關於 Libvirt Event Registration for Java Binding 的碎碎念

圖片來源：新浪收藏-抽絲剝繭

使用Opensource 讓人又愛又恨的就是遇到bug和問題，通常到最後只有三種路：

1. 回報社群等人修好  (但是通常會等到天荒地老~~~老闆請你來是做啥的!)
2. 翻Mail list看以前有沒有人解決過，或有什麼建議  (Hello~~有"沒有人"遇過或修過~~)
3. 看source code 然後自己下去patch (我也想當沒有人，但是往往能力不足...Orz..)

話說 Libvirt 雖然有提供Event Registration 的機制和 Java Binding 的Library，但是兩的湊在一起就是不work啊！！

一跑下去就遇到以下錯誤：

libvir: Remote Driver error : adding cb to list
exception caught:org.libvirt.LibvirtException: adding cb to list
level:VIR_ERR_ERROR
code:VIR_ERR_RPC
domain:VIR_FROM_REMOTE
hasConn:false
hasDom:false
hasNet:false
message:adding cb to list
str1:%s
str2:adding cb to list
str3:null
int1:-1
int2:-1

一路Trace source code 往下，到了JNA那一層就斷了...囧rz...只好上網看看有沒有人遇到這個問題。

首先看到的就是Redhat 的bug report：

• virConnectDomainEventRegisterAny won't register the same callback for the same event but for different domains

再來 OpenStack 目前也有遇到這個問題：

• does not support events: adding cb to list spew in compute log (2013 Nov)

然後看到有人說要使用Event Registration 前，要先初始化 (不過舉的是C和Python的範例)

Make sure you have registered in the libvirt event loop (or set up your own) before registering for events

最後從Libvirt 的mail 爬出一連串的討論：

• [libvirt] [PATCH] Java bindings for domain events (2008 Nov 07) -->開始討論
• [libvirt] [PATCH 1/2] Java bindings for domain events
• [libvirt] [PATCH 2/2] Java bindings for domain events (2008 Nov 18) -->被打槍
• Re: [libvirt] [PATCH 1/2] Java bindings for domain events (2008 Dec)  —>沒下文
• [libvirt-users] Using Java bindings to event callback  (2010 Jul) —>沒回應
• [libvirt] [PATCH 0/2] Libvirt-java event handling (2011Jul) —> I think most drivers don't support that. We have a custom driver for our hypervisor and it works. 
• [libvirt] [libvirt-java] [PATCH 00/12] event support (2013 Jan) 
• Re: [libvirt] [libvirt-java] [PATCH 00/12] event support (2013 Mar) 
• [libvirt] [PATCH 2/3] Add event callback implementation based on virConnectDomainEventRegisterAny (2013 Mar)

Ps. 2013 版的那個Patch 有在Github上找到，但是試了一下還是有問題....


所以其實這是一篇碎碎念文，因為結論是目前Java Binding 無法支援這個功能，除非自己跳下去把它改好.....