linux-kernel - How to tell when a gendisk has been freed?

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Message-ID: <20091002154447.62823bfv3qntxrrj@webmail.tau.ac.il>
Date:	Fri, 02 Oct 2009 15:44:47 +0200
From:	tomerma1@...t.tau.ac.il
To:	linux-kernel@...r.kernel.org
Subject: How to tell when a gendisk has been freed?

Hi,

Im writing a block device that does asynchronous mirroring. The user  
creates a device by giving a local device and
connecting to a remote device (on the net), mirroring writes to both.

When the user is done with the device i would like to give him the  
option of deleting the device. To do that, i first
stop taking requests (i disallow opens by looking at a variable i  
allocated for that device (a custom struct)), next
wait until there are no more active make_requests, and finally i free  
everything... However, theres a problem
with open - when i free the device, the open dereferences a variable i  
allocated for that device, but i have already
freed the device.

The only safe way to free the device is when i know for sure no more  
opens or make_requests can be called...
To do that i have to know when the gendisk is gone (even if i  
del_gendisk it, and wait until the opener counter drops to
zero, i cant be sure that another open isnt being executed at the moment)...
However, i didnt see any way to do it, so i was wondering what is the  
right way to do it?

Thanks,
      Tomer

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