On Mar 3, 2013, at 1:06 PM, Evan Huus <eapa...@gmail.com> wrote:

> Hmm, yes. So the one-pass mode should behave the same as wireshark
> except for fragmented packets then?

And except for response frame referencing in request frames, which I think was 
the reason the two-pass mode was added to begin with.  E.g., if you open a DNS 
capture file, the DNS request will have a 'dns.response_in' field that 
identifies the frame its response is in.  So that also requires two passes 
obviously.


> I think, in general, I'm still in favour of getting rid of the read
> filter. The file->open filter field which currently acts (sort of)
> like -R can instead act like Wireshark's current -d: prepopulating the
> display filter, but not actually removing the other packets from
> consideration (so that clearing the display filter shows them again).

But that's already available when you fill in the display field in the toolbar 
before opening a file. (though there's bug 8344 that it gets cleared sometimes 
from the toolbar box once the file is opened, but it's still being applied)

Although I guess letting the user fill in the display filter within the 
file->open dialog box as well has a nice usability aspect.  That file->open 
Filter field should be pre-populated with what's in the toolbar though, and if 
changed then replace what's in the toolbar too.


> There doesn't seem to be a coherent and usable behaviour for -R when
> dealing with fragmented packets.

Right but I think many people use tshark in a simple manner, just as a form of 
ngrep.  When just used to output to the screen/stdout, -R shows the reassembled 
packet details correctly, and doing only one pass it's faster.  The part that 
always causes confusion is when they do that and also choose to export the 
results into a file, because then that file won't have the fragments and when 
opening that new file with Wireshark, it won't be able to reasssemble to 
dissect.  Or they get confused if they choose certain fields that don't get 
populated with a single-pass model.

I think the real problem is what the "default" behavior is.  You have to know 
to do a '-2' to get what you expect; instead, there should be a '-1' option to 
only do one pass for those who care about the performance difference and don't 
care about fragments.  In other words, we should do the 'safest' thing by 
default, and the more-optimal-but-buggy thing only when explicitly told to do 
so.

-hadriel

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