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Date: Wed, 21 Jan 2004 13:08:15 -0600 (CST)
From: Brian Ford <ford AT vss DOT fsi DOT com>
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To: cygwin AT cygwin DOT com
Subject: Re: snapshot now == 1.5.7 soon, please try
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This is just to prove that I'm not a total idiot :).  I'll let this issue
die now.

On Wed, 21 Jan 2004, Christopher Faylor wrote:
> On Wed, Jan 21, 2004 at 12:27:52PM -0600, Brian Ford wrote:
> >On Wed, 21 Jan 2004, Christopher Faylor wrote:
> >> Ok.  So, I took ten minutes and debugged the problem myself and I'll
> >> check in a fix.
> >>
> >Thank you.
> >
> >That is why I asked.  You know your way around, so it takes you *much*
> >less time.
> >
> This was only a little knowing my way around.  It was really pretty
> basic debugging.
>
> The code was hanging in read.  So, I set a breakpoint in readv, which,
> on code inspection, is what read calls.  Single stepping along, I came
> to the function that was hanging.  Tracing that along I came to the
> Windows API function that was hanging.
>
I got here fast by attaching with gdb and backtracing.  Pretty simple.

> Realizing that this function obviously wasn't supposed to be hanging, I
> theorized that the com port wasn't being opened properly.
>
Not knowing the Windows API at all, that was not obvious to me.  After
all, the call was named WaitCommEvent.

I did gather that the port wasn't being opened properly, though.  I
assumed that the nonblocking flag had gotten lost somewhere, and we
weren't even supposed to be here.

> So, I set a breakpoint on fhandler_serial::open and notice nothing
> special there.  Then I noticed that fhandler_serial::open calls
> fhandler_base::open.
>
Saw that.  At this point, I started comparing strace output from 1.5.5
with 1.5.7.  Then, I got lost in some minor parameter differences to the
open and CreateFile calls.  There are some that I still don't understand.

Strace printed the mode argument as 6 in 1.5.5 and 1 in 1.5.7.  It
is supposed to be 0, and was via gdb, in both cases.  I'll see if I can
figure out why.

> I noticed that fhandler_base::open has special serial considerations.
>
I noticed this too, but failed to make the next leap (although I did
briefly consider it).  I was still puzzled by the above.

> Stepping over those, I saw they weren't being exercised.  So I fixed
> that using the same technique you used here:
>
> 2003-11-12  Brian Ford  <ford AT vss DOT fsi DOT com>
>
>         * dtable.cc (build_fh_pc): Use DEV_SERIAL_MAJOR to catch all serial
>         ports.
>
In a way, that was just my dumb luck :^D.  I do appreciate the
explanation, though.  And, I wouldn't have been able to extrapolate this
fix to all applicable calls and devices that quickly.

Anyway, thanks again.

-- 
Brian Ford
Senior Realtime Software Engineer
VITAL - Visual Simulation Systems
FlightSafety International
Phone: 314-551-8460
Fax:   314-551-8444

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