DbgPrint() display the diffrence value than variable. Why ?

NTFSD
1

I want to get the file size, and tried to get the ValidDataLength
(assosiated with FSRTL_COMMON_FCB_HEADER) with FileObject->FsContext.
When I copy the ValidDataLength to local variable, I got the difference
value than DbgPrint( “…%X”, pFcb->ValidDataLength) as following code.
Does anyone know, why DbgPrint() print the difference value ?

=== code ===
LONGLONG VLength;
FSRTL_COMMON_FCB_HEADER *pFcb;
pFcb = (FSRTL_COMMON_FCB_HEADER *)(irpStack->FileObject->FsContext);
VLength = pFcb->ValidDataLength.QuadPart;
DbgPrint(“VLength=%d\n”, VLength.QuadPart);
DbgPrint(“VDLen:%d\n”, pFcb->ValidDataLength.QuadPart);
// during FCB access, value may change. Then tried one more time.
DbgPrint(“VLength=%d\n”, VLength.QuadPart);
DbgPrint(“VDLen:%d\n”, pFcb->ValidDataLength.QuadPart);
== end of code ===
----- output ----
VLength=0
VDLen:57344
VLength=0
VDLen:57344
…
VLength=57344
VDLen:114688
VLength=57344
VDLen:114688
…
---- end of output —

2

Seems that the problem is in size of ValidDataLength.
It is 64-bit value, but “%d” expects 32-bit value.

try DbgPrint(“%lx-%lx”, VLength.HighPart, VLength.LowPart);

L.

3

> It is 64-bit value, but “%d” expects 32-bit value.

try DbgPrint(“%lx-%lx”, VLength.HighPart, VLength.LowPart);

DbgPrint(“%I64x”, VLength.QuadPart) is also a good idea.

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

4

Thank you for your reply.
I tried with “%I64d” and HighPart and LowPart member, and I got the value
(not 0).
But value for local variable and DbgPrint() was difference. yet.

Also, Itried with 3 machines, but one machine have this problem.
OS (Windows XP) and HDD format (NTFS) were same.

Tohru.

5

You can refer to the DDK Documentation of DbgPrint for your answer?

“Tohru” wrote in message news:xxxxx@ntfsd…
>I want to get the file size, and tried to get the ValidDataLength
> (assosiated with FSRTL_COMMON_FCB_HEADER) with FileObject->FsContext.
> When I copy the ValidDataLength to local variable, I got the difference
> value than DbgPrint( “…%X”, pFcb->ValidDataLength) as following code.
> Does anyone know, why DbgPrint() print the difference value ?
>
> === code ===
> LONGLONG VLength;
> FSRTL_COMMON_FCB_HEADER *pFcb;
> pFcb = (FSRTL_COMMON_FCB_HEADER *)(irpStack->FileObject->FsContext);
> VLength = pFcb->ValidDataLength.QuadPart;
> DbgPrint(“VLength=%d\n”, VLength.QuadPart);
> DbgPrint(“VDLen:%d\n”, pFcb->ValidDataLength.QuadPart);
> // during FCB access, value may change. Then tried one more time.
> DbgPrint(“VLength=%d\n”, VLength.QuadPart);
> DbgPrint(“VDLen:%d\n”, pFcb->ValidDataLength.QuadPart);
> == end of code ===
> ----- output ----
> VLength=0
> VDLen:57344
> VLength=0
> VDLen:57344
> …
> VLength=57344
> VDLen:114688
> VLength=57344
> VDLen:114688
> …
> ---- end of output —
>
>
>