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Android 2.3 SD卡挂载流程浅析(四)

 
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前面的三篇博文《Android 2.3 SD卡挂载流程浅析(一)》、《Android 2.3 SD卡挂载流程浅析(二)》、《Android 2.3 SD卡挂载流程浅析(三)》的分析，知道了SD卡挂载的消息是如何从底层传递到上层的，在《Android 2.3 SD卡挂载流程浅析(三)》中，我们已经知道了最后是在updatePublicVolumeState()中调用onStorageStateChanged()，从而达到更新SD卡挂载信息的。在本文《Android 2.3 SD卡挂载流程浅析(四)》中，我会将前文提到的程序调用流程图画出来，并对代码进行简单的分析。

首先，还是挂出这张老图(因为每次都用这张图0_0...)。

就权当复习吧，这是SD卡的整个挂载流程，而程序的调用也是根据这个流程图来的。

1.接收并处理uevent

首先是接收因为插入SD卡被内核检测到而发出的Event；

NetlinkHandler::onEvent(NetlinkEvent *evt)

//代码路径：AndroidSourcecode2.3/system/vold/NetlinkHandler.cpp

//该方法主要通过evt->getSubsystem();方法来获取系统的event

view plain
  1. voidNetlinkHandler::onEvent(NetlinkEvent*evt){
  2. VolumeManager*vm=VolumeManager::Instance();
  3. constchar*subsys=evt->getSubsystem();
  5. if(!subsys){
  6. SLOGW("Nosubsystemfoundinnetlinkevent");
  7. return;
  8. }
  10. if(!strcmp(subsys,"block")){
  11. vm->handleBlockEvent(evt);
  12. }elseif(!strcmp(subsys,"switch")){
  13. vm->handleSwitchEvent(evt);
  14. }elseif(!strcmp(subsys,"usb_composite")){
  15. vm->handleUsbCompositeEvent(evt);
  16. }elseif(!strcmp(subsys,"battery")){
  17. }elseif(!strcmp(subsys,"power_supply")){
  18. }
  19. }
2.对SD卡挂载事件开始处理

void VolumeManager::handleBlockEvent(NetlinkEvent *evt)

//代码路径：AndroidSourcecode2.3/system/vold/VolumeManager.cpp

//该方法的主要作用是：
//第一， 遍历mPath容器，寻找与event对应的sysfs_path是否存在与mPath容器中。
//第二， 针对Event中的action有4种处理方式：Add,Removed,Change,Noaction。

view plain
  1. voidVolumeManager::handleBlockEvent(NetlinkEvent*evt){
  2. constchar*devpath=evt->findParam("DEVPATH");
  4. /*Lookupavolumetohandlethisdevice*/
  5. VolumeCollection::iteratorit;
  6. boolhit=false;
  7. for(it=mVolumes->begin();it!=mVolumes->end();++it){
  8. if(!(*it)->handleBlockEvent(evt)){
  9. #ifdefNETLINK_DEBUG
  10. SLOGD("Device'%s'eventhandledbyvolume%s\n",devpath,(*it)->getLabel());
  11. #endif
  12. hit=true;
  13. break;
  14. }
  15. }
  17. if(!hit){
  18. #ifdefNETLINK_DEBUG
  19. SLOGW("Novolumeshandledblockeventfor'%s'",devpath);
  20. #endif
  21. }
  22. }
3.对Block挂载事件进行处理

DirectVolume::handleBlockEvent(NetlinkEvent *evt)

