[Click] FromDump restart

[Eddie Kohler]

I think you did not try this, because it should have worked, but who knows?  I 
checked in an update so that TIMING and FORCE_IP are compatible, and added a 
"FromDump::reset_timing" handler so that you can reset timing information when 
looping back into the file.

fd::FromDump(/tmp/foo.trace,
	TIMING true, FORCE_IP false, ACTIVE false, END_CALL restarter.step)
	-> Print(TIMESTAMP true) -> Discard;

restarter::Script(init first_offset $(fd.filepos),
	write fd.active true,
	pause,
	write fd.filepos $first_offset,
	write fd.reset_timing,
	loop)


Eddie


Robert Ross wrote:
>  
> I thought I had tried this already.  When I tried it, fd.filepose
> returned "0" as the starting position.  The only difference I see is
> that I did not use "FORCE_IP true" because need to use the "TIMING"
> keyword.  The two are apparently mutually exclusive.
> 
> Robert Ross
> DSCI Inc.
> Office: 732.542.3113 x173
> Home: 609.702.8114
> Cell: 609.509.5139
> Fax: 253.550.6198
> 
> -----Original Message-----
> From: Eddie Kohler [mailto:kohler at cs.ucla.edu] 
> Sent: Saturday, November 17, 2007 10:03 PM
> To: Robert Ross
> Cc: click at amsterdam.lcs.mit.edu
> Subject: Re: [Click] FromDump restart
> 
> Hi Robert,
> 
> The problem with filepos is that filepos=0 is the pcap file header.  You
> need to set it to the first byte of actual packet data, which might be
> 24 or 28 depending on pcap version.
> 
> This script works for me.  It relies on the fact that FromDump skips the
> header at initialization time, but does not actually read any packets
> until ACTIVE is true.
> 
> 
> fd::FromDump(~/src/ipsumdump/test/one-byte-payload.trace,
> 	FORCE_IP true, ACTIVE false, END_CALL restarter.step)
> 	-> IPPrint -> Discard;
> 
> restarter::Script(init first_offset $(fd.filepos),
> 	write fd.active true,
> 	pause,
> 	write fd.filepos $first_offset,
> 	loop)
> 
> 
> Eddie
> 
> 
> Robert Ross wrote:
>> I'm trying to use a Script element along with a FromDump to loop a
> small PCAP file several times with a delay between replays.  The script
> basically works except for one critical element:  I cannot seem to reset
> the FromDump "filepos" handler to the beginning of the file.  As
> indicated in the documentation, the issue appears to be determining the
> correct byte offset for the beginning of the first packet in the file.
> I've tried the following with no luck:
>>  
>> 1.  Setting filepos=0.  If only it were that simple...
>> 2.  Wait until the first packet has come out and "poke" the script
> using a Counter element.  Then use the script to calculate various
> starting positions using a combination of read handlers from FromDump
> and Counter.
>>  
>> Some of the questions I have are:
>>  
>> 1.  Both packet_filepos and filepos provide byte offsets, but the
> documentation does not adequately describe what these offsets represent.
> Is packet_filepos the end point of the last packet read?  The start
> point of the last packet read?  The start point of the next packet to be
> read?  Something else?  What is the difference between filepos and
> packet_filepos?
>> 2.  Is there another simpler way to loop a PCAP file that I'm missing?
>> 3.  Assuming I knew the correct offset, is it even possible to reset
> the filepos and re-play the PCAP file again?
>>  
>> As a general suggestion, added LOOP and LOOP_INTERVAL keywords to the
> various dump elements could be extremely useful.  In the absence of
> those, at the very least a "restart" or "start_pos" handler would be
> equally useful.  I'm currently wondering why the "filepos" handler is
> even writeable...
>>  
>> Thanks,
>> Robert A. Ross
>> DSCI Inc.
>> 609-509-5139
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