Operating Systems 2017F Lecture 19 - Revision history

Aleksp: /* Additional Notes */

2017-12-07T17:20:06Z

Additional Notes

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 * Memoryll.py program <br>
 * Always unmount a filesystem when youre done using it <br>
-*No class Thursday! no office hours on Wednesday
+==== Tut 7 ====

HebaJallad: /* In Class */

2017-12-07T16:19:08Z

In Class

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	</pre>		</pre>


			Additional Notes:

			Important notes:
			How can you recover a filesystem?
			How do you delete a file?
			What is a filesystem?:
			*persistent data structure
			* stored in fixed-sized blocks (at least 512 bytes in size)
			*maps hierarchical filenames to file contents
			*has metadata about files (somwhow)
			What is in a filesystem?
			*data blocks
			*metadata blocks
			How do you organize metdata:
			1) First you must identify characteristics of the file system
			Superblock : summary y block which tells you about the other blocks you have and it depends on which file system you have. It’s usually the first block of a file system.
			In the superblock? :
			1) What kind of file system is this? By checking what is the magic number it has
			2) How big is the file system?
			3) How is it organized?
			4) Where can I find the rest of the metadata?

			*How can you identify which file system it is from looking at the super class
			-> google “magic number of a file”
			-> ex: jpg ctr^c ctr^c : switched the pictures into a binary file
			-> look at the beginning of the file you will see JFIF: first several bytes in general that identifies the type of the file (magic number)
			File extension :
			 what is it ?
			 is it important
			 the kernel does not know and not care about it

			For POSIX file systems:
			-.> file metadata is stored in inodes
			-.> most have pre-reserved inodes
			-> the only way you can run out of inodes if you keep creating small files

			Usenet : al the things you use to post messages thro social media, email, etc. Those were made using Usenet. Like email but Local Usenet server. But it died over time. Every message is stored in an individual file.





			Important commands:
			File * : to identify the kind of file system
			1. As : Run dumpe2fs foo. What does the output of this command mean?
			 Does this give you info about the file system?
			 File bar : bar is the file name and cp comp3000-midterm-2017.pdf bar
			 Evince bar : opens up the pdf file

	=== Additional Notes ===		=== Additional Notes ===

Soma: /* [Notes] */

2017-11-21T19:24:42Z

[Notes]

@@ Line 1: / Line 1: @@
-== [Notes] ==
+==Video==
-Sample
+[http://homeostasis.scs.carleton.ca/~soma/os-2017f/lectures/comp3000-2017f-lec19-21Nov2017.mp4]
-sample<br>

Krithikasaravanan at 19:21, 21 November 2017

2017-11-21T19:21:30Z

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	-> unmount the file system when you are done using it <br>		-> unmount the file system when you are done using it <br>
	-> umount / you have to do it as root <br>		-> umount / you have to do it as root <br>

			Node web applications <br>
			* Theres not a dedicated main function but its the first thing that runs <br>
			* Every line in the node application terminates <br>
			* If you start a web server, the function call starting it will terminate <br>
			* Whats running? The main has finished. Is the program doing anything actively if theres no external input? <br>
			* In many systems main just sets up event handlers <br>
			* The event loop can be implicit or explicit <br>
			* Its possible to have no loop at all just handlers and interrupts of some kind <br>
			* Event loops check to see when there are new events <br>
			* Os kernels behave the same way as node applications <br>
			* Waiting for events <br>
			<br>

			What happens when you use insmod? <br>
			* In newgetpid: Init and exit are called when the insmod program makes system calls to load the module <br>
			* Init is run on behalf on insmod <br>
			* Kernel code fits into 3 categories <br>
			** Code that runs on behalf of a process <br>
			** Code that runs after an interrupt <br>
			** Kernel threads, has lots of functionality <br>
			<br>
			Why is a kernel thread not a process? <br>
			* The kernel maintains its own address space <br>
			* Has its own virtual address map <br>
			* The kernel always has just 1 address space regardless of how many threads there are <br>
			* Processes cannot manipulate its own memory map directly, needs to ask kernel first <br>
			* Processes are limited, the kernel is not, has control over itself <br>
			<br>
			* Kernel tasks = kernel threads <br>
			* Independently scheduled <br>
			* Once we call insmod everything happens in user space <br>
			* Strace uses a system call called ptrace <br>
			<br>
			Tutorial 7: Fuse <br>
			* Memoryll.py program <br>
			* Always unmount a filesystem when youre done using it <br>

