1 00:00:00,005 --> 00:00:03,003 - [Instructor] Let's look at kernel's source code. 2 00:00:03,003 --> 00:00:09,008 So I cloned the Ubuntu Noble repository like this, 3 00:00:09,008 --> 00:00:12,007 like we showed earlier. 4 00:00:12,007 --> 00:00:15,003 That took a little while. 5 00:00:15,003 --> 00:00:19,001 And then I got something like this 6 00:00:19,001 --> 00:00:22,003 and I've done a make cscope and a make tags in here 7 00:00:22,003 --> 00:00:25,003 and that's why I've got those cscope.files 8 00:00:25,003 --> 00:00:28,005 and I've got the file called tags. 9 00:00:28,005 --> 00:00:32,003 You can see kernel Makefile is in here. 10 00:00:32,003 --> 00:00:37,000 Let's see how much space this takes up. 11 00:00:37,000 --> 00:00:41,004 Hoo, seven gig, pretty big. 12 00:00:41,004 --> 00:00:46,007 And get an idea of how many tags 13 00:00:46,007 --> 00:00:50,001 they have in the repo here we cloned. 14 00:00:50,001 --> 00:01:00,008 That start with the string ubuntu dash. 15 00:01:00,008 --> 00:01:03,003 What did I do different? 16 00:01:03,003 --> 00:01:06,004 You got to capitalize the U in Ubuntu. 17 00:01:06,004 --> 00:01:07,006 All right. 18 00:01:07,006 --> 00:01:12,004 And if we look at the Makefile, 19 00:01:12,004 --> 00:01:15,008 we can see the version there, so forth. 20 00:01:15,008 --> 00:01:19,008 How long is the Makefile? 21 00:01:19,008 --> 00:01:23,008 Over 2000 lines long. All right. 22 00:01:23,008 --> 00:01:29,009 And with that kind of length, having a help in there is nice. 23 00:01:29,009 --> 00:01:32,004 Get an idea. 24 00:01:32,004 --> 00:01:33,009 Starts with cleaning targets 25 00:01:33,009 --> 00:01:38,003 and there's lots of stuff you can make, right? 26 00:01:38,003 --> 00:01:41,007 And these days you can write kernel code in Rust. 27 00:01:41,007 --> 00:01:44,009 So there's a bunch of Rust stuff there. 28 00:01:44,009 --> 00:01:48,008 Let's make a PDF doc. 29 00:01:48,008 --> 00:01:53,003 So here's making the scheduler PDF. 30 00:01:53,003 --> 00:01:54,008 I already did that. 31 00:01:54,008 --> 00:01:57,003 That's part of the disk space taken up is 32 00:01:57,003 --> 00:01:59,003 I was doing stuff like this. 33 00:01:59,003 --> 00:02:04,003 The fresh clone was a little over four gig, not seven gig. 34 00:02:04,003 --> 00:02:10,004 And if we look in the Documentation/output/scheduler/pdf 35 00:02:10,004 --> 00:02:14,004 directory, there's the PDF. 36 00:02:14,004 --> 00:02:18,002 So I already did a make cscope 37 00:02:18,002 --> 00:02:19,004 so I'm not going to do that again. 38 00:02:19,004 --> 00:02:23,003 And I did a make tags so I'm not going to do that again. 39 00:02:23,003 --> 00:02:25,000 Those are ready to go like I showed you. 40 00:02:25,000 --> 00:02:26,008 So let's go cscope -d. 41 00:02:26,008 --> 00:02:30,008 The -d says don't make a new index, I already got one. 42 00:02:30,008 --> 00:02:33,006 And we get this simple little interface 43 00:02:33,006 --> 00:02:35,002 but we've indexed the kernel source code 44 00:02:35,002 --> 00:02:36,008 so we can look in the kernel source. 