Windows System Software -- Consulting, Training, Development -- Unique Expertise, Guaranteed Results

Home NTDEV
Before Posting...
Please check out the Community Guidelines in the Announcements and Administration Category.

More Info on Driver Writing and Debugging


The free OSR Learning Library has more than 50 articles on a wide variety of topics about writing and debugging device drivers and Minifilters. From introductory level to advanced. All the articles have been recently reviewed and updated, and are written using the clear and definitive style you've come to expect from OSR over the years.


Check out The OSR Learning Library at: https://www.osr.com/osr-learning-library/


using WdfExecutionLevelPassive for forcing EvtIoDeviceControl to be run at passive_level irql

Ehsan_TaheriEhsan_Taheri Member Posts: 190

Hi experts,
I am talking about a KMDF disk filter here.
I need to call some zwcreatefile and zwreadfile and kewaitfforsingleobject to wait for some event in my EvtIoDeviceControl routine.

Is it safe to do this in my device add callback to achieve my goal?

WDF_OBJECT_ATTRIBUTES_INIT_CONTEXT_TYPE(&objAtttributes,
                                        FILTER_DEVICE_CONTEXT);

objAtttributes.ExecutionLevel = WdfExecutionLevelPassive;

status = WdfDeviceCreate(&DeviceInit,
                         &objAtttributes,
                         &wdfDevice);

If it does the job, is there any overhead or consequences to forcing WdfExecutionLevelPassive?
Should I consider the device stack I am filtering or other filters too? Or I can freely force my callback being called in passive_level. (looks like kind of magic to me)

Comments

  • Peter_Viscarola_(OSR)Peter_Viscarola_(OSR) Administrator Posts: 8,158

    Is it safe to do this in my device add callback to achieve my goal

    Yes. By doing this you're establishing a "PASSIVE_LEVEL execution constraint."

    I can freely force my callback being called in passive_level.

    If you need to be at IRQL PASSIVE_LEVEL, then you need to be at IRQL PASSIVE_LEVEL. The device stack doesn't matter.

    It's not magic... the Framework simply looks at the current IRQL before it calls your EvtIoXxx Event Processing Callbacks. If the IRQL is > PASSIVE_LEVEL, and you've established a PASSIVE_LEVEL execution constraint, then the Framework sends your callback to a worker thread (thus, causing the callback to happen at IRQL PASSIVE_LEVEL as you required).

    There's no extra overhead (then majority of the time) when your EvtIoXxx Event Processing Callback is already called at IRQL PASSIVE_LEVEL.

    So, yup... go for it.

    Peter

    Peter Viscarola
    OSR
    @OSRDrivers

  • Ehsan_TaheriEhsan_Taheri Member Posts: 190

    Thanks for the answer.
    Actually since I was studying the IRQL lately and it was said that one should not lower the IRQL so I thought there might be some magic here.
    Well I was aware of the other solution and was planning if this did not work for me I should pass the work to a worker thread. I just do not know why I did not think the Microsoft developers might be as clever as me to know this and concluded they would resort to magic!

Sign In or Register to comment.

Howdy, Stranger!

It looks like you're new here. If you want to get involved, click one of these buttons!

Upcoming OSR Seminars
OSR has suspended in-person seminars due to the Covid-19 outbreak. But, don't miss your training! Attend via the internet instead!
Writing WDF Drivers 7 Dec 2020 LIVE ONLINE
Internals & Software Drivers 25 Jan 2021 LIVE ONLINE
Developing Minifilters 8 March 2021 LIVE ONLINE