Re: [PATCH] Add TPM hardware enablement driver

[Greg KH <greg@kroah.com>]

On Tue, Mar 22, 2005 at 09:02:24PM -0500, Jeff Garzik wrote:
> Kylene Hall wrote:
> >>what is the purpose of this pci_dev_get/put?  attempting to prevent 
> >>hotplug or
> >>something?
> >
> >
> >Seems that since there is a refernce to the device in the chip structure 
> >and I am making the file private data pointer point to that chip structure 
> >this is another reference that must be accounted for. If you remove it 
> >with it open and attempt read or write bad things will happen.  This isn't 
> >really hotpluggable either as the TPM is on the motherboard.
> 
> My point was that there will always be a reference -anyway-, AFAICS. 
> There is a pci_dev reference assigned to the pci_driver when the PCI 
> driver is loaded, and all uses by the TPM generic code of this pointer 
> are -inside- the pci_driver's pci_dev object lifetime.

Think of the following situation:
	- driver is bound to device.
	- userspace opens char dev node.
	- device is removed from the system (using fakephp I can do this
	  to _any_ pci device, even if it is on the motherboard.)
	- userspace writes to char dev node
	- driver attempts to access pci device structure that is no
	  longer present in memory.

Because of this open needs to get a reference to the pci device to
prevent oopses, or the driver needs to be aware of "device is now gone"
in some other manner.

thanks,

greg k-h