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William Cheng: Welcome to lecture.

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Lalit Gupta: Yeah. So hello professor. So I have a question in

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Lalit Gupta: The ancient in the VM map artsy

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William Cheng: Okay, let me switch screens to it.

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OK.

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Lalit Gupta: So the function of the math, science range.

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William Cheng: Okay, right. So that's the first fit algorithm. Yeah.

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Lalit Gupta: Yeah, so

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Lalit Gupta: So i don't i

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Lalit Gupta: Like, from what I understand is, we have a p. So we have a VM media and via media has a memory object and the memory of people, a lot of famous and that has pages inside it.

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Lalit Gupta: And so I thought, I thought, is when when the all the speakers are actually not free. If they are actually on this memory object. Right.

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William Cheng: Right, so the free the free spaces between the the memory segments.

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Lalit Gupta: Which

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William Cheng: Is kind of like the

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William Cheng: The sort of the opposite of the first fit algorithm that we talked about in chapter three. So, in chapter three. We keep track of the free blocks.

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William Cheng: So, so this first trade was that we would keep track of the allocated blocks.

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Lalit Gupta: Okay, so. Okay, so yes. Okay. So, so you're saying we have to be the know that whatever the whatever the whatever the region that is allocated.

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Lalit Gupta: And from

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Lalit Gupta: That we can somehow subtract out and find out what digits are free.

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William Cheng: Yeah, so anything between them. They're all free. Right.

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Lalit Gupta: Okay and. Okay, so those are not. Those are not those area do not have any

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Lalit Gupta: Pages allocated to it. So, so

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William Cheng: What is their allocate and then there's a VM area.

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Lalit Gupta: Wait. Now if I, if you

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Lalit Gupta: If you have a VMware. Yeah. And then we have the media gives us a range of range of address right and does the all that's all the range in the address has to have some patience associated with it.

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William Cheng: Was a memory segment. It's continuous, you know, virtual addresses. Right. So is that a VM area. There's no holes inside of that, but between the areas where the holes.

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Lalit Gupta: Oh, okay. So, seems like we we have to find a place the

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Lalit Gupta: Address started from the lake.

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Lalit Gupta: Yeah, we have to find a address which has no via media associated with it.

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William Cheng: Right.

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William Cheng: Right, so find find the, you know,

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William Cheng: You know, find the space in the gap.

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Lalit Gupta: I'm sorry, but

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Lalit Gupta: Yeah, yeah, what you're saying is making sense. But I just want to read it one more time so that

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William Cheng: For example, I over here. I'm going to sort of type example. Right. So, for example, one of the VMware is go from 10 1112 right so that's, you know,

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William Cheng: You know, a three at length of three pages, right, and then the next one is 15 1617 1819 so that's another one, five right and then followed by 500 by 100 and 102, you know, etc. So in this case,

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William Cheng: You know there are 10 pages at the beginning between zero and and and and before 10 right and then there's 13 and 14 so there's another empty space that's two pages long. I'm sorry.

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William Cheng: 1342 pages long. Right. And then, between these two. There's another gap that's, you know, you know, 500 minus 20 that's 480 pages long. And then at the end, compile three all the way to the end, the memory. There's another you know a free free

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William Cheng: free range.

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Lalit Gupta: Yes. Okay, so free range makes sense because the free version is next lesson, because these are the other places where it's a we do not have any virtual because pages means like

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William Cheng: Was born into this picture right. The, the, you know, the virtual page number zero to nine nobody's using it right

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William Cheng: And then from reversal page 13 and 14 there's no you know nobody using. So again, we can think about them as individual pages or it's easier to think about as

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William Cheng: As a range rather you have a beginning number and a link right and then over here, there's another range. You can also say that all these individual pages. They're all available if on 2021 all the way to 499

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William Cheng: It's the same thing.

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Lalit Gupta: Okay, yeah.

