RE: [PATCH 1/1] Staging: hv: storvsc: Move the storage driver outof the staging area

[KY Srinivasan]

> -----Original Message-----
> From: KY Srinivasan
> Sent: Thursday, November 17, 2011 11:53 PM
> To: 'James Bottomley'
> Cc: gregkh@xxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> devel@xxxxxxxxxxxxxxxxxxxxxx; virtualization@xxxxxxxxxxxxxx; linux-
> scsi@xxxxxxxxxxxxxxx; ohering@xxxxxxxx; hch@xxxxxxxxxxxxx
> Subject: RE: [PATCH 1/1] Staging: hv: storvsc: Move the storage driver out of the
> staging area
> 
> 
> 
> > -----Original Message-----
> > From: James Bottomley [mailto:James.Bottomley@xxxxxxxxxxxxxxxxxxxxx]
> > Sent: Thursday, November 17, 2011 1:27 PM
> > To: KY Srinivasan
> > Cc: gregkh@xxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> > devel@xxxxxxxxxxxxxxxxxxxxxx; virtualization@xxxxxxxxxxxxxx; linux-
> > scsi@xxxxxxxxxxxxxxx; ohering@xxxxxxxx; hch@xxxxxxxxxxxxx
> > Subject: Re: [PATCH 1/1] Staging: hv: storvsc: Move the storage driver out of
> the
> > staging area
> >
> > On Tue, 2011-11-08 at 10:13 -0800, K. Y. Srinivasan wrote:
> > > The storage driver (storvsc_drv.c) handles all block storage devices
> > > assigned to Linux guests hosted on Hyper-V. This driver has been in the
> > > staging tree for a while and this patch moves it out of the staging area.
> > > As per Greg's recommendation, this patch makes no changes to the
> staging/hv
> > > directory. Once the driver moves out of staging, we will cleanup the
> > > staging/hv directory.
> > >
> > > This patch includes all the patches that I have sent against the staging/hv
> > > tree to address the comments I have gotten to date on this storage driver.
> >
> > First comment is that it would have been easier to see the individual
> > patches for comment before you committed them.
> 
> I am not sure if the patches have been committed yet. All patches were sent
> to various mailing lists and you were copied as well. In the future, I will include
> the scsi mailing list in the set of lists I include for the staging patches.

Greg has checked in these patches now.

> 
> >
> > The way you did mempool isn't entirely right: the problem is that to
> > prevent a memory to I/O deadlock we need to ensure forward progress on
> > the drain device.  Just having 64 commands available to the host doesn't
> > necessarily achieve this because LUN1 could consume them all and starve
> > LUN0 which is the drain device leading to the deadlock, so the mempool
> > really needs to be per device using slave_alloc.
> 

Presently, Linux on Hyper-V can only boot from IDE devices. While IDE devices are
handled via this stor driver, the way we handle them is a little different compared
to block devices configured as scsi devices:

For  IDE devices; we have a HBA per LUN. Given that for a long time the drain device will
be an IDE device, my current implementation does address the concern that you had raised 
with regards to deadlock avoidance. 

> 
> >
> > +static int storvsc_device_alloc(struct scsi_device *sdevice)
> > +{
> > +	/*
> > +	 * This enables luns to be located sparsely. Otherwise, we may not
> > +	 * discovered them.
> > +	 */
> > +	sdevice->sdev_bflags |= BLIST_SPARSELUN | BLIST_LARGELUN;
> > +	return 0;
> > +}
> >
> > Looks bogus ... this should happen automatically for SCSI-3 devices ...
> > unless your hypervisor has some strange (and wrong) identification?  I
> > really think you want to use SCSI-3 because it will do report LUN
> > scanning, which consumes far fewer resources.
> 

Done.

> 
> >
> > I still think you need to disable clustering and junk the bvec merge
> > function.  Your object seems to be to accumulate in page size multiples
> > (and not aggregate over this) ... that's what clustering is designed to
> > do.

Done. James, I am going to send you (and the scsi mailing list) the patches addressing 
your comments. I will also send out a consolidated patch for getting the driver out of 
staging as well. I would like to thank you for your help in cleaning up this driver.

Regards,

K. Y
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