HebaJallad at 19:14, 21 November 2017

2017-11-21T19:14:51Z

@@ Line 9: / Line 9: @@
 Where's main?
-* lots of program shave "main" functions - a function that runs first and controls the execution of the program
+* lots of program shave "main" functions - a function that runs first and controls the execution of the program<br>
-* Do these have "main" functions?
+* Do these have "main" functions?<br>
-** Linux kernel modules
+** Linux kernel modules<br>
-** FUSE applications?
+** FUSE applications?<br>
-** the linux kernel?
+** the linux kernel?<br>
-** node web applications?
+** node web applications?<br>
@@ Line 68: / Line 68: @@
-OS kernels are essentially the same thing
+OS kernels are essentially the same thing<br>

KYuan: /* Additional Notes */

2017-11-21T19:14:32Z

Additional Notes

← Older revision		Revision as of 19:14, 21 November 2017
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			When running <br>
			"time ls" <br>
			real = realtime it took to run
			user = the user space time
			sys = kernel time


			What's flow of control in tutorial 7? <br>
			What is the connection? <br>
			To exit the program, we must unmount the filesystem, run "sudo umount mnt" <br>


	OS kernels are essentially the same thing		OS kernels are essentially the same thing

HebaJallad at 18:56, 21 November 2017

2017-11-21T18:56:50Z

← Older revision		Revision as of 18:56, 21 November 2017
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	== [Notes] ==		== [Notes] ==

	Sample ~~<br>~~		Sample
	sample<br>		sample<br>

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	multi- threaded: maintains multiple address processes , ex: fire fox. <br>		multi- threaded: maintains multiple address processes , ex: fire fox. <br>

	ps -elF \| less "number" : ~~displayes~~ threads.		ps -elF \| less "number" : displays threads.

			top : displays all the processes <br>

			ls time : shows you the time .

			sys: how much time in the kernel space
			real: how much time
			user : how much time in user space

			process : can't manipulate its own memory map directly, it has an address space, but cant change it. Process: is limited but the kernel is not and the kernel can change it's own address and in charge of its self. <br>

			Kernel tasks : are threads, when a process makes a system call , thi sis schedules in the process priority. <br>

HebaJallad: /* [Notes] */

2017-11-21T18:50:28Z

[Notes]

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	In many systems, "main" just sets up even handlers		In many systems, "main" just sets up even handlers<br>
	* the event loop can be implicit or explicit		* the event loop can be implicit or explicit<br>
	** or there may be no loop at all, just handlers and "interrupts" some kind		** or there may be no loop at all, just handlers and "interrupts" some kind<br>
	* event loops poll (check) to see when there are new events		* event loops poll (check) to see when there are new events<br>
	* what are event loops for node app?		* what are event loops for node app?<br>
	** where are interrupts for node apps?		** where are interrupts for node apps? <br>
	***Incoming network requests, it's an event		***Incoming network requests, it's an event<br>

			Code run differently in the kernel : <br>

			1)functions runs on the bhealf of insmod, unles sit is Independence context <br>

			2)codes that run on the bhelaf o the process<br>


			3)after an interrupt: no process , it is an interrupt cotext <br>

			4) file names : regular programs but the square brackets, execution context + address space. they share the kernel's address space, they are called kernel threads which are independently scheduling . You can not kill them but you can change their scheduling , maybe their priority but not 100%. <br>

			does it create a proces? no , but it can create a kernel thread (is it a process? virtual adress space, .<br>
			multi- threaded: maintains multiple address processes , ex: fire fox. <br>

			ps -elF \| less "number" : displayes threads.




	OS kernels are essentially the same thing		OS kernels are essentially the same thing

KYuan: /* Additional Notes */

2017-11-21T18:37:13Z

Additional Notes

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 ** FUSE applications?
 ** the linux kernel?
-** node web applications
+** node web applications?

KYuan: /* [Notes] */

2017-11-21T18:31:42Z

[Notes]

← Older revision		Revision as of 18:31, 21 November 2017
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	Sample <br>		Sample <br>
	sample<br>		sample<br>


			=== Additional Notes ===

			Where's main?
			* lots of program shave "main" functions - a function that runs first and controls the execution of the program
			* Do these have "main" functions?
			** Linux kernel modules
			** FUSE applications?
			** the linux kernel?
			** node web applications