//代码路径：AndroidSourcecode2.3/system/vold/DirectVolume.cpp

//在Add action中首先会创建设备节点，然后对disk和partion两种格式的设备分别进行处理。这里是disk格式。

view plain
  1. intDirectVolume::handleBlockEvent(NetlinkEvent*evt){
  2. constchar*dp=evt->findParam("DEVPATH");
  4. PathCollection::iteratorit;
  5. for(it=mPaths->begin();it!=mPaths->end();++it){
  6. if(!strncmp(dp,*it,strlen(*it))){
  7. /*Wecanhandlethisdisk*/
  8. intaction=evt->getAction();
  9. constchar*devtype=evt->findParam("DEVTYPE");
  11. if(action==NetlinkEvent::NlActionAdd){
  12. intmajor=atoi(evt->findParam("MAJOR"));
  13. intminor=atoi(evt->findParam("MINOR"));
  14. charnodepath[255];
  16. snprintf(nodepath,
  17. sizeof(nodepath),"/dev/block/vold/%d:%d",
  18. major,minor);
  19. if(createDeviceNode(nodepath,major,minor)){
  20. SLOGE("Errormakingdevicenode'%s'(%s)",nodepath,
  21. strerror(errno));
  22. }
  23. if(!strcmp(devtype,"disk")){
  24. <spanstyle="color:#ff0000;">handleDiskAdded(dp,evt);<spanstyle="color:#33cc00;">//SD卡插入是Add事件</span></span>
  25. }else{
  26. handlePartitionAdded(dp,evt);
  27. }
  28. }elseif(action==NetlinkEvent::NlActionRemove){
  29. if(!strcmp(devtype,"disk")){
  30. handleDiskRemoved(dp,evt);
  31. }else{
  32. handlePartitionRemoved(dp,evt);
  33. }
  34. }elseif(action==NetlinkEvent::NlActionChange){
  35. if(!strcmp(devtype,"disk")){
  36. handleDiskChanged(dp,evt);
  37. }else{
  38. handlePartitionChanged(dp,evt);
  39. }
  40. }else{
  41. SLOGW("Ignoringnonadd/remove/changeevent");
  42. }
  44. return0;
  45. }
  46. }
  47. errno=ENODEV;
  48. return-1;
  49. }
4.处理DiskAdd事件

DirectVolume::handleDiskAdded(const char *devpath, NetlinkEvent *evt)

//代码路径：AndroidSourcecode2.3/system/vold/DirectVolume.cpp

//在该方法中广播disk insert的广播消息(这里的广播不同于Java中的广播，这里实际上是Socket)。

view plain
  1. voidDirectVolume::handleDiskAdded(constchar*devpath,NetlinkEvent*evt){
  2. mDiskMajor=atoi(evt->findParam("MAJOR"));
  3. mDiskMinor=atoi(evt->findParam("MINOR"));
  5. constchar*tmp=evt->findParam("NPARTS");
  6. if(tmp){
  7. mDiskNumParts=atoi(tmp);
  8. }else{
  9. SLOGW("Kernelblockueventmissing'NPARTS'");
  10. mDiskNumParts=1;
  11. }
  13. charmsg[255];
  15. intpartmask=0;
  16. inti;
  17. for(i=1;i<=mDiskNumParts;i++){
  18. partmask|=(1<<i);
  19. }
  20. mPendingPartMap=partmask;
  22. if(mDiskNumParts==0){
  23. #ifdefPARTITION_DEBUG
  24. SLOGD("Dv::diskIns-Nopartitions-goodtogoson!");
  25. #endif
  26. setState(Volume::State_Idle);
  27. }else{
  28. #ifdefPARTITION_DEBUG
  29. SLOGD("Dv::diskIns-waitingfor%dpartitions(mask0x%x)",
  30. mDiskNumParts,mPendingPartMap);
  31. #endif
  32. setState(Volume::State_Pending);
  33. }
  35. snprintf(msg,sizeof(msg),"Volume%s%sdiskinserted(%d:%d)",
  36. getLabel(),getMountpoint(),mDiskMajor,mDiskMinor);
  37. mVm->getBroadcaster()->sendBroadcast(ResponseCode::VolumeDiskInserted,
  38. msg,false);


5.处理广播消息
SocketListener::runListener()