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Lalit Gupta: Even though I understand the structure to represent them right so

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Lalit Gupta: Okay, even though I understand. I feel like because pages slightly confusing because I always think that pages associated with the page frame and that is actually managed by a memory object.

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William Cheng: Well, it's because every patient can have many, many versions of it right so that's why things get complicated, right, because of copy on write all that kind of stuff. So, you know, so, so things are more complicated inside the operating system.

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Lalit Gupta: Okay, so I think there's no further than

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Lalit Gupta: And my next

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Lalit Gupta: Yeah, so they don't function in a VM map, map.

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William Cheng: Right, so that one is the one that I just answer some question in class move this morning. Yeah.

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William Cheng: So many, many arguments.

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Lalit Gupta: Yeah, can you go, can you can you start at the beginning of the moment.

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William Cheng: So, so again, this is the function that used to map a file into address space.

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William Cheng: So therefore you build a memory segments from a file.

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Lalit Gupta: Yeah. So it seems like it is. It will give us some

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Lalit Gupta: Location number and from that low page. And it also gave us pages to from that we can find a range that is not located that that is that that do that has no associated VM area with it.

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William Cheng: Wasn't like the example that I gave right 1011 right. So, so, you know, so you might end up with a so so when this one is done. So let's say that when this function is returning, you're going to have, you know, 10 1111 and 12

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William Cheng: Okay, so you'll build a memory map that's three pages long. Right now, that will be the result of this

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William Cheng: So in this case, I think, low page.

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Lalit Gupta: I cannot have 10 1112 because you already. We already have a VM media for 1011

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William Cheng: We'll start with the empty wine. So, you know, maybe this is the function, you are used to build the first 110 1112

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Okay.

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William Cheng: I think know page is a virtual page number so it will be 10 right and pages will be able to three right

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Lalit Gupta: Yes. So let's say we have a non do page. And it's, I think there's a comment in the same paragraph.

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William Cheng: Zero page.

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Lalit Gupta: If the low pages non do and specified region countries and other mapping, then that mapping should be unmapped

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William Cheng: Right.

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William Cheng: Yeah, so does the because so. So again, what's important to understand is that in the end.

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William Cheng: You know, the memory segments can overlap. Right. So if you try to map something in the memory and there's something already there. You have a map. The first

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Lalit Gupta: Basically, we have to remove that the media and

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William Cheng: You have to. You don't have to remove it, you need to

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William Cheng: You need to shrink it so that they don't overlap anymore.

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William Cheng: You don't necessarily have to remove it. Right, there's an overlap, you get rid of the overlap.

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Lalit Gupta: Yeah, if there's overlap, which we shrink shrink it or remove that part that is the overlapping part or shrinking you're removing that part which is overlapping

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Lalit Gupta: Right. And then, that part is now not being used by any memory. After we do that process and then we can create a

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Lalit Gupta: VM area.

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Lalit Gupta: For that for that range of actress.

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Correct.

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Lalit Gupta: Oh me know

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William Cheng: Right. So in this example. So let's uh, let's say that I already have a have a VM area that go from 10 1112 right okay so if I called VM M AP and low page equal to 10 and then n pages equal to three. I need to wipe out this entire area before and then build a new one.

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Lalit Gupta: Yes, yes.

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Lalit Gupta: And there's a comment. I think in this second paragraph, use the

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Lalit Gupta: vino

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Lalit Gupta: vino vineyard and map operation to get the MO, which are for the file it say now. Do not assume that it is file underscore VR ops. Why, why, why would it not be the case.

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William Cheng: Over here, this was this file is no the file is no and I'm not sure views in file is not know that Venus file will be mapped from the given range. Use the Venus. So let's take a look at that function. Where is that

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William Cheng: FS VN this one right. Is there a map function.

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William Cheng: Operation.

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Lalit Gupta: Operation.

