Re: [PATCHv2 7/9] archive: implement configurable tar filters

> diff --git a/Documentation/git-archive.txt b/Documentation/git-archive.txt
> index 9c750e2..726bf63 100644
> --- a/Documentation/git-archive.txt
> +++ b/Documentation/git-archive.txt
> @@ -101,6 +101,16 @@ tar.umask::
>  	details.  If `--remote` is used then only the configuration of
>  	the remote repository takes effect.
>  
> +tar.<format>.command::

> diff --git a/archive-tar.c b/archive-tar.c
> index bed9a9b..5c30747 100644
> --- a/archive-tar.c
> +++ b/archive-tar.c
> @@ -4,6 +4,7 @@
>  #include "cache.h"
>  #include "tar.h"
>  #include "archive.h"
> +#include "run-command.h"
>  
>  #define RECORDSIZE	(512)
>  #define BLOCKSIZE	(RECORDSIZE * 20)
> @@ -13,6 +14,9 @@ static unsigned long offset;
>  
>  static int tar_umask = 002;
>  
> +static int write_tar_filter_archive(const struct archiver *ar,
> +				    struct archiver_args *args);
> +
>  /* writes out the whole block, but only if it is full */
>  static void write_if_needed(void)
>  {
> @@ -220,6 +224,60 @@ static int write_global_extended_header(struct archiver_args *args)
>  	return err;
>  }
>  
> +static struct archiver **tar_filters;
> +static int nr_tar_filters;
> +static int alloc_tar_filters;
> +
> +static struct archiver *find_tar_filter(const char *name, int len)
> +{
> +	int i;
> +	for (i = 0; i < nr_tar_filters; i++) {
> +		struct archiver *ar = tar_filters[i];
> +		if (!strncmp(ar->name, name, len) && !ar->name[len])
> +			return ar;
> +	}
> +	return NULL;
> +}
> +
> +static int tar_filter_config(const char *var, const char *value, void *data)
> +{
> +	struct archiver *ar;
> +	const char *dot;
> +	const char *name;
> +	const char *type;
> +	int namelen;
> +
> +	if (prefixcmp(var, "tar."))
> +		return 0;
> +	dot = strrchr(var, '.');
> +	if (dot == var + 9)
> +		return 0;
> +
> +	name = var + 4;
> +	namelen = dot - name;
> +	type = dot + 1;
> +
> +	ar = find_tar_filter(name, namelen);
> +	if (!ar) {
> +		ar = xcalloc(1, sizeof(*ar));
> +		ar->name = xmemdupz(name, namelen);
> +		ar->write_archive = write_tar_filter_archive;
> +		ar->flags = ARCHIVER_WANT_COMPRESSION_LEVELS;
> +		ALLOC_GROW(tar_filters, nr_tar_filters + 1, alloc_tar_filters);
> +		tar_filters[nr_tar_filters++] = ar;
> +	}
> +
> +	if (!strcmp(type, "command")) {
> +		if (!value)
> +			return config_error_nonbool(var);
> +		free(ar->data);
> +		ar->data = xstrdup(value);
> +		return 0;
> +	}