//代码路径：AndroidSourcecode2.3/system/core/libsysutils/src/SocketListener.cpp

//完成对Socket的监听以及对数据的处理onDataAvailable(* it );

view plain
  1. voidSocketListener::runListener(){
  3. while(1){
  4. SocketClientCollection::iteratorit;
  5. fd_setread_fds;
  6. intrc=0;
  7. intmax=0;
  9. FD_ZERO(&read_fds);
  11. if(mListen){
  12. max=mSock;
  13. FD_SET(mSock,&read_fds);
  14. }
  16. FD_SET(mCtrlPipe[0],&read_fds);
  17. if(mCtrlPipe[0]>max)
  18. max=mCtrlPipe[0];
  20. pthread_mutex_lock(&mClientsLock);
  21. for(it=mClients->begin();it!=mClients->end();++it){
  22. FD_SET((*it)->getSocket(),&read_fds);
  23. if((*it)->getSocket()>max)
  24. max=(*it)->getSocket();
  25. }
  26. pthread_mutex_unlock(&mClientsLock);
  28. if((rc=select(max+1,&read_fds,NULL,NULL,NULL))<0){
  29. SLOGE("selectfailed(%s)",strerror(errno));
  30. sleep(1);
  31. continue;
  32. }elseif(!rc)
  33. continue;
  35. if(FD_ISSET(mCtrlPipe[0],&read_fds))
  36. break;
  37. if(mListen&&FD_ISSET(mSock,&read_fds)){
  38. structsockaddraddr;
  39. socklen_talen=sizeof(addr);
  40. intc;
  42. if((c=accept(mSock,&addr,&alen))<0){
  43. SLOGE("acceptfailed(%s)",strerror(errno));
  44. sleep(1);
  45. continue;
  46. }
  47. pthread_mutex_lock(&mClientsLock);
  48. mClients->push_back(newSocketClient(c));
  49. pthread_mutex_unlock(&mClientsLock);
  50. }
  52. do{
  53. pthread_mutex_lock(&mClientsLock);
  54. for(it=mClients->begin();it!=mClients->end();++it){
  55. intfd=(*it)->getSocket();
  56. if(FD_ISSET(fd,&read_fds)){
  57. pthread_mutex_unlock(&mClientsLock);
  58. if(!<spanstyle="color:#ff0000;">onDataAvailable(*it)</span>){
  59. close(fd);
  60. pthread_mutex_lock(&mClientsLock);
  61. delete*it;
  62. it=mClients->erase(it);
  63. pthread_mutex_unlock(&mClientsLock);
  64. }
  65. FD_CLR(fd,&read_fds);
  66. pthread_mutex_lock(&mClientsLock);
  67. continue;
  68. }
  69. }
  70. pthread_mutex_unlock(&mClientsLock);
  71. }while(0);
  72. }
  73. }

6.处理消息内容

FrameworkListener::onDataAvailable(SocketClient *c)

//代码路径：AndroidSourcecode2.3/system/core/libsysutils/src/FrameworkListener.cpp

//对接收到的广播消息进行处理

view plain
  1. boolFrameworkListener::onDataAvailable(SocketClient*c){
  2. charbuffer[255];
  3. intlen;
  5. if((len=read(c->getSocket(),buffer,sizeof(buffer)-1))<0){
  6. SLOGE("read()failed(%s)",strerror(errno));
  7. returnfalse;
  8. }elseif(!len)
  9. returnfalse;
  11. intoffset=0;
  12. inti;
  14. for(i=0;i<len;i++){
  15. if(buffer[i]=='\0'){
  16. dispatchCommand(c,buffer+offset);
  17. offset=i+1;
  18. }
  19. }
  20. returntrue;
  21. }
7.分发指令

FrameworkListener::dispatchCommand(SocketClient *cli, char *data)

