >> The second patch in this series enables opening a FIFO with O_RDWR
> >> access.  The underlying Windows named pipe is created with duplex
> >> access, and its handle is made the I/O handle of the first client.
> >>
> >> I tested the patch in two ways.
> >>
> >> First,
> > 
> > [...]
> > 
> >> The second test was the following sequence of commands in a bash
> >> shell:
> >>
> >> $ mkfifo foo
> >>
> >> $ exec 7<>foo
> >>
> >> $ echo blah > foo
> >>
> >> $ read bar <&7
> >>
> >> $ echo $bar
> >> blah
> > 
> > I just realized that this doesn't test *writing* to the fd of a FIFO
> > opened with O_RDWR.  If I change the third command to "echo blah
> > >&7", it does test this, and the write fails with ECOMM.  It turns
> > >out that the call to NtWriteFile in fhandler_fifo::raw_write fails
> > >with STATUS_PIPE_LISTENING.
> > 
> > Corinna, I'll try to debug this, but since I know you're about to be
> > AFK for a month, I thought I'd check to see if you have any idea why
> > this would happen.
> 
> Actually, the answer might be obvious.  Looking at MSDN, it now seems
> clear to me that you can't do I/O on the server side of a pipe until
> the pipe connects to a client.  So I'll have to rethink how to deal
> with the O_RDWR case.

Sorry being late, but yeah, STATUS_PIPE_LISTENING means no client is
connected.  This is one of the more ugly implementation details of
Windows pipes.  There just isn't a generic buffer which can be filled
even if no one is listening yet on the other side :-P


Corinna

-- 
Corinna Vinschen
Cygwin Maintainer
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