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1 title: Studying Operating System Using Docker Platform
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2 author: Shivani Dubey
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3 profile: Madan Mohan Malaviya University of Technology, Gorakhpur
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5 ## Why do we study Operating System?
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6
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7 - Every computer system has an operating system, which manages the resources of the computer.
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8
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9 - IoT or IT Services can't work well without resource managements.
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10
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11 - To handle it, we have to understand the API of OS.
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12
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13 - To understand the API, it is better to see the implementations.
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14
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15 - For example, API for tuning priorities of the processes.
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16
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17 ## Xv6 Operating System as an educational tool
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18
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19 - A Unix-like operating system developed in MIT, based on V6 kernel
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20
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21 - xv6 is written in ANSI C ( not in C++ )
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22
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23 - xv6 is small and simple (9628 lines of codes)
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24
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25 - It can run on Raspberry Pi ( Small PC board )
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26
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27 - Or on ARM emulator such as QEMU
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28
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29 ## Xv6 development environment with QEMU
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30
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31 - QEMU emulates ARM CPU with virtual memory
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32
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33 - Xv6 operating sytem itself is running on QEMU
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34
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35 - gdb debugger can be attached to the emulated program (both in user space and system space)
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36
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37 - We can step and trace inside xv6 kernel
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38
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39 ... but it requires complex development environments setup
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40 ... very time consuming
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41
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42 ## Our development environments
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43
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44
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45 - homebrew (it simplifies installation of software in macOS)
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46
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47 - Mercurial repository of the lab where we saved everything using ssh
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48
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49 - Cross Compilers
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50
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51 - ARM libraries for C language
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52
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53 - QEMU (ARM Emulator)
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54
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55 ## Introducing Docker
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56
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57 - What is Docker? It is a container.
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58
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59 - What is Container? An isolated envirornment such as file system.
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60
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61 - It has DockerFile, which describes how to setup the envrionment in the container.
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62
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63 - Docker can run on any computer using an emulator such as QEMU.
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64
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65 - Complex development environment can be build using DockerFile and docker built command.
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66
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67 # The DockerFile
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68
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69 ```
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70 FROM phitek/qemu-arm
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71 RUN apt-get update -y
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72 RUN apt-get remove gdb -y
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73 RUN apt-get install gcc-arm-none-eabi gdb-arm-none-eabi qemu-system-arm -y
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74 WORKDIR /code
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75 COPY ["src", "."]
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76 RUN make
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77 CMD /bin/bash
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78 ```
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79
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80 - FROM line specifies the shared image in Docker repository.
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81
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82 - apt-get installs Linux cross compiling tools.
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83
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84 - Then it creates working directory, copies our sources to it, and executes make.
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85
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86 ## Docker commands
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87
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88 - Create docker image and environment, and build xv6 kernel
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89
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90 docker build --tag xv6-docker
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91
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92 - Run xv6 kernel on QEMU in the container
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93
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94 docker run --rm --privileged -it xv6-docker ./run-debug.sh
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95
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96 - Run gdb to connect the xv6 kernel running in the QEMU
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97
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98 docker exec -it xv6-docker ./debug.sh
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99
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100
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102
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103
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104 # Exercise : Adding priorities to the xv6 scheduler
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105
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106 - Added getpriority() and setpriority()
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107
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108 - get_highest_priority() functions in proc.c file of xv6
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109
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110 - Implemented it in schelduler()
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111
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112 - Added a test function testpriority() in usertests.c file of xv6 to implement our algorithm
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113
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114 ## Function used in our exercise to find highest priority process
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115 ```c
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116 int get_highest_priority_proc(void)
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117 {
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118 int highest_priority;
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119 int pid = 0;
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120 int hpid = -1;
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121 int rpid = 0;
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122
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123 highest_priority=100;
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124 struct proc *p;
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125 for(p = ptable.proc; p < &ptable.proc[NPROC]; p++, pid++){
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126 if(p->state != RUNNABLE) {
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127 continue;
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128 }
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129 rpid = pid;
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130 if (highest_priority > p->priority) {
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131 highest_priority=p->priority;
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132 hpid = pid; }
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133 }
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134 return hpid > 0?hpid:rpid;
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135 }
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136 ```
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137 - It assumes at least one process to be RUNNABLE.
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138
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139 - It may allow no highest priority process.
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140
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141 - The correctness of the function is *important*.
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142
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143 ## Docker Limitation
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145
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146 - If repository breaks, Docker poses a problem (a cloud problem).
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147
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148 - Cloud may be used conveniently but we must not rely on it.
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149
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150 - We can use a direct environment without Docker, since we have a Linux server.
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151
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152 - Docker images can easily eat up our disk spaces.
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153
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154 in ~/.zsh_history
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155
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156 ```c
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157 : 1561014922:0;docker system prune
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158 : 1561014973:0;docker container prune
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159 : 1561015350:0;docker image prune
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160 : 1561015362:0;docker volume prune
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161 ```
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162 # Conclusion
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163
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164
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165 - Docker environment poses some problems, some of which are difficult to comprehend.
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166
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167
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169 - Yet, it gives a good insight of the underlying important concepts of operating system because it is well documented, fast and uses less resources.
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