1 00:00:00,005 --> 00:00:02,000 - [Instructor] Fun with modules. 2 00:00:02,000 --> 00:00:05,003 Let's look at commands related to working 3 00:00:05,003 --> 00:00:08,005 with loadable kernel modules. 4 00:00:08,005 --> 00:00:11,002 We'll start with lsmod, list the modules 5 00:00:11,002 --> 00:00:14,006 that are currently loaded into your kernel. 6 00:00:14,006 --> 00:00:18,000 These are listed chronologically. 7 00:00:18,000 --> 00:00:22,001 The top of the list there, in this case, vhost_net 8 00:00:22,001 --> 00:00:26,000 is the most recently loaded module. 9 00:00:26,000 --> 00:00:29,006 And then there's probably more than just four. 10 00:00:29,006 --> 00:00:33,003 The very last one would be the very first module loaded. 11 00:00:33,003 --> 00:00:37,001 And we can see there's actually four columns, 12 00:00:37,001 --> 00:00:38,009 but only three headers. 13 00:00:38,009 --> 00:00:40,009 The first column is the name of the module, 14 00:00:40,009 --> 00:00:45,006 so that would be typically the .ko name, 15 00:00:45,006 --> 00:00:49,000 and then size and bytes, and then a number, 16 00:00:49,000 --> 00:00:51,006 that's the use count. 17 00:00:51,006 --> 00:00:55,009 And then, after that is the used by column. 18 00:00:55,009 --> 00:01:04,000 So we see, for example here, macvtap is used by vhost_net 19 00:01:04,000 --> 00:01:09,007 and mtacvlan is used by macvtap. 20 00:01:09,007 --> 00:01:12,009 And we could tell by the order here 21 00:01:12,009 --> 00:01:15,006 that they have to be loaded in an order 22 00:01:15,006 --> 00:01:21,002 to satisfy these used by requirements. 23 00:01:21,002 --> 00:01:24,007 You remove a module with rmmod. 24 00:01:24,007 --> 00:01:27,009 It is possible to configure a kernel 25 00:01:27,009 --> 00:01:29,007 where you're not allowed to remove modules. 26 00:01:29,007 --> 00:01:32,003 You can load 'em but not remove 'em. 27 00:01:32,003 --> 00:01:36,000 Now, you might not be able to remove a module 28 00:01:36,000 --> 00:01:40,002 if it's in use, kind of a good idea. 29 00:01:40,002 --> 00:01:43,002 There could be pointers into it, for example, 30 00:01:43,002 --> 00:01:44,002 in use by the kernel. 31 00:01:44,002 --> 00:01:45,005 And if you remove the module, 32 00:01:45,005 --> 00:01:48,005 then there's a pointer in the kernel that doesn't point 33 00:01:48,005 --> 00:01:50,007 to something valid anymore. 34 00:01:50,007 --> 00:01:54,008 You can try to force-remove a module with the -f. 35 00:01:54,008 --> 00:01:56,009 Not such a good idea. 36 00:01:56,009 --> 00:01:59,001 During development, when you got a system of yourself 37 00:01:59,001 --> 00:02:03,000 and you're writing a driver, it might be kind of handy, 38 00:02:03,000 --> 00:02:06,006 but still pretty risky. 39 00:02:06,006 --> 00:02:12,005 And again, I would caution you in ever removing a module. 40 00:02:12,005 --> 00:02:17,008 It's really easy for a module to have some code in it 41 00:02:17,008 --> 00:02:21,003 that leaves the kernel in a fragile state. 42 00:02:21,003 --> 00:02:25,002 So generally load 'em, leave them there, 43 00:02:25,002 --> 00:02:27,004 don't ever remove them. 44 00:02:27,004 --> 00:02:32,004 Baked into a module can be some additional information. 45 00:02:32,004 --> 00:02:37,006 There's macros to specify the author, for example. 46 00:02:37,006 --> 00:02:42,008 And a parameter list can exist for a module. 47 00:02:42,008 --> 00:02:44,004 So when you load a module, 48 00:02:44,004 --> 00:02:48,006 you can set various tunable parameters 49 00:02:48,006 --> 00:02:51,002 and there could be a list 50 00:02:51,002 --> 00:02:55,005 of what kind of devices this module supports. 