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William Cheng: Okay, so over here. Yeah. So there's the one of the function over here is is a map right so i think it's asking you to use that for you. So let's take a look at the SV is this called does see

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William Cheng: So it's all in Vino de see Colonel FS vino see

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William Cheng: Okay, so there's read, and then there's right

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William Cheng: Special

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William Cheng: Okay. So inside the know there's a ray of function point or you're supposed to use the map function there to to do the operation now.

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William Cheng: Because others.

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Lalit Gupta: Yeah, so that I understand that you have to use this operation to get the memory object using that function.

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William Cheng: Yeah, we just got to trust that it works. And we just call it. Yeah.

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Lalit Gupta: Yeah, yeah. So this apart. I understand. But why I was just trying to just see why why they are, why they're stressing that do not assume that it is

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Lalit Gupta: File under arrow we have that memory of. Okay, so there will be an empty object that will be determined by this function and and there is also a member of that that is file. We are both our memory object.

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Lalit Gupta: What is the difference between too distant memory.

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William Cheng: Well, I think in the wind is kind of there's some other you know mmm LBJ code that's written for you that you don't know what they are.

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William Cheng: I think in the device driver. There's some other mm will be J. And sometimes those are the one that you have to use, right, for example, you don't want the map.

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William Cheng: Map of file into address space, you know, there's, I think there's the block device. And then there's a character device. So I think when you try to transfer data from the file into

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William Cheng: Memory, you have to use a block device, but we you know we didn't write the code there. So, so, you know, we should just, you know, sort of follow using the polymorphous in principle, just follow the pointer there.

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William Cheng: Cool. So, so there are other mo BJ that we don't that we don't write whether we can ride.

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Lalit Gupta: On I think I had related note, can you also go to this P frame dot c data essential function.

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William Cheng: Or no mmm keyframe that see

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William Cheng: Yes.

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Lalit Gupta: So here

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Lalit Gupta: We have SPP and MSP frame of jack, we get this memory of

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Lalit Gupta: From the speaking, we get a memory object.

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Lalit Gupta: Right and and memory and

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Lalit Gupta: Yes. And that has some operations available and we are calling Phil page.

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Lalit Gupta: And then we are giving the map, the Philippines X amount of the object. And I think that pitch him probably

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Lalit Gupta: I'm trying to understand

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Lalit Gupta: Is it, is it possible that this the argument that this object in the argument filthy document beef zero PM underscore opt and the the the

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Lalit Gupta: The function pointed out is that we are using PF underscore piece of data can be different.

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William Cheng: Yeah of course it's polymorphous than yeah

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William Cheng: So, so remember every page rank is identified by two things, right, the MO BJ that owns it, and also a page now. Right. Remember that

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William Cheng: Yes. Okay, so, so if you look at a PDF right over here. PM, right arrow PF LBJ right and then PDF of a PDF page now. Right. So if you use these to as the key, you will find the object. Right, so, so, so every page, page frame has a self identifying information that's stored inside of data structure.

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William Cheng: Okay, so therefore you can always just go to the object over here to find out you know which object actually own this page rank.

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William Cheng: Okay, and then you will. So in Colonel three, the kind of obviously you have to deal with is the one that's inside the vino and also there is the one that is the anonymous object. This is shut off yet.

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William Cheng: So if you want to fill the page with data, all you need to do is to call the Philippines function.

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William Cheng: Right over here, this function is called fill a page frame right okay we tried to fill a page frame.

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William Cheng: But depends on what kind of object it is there's a different function. They used to call. So therefore, we call the polymorphous to paste function.

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William Cheng: And then if it turns out that this is anonymous object then anonymous Phil page will get called if this one is the shadow object and shadow Phil page with your colleagues, but this one is the one the vino then the V read page will get called

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William Cheng: Does that make sense. Did you want to fill the page different ways, right, because, I mean, clearly, if you want to fill the page on the desk.

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William Cheng: You have to use a different operation. If you want to fill the data from anonymous, then you just create a page Twitter page, fill it with zeros.