//代码路径：AndroidSourcecode2.3/system/core/libsysutils/src/FrameworkListener.cpp

//分配指令：DumpCmd、VolumeCmd、AsecCmd、ShareCmd、StorageCmd、XwarpCmd

view plain
  1. voidFrameworkListener::dispatchCommand(SocketClient*cli,char*data){
  2. FrameworkCommandCollection::iteratori;
  3. intargc=0;
  4. char*argv[FrameworkListener::CMD_ARGS_MAX];
  5. chartmp[255];
  6. char*p=data;
  7. char*q=tmp;
  8. boolesc=false;
  9. boolquote=false;
  10. intk;
  12. memset(argv,0,sizeof(argv));
  13. memset(tmp,0,sizeof(tmp));
  14. while(*p){
  15. if(*p=='\\'){
  16. if(esc){
  17. *q++='\\';
  18. esc=false;
  19. }else
  20. esc=true;
  21. p++;
  22. continue;
  23. }elseif(esc){
  24. if(*p=='"')
  25. *q++='"';
  26. elseif(*p=='\\')
  27. *q++='\\';
  28. else{
  29. cli->sendMsg(500,"Unsupportedescapesequence",false);
  30. gotoout;
  31. }
  32. p++;
  33. esc=false;
  34. continue;
  35. }
  37. if(*p=='"'){
  38. if(quote)
  39. quote=false;
  40. else
  41. quote=true;
  42. p++;
  43. continue;
  44. }
  46. *q=*p++;
  47. if(!quote&&*q==''){
  48. *q='\0';
  49. argv[argc++]=strdup(tmp);
  50. memset(tmp,0,sizeof(tmp));
  51. q=tmp;
  52. continue;
  53. }
  54. q++;
  55. }
  57. argv[argc++]=strdup(tmp);
  58. #if0
  59. for(k=0;k<argc;k++){
  60. SLOGD("arg[%d]='%s'",k,argv[k]);
  61. }
  62. #endif
  64. if(quote){
  65. cli->sendMsg(500,"Unclosedquoteserror",false);
  66. gotoout;
  67. }
  69. for(i=mCommands->begin();i!=mCommands->end();++i){
  70. FrameworkCommand*c=*i;
  72. if(!strcmp(argv[0],c->getCommand())){
  73. if(c-><spanstyle="color:#ff0000;">runCommand</span>(cli,argc,argv)){
  74. SLOGW("Handler'%s'error(%s)",c->getCommand(),strerror(errno));
  75. }
  76. gotoout;
  77. }
  78. }
  80. cli->sendMsg(500,"Commandnotrecognized",false);
  81. out:
  82. intj;
  83. for(j=0;j<argc;j++)
  84. free(argv[j]);
  85. return;
  86. }
8.开始执行挂载

CommandListener::VolumeCmd::runCommand(SocketClient *cli,int argc, char **argv)

//代码路径：AndroidSourcecode2.3/system/vold/CommandListener.cpp

//rc = vm->mountVolume(argv[2]);

