pkg/vcs: add freebsd

This is currently identical to support for OpenBSD and NetBSD.  A
FreeBSD git repo is available at github.com/freebsd/freebsd.

pkg/vcs/freebsd.go

@@ -0,0 +1,31 @@
+// Copyright 2019 syzkaller project authors. All rights reserved.
+// Use of this source code is governed by Apache 2 LICENSE that can be found in the LICENSE file.
+
+package vcs
+
+import (
+	"fmt"
+	"io"
+)
+
+type freebsd struct {
+	*git
+}
+
+func newFreeBSD(vm, dir string) *freebsd {
+	return &freebsd{
+		git: newGit(dir),
+	}
+}
+
+func (ctx *freebsd) ExtractFixTagsFromCommits(baseCommit, email string) ([]*Commit, error) {
+	return ctx.git.ExtractFixTagsFromCommits(baseCommit, email)
+}
+
+func (ctx *freebsd) Bisect(bad, good string, trace io.Writer, pred func() (BisectResult, error)) (*Commit, error) {
+	return nil, fmt.Errorf("not implemented for freebsd")
+}
+
+func (ctx *freebsd) PreviousReleaseTags(commit string) ([]string, error) {
+	return nil, fmt.Errorf("not implemented for freebsd")
+}

pkg/vcs/vcs.go

@@ -90,6 +90,8 @@ func NewRepo(os, vm, dir string) (Repo, error) {
 		return newOpenBSD(vm, dir), nil
 	case "netbsd":
 		return newNetBSD(vm, dir), nil
+	case "freebsd":
+		return newFreeBSD(vm, dir), nil
 	}
 	return nil, fmt.Errorf("vcs is unsupported for %v", os)
 }