開(kāi)發(fā)linux兼容內(nèi)核的策略與路線(xiàn)

1、開(kāi)發(fā)LinuxLinux兼容內(nèi)核的策略與路線(xiàn)LinuxLinuxkerneldevelopmentstrategiescompatiblewiththeline毛德操M(fèi)audoperation筆者自從提出Linux兼容內(nèi)核的構(gòu)想以后，聽(tīng)到了不少反響。SinceIproposedtheideaofLinuxcompatiblekernellaterIheardalotofrepercussions.其中支持者固然不乏其人，如開(kāi)源軟件推進(jìn)聯(lián)

2、盟主WhichiscertainlynoshtageofsuppterssuchastheOpenSourceSoftwarePromotionUnion席陸首群Ilthefirstgroup先生、倪光南院士、還有OSDL的平野正信先生，都是支持的。Mr.NiGuangnanacademiciansaswellasOSDLsMr.Hiranoisbelievedaresuppted.但是無(wú)庸諱言，對(duì)此不以為然的意見(jiàn)也有不少。Needle

3、sstosayhoweverdonotagreewiththeviewstherearemany.有趣的是，這些不以為然的意見(jiàn)往往分成兩個(gè)極端。Interestinglytheseviewsdisagreeoftendividedintotwoextremes.一個(gè)極端說(shuō)，Linux兼容內(nèi)核要達(dá)到的目標(biāo)已經(jīng)達(dá)到了，因此根本就不用多此一舉。AnextremethatLinuxcompatiblekerneltoachievehasbeen

4、achievedsothereisnoneedredundant.說(shuō)已經(jīng)達(dá)到，是因?yàn)樵谟脩?hù)空間我們已經(jīng)有了Wine，而NdisWrapper則已經(jīng)解決了把Windows設(shè)備驅(qū)動(dòng)裝入Linux內(nèi)核的問(wèn)題。SaidtohavebeenreachedbecausewealreadyhaveintheuserspaceWinebutithasbeenresolvedNdisWrapperWindowsdevicedrivertoloadLinu

5、xkernelproblem.另一個(gè)極端呢，則是說(shuō)兼容內(nèi)核的難度太大，根本就不可能成功，所以只是一個(gè)“夢(mèng)”。Theotherextremeitiscompatiblewiththekernelisthattoodifficultsimplycannotsucceedsoonlya“dream.“顯然，在談?wù)撻_(kāi)發(fā)路線(xiàn)圖之前首先應(yīng)該回答這兩種意見(jiàn)。Obviouslytalkingabouttheroadmapshouldbeanswered

6、befethefirstofthesetwoviews.幸好它們正好互相構(gòu)成回答。Ftunatelytheyarejustanotherfmanswer.首先，正如筆者在另幾篇文章中所說(shuō)，Wine只是在邏輯上、功能上基本解決了用Linux內(nèi)核來(lái)模擬仿真Windows內(nèi)核的問(wèn)題，但是性能上是無(wú)法令人滿(mǎn)意的，而且說(shuō)基本上解決其實(shí)也很勉強(qiáng)。FirstasIhavesaidinotherarticlesWineisonlylogicalfunc

7、tionbasicallysolvedwiththeLinuxkerneltosimulateSimulationWindowskernelproblembutperfmanceisnotsatisfactythatbasicallysolutionisactuallyveryreluctant.至于NdisWrapper，它所解決的是一些網(wǎng)絡(luò)設(shè)備(網(wǎng)卡)的驅(qū)動(dòng)，而不是普遍意義上的設(shè)備驅(qū)動(dòng)。AsNdisWrapperitsolvedso

8、mewkdevice(NIC)drivernotthegeneralsenseofthedevicedriver.更何況NdisWrapper設(shè)備驅(qū)動(dòng)的上層只能是Linux的Socket，而不能與諸多文件操作的系統(tǒng)調(diào)用掛上鉤。MeovertheupperNdisWrapperdevicedrivercanonlybeLinuxSocketnotwithalotoffilemanipulationsystemcallsprocessisl

