Block device and cached I/O question

NTDEV
1

Hello,

I have a virtual disk device that sits on top of a block device.
Is there any way I can employ cached I/o (CcCopyRead, CcCopyWrite,…)
to do R/W from the block device?

I try CcInitializeCacheMap on a FILE_OBJECT returned from
IoGetDeviceObjectPointer but it always throws an exception with error code
0xc0000005. I look at file object and most of its fields are NULL.
Do I need to somehow populate these fields or
am I taking a wrong approach here. Please help. Thanks

Chu Bun

/////
status = IoGetDeviceObjectPointer(&blockDevice /*
\Device\Hardisk1\Partition0 */,
FILE_READ_ATTRIBUTES | FILE_WRITE_ATTRIBUTES,
&(pFileObj),
&(pDevObj));

try
{
CcInitializeCacheMap(pFileObj, // File obj
&FileSizes, // file sizes are set to size of the
block device
TRUE, // use PinAccess
&(MyGlobalData.CacheMgrCallBacks), // CM callbacks
pMyContext); // context used by callbacks
}
except(EXCEPTION_EXECUTE_HANDLER)
{
status = GetExceptionCode(); // 0xc0000005
}

/////

2

Why on earth would you want to do this? The FSD on top of your driver will
handle caching.

Jamey Kirby, Windows DDK MVP
StorageCraft Inc.
xxxxx@storagecraft.com
http://www.storagecraft.com

-----Original Message-----
From: xxxxx@lists.osr.com
[mailto:xxxxx@lists.osr.com] On Behalf Of ChuBun
Sent: Wednesday, January 28, 2004 9:57 AM
To: Windows System Software Devs Interest List
Subject: [ntdev] Block device and cached I/O question

Hello,

I have a virtual disk device that sits on top of a block device.
Is there any way I can employ cached I/o (CcCopyRead, CcCopyWrite,…)
to do R/W from the block device?

I try CcInitializeCacheMap on a FILE_OBJECT returned from
IoGetDeviceObjectPointer but it always throws an exception with error code
0xc0000005. I look at file object and most of its fields are NULL.
Do I need to somehow populate these fields or
am I taking a wrong approach here. Please help. Thanks

Chu Bun

/////
status = IoGetDeviceObjectPointer(&blockDevice /*
\Device\Hardisk1\Partition0 */,
FILE_READ_ATTRIBUTES | FILE_WRITE_ATTRIBUTES,
&(pFileObj),
&(pDevObj));

try
{
CcInitializeCacheMap(pFileObj, // File obj
&FileSizes, // file sizes are set to size of the
block device
TRUE, // use PinAccess
&(MyGlobalData.CacheMgrCallBacks), // CM callbacks
pMyContext); // context used by callbacks
}
except(EXCEPTION_EXECUTE_HANDLER)
{
status = GetExceptionCode(); // 0xc0000005
}

/////

Questions? First check the Kernel Driver FAQ at
http://www.osronline.com/article.cfm?id=256

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3

No, Cache Manager is a library provided for filesystems, and only the
filesystems can use it.

If you’re planning to run the usual NT filesystems on your disk - then you
do not need any disk level caching at all. Otherwise, write your own
filesystem, which will use Cc services.

Maxim Shatskih, Windows DDK MVP
StorageCraft Corporation
xxxxx@storagecraft.com
http://www.storagecraft.com

----- Original Message -----
From: “ChuBun”
Newsgroups: ntdev
To: “Windows System Software Devs Interest List”
Sent: Wednesday, January 28, 2004 8:57 PM
Subject: [ntdev] Block device and cached I/O question

> Hello,
>
> I have a virtual disk device that sits on top of a block device.
> Is there any way I can employ cached I/o (CcCopyRead, CcCopyWrite,…)
> to do R/W from the block device?
>
> I try CcInitializeCacheMap on a FILE_OBJECT returned from
> IoGetDeviceObjectPointer but it always throws an exception with error code
> 0xc0000005. I look at file object and most of its fields are NULL.
> Do I need to somehow populate these fields or
> am I taking a wrong approach here. Please help. Thanks
>
> Chu Bun
>
> /////
> status = IoGetDeviceObjectPointer(&blockDevice /*
> \Device\Hardisk1\Partition0 */,
> FILE_READ_ATTRIBUTES | FILE_WRITE_ATTRIBUTES,
> &(pFileObj),
> &(pDevObj));
>
> try
> {
> CcInitializeCacheMap(pFileObj, // File obj
> &FileSizes, // file sizes are set to size of the
> block device
> TRUE, // use PinAccess
> &(MyGlobalData.CacheMgrCallBacks), // CM callbacks
> pMyContext); // context used by callbacks
> }
> except(EXCEPTION_EXECUTE_HANDLER)
> {
> status = GetExceptionCode(); // 0xc0000005
> }
>
> /////
>
>
>
> —
> Questions? First check the Kernel Driver FAQ at
http://www.osronline.com/article.cfm?id=256
>
> You are currently subscribed to ntdev as: xxxxx@storagecraft.com
> To unsubscribe send a blank email to xxxxx@lists.osr.com

4

Thank you all for the quick reply.

I monitor the Dispatch R/W routines of my driver and don’t see any activity
that seems to relate to caching I/Os. So I thought maybe this is something
that I need to handle.