RE: [PATCH 00/40] Staging: hv: Driver cleanup

-----Original Message-----
From: Christoph Hellwig [mailto:hch@infradead.org]
Sent: Friday, July 01, 2011 4:22 AM
To: KY Srinivasan
Cc: Christoph Hellwig; gregkh@suse.de; linux-kernel@vger.kernel.org;
devel@linuxdriverproject.org; virtualization@lists.osdl.org
Subject: Re: [PATCH 00/40] Staging: hv: Driver cleanup

On Thu, Jun 30, 2011 at 11:28:27PM +0000, KY Srinivasan wrote:

quoted

quoted

On Wed, Jun 29, 2011 at 07:38:21AM -0700, K. Y. Srinivasan wrote:

quoted

Further cleanup of the hv drivers:

	1) Cleanup the reference counting mess for both stor and net devices.

I really don't understand the need for reference counting on the storage
side, especially now that you only have a SCSI driver.  The SCSI
midlayer does proper counting on it's objects (Scsi_Host, scsi_device,
scsi_cmnd), so you'll get that for free given that SCSI drivers just
piggyback on the midlayer lifetime rules.

The reference counting allows us to properly deal with messages coming back

from the host

quoted

to the guest with a racing remove of the device. I am told these messages could

potentially be

quoted

not a response to a message sent from the guest.

To deal with that the scsi subsystem has a two stage teardown for the
SCSI host.  First you call scsi_remove_host, at which point no new I/O
to it can be started.  After that you can wait for all outstanding
messages, and finally you do a scsi_host_put to drop the long-term
reference to it, and eventually free it.

That is what I have currently implemented both on the stor as well
as the net side with regards to the device specific objects hanging off of
struct hv_device (the ext field). If it is ok with you, I want to do what you
had suggested earlier. Keep the patches as they are with regards to 
reference counting for now. We can always simplify the code later.

Regards,

K. Y