Ldd3 学习笔记3 —file_operations

intregister_chrdev(unsignedintmajor,constchar*name,structfile_operations*fops);

UnregisteringADevice

chardev.c

/*chardev.c:Createsaread-onlychardevicethatsayshowmanytimes*you'vereadfromthedevfile**Copyright(C)2001byPeterJaySalzman**08/02/2006-UpdatedbyRodrigoRubiraBranco<rodrigo@kernelhacking.com>*/
/*KernelProgramming*/#defineMODULE#defineLINUX#define__KERNEL__
#ifdefined(CONFIG_MODVERSIONS)&&!defined(MODVERSIONS)#include<linux/modversions.h>#defineMODVERSIONS#endif#include<linux/kernel.h>#include<linux/module.h>#include<linux/fs.h>#include<asm/uaccess.h>/*forput_user*/#include<asm/errno.h>
/*Prototypes-thiswouldnormallygoina.hfile*/intinit_module(void);voidcleanup_module(void);staticintdevice_open(structinode*,structfile*);staticintdevice_release(structinode*,structfile*);staticssize_tdevice_read(structfile*,char*,size_t,loff_t*);staticssize_tdevice_write(structfile*,constchar*,size_t,loff_t*);
#defineSUCCESS0#defineDEVICE_NAME"chardev"/*Devnameasitappearsin/proc/devices*/#defineBUF_LEN80/*Maxlengthofthemessagefromthedevice*/

/*Globalvariablesaredeclaredasstatic,soareglobalwithinthefile.*/
staticintMajor;/*Majornumberassignedtoourdevicedriver*/staticintDevice_Open=0;/*Isdeviceopen?Usedtopreventmultipleaccesstothedevice*/staticcharmsg[BUF_LEN];/*Themsgthedevicewillgivewhenasked*/staticchar*msg_Ptr;
staticstructfile_operationsfops={.read=device_read,.write=device_write,.open=device_open,.release=device_release};

/*Functions*/
intinit_module(void){Major=register_chrdev(0,DEVICE_NAME,&fops);
if(Major<0){printk("Registeringthecharacterdevicefailedwith%d\n",Major);returnMajor;}
printk("<1>Iwasassignedmajornumber%d.Totalkto\n",Major);printk("<1>thedriver,createadevfilewith\n");printk("'mknod/dev/helloc%d0'.\n",Major);printk("<1>Tryvariousminornumbers.Trytocatandechoto\n");printk("thedevicefile.\n");printk("<1>Removethedevicefileandmodulewhendone.\n");
return0;}

voidcleanup_module(void){/*Unregisterthedevice*/intret=unregister_chrdev(Major,DEVICE_NAME);if(ret<0)printk("Errorinunregister_chrdev:%d\n",ret);}

/*Methods*/
/*Calledwhenaprocesstriestoopenthedevicefile,like*"cat/dev/mycharfile"*/staticintdevice_open(structinode*inode,structfile*file){staticintcounter=0;if(Device_Open)return-EBUSY;
Device_Open++;sprintf(msg,"Ialreadytoldyou%dtimesHelloworld!\n",counter++);msg_Ptr=msg;MOD_INC_USE_COUNT;
returnSUCCESS;}

/*Calledwhenaprocessclosesthedevicefile*/staticintdevice_release(structinode*inode,structfile*file){Device_Open--;/*We'renowreadyforournextcaller*/
/*Decrementtheusagecount,orelseonceyouopenedthefile,you'llnevergetgetridofthemodule.*/MOD_DEC_USE_COUNT;
return0;}

/*Calledwhenaprocess,whichalreadyopenedthedevfile,attemptstoreadfromit.*/staticssize_tdevice_read(structfile*filp,char*buffer,/*Thebuffertofillwithdata*/size_tlength,/*Thelengthofthebuffer*/loff_t*offset)/*Ouroffsetinthefile*/{/*Numberofbytesactuallywrittentothebuffer*/intbytes_read=0;
/*Ifwe'reattheendofthemessage,return0signifyingendoffile*/if(*msg_Ptr==0)return0;
/*Actuallyputthedataintothebuffer*/while(length&&*msg_Ptr){
/*Thebufferisintheuserdatasegment,notthekernelsegment;*assignmentwon'twork.Wehavetouseput_userwhichcopiesdatafrom*thekerneldatasegmenttotheuserdatasegment.*/put_user(*(msg_Ptr++),buffer++);
length--;bytes_read++;}
/*Mostreadfunctionsreturnthenumberofbytesputintothebuffer*/returnbytes_read;}

/*Calledwhenaprocesswritestodevfile:echo"hi">/dev/hello*/staticssize_tdevice_write(structfile*filp,constchar*buff,size_tlen,loff_t*off){printk("<1>Sorry,thisoperationisn'tsupported.\n");return-EINVAL;}
MODULE_LICENSE("GPL");

WritingModulesforMultipleKernelVersions

#ifLINUX_KERNEL_VERSION>=KERNEL_VERSION(2,2,0)#defineKERNEL_VERSION(a,b,c)((a)*65536+(b)*256+(c))#endif

Notes