[PATCH v2 9/9] svn-fe: reuse import-marks in remote-svn-alpha

[Dmitry Ivankov <divanorama@gmail.com>]

remote-svn-alpha needs to prepare import marks file when doing an
incremental import. This file can be left after previous imports.

Take the last imported commit and a note with corresponding svn
revision number. If the marks file exists and defines a :revision
mark pointing to the last imported commit, consider it valid.
It may accidentally contain newer revisions, they are silently
ignored. In practice the check for :revision last_commit should
be sufficient to rely on this file defining any lesser revision
marks needed correctly.

So if the import marks file looks valid, do not regenerate it from
the notes tree and have save some performance saved.

Signed-off-by: Dmitry Ivankov <divanorama@gmail.com>
---
 contrib/svn-fe/git-remote-svn-alpha |   26 ++++++++++++++++++++++----
 1 files changed, 22 insertions(+), 4 deletions(-)

diff --git a/contrib/svn-fe/git-remote-svn-alpha b/contrib/svn-fe/git-remote-svn-alpha
index f4e737d..8096ef2 100755
--- a/contrib/svn-fe/git-remote-svn-alpha
+++ b/contrib/svn-fe/git-remote-svn-alpha
@@ -78,14 +78,31 @@ do_gen_marks () {
 prepare_marks () {
 	dst=$1 notes=$2 rev=$3
 	test "z$git_dir" != "$z" || die "we were not told the gitdir"
-	mkdir -p "$git_dir/$marks_dir"
-	if test ! -f "$git_dir/$marks_dir/marks"; then
-		touch "$git_dir/$marks_dir/marks"
+	path="$git_dir/$marks_dir"
+	mkdir -p "$path"
+	path="$path/marks"
+
+	if test ! -f "$path"; then
+		touch "$path"
 	fi
 	if test "$rev" = "-1"; then
 		return 0
 	fi
-	do_gen_marks "$notes" >"$git_dir/$marks_dir/marks"
+	mark_sha=""
+	{
+		while read -r m sha
+		do
+			if test "$m" = ":$rev"; then
+				mark_sha="$sha"
+			fi
+		done
+	} <"$path"
+	dst_sha=$( git rev-parse "$dst" )
+	if test -n "$mark_sha"; then
+		test "$mark_sha" = "$dst_sha" || die "latest mark and note diverge"
+	else
+		do_gen_marks "$notes" >"$path"
+	fi
 }
 
 last_imported_rev () {
@@ -110,6 +127,7 @@ do_import () {
 	revs="$start_rev:HEAD"
 	prepare_marks $dst $notes $rev
 	echo "feature import-marks=$git_dir/$marks_dir/marks"
+	echo "feature export-marks=$git_dir/$marks_dir/marks"
 	(eval "$SVNDUMP \"$url\" -r\"$revs\"" |	svn-fe --ref="$dst" --notes-ref="$notes" --incremental --no-progress) 3<&0 || die "FAILURE"
 	exec 1>&-
 }
-- 
1.7.3.4