Date: Wed, 22 Dec 2010 01:47:41 -0500
From: Christopher Faylor <cgf-use-the-mailinglist-please AT cygwin DOT com>
To: cygwin AT cygwin DOT com
Subject: Re: Bug? UDP packet transmitted via sendto() intermitently not being transmitted to network
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On Tue, Dec 21, 2010 at 02:05:43PM -0800, Estabrook, Edward wrote:
>On Dec 10 14:37, Estabrook, Edward wrote:
>>> Generally I am seeking information regarding:
>>> 1) Where can I download and install an older version of Cygwin (say
>>> 1.5 era) to test if the problem is newly introduced?
>>
>> Corinna wrote:
>What for?  If it doesn't work on 1.5 you're exactly at the same spot as
>>now.  If it works on 1.5, we know it works on 1.5 but we still don't
>>know why it doesn't work on 1.7, which means, you're still exactly at
>>the same spot as now.  So that's not really an option.  The best option
>>is either to debug the (slim) layer in Cygwin which provides send/recv,
>>or at least to send an as-simple-as-possible, self-sufficient testcase,
>>preferredly in plain C, which allows to reproduce the problem.
>
>Two reasons.  If it works on 1.5, I'll simply use it to perform my testing
>and the time-pressure to solve the root cause is lessened.  
>Whether it works or not, it'll tell me if the issue is a change between 
>those versions or something older.  (Plus the build instructions and 
>distributed executable are for SIPp are written with cygwin 1.5 in mind.
>
>The setup-legacy installer for older versions of Windows is exactly what I
>needed.  I tested this out and confirmed the issue exists in the old version as well.
>
>>> 2) What tools are available to measure potential packet loss within
>>> cygwin itself? (the Windows stack is not reporting dropped UDP
>>> packets, and the packets are not even making it into a locally running
>>> instance of wireshark).  Is there a way to dump / access / sniff the
>>> inputs and outputs to the cygwin IP stack?  Traffic volume is low so
>>> verbosity would not pose a problem.
>>
>> Corinna wrote:
>>You can add debug output to Cygwin's send and receive functions and use
>>strace.
>
>OK, thanks.  I see debug_printf() and syscall_printf() statements
>sprinkled around the source.  Where do these end up displayed / logged?
>How are they enabled?

Via strace, as Corinna said.

strace is a program which is somewhat similar to the linux program
of the same name.

"man strace"

cgf

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