v6, 16 partsRe: [PATCH v6 15/16] remote-svn: add marks-file regeneration

> fast-import mark files are stored outside the object database and are
> therefore not fetched and can be lost somehow else.  marks provide a
> svn revision --> git sha1 mapping, while the notes that are attached
> to each commit when it is imported provide a git sha1 --> svn revision
> mapping.
> 
> If the marks file is not available or not plausible, regenerate it by
> walking through the notes tree.  , i.e.  The plausibility check tests
> if the highest revision in the marks file matches the revision of the
> top ref. It doesn't ensure that the mark file is completely correct.
> This could only be done with an effort equal to unconditional
> regeneration.
> 
> Signed-off-by: Florian Achleitner <florian.achleitner.2.6.31@gmail.com>
> Signed-off-by: Junio C Hamano <gitster@pobox.com>
> ---
>  remote-testsvn.c |   68 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 68 insertions(+)
> 
> diff --git a/remote-testsvn.c b/remote-testsvn.c
> index e90d221..09dc304 100644
> --- a/remote-testsvn.c
> +++ b/remote-testsvn.c

> +static void check_or_regenerate_marks(int latestrev) {
> +	FILE *marksfile;
> +	char *line = NULL;
> +	size_t linelen = 0;
> +	struct strbuf sb = STRBUF_INIT;
> +	int found = 0;
> +
> +	if (latestrev < 1)
> +		return;
> +
> +	init_notes(NULL, notes_ref, NULL, 0);
> +	marksfile = fopen(marksfilename, "r");
> +	if (!marksfile) {
> +		regenerate_marks();
> +		marksfile = fopen(marksfilename, "r");
> +		if (!marksfile)
> +			die_errno("cannot read marks file %s!", marksfilename);
> +		fclose(marksfile);
> +	} else {
> +		strbuf_addf(&sb, ":%d ", latestrev);
> +		while (getline(&line, &linelen, marksfile) != -1) {