Wireshark · Wireshark-dev: Re: [Wireshark-dev] [Wireshark-commits] rev 39149: /trunk/epan/dissectors/ /trunk/epan/dissectors/:

[Jeff Morriss <jeff.morriss.ws@xxxxxxxxx>]

Anders Broman wrote:
> Anders Broman skrev 2011-09-26 18:25:
> > Stig Bjørlykke skrev 2011-09-26 18:14:
> > > On Mon, Sep 26, 2011 at 4:51 PM,<etxrab@xxxxxxxxxxxxx>  wrote:
> > > > Log:
> > > >   Get rid of check_col, while at it set ENC.
> > > >
> > > > Directory: /trunk/epan/dissectors/
> > > >   Changes    Path                      Action
> > > >   +35 -37    packet-dmp.c              Modified
> > > The remaining check_col in packet-dmp.c was left on purpose, because
> > > we do not need this calculations if not having COL_INFO.
> > >
> > > Should we really remove all occurrences of check_col?
> > Perhaps not, but how often isn't the info column present?
> Thinking about it this raises the question
> - is check_col deprecated or not?
> Should lengthy code to compute column info be protected in some other 
> manner?
>  fd->visited? (!tree)? We only fill in the column info on the first pass 
> before the tree is built, right?

Actually a quick test indicates that we only build the column info on 
the 2nd pass (for those frames which are currently displayed).

In other words, if you've got 10,000 frames of which 25 are displayed in 
your Wireshark window, your dissector is called 10,000 times with 
check_col(COL_INFO)==0 and 25 times with check_col(COL_INFO)==1.  As you 
scroll down the dissector is called again for the newly-visible frames 
with check_col(COL_INFO)==1.  (It does appear that Wireshark does cache 
the column information; scrolling back or clicking on earlier packets 
does not result in the column info being rebuilt, even if the dissector 
is called again.)

Actually another case when column info won't be present is tshark when 
doing statistics, etc., but not printing the packet details.

This suggests that check_col()'s should be left in--at least if they are 
protecting us from doing some work, including val_to_str()'s.