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Task snapshoting in HelenOS
Brambora, Tomáš ; Děcký, Martin (advisor) ; Babka, Vlastimil (referee)
HelenOS is a modern micro-kernel based operating system being developed at the Faculty of Mathematics and Physics of the Charles University in Prague. Application checkpointing is a feature which is primarily used for adding fault tolerance to computing systems, however, it can also be used as a basis for process migration. HelenOS has not been developed with support for application checkpointing in mind; the aim of this thesis is to explore the possibilities of adding such support to HelenOS and provide a prototype implemetation.
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History and Backup Support for zlomekFS
Wartiak, Rastislav ; Babka, Vlastimil (advisor) ; Marek, Lukáš (referee)
zlomekFS is a distributed file system that supports disconnected operation using local cache. During synchronization of local changes it offers easytouse conflict resolution mechanism. Further improved it became a file system with no specific kernel code. It has therefore a good potential in future public use. As the content of this file system can be updated by many users, keeping history of the changes can be a useful feature. This thesis implements file versioning in zlomekFS, answering the questions such as how to store and access the history. On top of the versioning, the possibility of consistent backup is introduced into the file system. New functionality is derived from the analysis of other file systems with similar features and selection of the most suitable approach for zlomekFS.
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Syllable-based PPM
Unger, Lukáš ; Babka, Vlastimil (referee) ; Lánský, Jan (advisor)
PPM is an adaptive comprimation method which works with the data's context. During PPM compression, a tree of contexts of maximum length k is built based on the already processed part of the file, which is then used to predict the probability of the next character using variablelength context of maximum length k. Codes are then assigned to different characters based on these probabilities. The goal of this work is the implementation of a syllable-based version of a PPM algorithm and comparison of it's results with symbol-based and word-based versions. This work is based on the implementation of a syllable parser as described in [7].
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Interactive Data Visualization Tool
Fabian, Peter ; Babka, Vlastimil (referee) ; Parízek, Pavel (advisor)
The goal of the work was to design and implement a tool, which would allow the users to work with a graphical representation of statistic data easily in an interactive manner. The IVP tool supports both the basic adjustments of graphs and advanced modifications, which are either very hard or impossible to achieve in similar tools. However, the key feature of the tool is its extensibility. The particular graph types and the interactive features are implemented as plug-ins and their functionality is provided to the tool's core. The thesis also presents a description of the IVP tool's implementation details, user documentation, an overview of the existing graphing software and its comparison to the IVP tool.
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Influence of Resource Sharing on Performance
Babka, Vlastimil ; Bulej, Lubomír (referee) ; Tůma, Petr (advisor)
Resource sharing occurs when multiple active processes or software components compete for system resources, which influences the observed performance compared to an individual execution. Isolated benchmarking of durations of key operations for solving of performance prediction models may therefore yield imprecise results. Resource sharing also occurs between the measured code and the benchmark infrastructure for obtaining and storing samples, imposing an indirect overhead. This thesis quantifies the effects of sharing on performance for several resources that are often shared, namely the processor caches and the file systems. The highest possible performance impact of cache sharing is determined by synthetic benchmarks. Impact on practical code and its dependency on a number of factors such as cache trashing frequency and intensity are then determined by experiments with existing implementations of FFT and LZW algorithms and a video stream processing application. Effects of file system sharing are measured by experiments that read and write multiple files simultaneously. For both resources, situations with significant performance impact of sharing have been observed. Based on the results of the experiments, several suggestions for dealing with the overhead of performance monitoring infrastructure are...
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Automated detection of vulnerabilities in web applications
Tomori, Rudolf ; Babka, Vlastimil (referee) ; Parízek, Pavel (advisor)
Security vulnerabilities, while being an important and common problem of web applications, are often easily detectable by using specialised software. The WebCop tool developed in this thesis is able to spot some of the common web application security vulnerabilities. Its main advantage over other similar software lies in its ability to configure the way in which the individual tests are performed, also allowing the user to specify the conditions that are required to be met in order to acknoledge the presence of the given security vulnerability. The tool is developed for the Unix/Linux platform using the C++ language.
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The use of simulation and computational environments in physics education
Dekar, Martin ; Babka, Vlastimil (referee) ; Holub, Viliam (advisor)
In the presented work we study usage of interactive simulations (a modern approach to e-learning) in science education from the programmer's point of view. A concept of interactive simulation is presented in the beginning of the presented work, followed by guidelines for choosing suitable authoring environment for development of large number of such simulations. Next we introduce four existing development tools and we verify their practical usability by implementing suitable physics test problem - damped harmonic oscilator. This implementation is also described. In the end of the work we introduce a new kind of educational simulation allowing experimental data to be obtained from the simulation which gets simulation closer to real experiment. This approach shows a new course of e-learning. This simulation together with a library consisting of more than 100 reusable graphical objects is created in the Adobe Flash CS3 environment.
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IMAP E-mail Client
Kundrát, Jan ; Peterka, Jiří (referee) ; Babka, Vlastimil (advisor)
This thesis describes the implementation of an advanced IMAP e-mail client, Trojita. Focusing on standards compliance, the client supports a wide range of IMAP features crucial for an efficient implementation such as IDLE notifications, server-side message parsing and caching of retrieved body data for offline operation. Connecting to the IMAP server is supported over TCP sockets, optionally secured via the TLS encryption, as well as through a local process. Basic message composition and sending via both SMTP and a local sendmail instance is supported. The target platform is the Qt framework on Linux, but the application is reasonably portable.
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Influence of Resource Sharing on Performance
Babka, Vlastimil
Resource sharing occurs when multiple active processes or software components compete for system resources, which influences the observed performance compared to an individual execution. Isolated benchmarking of durations of key operations for solving of performance prediction models may therefore yield imprecise results. Resource sharing also occurs between the measured code and the benchmark infrastructure for obtaining and storing samples, imposing an indirect overhead. This thesis quantifies the effects of sharing on performance for several resources that are often shared, namely the processor caches and the file systems. The highest possible performance impact of cache sharing is determined by synthetic benchmarks. Impact on practical code and its dependency on a number of factors such as cache trashing frequency and intensity are then determined by experiments with existing implementations of FFT and LZW algorithms and a video stream processing application. Effects of file system sharing are measured by experiments that read and write multiple files simultaneously. For both resources, situations with significant performance impact of sharing have been observed. Based on the results of the experiments, several suggestions for dealing with the overhead of performance monitoring infrastructure are...
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History and Backup Support for zlomekFS
Wartiak, Rastislav ; Babka, Vlastimil (advisor) ; Obdržálek, David (referee)
zlomekFS is a distributed file system that supports disconnected operation using local cache. During synchronization of local changes it offers easyto-use conflict resolution mechanism. Further improved it became a file system with no specific kernel code. It has therefore a good potential in future public use. As the content of this file system can be updated by many users, keeping history of the changes can be a useful feature. This thesis implements file versioning in zlomekFS, answering the questions such as how to store and access the history. On top of the versioning, the possibility of consistent backup is introduced into the file system. New functionality is derived from the analysis of other file systems with similar features and selection of the most suitable approach for zlomekFS.
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