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William Cheng: If you want to fill the page with a foreshadow object, you have to do the, you know, copyright, you have to find it. And you have to copy it. So they're all they're completely different.

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Lalit Gupta: Yes. So say we have a mess. Stevie because

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Lalit Gupta: I think, I think you are asking in relation to this, there is a function and an object. So sometimes we are already given a memory object and we have to we have to fill the page.

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Lalit Gupta: So do we have to call that filthy, filthy operation of that object that is given to us.

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William Cheng: Well, it depends on you know who's code that you're writing right if he already had an anonymous function that you know the object is anonymous function. Right. So in that case, you can just directly

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William Cheng: You know, you can call whatever function that's inside of web, but at this level where you know when somebody has a page rain is it filled with data, but they don't even know what kind of page frame it is right.

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William Cheng: Yes. Well, in that case you need to call a higher level function because high low function will use appalling morphic pointer to to to to to to sort of deal with how to

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William Cheng: How to fill a page right because filling a page we needs to be, you know, sort of a memory object mmm object independent way to Philip, Philip pace. Right.

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William Cheng: Right. So if you're doing something that's independent of the mm object. Well, then in that case you will call this function.

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Lalit Gupta: Starting this multi objective.

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William Cheng: Is that are really means is that if you have a page frame, you don't really know what kind of what it is because the polymer prism right

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William Cheng: So they will all you have to do is to call the function right over here says why this is how you call the function and then you trust that you know if everything is set up correctly, while then the in this case the right, the right function will be called

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William Cheng: You know, like the example that I gave in class. Right. That's a you have a disk up Jaguar you tell this object to say read data from the data into memory.

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William Cheng: He said, well, but I don't know what kind of disk it so it doesn't really matter. You just, you just use that this point or call a function and then you know polymorphous and we'll take care of it.

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William Cheng: So this is the same situation. I have a page frame, I need to fill it. I don't know what kind of pays for him. It is. It's okay, just call the palm of a function and then the right, the right kind of stuff will happen. I mean, assuming that all the pointers are set up correctly.

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William Cheng: Okay. So, by the way, you know, for this code. If you set a breakpoint. A P frame fill or set a breakpoint right on this line. Okay.

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William Cheng: Will you get there you can actually print use a print PM, right arrow pa pa or BJ. And then, and then you know. Mm, oh underscore OBS it will actually tell you what functional will call

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William Cheng: It will say anonymous filters over here. It's a real function pointer. Right, so it will actually show you that this one is this one Billington anonymous object is one bill to the shadow object. This one belongs to the by device to help us even show that

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William Cheng: You know, so, so, so, so set a breakpoint here and that you can actually see what kind of, you know, a real function point you get

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Lalit Gupta: Oh,

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William Cheng: Russia remember all these functions. They all these functions are in the data structure. So when you print PLP LBJ mmm LPS they are you going to get that the name of that a real function pointer.

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Lalit Gupta: Sometimes what happens is if you if you were to this this which which fine.

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Lalit Gupta: I think it's VM memorable ops are underscore upstart see we are we have to pee French

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William Cheng: Colonel

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Lalit Gupta: Colonel Fs.

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William Cheng: SF s

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Lalit Gupta: in Malmo

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Lalit Gupta: One. Yes. Okay.

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Lalit Gupta: If you look at this

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Lalit Gupta: Maybe we dirty page something in this

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William Cheng: Dirty page.

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Lalit Gupta: Yes. In this case, we have this because of that the frame itself has a memory object. And now we are also having another memory object so

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William Cheng: Yeah, so, so I think P frame PF underscore LBJ, I think it's equal to em, they're the same thing.

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Lalit Gupta: Oh dear. Same thing.

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William Cheng: I think so. Okay, remember every page frame inside of a store self identifying information which M. O. B data belongs to. And also, what is the page now.

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William Cheng: Okay, so, so, so this is I, you know,

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William Cheng: It will kind of make sense that you will use the same object is what is IP for it.

