linux-kernel - RE: [PATCH 0000/0046] Staging: hv: Driver cleanup

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Message-ID: <6E21E5352C11B742B20C142EB499E048081B551C@TK5EX14MBXC126.redmond.corp.microsoft.com>
Date:	Wed, 31 Aug 2011 14:18:42 +0000
From:	KY Srinivasan <kys@...rosoft.com>
To:	Greg KH <greg@...ah.com>
CC:	Olaf Hering <olaf@...fle.de>,
	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
	"gregkh@...e.de" <gregkh@...e.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"virtualization@...ts.osdl.org" <virtualization@...ts.osdl.org>
Subject: RE: [PATCH 0000/0046] Staging: hv: Driver cleanup



> -----Original Message-----
> From: Greg KH [mailto:greg@...ah.com]
> Sent: Tuesday, August 30, 2011 1:44 PM
> To: KY Srinivasan
> Cc: Olaf Hering; devel@...uxdriverproject.org; gregkh@...e.de; linux-
> kernel@...r.kernel.org; virtualization@...ts.osdl.org
> Subject: Re: [PATCH 0000/0046] Staging: hv: Driver cleanup
> 
> On Tue, Aug 30, 2011 at 05:22:54PM +0000, KY Srinivasan wrote:
> >
> >
> > > -----Original Message-----
> > > From: Olaf Hering [mailto:olaf@...fle.de]
> > > Sent: Tuesday, August 30, 2011 8:49 AM
> > > To: KY Srinivasan
> > > Cc: gregkh@...e.de; linux-kernel@...r.kernel.org;
> > > devel@...uxdriverproject.org; virtualization@...ts.osdl.org
> > > Subject: Re: [PATCH 0000/0046] Staging: hv: Driver cleanup
> > >
> > > On Sat, Aug 27, K. Y. Srinivasan wrote:
> > >
> > > > 	2) Handle all block devices using the storvsc driver. I have modified
> > > > 	   the implementation here based on Christoph's feedback on my earlier
> > > > 	   implementation.
> > >
> > > The upgrade path from hv_blkvsc to hv_storvsc is difficult.
> > >
> > > hv_storvsc does not provide the vmbus:hv_block modalias, so mkinitrd
> > > does not know what module to choose when mkinitrd is called in a
> > > previous kernel (like sles11sp1).
> > >
> > >
> > > In a guest with both SCSI and IDE controllers the IDE disks are
> > > discovered first, so the SCSI drives will also change their names.
> > > Thats not a problem for data partitions because they could be mounted by
> > > UUID or LABEL in fstab.
> > > But its difficult to adjust /boot/grub/device.map for example because
> > > the old  IDE drives do not provide an identifier. What is the best way
> > > to make sure the rename from hd* to sd* in such config files is done
> > > correctly? Is it safe to assume that all drives with a class_id of
> > > 32412632-86cb-44a2-9b5c50d1417354f5 are connected to IDE ports?
> >
> > The class_id is invariant as we are returning the guid of the device under
> class_id.
> >
> > So, if you see a IDE guid under class_id, you can be sure (a) it is an ide device
> and (b)
> > it is a device managed via the PV drivers.
> >
> > >
> > > localhost:~ # head /sys/bus/vmbus/devices/vmbus_0_{1,2,3,10,11}/class_id
> > > ==> /sys/bus/vmbus/devices/vmbus_0_1/class_id <==
> > > {32412632-86cb-44a2-9b5c50d1417354f5}
> > >
> > > ==> /sys/bus/vmbus/devices/vmbus_0_2/class_id <==
> > > {32412632-86cb-44a2-9b5c50d1417354f5}
> > >
> > > ==> /sys/bus/vmbus/devices/vmbus_0_3/class_id <==
> > > {32412632-86cb-44a2-9b5c50d1417354f5}
> > >
> > > ==> /sys/bus/vmbus/devices/vmbus_0_10/class_id <==
> > > {ba6163d9-04a1-4d29-b60572e2ffb1dc7f}
> > >
> > > ==> /sys/bus/vmbus/devices/vmbus_0_11/class_id <==
> > > {ba6163d9-04a1-4d29-b60572e2ffb1dc7f}
> > >
> > >
> > > In my test system, the IDE drives are now discovered twice, once by
> > > hv_storvsc and once by libata:
> >
> > This is a known (old problem). The way this was handled earlier was to have the
> > modprobe rules in place to setup a dependency that would force the load of
> the
> > hyper-v driver (blk / stor) ahead of the native driver and if the load of the PV
> > driver succeeded, we would not load the native driver. In sles11 sp1, we had a
> rule for
> > loading blkvsc. With the merge of blkvsc and storvsc, the only change we need
> to make
> > is to have storvsc in the rule (instaed of blkvsc).
> 
> Why do we need a rule at all?  Shouldn't the module dependancy stuff
> handle the autoloading of the drivers properly from the initrd now that
> the hotplug logic is hooked up properly?
> 
> What am I missing here?

On sles11 the PV drivers are used to manage the root device. Autoloading is not
the issue here; to manage the root device, we want to load the Hyper-V disk driver
before the native Linux disk driver for the emulated IDE device.

> 
> Or is the hotplug code not working correctly?

Hotplug code is working as expected; the issue is taking control of the root device and
preventing the same device being presented once through native drivers and once through
Hyper-V drivers.

Regards,

K. Y 
> 
> greg k-h

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