reactos操作系统实现(123)

目前，Reactos主要使用FAT的文件系统，因此下面就先来分析这个文件系统，以便了解这个文件系统的功能。这个文件系统的实现是在驱动程序FASTFAT.SYS里实现的，所以来分析这个驱动程序的源码，就可以了解FAT文件系统了。

6.2.1 FAT文件系统驱动程序入口函数

FAT的文件系统是当作一个驱动程序来加载到系统里，因此它也有驱动程序的形式了，也就是它的入口点函数，还是DriverEntry函数，它的实现代码如下：

#001 NTSTATUS NTAPI

#002 DriverEntry(PDRIVER_OBJECT
DriverObject,

#003 PUNICODE_STRING
RegistryPath)

#004 /*

#005 * FUNCTION: Called by the
system to initialize the driver

#006 * ARGUMENTS:

#007 * DriverObject = object describing
this driver

#008 * RegistryPath = path to our
configuration entries

#009 * RETURNS: Success or
failure

#010 */

#011 {

#012 PDEVICE_OBJECT
DeviceObject;

FAT作为设备名称。

#013 UNICODE_STRING DeviceName
= RTL_CONSTANT_STRING(L"//Fat");

#014 NTSTATUS Status;

#015

创建文件系统设备对象。

#016 Status =
IoCreateDevice(DriverObject,

#017 sizeof(VFAT_GLOBAL_DATA),

#018 &DeviceName,

#019 FILE_DEVICE_DISK_FILE_SYSTEM,

#020 0,

#021 FALSE,

#022 &DeviceObject);

#023

如果创建这个设备名称已经存在，就使用RosFat的名称来创建设备。

#024 if (Status ==
STATUS_OBJECT_NAME_EXISTS ||

#025 Status ==
STATUS_OBJECT_NAME_COLLISION)

#026 {

#027 /* Try an other name,
if 'Fat' is already in use. 'Fat' is also used by fastfat.sys on W2K */

#028
RtlInitUnicodeString(&DeviceName, L"//RosFat");

#029 Status =
IoCreateDevice(DriverObject,

#030
sizeof(VFAT_GLOBAL_DATA),

#031
&DeviceName,

#032
FILE_DEVICE_DISK_FILE_SYSTEM,

#033
0,

#034
FALSE,

#035
&DeviceObject);

#036 }

#037

#038

#039

#040 if (!NT_SUCCESS(Status))

#041 {

#042 return (Status);

#043 }

#044

获取FAT全局数据区的指针。

#045 VfatGlobalData =
DeviceObject->DeviceExtension;

清空FAT全局数据区。

#046 RtlZeroMemory (VfatGlobalData,
sizeof(VFAT_GLOBAL_DATA));

#047
VfatGlobalData->DriverObject = DriverObject;

#048
VfatGlobalData->DeviceObject = DeviceObject;

#049

设置设备是直接访问IO的方式。

#050 DeviceObject->Flags |=
DO_DIRECT_IO;

设置驱动程序的IRP消息处理函数。

#051 DriverObject->MajorFunction[IRP_MJ_CLOSE]
= VfatBuildRequest;

#052
DriverObject->MajorFunction[IRP_MJ_CREATE] = VfatBuildRequest;

#053
DriverObject->MajorFunction[IRP_MJ_READ] = VfatBuildRequest;

#054
DriverObject->MajorFunction[IRP_MJ_WRITE] = VfatBuildRequest;

#055
DriverObject->MajorFunction[IRP_MJ_FILE_SYSTEM_CONTROL] =
VfatBuildRequest;

#056
DriverObject->MajorFunction[IRP_MJ_QUERY_INFORMATION] =
VfatBuildRequest;

#057
DriverObject->MajorFunction[IRP_MJ_SET_INFORMATION] =
VfatBuildRequest;

#058
DriverObject->MajorFunction[IRP_MJ_DIRECTORY_CONTROL] =
VfatBuildRequest;

#059
DriverObject->MajorFunction[IRP_MJ_QUERY_VOLUME_INFORMATION] =

#060 VfatBuildRequest;

#061
DriverObject->MajorFunction[IRP_MJ_SET_VOLUME_INFORMATION] =

#062 VfatBuildRequest;

#063
DriverObject->MajorFunction[IRP_MJ_SHUTDOWN] = VfatShutdown;

#064
DriverObject->MajorFunction[IRP_MJ_LOCK_CONTROL] = VfatBuildRequest;

#065
DriverObject->MajorFunction[IRP_MJ_CLEANUP] = VfatBuildRequest;

#066 DriverObject->MajorFunction[IRP_MJ_FLUSH_BUFFERS]
= VfatBuildRequest;

#067

#068
DriverObject->DriverUnload = NULL;

#069

缓存管理函数。

#070 /* Cache manager */

#071
VfatGlobalData->CacheMgrCallbacks.AcquireForLazyWrite =
VfatAcquireForLazyWrite;

#072
VfatGlobalData->CacheMgrCallbacks.ReleaseFromLazyWrite =
VfatReleaseFromLazyWrite;

#073
VfatGlobalData->CacheMgrCallbacks.AcquireForReadAhead =
VfatAcquireForReadAhead;

#074
VfatGlobalData->CacheMgrCallbacks.ReleaseFromReadAhead = VfatReleaseFromReadAhead;

#075

快速的I/O操作函数。

#076 /* Fast I/O */

#077
VfatInitFastIoRoutines(&VfatGlobalData->FastIoDispatch);

#078
DriverObject->FastIoDispatch =
&VfatGlobalData->FastIoDispatch;

#079

后备列表，以便提高速度。

#080 /* Private lists */

#081 ExInitializeNPagedLookasideList(&VfatGlobalData->FcbLookasideList,

#082
NULL, NULL, 0, sizeof(VFATFCB), TAG_FCB, 0);

#083
ExInitializeNPagedLookasideList(&VfatGlobalData->CcbLookasideList,

#084
NULL, NULL, 0, sizeof(VFATCCB), TAG_CCB, 0);

#085
ExInitializeNPagedLookasideList(&VfatGlobalData->IrpContextLookasideList,

#086
NULL, NULL, 0, sizeof(VFAT_IRP_CONTEXT), TAG_IRP, 0);

#087

初始化资源列表。

#088
ExInitializeResourceLite(&VfatGlobalData->VolumeListLock);

#089
InitializeListHead(&VfatGlobalData->VolumeListHead);

注册文件系统到系统列表里。

#090
IoRegisterFileSystem(DeviceObject);

#091 return(STATUS_SUCCESS);

#092 }