syz-ci: introduce gitCache parameters

Some commits don't live long remotely.
It sometimes happens we need them later to:
1. Merge coverage.
2. Mention during communication.

pkg/vcs/fuchsia.go

@@ -107,3 +107,7 @@ func (ctx *fuchsia) MergeBases(firstCommit, secondCommit string) ([]*Commit, err
 func (ctx *fuchsia) CommitExists(string) (bool, error) {
 	return false, fmt.Errorf("not implemented for fuchsia")
 }
+
+func (ctx *fuchsia) PushCurrentCommitAsTagTo(repo string, config ...string) error {
+	return ctx.repo.PushCurrentCommitAsTagTo(repo, config...)
+}

pkg/vcs/git.go

@@ -635,3 +635,26 @@ func (git *git) CommitExists(commit string) (bool, error) {
 	}
 	return true, nil
 }
+
+func (git *git) PushCurrentCommitAsTagTo(repo string, gitConfig ...string) error {
+	if "" == repo {
+		return nil
+	}
+	if len(gitConfig) != 0 {
+		gitConfigParams := append([]string{"config"}, gitConfig...)
+		if _, err := git.git(gitConfigParams...); err != nil {
+			return fmt.Errorf("git %s: %w", strings.Join(gitConfigParams, " "), err)
+		}
+	}
+	commit, err := git.HeadCommit()
+	if err != nil {
+		return fmt.Errorf("git.HeadCommit: %w", err)
+	}
+	tagName := commit.Hash
+	git.git("remote", "add", "syz-gitcache", repo) // ignore errors on re-adding
+	git.git("tag", tagName)                        // ignore errors on re-tagging
+	if _, err := git.git("push", "syz-gitcache", tagName); err != nil {
+		return fmt.Errorf("git push syz-gitcache %s: %w", tagName, err)
+	}
+	return nil
+}

pkg/vcs/vcs.go

@@ -72,6 +72,10 @@ type Repo interface {
 
 	// CommitExists check for the commit presence in local checkout.
 	CommitExists(commit string) (bool, error)
+
+	//PushCurrentCommitAsTagTo is used to cache commits elsewhere.
+	//Returns nil error is called with empty string.
+	PushCurrentCommitAsTagTo(string, ...string) error
 }
 
 // Bisecter may be optionally implemented by Repo.

syz-ci/manager.go

@@ -271,6 +271,10 @@ func (mgr *Manager) pollAndBuild(lastCommit string, latestInfo *BuildInfo) (
 		mgr.buildFailed = needsUpdate
 		if commit.Hash != lastCommit && needsUpdate {
 			lastCommit = commit.Hash
+			if err := mgr.repo.PushCurrentCommitAsTagTo(mgr.cfg.GitCache); err != nil {
+				log.Logf(0, "%v: failed to cache commit %s from repo %s: %s",
+					mgr.name, lastCommit, mgr.mgrcfg.Repo, err.Error())
+			}
 			select {
 			case <-buildSem.WaitC():
 				log.Logf(0, "%v: building kernel...", mgr.name)

syz-ci/syz-ci.go

@@ -144,6 +144,12 @@ type Config struct {
 	// Per-vm type JSON diffs that will be applied to every instace of the
 	// corresponding VM type.
 	PatchVMConfigs map[string]json.RawMessage `json:"patch_vm_configs"`
+	// Some commits don't live long. Cache them somewhere to increase lifetime.
+	// The cache is used by coverage merger.
+	GitCache string
+	// "git config" params you want to be called to configure git cache.
+	// Only one git config command will be called.
+	GitCacheConfig []string
 }
 
 type ManagerConfig struct {