In this thesis, we exercised the componentization technique to componentize the Netfilter architecture in Linux network system. Netfilter is a software architecture for filtering packets. System administrator can register packet-matching rules and target handling function into the system. Netfilter matches packets according to the rules and processes them by the corresponding target functions. By componentizing the architecture, we can improve the elasticity and the reusability of Netfilter. Hot-swapping is an important procedure in componentized software system. In this study, we implemented hot-swapping based on the work developed by Fan[1]. It stores the relocation information of exporting symbols into the module symbol table. With this information, we are able to dynamically change the caller-callee relationship of modular components at run time. In addition, we extend their work to allow the same modular component to be loaded into Linux kernel for more than once so that the same component can be replicated in the system. We started with decomposing all the ¡§hook¡¨ functions into smaller and simpler components and then for each component, we added in-ports and out-ports and registered its own iptables, and we fixed the limitation of only one instance of a module allowed in kernel and broke the hard rule in iptables. As a result, after Netfilter componentization, we are able to illustrate new configurations that cannot be done in the original architecture, and the system becomes further compact with only necessary components loaded in the system. This reflects in slight performance improvement in our experiments, which is not usually seen in other frameworks due to componentization overhead.

In this thesis, we studied a component-based software design for componentizing Linux kernel. Our goal is to componentize kernel modules and explicitly define the dependency relation of components in the kernel. Componentization can greatly improve composability, evolvability, extensibility and testability of a software system, and can thus increase the productivity of software development and reduce the cost of maintenance. On top of the componentized kernel, we developed a suite of tools to facilitate the operations on kernel components. In the component-based design, the basic software unit is a component. We envision any subsystem in kernel as a composition of components. To realize the concept, we explicitly create the output ports by augmenting the symbol table of a kernel module to record the relocation information, i.e., the locations where the module invokes the functions exported by other modules. We developed tools to discover the data passing among components such that the dependency relation among components can be clearly disclosed. With componentization in place, we are able to implement the hot-swapping technique which allows the system structure to be dynamically changed at run time. The technique makes it possible to test, swap or re-compose components when part of the system cannot be terminated or removed. The proposed system is implemented on Linux kernel 2.6.17.1. While our componentization does not introduce any time overhead when modules are in action, we evaluated our approach in terms of module loading time, memory consumption and hot-swapping time. We found that the module loading time and memory consumption of a componentized module are both proportional to the number of relocations in the module. The hot-swapping time is related to the position of the symbol to be swapped in the symbol table. All these suggest that we still have room to improve the way we realized the componentization in Linux kernel.

Detta examensarbete har varit inriktat på att studera nyttan av att omstrukturera ett mjukvarusystem till ett moderniserat system. Frågan som skulle besvaras av detta projekt var: vad är fördelarna med komponentiseringen av ett legacysystem, med avseende på utvecklingstid som krävs för vidareutveckling av systemet? Denna fråga besvarades med hjälp av en analys av forskningsfronten över ämnet samt att en fallstudie genomfördes. Det som framkom under analysen av forskningsfronten tydde väldigt mycket på att detta var lönsamt att göra. Trots att fallet var för en specifik aktör var det väldigt relevant att genomföra det för detta projekt för att på sätt få ett praktiskt exempel som hjälpte till att besvara forskningsfrågan. Genom att genomföra dessa undersökningar besvarade vi forskningsfrågan. Många slutsatser kunde dras och det blev ett tydligt resultat. Efter våra estimeringar skulle en aktör vinna på en modernisering av sitt legacysystem i de flesta fallen, om kompetensen för att genomföra detta finns. Fallstudien som genomfördes visade på tydliga vinster med att genomföra en moderniseringsprocess för ett legacysystem. / This thesis work has been focused on studying the benefits of restructuring a legacy system to a modernized software system. The question that was to be answered was: What are the benefits of componentization of a legacy system with respect to the software development time required for further system development? This question was answered by doing a state of the art on the subject and also by performing a case study. What was discovered during the state of the art implicated that this kind of work is very profitable to undergo. Even though the case was aimed at a certain system it was relevant to this study because it helped to get a practical example which in turn helped with answering the question for this thesis. By doing these studies the question for this report got answered. Many conclusions could be drawn and the result was clear. By our estimations an actor would benefit greatly by modernizing their legacy system in most cases, if they have the right knowledge for doing this. The case study that was performed showed obvious benefits of the process of modernizing a legacy system.

Komponentmetoden berör den bokföringsmässiga hanteringen av materiella anläggningstillgångar. I många avseenden kan dessa bestå av olika delar förknippade med olika förbrukningstakt och nyttjandeperioder. Fastigheter är en typisk sådan anläggningstillgång där exempelvis stomme, tak och fasad då utgör sådana komponenter vilka enligt komponentmetoden ska redovisas separat. Företag som tillämpar K3-regelverket behöver förhålla sig till detta. Följande studie fokuserar på redovisning av komponenter utifrån fastighetsförvaltande företag. Studien ämnar undersöka skillnader samt likheter i företagens tillämpning såväl som hur detta förhåller sig mot publicerade vägledningar kring hur metoden kan tillämpas. Likaså söker studien förståelse för vilka implikationer komponentmetoden medför för företagen. Studien utgår från en kvalitativ metod där intervjuer av fyra företag utgör grunden för det empiriska materialet. Vidare har en komparativ multipel fallstudiedesign använts för att uppnå studiens syfte. Resultatet påvisar att komponentmetodens tillämpning är företagsunik och består i många fall av uppskattningar hos respektive företag. Även likheter mellan företag och vägledningar har såväl identifierats. De implikationer som följer beror delvis på hur metoden tillämpas. Ökade avskrivningskostnader, jämnare resultat, en ökning av fastigheternas bokförda värden samt dess påverkan på redovisningens jämförbarhet är dock att betrakta som några av de huvudsakliga konsekvenserna. / Component accounting concerns the accounting management of tangible fixed assets. In many cases, these assets consist of different parts with varying economical and technical lifespans. Real estates are regarded as such assets whereby the building frame, roof and facade could be examples of distinguished components that should be accounted for separately. Swedish companies applying the K3-framework need to manage their accounting accordingly. This study´s focus relates to real estate companies’ application of component accounting. The aim of the study is to investigate differences and similarities between different companies, also in comparison to published guidelines on this topic. Furthermore, the study seeks to understand the implications of component accounting. A qualitative method has been applied where interviews have been conducted with four companies that form the basis of the empirical data. To achieve the purpose of the study a comparative multiple case design has been used.  The results show that component accounting is uniquely applied between companies and is often characterized by estimations. However, similarities between the companies as well as the guidelines do also exist. The implications that follow depend in part on how it´s applied, although increased depreciations, profit smoothing, increased book values and the componentization´s impact on comparability have been found to be some of the main consequences.