Re: Filter Hook

Hi there folks,

I didn't mean to be stubborn.

Thank you all for helping me.

Guy

soviet_bloke@xxxxxxxxxxx wrote:
Hi mate

It looks like guys have already told you that you cannot wait at IRQL
= DISPATCH_LEVEL. It is understandable that you don't take "No" for an answer ( in your place I would not do it either), so that you are looking for some way around - after all,
no one explained to you why you cannot wait at IRQL >= DISPATCH_LEVEL.
Therefore, let me explain it to you in a very simple way, so that,
hopefully, you will stop thinking about trying to get around this
limitation


By calling any of Wait....() functions, your thread tells the system
that it does not want to run until something gets done by some other
thread (in your particular case, until packet gets processed). In order
for some other thread to start running, context switch is needed.
Context switch may occur only at IRQL < DISPATCH_LEVEL - as long as
IRQL is at or above DISPATCH_LEVEL, the system is not going to proceed
to the context switch.


In other words, logical chain stands as following:


Your thread does not want to run until "something" happens => this
"something" has to get done by some other thread => context switch is
required => IRQL must be below DISPATCH_LEVEL.


I hope by now you have already understood that waiting at IRQL >=
DISPATCH_LEVEL is among those things that just defeat the common sense,
so that a program that requires waiting at IRQL >= DISPATCH_LEVEL is
built upon some fundamental logical fallacy. Therefore, you have to
re-design your problem

Anton Bassov




x856256@xxxxxxxxx wrote:
Hello,

Either queueing the job or doing it asynchronously I will have to do
the job in another thread, and wait for the process of the packet to
finish (in order to return the drop, forward or pass reply), and this
is exactly where my problem began, when I tried to use the
KeWaitForSingleObject function.
So let me ask this again: How can I use this wait function, or any
other substitution that will allow me process the packet on another
thread (queued or not) and wait for it to finish processing in order to
return the value?

Thanks,
Guy

Doron Holan [MS] wrote:
you can't reduce IRQL inline, you can only raise it and then lower it. if
you truly want to synchronously process soemthing, then queue it to a work
item. if you want your filter to not negatively affect performance, learn
how to process the results in the completion routine asynchronously

d

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This posting is provided "AS IS" with no warranties, and confers no rights.


<x856256@xxxxxxxxx> wrote in message
news:1154873993.596484.241370@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
No,

The code is not taking any spinlocks.
Anyone has an idea how can I reduce the IRQL level inside the filter
hook function?

Thanks,
Guy

Don Burn wrote:
You cannot call a lot of functions at DISPATCH_LEVEL. I am not well
versed
in filter hooks, so you need to determine if the raising to DISPATCH is
avoidable. For instance, if the code takes a spinlock, could it take an
ERESOURCE instead.


--
Don Burn (MVP, Windows DDK)
Windows 2k/XP/2k3 Filesystem and Driver Consulting
http://www.windrvr.com
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<x856256@xxxxxxxxx> wrote in message
news:1154861486.219608.122660@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Hello and thanks Don for the answer.

It is running in IRQL_DISPATCH, I will try to reduce it and see what
happens.

Thanks,
Guy

Don Burn wrote:
A filter hook driver should not have an interrupt handler it is only
concerned with packets as they are presented to it. You should not
try
to
use IoConnectInterrupt with a software interrupt.

What IRQL are you running at when you crash, a common problem here
would
be
calling the functions you mentioned at IRQL_DISPATCH or higher.


--
Don Burn (MVP, Windows DDK)
Windows 2k/XP/2k3 Filesystem and Driver Consulting
http://www.windrvr.com
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<x856256@xxxxxxxxx> wrote in message
news:1154814887.364085.142850@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Hi,

Drivers are very new to me, can someone help me with the next issue
please:

I have tried to set up a Filter Hook driver.
I took an example code from codeproject (DrvFltIp) and it works ok
on
my computer (Windows XP).

When I try to process the packets more thoroughly than in this
example
code, my computer crashed (freezes or restarts immediately).
The crash happens when I do something that involves a
KeWaitForSingleObject or a KeDelayExecutionThread call (but I am not
sure these are the only scenarios that cause a crash).

I looked in the dump file with WinDbg after the crash and saw that
one
of the last actions of the kernel were sending an interrupt and
afterwards an exception. So my guess was that the kernel is sending
a
trap that was sent to it by the hardware to my driver to handle, but
since I didn't set up an interrupt call back function, an exception
is
raised.
The next thing I did was to try and set up an interrupt call back
function, but this also caused a similar crash to the system (when I
tried to pull out the parameters that I have to pass to the function
"IoConnectInterrupt" from the isrStack). I tried to call the
function
"IoConnectInterrupt" from the function
"DriverObject->MajorFunction[IRP_MJ_CREATE]" when got
"IRP_MJ_CREATE"
in "irpStack->MajorFunction" or when I got "IRP_MN_START_DEVICE IRP"
in
"irpStack->MinorFunction". When I tried even to access the parameter
"irpStack->Parameters->StartDevice.AllocatedResourcesTranslated->Count"
(even without calling "IoConnectInterrupt") it caused a crash.

If anyone can help me understand what I am doing wrong, and why I am
getting all these crashes I would be grateful.

Thanks,
Guy




.

Relevant Pages

  • Re: Filter Hook
    ... you can't reduce IRQL inline, you can only raise it and then lower it. ... Windows 2k/XP/2k3 Filesystem and Driver Consulting ... What IRQL are you running at when you crash, ...
    (microsoft.public.development.device.drivers)
  • Re: IRQL_NOT_LESS_OR_EQUAL at KeWaitForMultipleObjects
    ... IRQL at the crash moment is not the same as at Wait call. ... I think the crash is because the array of object pointers is allocated from ... >> If a kernel debugger is available get the stack backtrace. ...
    (microsoft.public.development.device.drivers)
  • Re: What does it mean this assert, but still question
    ... the assertions in Windows components are not very helpful: ... to design control paths based on IRQL known as part of the contract. ... it is a fixed characteristic of the driver design, ... If I did it, all should be OK and asserts should not appear, ...
    (microsoft.public.development.device.drivers)
  • Re: Filter Hook
    ... It looks like guys have already told you that you cannot wait at IRQL ... Windows 2k/XP/2k3 Filesystem and Driver Consulting ... What IRQL are you running at when you crash, ...
    (microsoft.public.development.device.drivers)
  • Re: Filter Hook
    ... Windows 2k/XP/2k3 Filesystem and Driver Consulting ... use IoConnectInterrupt with a software interrupt. ... What IRQL are you running at when you crash, ...
    (microsoft.public.development.device.drivers)
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