Re: [PATCH v3] xen-blk(front|back): Handle large physical sector disks

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Wed, May 22, 2013 at 01:48:02PM +0200, Stefan Bader wrote:
> On 15.05.2013 17:02, Stefan Bader wrote:
> > Changed the xenbus_gather but kept the xenbus_dev_error (without being fatal) as
> > that seems closer to the style of the other calls.
> 
> Was this ok as is or pending some answers/discussion which I may have not
> given/missed?

I think that was it. Thanks for ping!
> 
> -Stefan
> 
> > 
> > -Stefan
> > 
> > From cddea87d842cc5feb427f3eedefc0566d69fb9b6 Mon Sep 17 00:00:00 2001
> > From: Stefan Bader <stefan.bader@canonical.com>
> > Date: Mon, 13 May 2013 16:28:15 +0200
> > Subject: [PATCH] xen/blk: Use physical sector size for setup
> > 
> > Currently xen-blkback passes the logical sector size over xenbus and
> > xen-blkfront sets up the paravirt disk with that logical block size.
> > But newer drives usually have the logical sector size set to 512 for
> > compatibility reasons and would show the actual sector size only in
> > physical sector size.
> > This results in the device being partitioned and accessed in dom0 with
> > the correct sector size, but the guest thinks 512 bytes is the correct
> > block size. And that results in poor performance.
> > 
> > To fix this, blkback gets modified to pass also physical-sector-size
> > over xenbus and blkfront to use both values to set up the paravirt
> > disk. I did not just change the passed in sector-size because I am
> > not sure having a bigger logical sector size than the physical one
> > is valid (and that would happen if a newer dom0 kernel hits an older
> > domU kernel). Also this way a domU set up before should still be
> > accessible (just some tools might detect the unaligned setup).
> > 
> > [v2: Make xenbus write failure non-fatal]
> > [v3: Use xenbus_scanf instead of xenbus_gather]
> > 
> > Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
> > ---
> >  drivers/block/xen-blkback/xenbus.c |    5 +++++
> >  drivers/block/xen-blkfront.c       |   23 +++++++++++++++++++----
> >  2 files changed, 24 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
> > index 8bfd1bc..25463e3 100644
> > --- a/drivers/block/xen-blkback/xenbus.c
> > +++ b/drivers/block/xen-blkback/xenbus.c
> > @@ -704,6 +704,11 @@ again:
> >  				 dev->nodename);
> >  		goto abort;
> >  	}
> > +	err = xenbus_printf(xbt, dev->nodename, "physical-sector-size", "%u",
> > +			    bdev_physical_block_size(be->blkif->vbd.bdev));
> > +	if (err)
> > +		xenbus_dev_error(dev, err, "writing %s/physical-sector-size",
> > +				 dev->nodename);
> > 
> >  	err = xenbus_transaction_end(xbt, 0);
> >  	if (err == -EAGAIN)
> > diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
> > index d89ef86..33b5618 100644
> > --- a/drivers/block/xen-blkfront.c
> > +++ b/drivers/block/xen-blkfront.c
> > @@ -542,7 +542,8 @@ wait:
> >  		flush_requests(info);
> >  }
> > 
> > -static int xlvbd_init_blk_queue(struct gendisk *gd, u16 sector_size)
> > +static int xlvbd_init_blk_queue(struct gendisk *gd, u16 sector_size,
> > +				unsigned int physical_sector_size)
> >  {
> >  	struct request_queue *rq;
> >  	struct blkfront_info *info = gd->private_data;
> > @@ -564,6 +565,7 @@ static int xlvbd_init_blk_queue(struct gendisk *gd, u16
> > sector_size)
> > 
> >  	/* Hard sector size and max sectors impersonate the equiv. hardware. */
> >  	blk_queue_logical_block_size(rq, sector_size);
> > +	blk_queue_physical_block_size(rq, physical_sector_size);
> >  	blk_queue_max_hw_sectors(rq, 512);
> > 
> >  	/* Each segment in a request is up to an aligned page in size. */
> > @@ -667,7 +669,8 @@ static char *encode_disk_name(char *ptr, unsigned int n)
> > 
> >  static int xlvbd_alloc_gendisk(blkif_sector_t capacity,
> >  			       struct blkfront_info *info,
> > -			       u16 vdisk_info, u16 sector_size)
> > +			       u16 vdisk_info, u16 sector_size,
> > +			       unsigned int physical_sector_size)
> >  {
> >  	struct gendisk *gd;
> >  	int nr_minors = 1;
> > @@ -734,7 +737,7 @@ static int xlvbd_alloc_gendisk(blkif_sector_t capacity,
> >  	gd->driverfs_dev = &(info->xbdev->dev);
> >  	set_capacity(gd, capacity);
> > 
> > -	if (xlvbd_init_blk_queue(gd, sector_size)) {
> > +	if (xlvbd_init_blk_queue(gd, sector_size, physical_sector_size)) {
> >  		del_gendisk(gd);
> >  		goto release;
> >  	}
> > @@ -1395,6 +1398,7 @@ static void blkfront_connect(struct blkfront_info *info)
> >  {
> >  	unsigned long long sectors;
> >  	unsigned long sector_size;
> > +	unsigned int physical_sector_size;
> >  	unsigned int binfo;
> >  	int err;
> >  	int barrier, flush, discard, persistent;
> > @@ -1437,6 +1441,16 @@ static void blkfront_connect(struct blkfront_info *info)
> >  		return;
> >  	}
> > 
> > +	/*
> > +	 * physcial-sector-size is a newer field, so old backends may not
> > +	 * provide this. Assume physical sector size to be the same as
> > +	 * sector_size in that case.
> > +	 */
> > +	err = xenbus_scanf(XBT_NIL, info->xbdev->otherend,
> > +			   "physical-sector-size", "%u", &physical_sector_size);
> > +	if (err != 1)
> > +		physical_sector_size = sector_size;
> > +
> >  	info->feature_flush = 0;
> >  	info->flush_op = 0;
> > 
> > @@ -1483,7 +1497,8 @@ static void blkfront_connect(struct blkfront_info *info)
> >  	else
> >  		info->feature_persistent = persistent;
> > 
> > -	err = xlvbd_alloc_gendisk(sectors, info, binfo, sector_size);
> > +	err = xlvbd_alloc_gendisk(sectors, info, binfo, sector_size,
> > +				  physical_sector_size);
> >  	if (err) {
> >  		xenbus_dev_fatal(info->xbdev, err, "xlvbd_add at %s",
> >  				 info->xbdev->otherend);
> > 
> > 
> > 
> > _______________________________________________
> > Xen-devel mailing list
> > Xen-devel@lists.xen.org
> > http://lists.xen.org/xen-devel
> > 
> 
> 



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