cygrunsrv + sshd + rsync = 20 times too slow -- throttled?

[Takashi Yano]

On Mon, 13 Sep 2021 11:07:42 +0200
Corinna Vinschen wrote:
> On Sep 11 11:35, Takashi Yano wrote:
> > Keeping read handle in write pipe (Corinna's query_hdl) causes problem
> > that write side cannot detect close on read side.
> > Is it possible to open read handle temporally when pipe_data_available()
> > is called?
> 
> 1. You would have to know which process keeps the other side of the pipe.
> 2. You would have to have the permission to open the other process to
>    duplicate the pipe into your own process
> 3. You would have to know the HANDLE value of the read side of your pipe
>    in that other process.
> 
> Point 1 is (kind of) doable using GetNamedPipeClientProcessId or
> GetNamedPipeServerProcessId.  ZIt's not clear how reliable these
> functions are, given that both pipe sides are created by the same
> process and then usually inherited by two child processes communicating
> over that pipe.
> 
> Point 2 is most of the time the case, especially when talking with
> native processes.
> 
> Point 3 requires some sort of IPC.
> 
> Having said that, I think this is too complicated.

In the current implementation, there is a potential risk that
write side fails to detect the closure of read side if more than
one writers exist and one of them is non-cygwin process.

Therefore, I had tried to implement the above idea (tentative
query handle). Finally, I could convince myself to some extent,
so I attach a patch for that.

As for point 1 and 3, I used NtQuerySystemInformation() with
SystemHandleInformation. I also used NtQueryObject() with
ObjectNameInformation in order to know which handle is the
other side of the pipe. As for point 2, it is not possible to
open the process which is running as a service, so the current
query_hdl is used for such process as an exception.

Ken, WDYT of this implementation?

-- 
Takashi Yano <takashi.yano@nifty.ne.jp>
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