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Lalit Gupta: Yeah, that makes makes sense so

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William Cheng: If you want to make sure you can add another you can add another line over here i k assert obsesses a kisser PDF. PDF LBJ

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William Cheng: Equal. Oh.

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Lalit Gupta: Yes.

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William Cheng: Again, you know, you want to make sure that they're the same. You can just add a concert. So this way if it turns out that's not true. You're going to crash and then then they, you know, OK.

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Lalit Gupta: OK, I think. So this to me. Try to look this way. Okay.

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William Cheng: Yeah, so, so for your for the vino I'm pretty sure that the Wii and ops over here. So again, if you set a breakpoint right here. I could print be an ops. I think that will be the the by device array of function pointers.

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William Cheng: OK. OK. So I think, whereas the colonel drivers right device to see

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William Cheng: Her know maybe it's in Vino de see

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William Cheng: Yeah, here's the by device right array of function pointer is you know so. So what we do is that, the better you will. I think you will see the name of this real function pointer is by dev spec VR Ops or something like it is a device.

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William Cheng: Yeah, I think a vino can be represented a, you know,

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William Cheng: Sort of a keyboard device.

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William Cheng: That this device, you know, but at the higher level. It's either character device or a block device.

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Lalit Gupta: Okay.

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Lalit Gupta: But we didn't write all those code because those codes are in, you know,

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William Cheng: I guess the in the drivers.

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William Cheng: Assignment that we didn't do

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Lalit Gupta: Yeah, actually. Sometimes, if you like, if we actually had those like this as five and tribal court, I would like, we could probably like trace back to the actual thing. What is actually happening. But that's fine.

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William Cheng: Yeah, but then everybody in this class will be dead. Yeah.

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Lalit Gupta: Yes.

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Lalit Gupta: Okay, so another thing is

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Lalit Gupta: The in the

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Lalit Gupta: In the VM area of data structure, we have this

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Lalit Gupta: member variable which has which takes which which which takes here of the, what is the protection at has the VM area.

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William Cheng: Which function that is which was filed, Colonel.

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Lalit Gupta: colonel colonel.

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Lalit Gupta: Include VM.

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Lalit Gupta: And I think we met dot html thought it's probably

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William Cheng: Okay, which feel so

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William Cheng: Yeah, Mary, I guess.

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Lalit Gupta: Yeah, yeah. The

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Lalit Gupta: DMA plot the provision of mapping

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Lalit Gupta: And we have this permission and the page table also so he will also have a permission. That is it is it has a bit. I think it's a sec.

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Lalit Gupta: I think the second was

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William Cheng: Okay, the

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Lalit Gupta: Page has

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William Cheng: Got to be very careful, right, because they need to match the hardware.

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William Cheng: Okay, the VM area that's just a data structure inside the current. All right, so remember the the the VMware production can be what you know execute read and write and things like that.

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Lalit Gupta: Yeah, it has full kind of protection. Whereas, whereas the x86 only has one bit for protection, either it is a reader. Right.

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William Cheng: Right so so inside the VM area right that you know that information is not hardware specific

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William Cheng: Okay, so typically can be more general. But when you try to put things inside of page table, whether in that case you have to look up the

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William Cheng: You know, the hardware manual to see exactly which bill that you're allowed to set right so i think for Intel. There's no execute bit you know inside the page table entry. Yeah.

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Lalit Gupta: There is no. You're the only one.

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William Cheng: Right, so, so, so in that case, when you look at the VMware where you need to ignore the execute it.

