https://homeostasis.scs.carleton.ca/wiki/index.php?action=history&feed=atom&title=Operating_Systems_2022F_Lecture_18 2026-04-05T22:41:56Z Revision history for this page on the wiki MediaWiki 1.42.1 https://homeostasis.scs.carleton.ca/wiki/index.php?title=Operating_Systems_2022F_Lecture_18&diff=24145&oldid=prev 2022-11-17T22:06:22Z

<p>Created page with &quot;==Video== Video from the lecture given on November 17, 2022 is now available: * [https://homeostasis.scs.carleton.ca/~soma/os-2022f/lectures/comp3000-2022f-lec18-20221117.m4v video] * [https://homeostasis.scs.carleton.ca/~soma/os-2022f/lectures/comp3000-2022f-lec18-20221117.cc.vtt auto-generated captions] Video is also available through Brightspace (Resources-&gt;Zoom meeting-&gt;Cloud Recordings tab) ==Notes== &lt;pre&gt; Lecture 18 ---------- Side note: - there are only *thre...&quot;</p> <p><b>New page</b></p><div>==Video==<br /> <br /> Video from the lecture given on November 17, 2022 is now available:<br /> * [https://homeostasis.scs.carleton.ca/~soma/os-2022f/lectures/comp3000-2022f-lec18-20221117.m4v video]<br /> * [https://homeostasis.scs.carleton.ca/~soma/os-2022f/lectures/comp3000-2022f-lec18-20221117.cc.vtt auto-generated captions]<br /> Video is also available through Brightspace (Resources-&gt;Zoom meeting-&gt;Cloud Recordings tab)<br /> <br /> ==Notes==<br /> <br /> &lt;pre&gt;<br /> Lecture 18<br /> ----------<br /> <br /> Side note:<br /> - there are only *three* rendering engines that can handle the modern web:<br /> - Blink (Chrome), a fork of WebKit<br /> - WebKit (Safari)<br /> - Gecko (Firefox)<br /> <br /> Note Edge uses Blink<br /> <br /> On iOS everything must use WebKit, so even Firefox on iOS uses WebKit not Gecko<br /> (On Android things are different, Firefox is its own thing there)<br /> <br /> A3 is due on Monday, Nov. 21st<br /> - will be accepted until just before class on Tuesday, Nov. 22nd<br /> - I&#039;ll be posting solutions and going over them in class on the 22nd<br /> - so T5 &amp; T6 is also due then<br /> <br /> A4 will be released before Nov. 21st<br /> - T7, T8, &amp; T9 will be due when A4 is due on Dec. 7th<br /> <br /> <br /> Tutorial 8 (cont.)<br /> ----------<br /> <br /> Remember that all devices have a major and minor number<br /> - major number designates the driver<br /> - minor specifies which device (in case one driver can be<br /> responsible for multiple devices)<br /> <br /> When we create a new device with a module, we must allocate a new major number for this device (dynamically) and then we can number off our own devices for the minor number (so, probably just use 0 if we just have one instance)<br /> <br /> In ones_read(), why do we call put_user() rather than just writing something like<br /> *buf++ = &#039;1&#039;;<br /> <br /> Remember that buf is a pointer to userspace, i.e., the address space of a specific process!<br /> - we have to treat accessing userspace differently from regular kernel data<br /> <br /> Remember that every process, and the kernel itself, have their own address space<br /> <br /> <br /> Also, note that ones_read() only writes a finite amount. Why does reading from /dev/ones appear infinite?<br /> - where is the loop that makes it infinite? Is it in the kernel?<br /> - NO, it is in userspace!<br /> - it becomes infinite because programs keep making read system calls<br /> because they don&#039;t get an end of file<br /> <br /> &quot;current&quot; in the Linux kernel always refers to the currently running task (process/thread)<br /> - in other words, the task that made the system call that got us into the kernel<br /> - in the kernel, a &quot;task&quot; is the abstraction applied to kernel threads and processes<br /> - a task is something that can be run on a core<br /> <br /> <br /> How did I know to use task_tgid_vnr() to get the process ID of the current task?<br /> - look at the source for the getpid system call!<br /> <br /> When you want to do something in the kernel, best bet is to find source from a part of the kernel that does something similar<br /> - then you can adapt what it does to your problem!<br /> &lt;/pre&gt;</div>

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