view plain
  1. intCommandListener::VolumeCmd::runCommand(SocketClient*cli,intargc,char**argv){
  2. dumpArgs(argc,argv,-1);
  4. if(argc<2){
  5. cli->sendMsg(ResponseCode::CommandSyntaxError,"MissingArgument",false);
  6. return0;
  7. }
  9. VolumeManager*vm=VolumeManager::Instance();
  10. intrc=0;
  12. if(!strcmp(argv[1],"list")){
  13. returnvm->listVolumes(cli);
  14. }elseif(!strcmp(argv[1],"debug")){
  15. if(argc!=3||(argc==3&&(strcmp(argv[2],"off")&&strcmp(argv[2],"on")))){
  16. cli->sendMsg(ResponseCode::CommandSyntaxError,"Usage:volumedebug<off/on>",false);
  17. return0;
  18. }
  19. vm->setDebug(!strcmp(argv[2],"on")?true:false);
  20. }elseif(!strcmp(argv[1],"mount")){
  21. if(argc!=3){
  22. cli->sendMsg(ResponseCode::CommandSyntaxError,"Usage:volumemount<path>",false);
  23. return0;
  24. }
  25. <spanstyle="color:#ff0000;">rc=vm->mountVolume(argv[2]);</span>
  26. }elseif(!strcmp(argv[1],"unmount")){
  27. if(argc<3||argc>4||(argc==4&&strcmp(argv[3],"force"))){
  28. cli->sendMsg(ResponseCode::CommandSyntaxError,"Usage:volumeunmount<path>[force]",false);
  29. return0;
  30. }
  32. boolforce=false;
  33. if(argc>=4&&!strcmp(argv[3],"force")){
  34. force=true;
  35. }
  36. rc=vm->unmountVolume(argv[2],force);
  37. }elseif(!strcmp(argv[1],"format")){
  38. if(argc!=3){
  39. cli->sendMsg(ResponseCode::CommandSyntaxError,"Usage:volumeformat<path>",false);
  40. return0;
  41. }
  42. rc=vm->formatVolume(argv[2]);
  43. }elseif(!strcmp(argv[1],"share")){
  44. if(argc!=4){
  45. cli->sendMsg(ResponseCode::CommandSyntaxError,
  46. "Usage:volumeshare<path><method>",false);
  47. return0;
  48. }
  49. rc=vm->shareVolume(argv[2],argv[3]);
  50. }elseif(!strcmp(argv[1],"unshare")){
  51. if(argc!=4){
  52. cli->sendMsg(ResponseCode::CommandSyntaxError,
  53. "Usage:volumeunshare<path><method>",false);
  54. return0;
  55. }
  56. rc=vm->unshareVolume(argv[2],argv[3]);
  57. }elseif(!strcmp(argv[1],"shared")){
  58. boolenabled=false;
  59. if(argc!=4){
  60. cli->sendMsg(ResponseCode::CommandSyntaxError,
  61. "Usage:volumeshared<path><method>",false);
  62. return0;
  63. }
  65. if(vm->shareEnabled(argv[2],argv[3],&enabled)){
  66. cli->sendMsg(
  67. ResponseCode::OperationFailed,"Failedtodetermineshareenablestate",true);
  68. }else{
  69. cli->sendMsg(ResponseCode::ShareEnabledResult,
  70. (enabled?"Shareenabled":"Sharedisabled"),false);
  71. }
  72. return0;
  73. }else{
  74. cli->sendMsg(ResponseCode::CommandSyntaxError,"Unknownvolumecmd",false);
  75. }
  77. if(!rc){
  78. cli->sendMsg(ResponseCode::CommandOkay,"volumeoperationsucceeded",false);
  79. }else{
  80. interno=errno;
  81. rc=ResponseCode::convertFromErrno();
  82. cli->sendMsg(rc,"volumeoperationfailed",true);
  83. }
  85. return0;
  86. }

9.调用方法执行挂载动作

VolumeManager::mountVolume(const char *label)

//代码路径：AndroidSourcecode2.3/system/vold/VolumeManager.cpp
//v->mountVol();

view plain
  1. intVolumeManager::mountVolume(constchar*label){
  2. Volume*v=lookupVolume(label);
  4. if(!v){
  5. errno=ENOENT;
  6. return-1;
  7. }
  9. return<spanstyle="color:#ff0000;">v->mountVol();
  10. </span>}
view plain
  1. intVolumeManager::mountVolume(constchar*label){
  2. Volume*v=lookupVolume(label);
  4. if(!v){
  5. errno=ENOENT;
  6. return-1;
  7. }
  9. return<spanstyle="color:#ff0000;">v->mountVol();
  10. </span>}
10.真正的挂载者

Volume::mountVol()