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William Cheng: Because all you care is whether that page table. Well, actually, a four page table entry, you need to manipulate it right because when you're doing copy on write your first you have to set it to read only. So they don't really have to reflect exactly why is that a VM area right

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William Cheng: Because you're doing copy on write

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Lalit Gupta: Oh,

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Lalit Gupta: Okay, so

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Lalit Gupta: In which case is Candice. Candice to be different this VM and this that and the pasty will entry, but we should

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William Cheng: We should always be, you know, I mean, always assume the worst case that that can be done guys. So, for example, right, I mean, how you know you need to copy on write right if the BMA flag is private, right, and also the protection over here is is rewrite

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William Cheng: Right, that by definition, you know, if the if the memory segment is private and rewrite you are performing copy on right

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William Cheng: Okay, so that means that when you set up the page table entry, you know, before you, you know, be be before you actually, you know, carbon copy on write well in that case should be read only. And, you know, from that point on, you know, if you

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William Cheng: If you try to write to it, then in that case you need to perform copy on write and from this point on that page table entry will be right.

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Lalit Gupta: OK.

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William Cheng: So again, the VM area just give you a hint of what to do in case, in case you get a page home.

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Lalit Gupta: Okay, so it seems like this this database. The page differently, but can change depending on when we do copy after we to copyright and before that it becomes a read only to rewrite

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Lalit Gupta: You and this is equal to zero, right, to, to be invalid. Yeah.

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Lalit Gupta: Yes.

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William Cheng: It is invalid and everything else is wrong. So you just ignore it.

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Lalit Gupta: But this VM a plotter roughly the same.

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William Cheng: Well, because when you create a memory said when you have to, you have to remember it, because that's that's the memory segments created by the

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William Cheng: Well, I mean, in the beginning, when you do the hello program the memory segment is created by the loader. Right.

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William Cheng: So the loader tell you that this memory segment is read only this memory segment is rewrite. Well then, then you have to follow the instruction to remember them that this memory segments read only. And the other segments. Right.

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William Cheng: Yes. Okay, so this way you will implement things correctly right if you ignore the instruction from the loader. Well, then in that case doesn't work.

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William Cheng: Okay, and later on when you do the end map system call you try to map them, you know, memory segment on the DIS into

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William Cheng: This into your address space. So in that case, you need to look at the arguments and map my, I guess it's a map does

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William Cheng: The, the argument of of em map is very similar to VM map, map where the first function that we look at.

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William Cheng: Okay, so in that case you can map a file into your address space read only rewrite, you know, these different ways. Again, you need to remember how you map it right

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William Cheng: Because at the time when you map it he checked for permission to make sure everything's okay and then from this point on, you're going to use it. So again, you remember how you

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William Cheng: How you set up the protection when you first when you create the memory segment.

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Lalit Gupta: Did is just like a minor doubt like it not doesn't even matter. So it's a cardinal API ex ex ex Nazi

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William Cheng: Or no API.

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William Cheng: Alright.

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Lalit Gupta: So if you go to this user land entry. Why, yes, the user and anti friendship.

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William Cheng: Okay, yeah, the assembly call. Yeah.

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Lalit Gupta: Yeah, so we have this first interact disabled.

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Lalit Gupta: Yeah. And then, why, why are we setting this IPL till after this interface disabled.

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William Cheng: Um, you know, when you said IPL too low.

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William Cheng: So, so let's say we can call this function right the IPL is is high.

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William Cheng: Okay. And then if you set up if you don't disable interrupt and you said IPL too low, then maybe something terrible get delivered

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William Cheng: So we here if you disable interrupt and then you said IPL too low then in a row, and I get a little bit

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Lalit Gupta: But even if he said the IPL too high, we should not also get the word because we have into stable, they interrupt.

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William Cheng: Well, so what happened is that when you go into the user space right as soon as you get into us page you want to enable interrupt maybe doesn't use a space program can always be preempted.

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William Cheng: Yes. Okay. So, therefore, you want to sort of set everything as low as possible so IPO needs to be below and also the, you know, we need to be, you know,

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William Cheng: I guess we'll you execute I return instruction, he will change from interrupt disable to enable

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Lalit Gupta: Oh, OK.

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William Cheng: OK. So I think there's an implied enabling interrupt me as if I return. And that's why you haven't disable it first.