51 00:02:55,005 --> 00:02:57,002 So you got an ethernet driver, 52 00:02:57,002 --> 00:03:00,008 which ethernet devices does it support, could be in there. 53 00:03:00,008 --> 00:03:04,004 And there's a version magic string coding 54 00:03:04,004 --> 00:03:07,005 which kernel version the module goes to, 55 00:03:07,005 --> 00:03:12,001 that is checked when you try to load a module. 56 00:03:12,001 --> 00:03:16,003 We saw the file modules.dep, that gets created 57 00:03:16,003 --> 00:03:18,000 by a command called depmod, 58 00:03:18,000 --> 00:03:20,009 that file as well as some others. 59 00:03:20,009 --> 00:03:23,007 Now, you probably don't have to run depmod, 60 00:03:23,007 --> 00:03:26,006 but it's kind of good to know it exists. 61 00:03:26,006 --> 00:03:30,001 And if you install some modules, like from a package, 62 00:03:30,001 --> 00:03:34,000 that package should run the depmod command for you 63 00:03:34,000 --> 00:03:39,001 to rebuild the files, like modules about dep. 64 00:03:39,001 --> 00:03:42,002 Let's say you have a module, maybe you built your own, 65 00:03:42,002 --> 00:03:46,003 you got this .ko or .kozst file. 66 00:03:46,003 --> 00:03:49,009 You load it into the kernel, you insert it into the kernel 67 00:03:49,009 --> 00:03:52,003 with the insmod command. 68 00:03:52,003 --> 00:03:55,003 And then what happens is, the kernel runs 69 00:03:55,003 --> 00:03:58,008 and initialization function in the module. 70 00:03:58,008 --> 00:04:01,004 And when that function returns, 71 00:04:01,004 --> 00:04:04,008 then the insmod command returns. 72 00:04:04,008 --> 00:04:06,009 It's possible for the module to fail 73 00:04:06,009 --> 00:04:10,001 for that initialization function to fail. 74 00:04:10,001 --> 00:04:11,009 Maybe it's looking for something 75 00:04:11,009 --> 00:04:16,003 that's something's not there, so it's going to return. 76 00:04:16,003 --> 00:04:19,006 And the insmod could print an error message. 77 00:04:19,006 --> 00:04:22,003 There might be more information from the module. 78 00:04:22,003 --> 00:04:25,006 You could check that with dmesg. 79 00:04:25,006 --> 00:04:29,001 With the insmod command, you provide the path to the module, 80 00:04:29,001 --> 00:04:35,001 insmod/mysubdur/mymodule.ko, say. 81 00:04:35,001 --> 00:04:38,007 An alternative to insmod is modprobe. 82 00:04:38,007 --> 00:04:41,008 modprobe uses the information 83 00:04:41,008 --> 00:04:44,002 in the lib modules kernel version directory, 84 00:04:44,002 --> 00:04:47,001 like the modules.dep file. 85 00:04:47,001 --> 00:04:49,008 So you don't give a path name to a module with modprobe. 86 00:04:49,008 --> 00:04:52,001 You just say the name of the module. 87 00:04:52,001 --> 00:04:55,008 And that makes it easier in some ways than insmod. 88 00:04:55,008 --> 00:04:58,003 But if you wrote your own module, then you'd have 89 00:04:58,003 --> 00:05:00,002 to put it in the lib module directory. 90 00:05:00,002 --> 00:05:02,000 You'd have to run the depmod command 91 00:05:02,000 --> 00:05:03,005 if you wanted to use modprobe. 92 00:05:03,005 --> 00:05:08,007 So insmod's easier when you're writing your own module, 93 00:05:08,007 --> 00:05:10,007 like we'll do later on. 94 00:05:10,007 --> 00:05:13,004 modprobe also lets you remove modules 95 00:05:13,004 --> 00:05:16,001 and it'll remove the dependencies also. 96 00:05:16,001 --> 00:05:20,000 And there's a number of other options for modprobe. 97 00:05:20,000 --> 00:05:24,007 modprobe is what you'll most commonly use for working 98 00:05:24,007 --> 00:05:29,000 with installed loadable kernel modules.