i/o requests are serialized per process

NTDEV
1

My coworker is writing an app to interface my driver.
My kmdf driver has two ioctls:

IOCTL_NOTIFY which blocks indefinitely with STATUS_PENDING
IOCTL_CANCEL_NOTIFY which cancels the first ioctl.

If I run the app:

Process A:
Thread 1) issues IOCTL_NOTIFY and blocks (non-overlapped i/o)
Thread 2) issues IOCTL_CANCEL_NOTIFY, but the ioctl never makes it to the driver.

However if I run a second instance of the app from process B:

Process B:
Thread ) issues IOCTL_CANCEL_NOTIFY, it works.

It seems like i/o requests are serialized per process in this case not per thread. Any insight is appreciated.

Thanks,

2

Open the handle as overlapped. A non overlapped handle allows only one pending io at a time.

d

-----Original Message-----
From: xxxxx@lists.osr.com [mailto:xxxxx@lists.osr.com] On Behalf Of xxxxx@yahoo.com
Sent: Tuesday, April 20, 2010 10:40 AM
To: Windows System Software Devs Interest List
Subject: [ntdev] i/o requests are serialized per process

My coworker is writing an app to interface my driver.
My kmdf driver has two ioctls:

IOCTL_NOTIFY which blocks indefinitely with STATUS_PENDING IOCTL_CANCEL_NOTIFY which cancels the first ioctl.

If I run the app:

Process A:
Thread 1) issues IOCTL_NOTIFY and blocks (non-overlapped i/o)
Thread 2) issues IOCTL_CANCEL_NOTIFY, but the ioctl never makes it to the driver.

However if I run a second instance of the app from process B:

Process B:
Thread ) issues IOCTL_CANCEL_NOTIFY, it works.

It seems like i/o requests are serialized per process in this case not per thread. Any insight is appreciated.

Thanks,

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3

> It seems like i/o requests are serialized per process in this case not per thread

If FILE_FLAG_OVERLAPPED is not used, the IO requests are serialized per handle.

So, use FILE_FLAG_OVERLAPPED or open the second handle just to send a cancel.

–
Maxim S. Shatskih
Windows DDK MVP
xxxxx@storagecraft.com
http://www.storagecraft.com