45 00:02:36,008 --> 00:02:38,002 So let's look. 46 00:02:38,002 --> 00:02:41,001 There's a cool function called copy_to_user 47 00:02:41,001 --> 00:02:46,000 that's used throughout the kernel by device drivers 48 00:02:46,000 --> 00:02:49,001 and other things, to copy stuff back to user space, 49 00:02:49,001 --> 00:02:53,003 like when a process calls read, goes in the kernel, 50 00:02:53,003 --> 00:02:56,003 the kernel's got to fill stuff into that user space buffer 51 00:02:56,003 --> 00:02:59,001 to return that can use copy_to_user. 52 00:02:59,001 --> 00:03:03,000 So we're going to look for the definition of that function. 53 00:03:03,000 --> 00:03:05,001 It's got two hits, let's go in the first one, 54 00:03:05,001 --> 00:03:06,002 I just hit enter, 55 00:03:06,002 --> 00:03:08,009 but I could do down arrow to go to the next one. 56 00:03:08,009 --> 00:03:10,001 Up arrow to get back. 57 00:03:10,001 --> 00:03:16,000 So I hit enter, brings me into VI on the definition. 58 00:03:16,000 --> 00:03:18,007 Alright, and then I can move around in VI 59 00:03:18,007 --> 00:03:20,007 like I'm using my arrow key. 60 00:03:20,007 --> 00:03:23,006 Let's see, I put my cursor somewhere on this function 61 00:03:23,006 --> 00:03:26,005 that's getting called and I do control 62 00:03:26,005 --> 00:03:29,006 close square bracket. 63 00:03:29,006 --> 00:03:31,005 Control, close square bracket 64 00:03:31,005 --> 00:03:34,001 when I'm on a symbol like that. 65 00:03:34,001 --> 00:03:36,009 And it just jumped me up there. 66 00:03:36,009 --> 00:03:40,005 And I'm going to look for the next one. 67 00:03:40,005 --> 00:03:43,002 Next tag with that name. So I do :tn. 68 00:03:43,002 --> 00:03:47,000 You can see that at the bottom there, :tn. 69 00:03:47,000 --> 00:03:48,004 And there's the next one. 70 00:03:48,004 --> 00:03:50,003 And on the bottom it says tag 2 of 3. 71 00:03:50,003 --> 00:03:52,002 So there's actually three of 'em. 72 00:03:52,002 --> 00:03:55,004 And if you look up a couple lines here it says, 73 00:03:55,004 --> 00:03:57,003 ifdef INLINE_COPY_TO_USER, 74 00:03:57,003 --> 00:04:00,008 this is the inline definition of it. 75 00:04:00,008 --> 00:04:05,003 And if we do :tn, we can get to the third tag. 76 00:04:05,003 --> 00:04:08,000 And here it's if not defined. 77 00:04:08,000 --> 00:04:09,006 Right, so we're looking at the code, 78 00:04:09,006 --> 00:04:11,002 we can keep going. 79 00:04:11,002 --> 00:04:16,002 To go back, we do control T. 80 00:04:16,002 --> 00:04:21,000 I keep doing control T until I'm back 81 00:04:21,000 --> 00:04:23,000 for where the stack was. 82 00:04:23,000 --> 00:04:28,001 And then I can just get out of VI with usual :q. 83 00:04:28,001 --> 00:04:30,005 If I want to get back to the menu of choice down there, 84 00:04:30,005 --> 00:04:32,001 I hit the tab key. 85 00:04:32,001 --> 00:04:34,002 So I'm hitting tab, I'm down here. 86 00:04:34,002 --> 00:04:37,004 I can move between these with the arrow key. 87 00:04:37,004 --> 00:04:41,002 To get out of cscope, it's control D. 88 00:04:41,002 --> 00:04:44,005 Control D is also known as end of file for a lot of things. 89 00:04:44,005 --> 00:04:47,005 Control D as in dog. 90 00:04:47,005 --> 00:04:51,001 So we saw tags, we saw cscope, we saw kernel 91 00:04:51,001 --> 00:04:54,000 (indistinct) Makefile, good stuff.