xen-blkback: Implement discard requests ('feature-discard')

..aka ATA TRIM/SCSI UNMAP command to be passed through the frontend
and used as appropiately by the backend. We also advertise
certain granulity parameters to the frontend so it can plug them in.
If the backend is a realy device - we just end up using
'blkdev_issue_discard' while for loopback devices - we just punch
a hole in the image file.

Signed-off-by: Li Dongyang <lidongyang@novell.com>
[v1: Fixed up pr_debug and commit description]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

1 files changed, 58 insertions, 0 deletions

diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
index 3f129b45451..2b3aef0332f 100644
--- a/drivers/block/xen-blkback/xenbus.c
+++ b/drivers/block/xen-blkback/xenbus.c
@@ -272,6 +272,7 @@ VBD_SHOW(oo_req,  "%d\n", be->blkif->st_oo_req);
 VBD_SHOW(rd_req,  "%d\n", be->blkif->st_rd_req);
 VBD_SHOW(wr_req,  "%d\n", be->blkif->st_wr_req);
 VBD_SHOW(f_req,  "%d\n", be->blkif->st_f_req);
+VBD_SHOW(ds_req,  "%d\n", be->blkif->st_ds_req);
 VBD_SHOW(rd_sect, "%d\n", be->blkif->st_rd_sect);
 VBD_SHOW(wr_sect, "%d\n", be->blkif->st_wr_sect);
 
@@ -280,6 +281,7 @@ static struct attribute *xen_vbdstat_attrs[] = {
 	&dev_attr_rd_req.attr,
 	&dev_attr_wr_req.attr,
 	&dev_attr_f_req.attr,
+	&dev_attr_ds_req.attr,
 	&dev_attr_rd_sect.attr,
 	&dev_attr_wr_sect.attr,
 	NULL
@@ -419,6 +421,60 @@ int xen_blkbk_flush_diskcache(struct xenbus_transaction xbt,
 	return err;
 }
 
+int xen_blkbk_discard(struct xenbus_transaction xbt, struct backend_info *be)
+{
+	struct xenbus_device *dev = be->dev;
+	struct xen_blkif *blkif = be->blkif;
+	char *type;
+	int err;
+	int state = 0;
+
+	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 (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;
+			}
+		}
+	} 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)
+		xenbus_dev_fatal(dev, err, "writing feature-discard");
+kfree:
+	kfree(type);
+out:
+	return err;
+}
+
 /*
  * Entry point to this code when a new device is created.  Allocate the basic
  * structures, and watch the store waiting for the hotplug scripts to tell us
@@ -650,6 +706,8 @@ again:
 	if (err)
 		goto abort;
 
+	err = xen_blkbk_discard(xbt, be);
+
 	err = xenbus_printf(xbt, dev->nodename, "sectors", "%llu",
 			    (unsigned long long)vbd_sz(&be->blkif->vbd));
 	if (err) {