supporting --initially-drop-socket-file

- by default gh-ost will not delete an existing socket file
  and thus, will fail running if socket file exists. This is the desired behavior.
- The flag --initially-drop-socket-file indicates we take responsibility and wish gh-ost to delete this file on startup

build.sh

@@ -1,7 +1,7 @@
 #!/bin/bash
 #
 #
-RELEASE_VERSION="1.0.2"
+RELEASE_VERSION="1.0.3"
 
 buildpath=/tmp/gh-ost
 target=gh-ost

go/base/context.go

@@ -72,6 +72,7 @@ type MigrationContext struct {
 	CutOverLockTimeoutSeconds           int64
 	PanicFlagFile                       string
 
+	DropServeSocket bool
 	ServeSocketFile string
 	ServeTCPPort    int64
 

go/cmd/gh-ost/main.go

@@ -83,6 +83,7 @@ func main() {
 	flag.StringVar(&migrationContext.PostponeCutOverFlagFile, "postpone-cut-over-flag-file", "", "while this file exists, migration will postpone the final stage of swapping tables, and will keep on syncing the ghost table. Cut-over/swapping would be ready to perform the moment the file is deleted.")
 	flag.StringVar(&migrationContext.PanicFlagFile, "panic-flag-file", "", "when this file is created, gh-ost will immediately terminate, without cleanup")
 
+	flag.BoolVar(&migrationContext.DropServeSocket, "initially-drop-socket-file", false, "Should gh-ost forcibly delete an existing socket file. Be careful: this might drop the socket file of a running migration!")
 	flag.StringVar(&migrationContext.ServeSocketFile, "serve-socket-file", "", "Unix socket file to serve on. Default: auto-determined and advertised upon startup")
 	flag.Int64Var(&migrationContext.ServeTCPPort, "serve-tcp-port", 0, "TCP port to serve on. Default: disabled")
 

go/logic/server.go

@@ -36,7 +36,7 @@ func (this *Server) BindSocketFile() (err error) {
 	if this.migrationContext.ServeSocketFile == "" {
 		return nil
 	}
-	if base.FileExists(this.migrationContext.ServeSocketFile) {
+	if this.migrationContext.DropServeSocket && base.FileExists(this.migrationContext.ServeSocketFile) {
 		os.Remove(this.migrationContext.ServeSocketFile)
 	}
 	this.unixListener, err = net.Listen("unix", this.migrationContext.ServeSocketFile)