15.+Linux+Kernel+Modules.ppt

高级操作系统陈燕晖2020/5/22,Linux2.6KernelModules,高级操作系统陈燕晖2020/5/22,1.Concepts,LKM(LinuxKernelModules)AKA:kernelmodules,modulesmodulesareLinuxsrecipeforeffectivelyachievingmanyofthetheoreticaladvantagesofmicrokernelswithoutintroducingperformancepenalties.Amoduleisanobjectfilewhosecodecanbelinkedto(andunlinkedfrom)thekernelatruntime.,高级操作系统陈燕晖2020/5/22,LKMssharelotsofpropertiesofuserspaceprograms,buttheyaredefinitelyNOTuserspaceprograms!TheyarepartofthekernelTheysharethekernelscodespaceTheycaneasilycrashit,高级操作系统陈燕晖2020/5/22,WhatLKMsareusedfor,DevicedriversCommunicatewithaspecificpieceofhardwareFilesystemdriversInterpretthecontentofafilesystemNetworkdriversInterpretanetworkprotocolTTYlinediscipleExecutableinterpretersLoadandrunanexecutableEverythingthatmakessenseasanLKMhastheoptiontobebuiltthisway,高级操作系统陈燕晖2020/5/22,2Modulesinpratice,#include#includeMODULE_LICENSE(DualBSD/GPL);staticinthello_init(void)printk(KERN_ALERTHello,worldn);return0;staticvoidhello_exit(void)printk(KERN_ALERTGoodbye,cruelworldn);module_init(hello_init);module_exit(hello_exit);,高级操作系统陈燕晖2020/5/22,Makefile,ifneq($(KERNELRELEASE),)obj-m:=hello.oelseKERNELDIR?=/lib/modules/$(shelluname-r)/buildPWD:=$(shellpwd)default:$(MAKE)-C$(KERNELDIR)M=$(PWD)modulesendif,高级操作系统陈燕晖2020/5/22,CompilingandLoading,%makemake1:Enteringdirectory/usr/src/linux-2.6.10CCM/home/ldd3/src/misc-modules/hello.oBuildingmodules,stage2.MODPOSTCC/home/ldd3/src/misc-modules/hello.mod.oLDM/home/ldd3/src/misc-modules/hello.komake1:Leavingdirectory/usr/src/linux-2.6.10%suroot#insmod./hello.koHello,worldroot#rmmodhelloGoodbyecruelworld,高级操作系统陈燕晖2020/5/22,TheKernelSymbolTable,Ausercanlinkamoduleintotherunningkernelbyexecutingtheinsmodexternalprogram.Whenlinkingamodule,allreferencestoglobalkernelsymbols(variablesandfunctions)inthemodulesobjectcodemustbereplacedwithsuitableaddresses.,高级操作系统陈燕晖2020/5/22,Somespecialkernelsymboltablesstorethesymbolsandtheircorrespondingaddressesthatcanbeaccessedbymodules._kstrtab_ksymtab_ksymtab_gpl:forGPL-compatiblelicenseEXPORT_SYMBOL(name);EXPORT_SYMBOL_GPL(name);,高级操作系统陈燕晖2020/5/22,ModuleParameters,TheLinuxkernelallowsdriverstodeclareparametersthattheusercanspecifyoneitherbootormoduleloadandthenhavetheseparametersexposedinyourdriverasglobalvariables.Usage:module_param(name,type,perm);#insmodhellophowmany