feat(fsrepo): protect with a repo lockfile

NB: daemon is one spot the repo lock is typically acquired

repo/fsrepo/lock/lock.go

@@ -0,0 +1,31 @@
+package lock
+
+import (
+	"io"
+	"path"
+
+	lock "github.com/jbenet/go-ipfs/Godeps/_workspace/src/github.com/camlistore/lock"
+	"github.com/jbenet/go-ipfs/util"
+	"github.com/jbenet/go-ipfs/util/debugerror"
+)
+
+// LockFile is the filename of the daemon lock, relative to config dir
+// TODO rename repo lock and hide name
+const LockFile = "daemon.lock"
+
+func Lock(confdir string) (io.Closer, error) {
+	c, err := lock.Lock(path.Join(confdir, LockFile))
+	return c, debugerror.Wrap(err)
+}
+
+func Locked(confdir string) bool {
+	if !util.FileExists(path.Join(confdir, LockFile)) {
+		return false
+	}
+	if lk, err := Lock(confdir); err != nil {
+		return true
+	} else {
+		lk.Close()
+		return false
+	}
+}