//代码路径：AndroidSourcecode2.3/system/vold/Volume.cpp

//SD卡的挂载最终是在该方法中实现的，如果挂载有异常，也会在该方法的执行过程通过setState方法发出广播。

view plain
  1. intVolume::mountVol(){
  2. dev_tdeviceNodes[4];
  3. intn,i,rc=0;
  4. charerrmsg[255];
  6. if(getState()==Volume::State_NoMedia){
  7. snprintf(errmsg,sizeof(errmsg),
  8. "Volume%s%smountfailed-nomedia",
  9. getLabel(),getMountpoint());
  10. mVm->getBroadcaster()->sendBroadcast(
  11. ResponseCode::VolumeMountFailedNoMedia,
  12. errmsg,false);
  13. errno=ENODEV;
  14. return-1;
  15. }elseif(getState()!=Volume::State_Idle){
  16. errno=EBUSY;
  17. return-1;
  18. }
  20. if(isMountpointMounted(getMountpoint())){
  21. SLOGW("Volumeisidlebutappearstobemounted-fixing");
  22. setState(Volume::State_Mounted);
  23. //mCurrentlyMountedKdev=XXX
  24. return0;
  25. }
  27. n=getDeviceNodes((dev_t*)&deviceNodes,4);
  28. if(!n){
  29. SLOGE("Failedtogetdevicenodes(%s)\n",strerror(errno));
  30. return-1;
  31. }
  33. for(i=0;i<n;i++){
  34. chardevicePath[255];
  36. sprintf(devicePath,"/dev/block/vold/%d:%d",MAJOR(deviceNodes[i]),
  37. MINOR(deviceNodes[i]));
  39. SLOGI("%sbeingconsideredforvolume%s\n",devicePath,getLabel());
  41. errno=0;
  42. setState(Volume::State_Checking);
  44. if(Fat::check(devicePath)){//如果SD卡的格式不对是通不过这里的检测的
  45. if(errno==ENODATA){
  46. SLOGW("%sdoesnotcontainaFATfilesystem\n",devicePath);
  47. continue;
  48. }
  49. errno=EIO;
  50. /*Badness-abortthemount*/
  51. SLOGE("%sfailedFSchecks(%s)",devicePath,strerror(errno));
  52. setState(Volume::State_Idle);
  53. return-1;
  54. }
  56. /*
  57. *Mountthedeviceonourinternalstagingmountpointsowecan
  58. *muckwithitbeforeexposingittononpriviledgedusers.
  59. */
  60. errno=0;
  61. if(Fat::doMount(devicePath,"/mnt/secure/staging",false,false,false,
  62. 1000,1015,0702,true)){//真正的挂载方法doMount
  63. SLOGE("%sfailedtomountviaVFAT(%s)\n",devicePath,strerror(errno));
  64. continue;
  65. }
  67. SLOGI("Device%s,target%smounted@/mnt/secure/staging",devicePath,getMountpoint());
  69. protectFromAutorunStupidity();
  71. if(createBindMounts()){
  72. SLOGE("Failedtocreatebindmounts(%s)",strerror(errno));
  73. umount("/mnt/secure/staging");
  74. setState(Volume::State_Idle);
  75. return-1;
  76. }
  78. /*
  79. *Nowthatthebindmounttrickeryisdone,atomicallymovethe
  80. *wholesubtreetoexposeittononpriviledgedusers.
  81. */
  82. if(doMoveMount("/mnt/secure/staging",getMountpoint(),false)){
  83. SLOGE("Failedtomovemount(%s)",strerror(errno));
  84. umount("/mnt/secure/staging");
  85. setState(Volume::State_Idle);
  86. return-1;
  87. }
  88. setState(Volume::State_Mounted);
  89. mCurrentlyMountedKdev=deviceNodes[i];
  90. return0;
  91. }
  93. SLOGE("Volume%sfoundnosuitabledevicesformounting:(\n",getLabel());
  94. setState(Volume::State_Idle);
  96. return-1;
  97. }

到这里SD卡的挂载基本上已经完成，但是我们的目的是理清一条从底向上的路线,因此我会继续向上分析。我会将这一点在下一篇博文《Android 2.3 SD卡挂载流程浅析(五)》中继续分析。 因为这些都是我个人的一些见解，因此不见得都正确，希望读者抱着怀疑的态度阅读。不过不是有句名言叫“大胆假设，小心求证”吗！如文中有错误，还恳请各位看官指正。
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