1 00:00:00,005 --> 00:00:04,002 - [Instructor] So you want to read Linux kernel source code. 2 00:00:04,002 --> 00:00:05,006 Good for you. 3 00:00:05,006 --> 00:00:07,006 That's a fun hobby. 4 00:00:07,006 --> 00:00:09,009 So searching through the source code, 5 00:00:09,009 --> 00:00:13,006 something you want to do to find where in the source code 6 00:00:13,006 --> 00:00:16,007 is a thing that you're interested in. 7 00:00:16,007 --> 00:00:18,009 Well, of course you can use grep. 8 00:00:18,009 --> 00:00:21,001 I often do a recursive grep, 9 00:00:21,001 --> 00:00:23,001 maybe a dash little I to ignore case, 10 00:00:23,001 --> 00:00:25,009 maybe a dash l just to get the names of the files 11 00:00:25,009 --> 00:00:27,002 to look in further. 12 00:00:27,002 --> 00:00:31,008 For example, if I was interested in sys_read, 13 00:00:31,008 --> 00:00:35,003 which turns out to be a function for doing reading, 14 00:00:35,003 --> 00:00:38,008 maybe I want to find a prototype, something like that. 15 00:00:38,008 --> 00:00:40,003 I could look in the include directory. 16 00:00:40,003 --> 00:00:43,003 So if I'm in the top level of the kernel source, 17 00:00:43,003 --> 00:00:48,003 I'm going to do grep -rl sys_read include, 18 00:00:48,003 --> 00:00:50,004 it will look in the include directory 19 00:00:50,004 --> 00:00:52,009 and everything underneath the include directory 20 00:00:52,009 --> 00:00:55,008 and report the path to any file 21 00:00:55,008 --> 00:00:58,005 that had the string sys read. 22 00:00:58,005 --> 00:01:01,004 And you know, maybe get about a half a dozen or so of those 23 00:01:01,004 --> 00:01:04,000 that you can go look at. 24 00:01:04,000 --> 00:01:07,001 What I frequently use, this is the classic way 25 00:01:07,001 --> 00:01:13,002 of looking at kernel source, is the cscope tool. 26 00:01:13,002 --> 00:01:16,002 So the kernel make file supports building 27 00:01:16,002 --> 00:01:20,001 a cscope index file or files. 28 00:01:20,001 --> 00:01:22,003 So you can say make cscope 29 00:01:22,003 --> 00:01:24,007 and that takes a little while to run. 30 00:01:24,007 --> 00:01:29,002 And then you typically launch it by saying cscope -d. 31 00:01:29,002 --> 00:01:31,002 And then you're going to get this 32 00:01:31,002 --> 00:01:35,002 old-school kind of text interface, 33 00:01:35,002 --> 00:01:36,009 but it's very fast. 34 00:01:36,009 --> 00:01:38,002 So you can look for strings, 35 00:01:38,002 --> 00:01:40,001 you can look for definitions of things, 36 00:01:40,001 --> 00:01:43,006 you can look for who's calling what and so forth. 37 00:01:43,006 --> 00:01:47,001 We'll look at that and we'll let you give that a try. 38 00:01:47,001 --> 00:01:48,007 So you're going to get a list of output. 39 00:01:48,007 --> 00:01:52,001 You'll move between those with arrow keys, 40 00:01:52,001 --> 00:01:57,000 but you're going to have a search part and a result part, 41 00:01:57,000 --> 00:02:00,001 and you move between those parts with the tab key, 42 00:02:00,001 --> 00:02:02,000 so remember that tab key. 43 00:02:02,000 --> 00:02:05,006 And you get out of cscope with control D. 44 00:02:05,006 --> 00:02:07,002 And when you find a hit 45 00:02:07,002 --> 00:02:08,007 and you hit enter to go to it, 46 00:02:08,007 --> 00:02:11,005 it's going to launch an editor on that file 47 00:02:11,005 --> 00:02:15,006 and show you the line that it found. 48 00:02:15,006 --> 00:02:19,004 And usually that editor is VI or vim. 49 00:02:19,004 --> 00:02:25,005 So knowing how to use VI is always valuable on Linux. 50 00:02:25,005 --> 00:02:30,009 And the kernel make file also supports tags. 51 00:02:30,009 --> 00:02:33,006 And VI is an editor that supports tags, 52 00:02:33,006 --> 00:02:36,004 so within the editor you can search for things 53 00:02:36,004 --> 00:02:41,002 like you could launch VI -t and give it a symbol. 54 00:02:41,002 --> 00:02:46,002 Now it's going to go find sys read in a file. 55 00:02:46,002 --> 00:02:49,003 So the make tags also created an index. 56 00:02:49,003 --> 00:02:52,008 And while you're in VI, you could do 57 00:02:52,008 --> 00:02:58,001 control close square bracket on a symbol to go look it up. 58 00:02:58,001 --> 00:03:00,005 And so you can go from place to place to place. 59 00:03:00,005 --> 00:03:03,005 If you want to go back, you do control T, right? 60 00:03:03,005 --> 00:03:07,002 It's all cryptic, it's all VI kind of cryptic, 61 00:03:07,002 --> 00:03:11,004 but it could be fast and convenient and reliable. 62 00:03:11,004 --> 00:03:15,002 So I use cscope and tags in combination 63 00:03:15,002 --> 00:03:18,000 all the time looking at kernel source.