9、inked.實(shí)際上，退一步說(shuō)，即使NdisWrapper和Wine真的已經(jīng)分黑盒子中，光憑幾本書(shū)能得到多少信息、如何就能開(kāi)發(fā)出跟Windows兼容的內(nèi)核？ToodifficultfthepeoplethatthereisaconcernthatisWindowsthecodeisnotpublichiddenintheblackboxevenwiththefewbookstogetmuchinfmationhowcandevelopco

10、mpatiblewiththeWindowskernel這種顧慮當(dāng)然也有一些道理，但是ReactOS又在這方面給我們提供了參考。ThisconcernofcoursethereissometruthbutinthiscontextReactOShasprovideduswithinfmation.ReactOS以零為起點(diǎn)從頭開(kāi)發(fā)，Wine只在內(nèi)核外面做文章，尚且都能在一定程度上達(dá)到設(shè)計(jì)目標(biāo)，而我們站在它們的肩膀上，又有Linux內(nèi)核作為

11、原材料，至少條件比他們好多了。ReactOStozeroasastartingpointfromscratchWineonlymakeanissueoutofthekernelyetitcanbetosomeextenttomeetthedesigngoalswestontheirshouldersanotherLinuxkernelasarawmaterialatleastmuchbetterconditionsthantheyare

12、.當(dāng)然，把Wine、NdisWrapper和ReactOS作為參考意味著我們需要吃透、或者至少基本上理解它們的代碼。OfcoursetheWineNdisWrapperReactOSasareferencemeansthatweneedtounderstwellatleastbasicallyundersttheircode.為此筆者將陸續(xù)寫(xiě)一些分析文章在本網(wǎng)站上推出，起個(gè)拋轉(zhuǎn)引玉的作用。TodothisIwillgraduallywr

13、iteanalyticalarticlesonthissitelaunchsincetheroleofaparabolicquotedYu.總之，兼容內(nèi)核的開(kāi)發(fā)既不是唾手可得，也不是難于上青天，既不能一蹴而就，也不至于遙遙無(wú)期。Inshtneithercompatiblewiththedevelopmentofthekernelisaneasynisitimpossiblefthecountywecannotbedoneovernigh

14、tyouwillnotbeputoffindefinitely.說(shuō)起來(lái)還是那句老話(huà)：戰(zhàn)略上藐視困難，戰(zhàn)術(shù)上重視困難。Thatitisanoldsayinggoes:strategicdefianceofdifficultiestacticallydifficult.后發(fā)跟進(jìn)、逐步逼近后發(fā)跟進(jìn)、逐步逼近FollowupFollowupafterafterthethehairhairgraduallygraduallyapproaching

15、approaching我們開(kāi)發(fā)兼容內(nèi)核不能采取一步到位、而應(yīng)采取逐步逼近的策略。Wehavedevelopedcompatiblewiththekernelcannottakeonestepbutshouldadoptagradualapproachofthestrategy.以系統(tǒng)調(diào)用界面為例，我們完全可以先擱置那些用于GUI、即win32k.sys的擴(kuò)充系統(tǒng)調(diào)用，即便是對(duì)于248個(gè)常規(guī)系統(tǒng)調(diào)用也可以分期分批地實(shí)現(xiàn)。Thesystem

16、callinterfacefexamplewecansetasidethoseusedfthefirstGUIthewin32k.sysexpansionofsystemcallsevencallsftheconventionalsystem248canalsobeachievedinstages.實(shí)際上，我們甚至并無(wú)必要追求一個(gè)完整的實(shí)現(xiàn)。Infactweevendonotneedtopursueacompleteimplementa

17、tion.工程上有一個(gè)所謂2080原理，說(shuō)是20%的工作量往往可以實(shí)現(xiàn)80%的功能，而剩下的20%功能卻往往需要80%的工作量才能實(shí)現(xiàn)。Wksonasocalled2080principlethatis20%ofthewkloadcanoftenachieve80%ofthefunctionwhiletheremaining20%ofthefeaturesareoftenrequiredtoachieve80%ofthewkload.如