Re: [PATCH] xen/blkback: Squash the discard support for 'file' and 'phy' type.

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

On Wed, Mar 14, 2012 at 09:48:21AM +0000, Jan Beulich wrote:
> >>> On 13.03.12 at 23:52, Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> wrote:
> > The only reason for the distinction was for the special case of
> > 'file' (which is assumed to be loopback device), was to reach inside
> > the loopback device, find the underlaying file, and call fallocate on it.
> > Fortunately "xen-blkback: convert hole punching to discard request on
> > loop devices" removes that use-case and we now based the discard
> > support based on blk_queue_discard(q) and extract all appropriate
> > parameters from the 'struct request_queue'.
> > 
> > CC: Li Dongyang <lidongyang@novell.com>
> > CC: Jan Beulich <JBeulich@suse.com>
> > Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
> 
> Acked-by: Jan Beulich <jbeulich@suse.com>
> 
> (with a few minor remarks below)
> 
> > --- a/drivers/block/xen-blkback/blkback.c
> > +++ b/drivers/block/xen-blkback/blkback.c
> > @@ -419,21 +419,17 @@ static int dispatch_discard_io(struct xen_blkif *blkif,
> >  	int err = 0;
> >  	int status = BLKIF_RSP_OKAY;
> >  	struct block_device *bdev = blkif->vbd.bdev;
> > -
> > +	unsigned long secure = 0;
> 
> Mind keeping the blank line and dropping the pointless initializer (which
> future gcc is likely going to be warning about)?

<nods>
> 
> >  	blkif->st_ds_req++;
> >  
> >  	xen_blkif_get(blkif);
> > -	if (blkif->blk_backend_type == BLKIF_BACKEND_PHY ||
> > -	    blkif->blk_backend_type == BLKIF_BACKEND_FILE) {
> > -		unsigned long secure = (blkif->vbd.discard_secure &&
> > -			(req->u.discard.flag & BLKIF_DISCARD_SECURE)) ?
> > -			BLKDEV_DISCARD_SECURE : 0;
> > -		err = blkdev_issue_discard(bdev,
> > -				req->u.discard.sector_number,
> > -				req->u.discard.nr_sectors,
> > -				GFP_KERNEL, secure);
> > -	} else
> > -		err = -EOPNOTSUPP;
> > +	secure = (blkif->vbd.discard_secure &&
> > +		 (req->u.discard.flag & BLKIF_DISCARD_SECURE)) ?
> > +		 BLKDEV_DISCARD_SECURE : 0;
> > +
> > +	err = blkdev_issue_discard(bdev, req->u.discard.sector_number,
> > +				   req->u.discard.nr_sectors,
> > +				   GFP_KERNEL, secure);
> >  
> >  	if (err == -EOPNOTSUPP) {
> >  		pr_debug(DRV_PFX "discard op failed, not supported\n");
> > --- a/drivers/block/xen-blkback/xenbus.c
> > +++ b/drivers/block/xen-blkback/xenbus.c
> > @@ -393,52 +393,37 @@ int xen_blkbk_discard(struct xenbus_transaction xbt, 
> > struct backend_info *be)
> >  	char *type;
> >  	int err;
> >  	int state = 0;
> > +	struct block_device *bdev = be->blkif->vbd.bdev;
> > +	struct request_queue *q = bdev_get_queue(bdev);
> >  
> > -	type = xenbus_read(XBT_NIL, dev->nodename, "type", NULL);
> > -	if (!IS_ERR(type)) {
> > -		if (strncmp(type, "file", 4) == 0) {
> > -			state = 1;
> > -			blkif->blk_backend_type = BLKIF_BACKEND_FILE;
> > +	if (blk_queue_discard(q)) {
> > +		err = xenbus_printf(xbt, dev->nodename,
> > +			"discard-granularity", "%u",
> > +			q->limits.discard_granularity);
> > +		if (err) {
> > +			xenbus_dev_fatal(dev, err,
> > +				"writing discard-granularity");
> > +			goto kfree;
> 
> Unrelated to the patch here, but failure to write any sort of extension
> data shouldn't be considered fatal - the backend can well work without
> these, and it should be left to the frontend to decide whether it wants
> to live without the unavailable extensions.

<nods>. Let me whip up another patch that removes these 'fatal' cases
and is based on this one.

> 
> Jan
> 
> > +		}
> > +		err = xenbus_printf(xbt, dev->nodename,
> > +			"discard-alignment", "%u",
> > +			q->limits.discard_alignment);
> > +		if (err) {
> > +			xenbus_dev_fatal(dev, err,
> > +				"writing discard-alignment");
> > +			goto kfree;
> >  		}
> > -		if (strncmp(type, "phy", 3) == 0) {
> > -			struct block_device *bdev = be->blkif->vbd.bdev;
> > -			struct request_queue *q = bdev_get_queue(bdev);
> > -			if (blk_queue_discard(q)) {
> > -				err = xenbus_printf(xbt, dev->nodename,
> > -					"discard-granularity", "%u",
> > -					q->limits.discard_granularity);
> > -				if (err) {
> > -					xenbus_dev_fatal(dev, err,
> > -						"writing discard-granularity");
> > -					goto kfree;
> > -				}
> > -				err = xenbus_printf(xbt, dev->nodename,
> > -					"discard-alignment", "%u",
> > -					q->limits.discard_alignment);
> > -				if (err) {
> > -					xenbus_dev_fatal(dev, err,
> > -						"writing discard-alignment");
> > -					goto kfree;
> > -				}
> > -				state = 1;
> > -				blkif->blk_backend_type = BLKIF_BACKEND_PHY;
> > -			}
> > -			/* Optional. */
> > -			err = xenbus_printf(xbt, dev->nodename,
> > -				"discard-secure", "%d",
> > -				blkif->vbd.discard_secure);
> > -			if (err) {
> > -				xenbus_dev_fatal(dev, err,
> > +		state = 1;
> > +		/* Optional. */
> > +		err = xenbus_printf(xbt, dev->nodename,
> > +				    "discard-secure", "%d",
> > +				    blkif->vbd.discard_secure);
> > +		if (err) {
> > +			xenbus_dev_fatal(dev, err,
> >  					"writting discard-secure");
> > -				goto kfree;
> > -			}
> > +			goto kfree;
> >  		}
> > -	} else {
> > -		err = PTR_ERR(type);
> > -		xenbus_dev_fatal(dev, err, "reading type");
> > -		goto out;
> >  	}
> > -
> >  	err = xenbus_printf(xbt, dev->nodename, "feature-discard",
> >  			    "%d", state);
> >  	if (err)
>