Re: [PATCH 4/4] Add 'filter' attribute and external filter driver definition.

From: David Lang <david.lang@digitalinsight.com>
Date: Apr 22, 2007, 09:09 UTC
Message-ID: <Pine.LNX.4.63.0704220202550.5946@qynat.qvtvafvgr.pbz>
In-Reply-To: <7v4pn8rk8t.fsf@assigned-by-dhcp.cox.net>

On Sat, 21 Apr 2007, Junio C Hamano wrote:

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> David Lang <david.lang@digitalinsight.com> writes:
>
>> 1. it would be useful in many cases for the filter program to know
>> what file it's working on (and probably some other things), so there
>> are probably some command-line arguments that should be able to be
>> passed to the filter.
>
> I can see that you missed the class when Linus talked about how
> messy things would get once you allow the conversion to be
> stateful.  I was in the class and remembered it ;-)
>
> Although I initially considered interpolating "%P" with
> pathname, I ended up deciding against it, to discourage people
> from abusing the filter for stateful conversion that changes the
> results depending on time, pathname, commit, branch and stuff.

I didn't miss it, I just don't think that the path in the repository is nessasarily as dangerous as the other things (time, branch, etc)

one thing that was listed as a possibilty was to use the sha1 of the file, but you would force the filter to calculate that itself. it's already available when extracting and recalcuating it is a waste

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>> 2. should this be done as a modification of the in-memory buffer (s
>> this patch does it?) or should it be done at the time of the
>> read/write, makeing the filter be responsible for actually doing the
>> disk I/O, which would give it the benifit of being able to do things
>> like set permissions and other things ...
>
> The conversion is not about overriding the mode bits recorded in
> tree objects, nor making git as a replacement for build procedure.

what build procedures?

I'm talking about doing things like managing files in /etc

git doesn't have all the hooks to be able to set the permissions when you extract a file, but if the filters were actual readers/writers instead of in-memory operators, this becomes trivial to implement with no further changes to git itself

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>> 3. why specify seperate clean/smudge programs instead of just one
>> script with a read/write parameter?
>
> I think the most common two ways have clean as a cleaner and
> smudge as a no-op (similar to crlf=input conversion), or clean
> and smudge are inverse operations (similar to crlf=true
> conversion.  I do not see a sane case where clean and smudge are
> the same, unless you are thinking about the toy demonstration
> test piece I added to t0021 which uses rot13 as both clean and
> smudge filters.

actually, I'm thinking of much more complicated filters, where it's easier to have one program do both functions then it is to have two seperate programs (like tar -c /tar -x)

David Lang