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VMA merging in Linux
Matěna, Jakub ; Babka, Vlastimil (advisor) ; Bulej, Lubomír (referee)
This thesis deals with virtual memory management in the Linux kernel. Files or devices can be mapped into virtual memory using the mmap() sys- tem call, which is also capable of creating so-called anonymous mappings. Those do not map anything and serve only as a memory allocation method that can specify memory protection and flags for the created anonymous virtual memory area (VMA). A mapping can be merged or split depending on its flags, memory protection, location in the virtual memory and other parameters. However, in some cases even when two VMAs have practically identical parameters, they may not merge successfully because of implementation limitations. This thesis con- centrates on anonymous VMAs and their page offset and anon vma parameters, which in some cases prevent a merge in the current mainline kernel. It is demon- strated that in most of the cases with reasonable amount of effort the obstacles can be removed and the merges happen. v
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Stability and Security of ZlomekFS
Záloha, Jan ; Babka, Vlastimil (advisor) ; Podzimek, Andrej (referee)
- english version ZlomekFS is a distributed filesystem which is able to share data among nodes. These nodes can cooperate in various modes. Modes differ in caching of local data at the client side and in the way how data is synchronized between the client and the server. This synchronization has been implemented by an unsecured and untrusted network connection until now. The current implementation uses FUSE interface for the communication between the kernel of the filesystem and the user. The synchronization is triggered when the user performs a specific operation above the filesystem. For well functionality in modern network environment it is necessary to both communicating partners to be sure about the identity of the second end of a communicating channel. This thesis implements trustworthy connection between the server and the client part of filesystem. In addition, it separates machine and user type of client. Next important part of the thesis is correct data synchronization and precise definition of sharing semantics.
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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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IMAP E-mail Client
Kundrát, Jan ; Babka, Vlastimil (advisor) ; Peterka, Jiří (referee)
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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Automated detection of vulnerabilities in web applications
Tomori, Rudolf ; Parízek, Pavel (advisor) ; Babka, Vlastimil (referee)
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 ; Holub, Viliam (advisor) ; Babka, Vlastimil (referee)
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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Forensic RAM dump image analyzer
Kollár, Ivor ; Holub, Viliam (advisor) ; Babka, Vlastimil (referee)
While different techniques are used for physical memory dumping, most of them provide a hard-to-analyse image of raw data. The aim of the work is to develop an automatic analyser of physical memory dumps retrieving contained information in a user-friendly form. The analyser is supposed to simplify automatic data extraction and should be used by forensic experts. Among expected features are multiple target architecture/OS support, target architecture/OS guessing, automated password/crypto keys collecting, process listing, and module/driver listing.
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Extending Java Performance Monitoring Framework with Support for Linux Performance Data Sources
Júnoš, Peter ; Bulej, Lubomír (advisor) ; Babka, Vlastimil (referee)
Title: Extending Java Performance Monitoring Framework with Support for Linux Performance Data Sources Author: Peter Júnoš Department: Department of Distributed and Dependable Systems Supervisor: Ing. Lubomír Bulej, Ph.D Abstract: Java Perfomance Measurement Framework (JPMF) is a library, that is able to hook into program and gain performance information in given watchpoints. Notable drawback of currect implementation are missing sen- sors, that would be able to measure performance statistics related to stor- age, CPU, memory and network interfaces under Linux. Linux does not provide unified way of accessing such performance statis- tics. They can be accessed using virtual file systems, syscalls and netlink interface. The goal of this work is extending JPMF, so that it will provide measurement of mentioned performance statistics in a Linux-specific way. Keywords: performance measurement, JPMF, Linux, netlink stats, procfs stats 1
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Debugging the SLUB allocator in the Linux kernel
Glitta, Oliver ; Babka, Vlastimil (advisor) ; Horký, Vojtěch (referee)
This thesis is focused on the SLUB memory allocator and its debugging functionalities. The SLUB allocator implementation included several tests, but nobody was running them. It was because no automated kernel testing infrastructure existed for them. This project added one of the kernel testing frameworks, the KUnit testing, for SLUB. Existing tests were integrated into this framework with some minor changes. Also, new regression tests were added based on a systematic review of commits associated with SLUB. Another part of the thesis extends the SLUB debug options for tracking allocation events, including more efficient stack trace storage. The last part improves the virtual file system debugfs that provide information about kernel components to userspace by including stack traces in SLUB's virtual files. Also, this project helps to track the efficiency of the SLUB cache usage in terms of object size. All of these changes to the Linux kernel should help with SLUB debugging. Some of the changes were also submitted and even accepted by the community, they were added into Linux version 5.14. 1
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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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