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Lalit Gupta: Okay, okay. Then, then this low makes sense because then after that all their church should be

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Lalit Gupta: Accepted

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William Cheng: Well, so

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William Cheng: So this is kind of like, you know, chapter two, I will we tried to wind up the alarm clock, we need to, sort of, you know, disable

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William Cheng: We need to block the signal or something like that. So I think this is related to, you know, waiting for something as simple and as you and you got to make sure that you know asynchronous event cannot mess you up.

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William Cheng: So the right way to do it is to, you know, sort of the same in this case you're dealing with the anaerobic disabled first and then you can set IPL too low.

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William Cheng: Okay, if you don't disable it. I think there's going to be a race condition or some sort

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Lalit Gupta: Cool, so

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Lalit Gupta: Can you can you repeat it in this this particular set this

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William Cheng: So in chapter two. I did there was this example we try to, you know, why not have the alarm clock. And then there's a possibility that we might miss it. Right.

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William Cheng: So, therefore, what we do is that we blocked the signal first right and then why not be alarm clock and then we're going to wait for in one atomic operation.

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William Cheng: Okay, so I think the idea we hear this code is also very, very similar. We need to, you know, a block something and then India when we execute I return instruction that on blocks it

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William Cheng: And you know, I don't know, maybe you're not really waiting for interrupt, but I'm block and then you wait for the interruption one atomic operation.

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William Cheng: But in but in this case you when you go into the user space. Okay, so I think if you don't do these kind of things properly, you're going to end up with a race condition.

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William Cheng: Okay, okay, by looking at this code, I cannot tell exactly where the race condition it but I'm thinking that this must be the reason

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William Cheng: Okay, you can want to make sure you don't have a race condition this you know this code over here is written by the Brown University people and we assume they know what they're doing.

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William Cheng: Okay, so the proper way to, to, to not to have a race condition over here is you know you disable the interim and you said, I feel too low. And then what you do. I return you enable a narrow and never interrupt. And then, you know, if you rub is going to happen is going to get delivered safely.

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OK.

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William Cheng: OK. And again, before you know this Cohen men in the middle of here whenever you see a bunch of assembly coach says, Oh, well, you know, those things are CPU dependent right because they're assembly code.

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William Cheng: So therefore that's hardware abstraction layer cover. I will. You're using the horror objection. They are code over here.

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William Cheng: You want to make sure that you don't get another interrupt because if you get interrupted going to destroy data structure inside of our websites and so therefore I need to you know make sure bad things, doesn't happen.

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William Cheng: Okay, so, so therefore you have to disable to interrupt. Okay. And then in order for you to get ready to re enable the interrupt you need to say IPL to look

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William Cheng: So good.

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William Cheng: I think the other way to do it is that you said IP out low right before you execute I return.

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Lalit Gupta: Okay.

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William Cheng: But you know, I think the code is not written that way because over here. Here's the assembly code, right. It's kind of hard to insert a C function call in the middle of assembly code. So what they do is that they actually they switch the order

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Lalit Gupta: Okay, this seems like something similar mean the idea because instead switch there is a thing. I think at some point, you said there there's going to be a

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Lalit Gupta: This how this condition. And this seems like the idea seems like seems similar kind of thing we have to hold the CPU and then we have to wait for an asynchronous event in a correct way so

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Lalit Gupta: Okay.

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William Cheng: Okay, I'm laughing

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William Cheng: Yeah.

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William Cheng: You got it.

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Lalit Gupta: Thank you.

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William Cheng: See, this is why I'm asking people to read the code, read the code.

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Lalit Gupta: Yeah, there's a hint lake on

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William Cheng: The right question to say, well, why did they do this, why, why, and then maybe that's a good reason.

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Lalit Gupta: I think you know pieces of the doubt. I think

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That

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William Cheng: Alright, so, so I'm going to end the you know the today's live lecture, then. Okay. Okay. Thank you. Alright. Bye. Okay, bye.