From: Johannes Sixt <j6t@kdbg.org>
Date: Fri, 31 Dec 2010 17:09:24 GMT
Subject: Re: [RFC PATCH 1/3] filter-branch: optionally dump all mappings at the end
Message-ID: <201012311809.24205.j6t@kdbg.org>
In-Reply-To: <57609f1df897f19becc77d5c43c3c3608725160b.1293809100.git.trast@student.ethz.ch>

On Freitag, 31. Dezember 2010, Thomas Rast wrote:
> In some cases, like the sub/super-project filtering attempted in this
> series, it may be necessary to carry over the mappings from one or
> more filter-branch run to another.
>
> As the first part to this, make a --dump-map option that dumps a flat
> text file with lines of the form
>
>   $sha1 $(map $sha1)

Despite the alternative implementation that I suggest below, the commit 
message (and also the documentation to be written) should state the output 
format in this way.

> @@ -194,6 +195,16 @@ do
>  	--original)
>  		orig_namespace=$(expr "$OPTARG/" : '\(.*[^/]\)/*$')/
>  		;;
> +	--dump-map)
> +		case "$OPTARG" in
> +		/*)

Please use

	if is_absolute_path "$OPTARG"
	then
	...

> +# At this point the mappings are stable so we can dump them if
> +# requested
> +
> +if test -n "$dump_map"; then
> +	( cd "$workdir"/../map/; ls ) |
> +	while read sha1; do
> +		echo $sha1 $(map $sha1)

There must be a more efficient way than to spawn an additional process for 
each mapped SHA1. Since this excercises only one branch in the map() function 
anyway, how about this:

	( cd "$workdir"/../map/ && ls -1 ) |
	while read sha1; do
		read mapped << $sha1 &&
		echo $sha1 $mapped
	done > "$dump_map"

Though, there is some mechanism that maps one SHA1s to more than one, and my 
approach might not cover that case.

> +	done > "$dump_map"

-- Hannes