Kernel deferring driver 'close' call: workaround?

From: Evan Lavelle
Date: Wed Jan 26 2011 - 08:10:42 EST


I've written a PCIe driver for a specialist card, which can only have a single user ('open' returns EBUSY if the board is already open). A user has complained that they can't do this with the card:

1 - open() // Ok
2 - close()
3 - open() // fails

'strace' shows that the 'close' succeeds, but the driver debug output shows that the driver close/release (step 2) is not called before the next open (step 3), so the open fails.

I appreciate that the kernel may want to defer the driver 'close', even though the open count is only 1. However, I'm surprised that the kernel calls the driver open code at step (3) without first calling the deferred close from step (2).

Is this expected behaviour? If so, can anyone suggest a work-around, at either driver or user level?

Thanks.
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