linux-kernel - RE: [PATCH 08/25] Staging: hv: vmbus_driver cannot be unloaded; cleanup accordingly

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Message-ID: <6E21E5352C11B742B20C142EB499E0481DD1C9@TK5EX14MBXC124.redmond.corp.microsoft.com>
Date:	Wed, 27 Apr 2011 02:31:18 +0000
From:	KY Srinivasan <kys@...rosoft.com>
To:	Greg KH <greg@...ah.com>
CC:	"gregkh@...e.de" <gregkh@...e.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
	"virtualization@...ts.osdl.org" <virtualization@...ts.osdl.org>,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	"Abhishek Kane (Mindtree Consulting PVT LTD)" 
	<v-abkane@...rosoft.com>
Subject: RE: [PATCH 08/25] Staging: hv: vmbus_driver cannot be unloaded;
 cleanup accordingly



> -----Original Message-----
> From: Greg KH [mailto:greg@...ah.com]
> Sent: Tuesday, April 26, 2011 6:46 PM
> To: KY Srinivasan
> Cc: gregkh@...e.de; linux-kernel@...r.kernel.org;
> devel@...uxdriverproject.org; virtualization@...ts.osdl.org; Haiyang Zhang;
> Abhishek Kane (Mindtree Consulting PVT LTD)
> Subject: Re: [PATCH 08/25] Staging: hv: vmbus_driver cannot be unloaded;
> cleanup accordingly
> 
> On Tue, Apr 26, 2011 at 09:20:25AM -0700, K. Y. Srinivasan wrote:
> > The vmbus driver cannot be unloaded; the windows host does not
> > permit this. Cleanup accordingly.
> 
> Woah, you just prevented this driver from ever being able to be
> unloaded.

It was never unloadable; while the driver defined an exit routine, 
there were couple of issues unloading the vmbus driver:
 
1) All guest resources given to the host could not be recovered.

2) Windows host would not permit reloading the driver without 
rebooting the guest.

All I did was acknowledge the current state and cleanup 
accordingly. This is not unique to Hyper-V; for what it is worth,
the Xen platform_pci  driver which is equivalent to the vmbus driver
is also not unlodable (the last time I checked).

> 
> That's not a "cleanup" that's a major change in how things work.  I'm
> sure, if you want to continue down this line, there are more things you
> can remove from the code, right?
> 
> What is the real issue here?  What happens if you unload the bus?  What
> goes wrong?  Can it be fixed?

This needs to be fixed on the host side. I have notified them of the issue. 

> 
> This is a pretty big commitment...

These drivers only load when Linux is hosted on  a Hyper-V platform;
I am not sure why it is a "big commitment" given that the host does not 
permit reloading this driver without rebooting the guest. 

Regards,

K. Y

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