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, 72 insertions, 14 deletions

diff --git a/drivers/block/xen-blkback/blkback.c b/drivers/block/xen-blkback/blkback.c
index 2330a9a..9713d5a 100644
--- a/drivers/block/xen-blkback/blkback.c
+++ b/drivers/block/xen-blkback/blkback.c
@@ -39,6 +39,9 @@
 #include <linux/list.h>
 #include <linux/delay.h>
 #include <linux/freezer.h>
+#include <linux/loop.h>
+#include <linux/falloc.h>
+#include <linux/fs.h>
 
 #include <xen/events.h>
 #include <xen/page.h>
@@ -258,13 +261,16 @@ irqreturn_t xen_blkif_be_int(int irq, void *dev_id)
 
 static void print_stats(struct xen_blkif *blkif)
 {
-	pr_info("xen-blkback (%s): oo %3d  |  rd %4d  |  wr %4d  |  f %4d\n",
+	pr_info("xen-blkback (%s): oo %3d  |  rd %4d  |  wr %4d  |  f %4d"
+		 "  |  ds %4d\n",
 		 current->comm, blkif->st_oo_req,
-		 blkif->st_rd_req, blkif->st_wr_req, blkif->st_f_req);
+		 blkif->st_rd_req, blkif->st_wr_req,
+		 blkif->st_f_req, blkif->st_ds_req);
 	blkif->st_print = jiffies + msecs_to_jiffies(10 * 1000);
 	blkif->st_rd_req = 0;
 	blkif->st_wr_req = 0;
 	blkif->st_oo_req = 0;
+	blkif->st_ds_req = 0;
 }
 
 int xen_blkif_schedule(void *arg)
@@ -410,6 +416,42 @@ static int xen_blkbk_map(struct blkif_request *req,
 	return ret;
 }
 
+static void xen_blk_discard(struct xen_blkif *blkif, struct blkif_request *req)
+{
+	int err = 0;
+	int status = BLKIF_RSP_OKAY;
+	struct block_device *bdev = blkif->vbd.bdev;
+
+	if (blkif->blk_backend_type == BLKIF_BACKEND_PHY)
+		/* just forward the discard request */
+		err = blkdev_issue_discard(bdev,
+				req->u.discard.sector_number,
+				req->u.discard.nr_sectors,
+				GFP_KERNEL, 0);
+	else if (blkif->blk_backend_type == BLKIF_BACKEND_FILE) {
+		/* punch a hole in the backing file */
+		struct loop_device *lo = bdev->bd_disk->private_data;
+		struct file *file = lo->lo_backing_file;
+
+		if (file->f_op->fallocate)
+			err = file->f_op->fallocate(file,
+				FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE,
+				req->u.discard.sector_number << 9,
+				req->u.discard.nr_sectors << 9);
+		else
+			err = -EOPNOTSUPP;
+	} else
+		err = -EOPNOTSUPP;
+
+	if (err == -EOPNOTSUPP) {
+		pr_debug(DRV_PFX "discard op failed, not supported\n");
+		status = BLKIF_RSP_EOPNOTSUPP;
+	} else if (err)
+		status = BLKIF_RSP_ERROR;
+
+	make_response(blkif, req->id, req->operation, status);
+}
+
 /*
  * Completion callback on the bio's. Called as bh->b_end_io()
  */
@@ -563,6 +605,10 @@ static int dispatch_rw_block_io(struct xen_blkif *blkif,
 		blkif->st_f_req++;
 		operation = WRITE_FLUSH;
 		break;
+	case BLKIF_OP_DISCARD:
+		blkif->st_ds_req++;
+		operation = REQ_DISCARD;
+		break;
 	case BLKIF_OP_WRITE_BARRIER:
 	default:
 		operation = 0; /* make gcc happy */
@@ -572,7 +618,8 @@ static int dispatch_rw_block_io(struct xen_blkif *blkif,
 
 	/* Check that the number of segments is sane. */
 	nseg = req->nr_segments;
-	if (unlikely(nseg == 0 && operation != WRITE_FLUSH) ||
+	if (unlikely(nseg == 0 && operation != WRITE_FLUSH &&
+				operation != REQ_DISCARD) ||
 	    unlikely(nseg > BLKIF_MAX_SEGMENTS_PER_REQUEST)) {
 		pr_debug(DRV_PFX "Bad number of segments in request (%d)\n",
 			 nseg);
@@ -627,10 +674,14 @@ static int dispatch_rw_block_io(struct xen_blkif *blkif,
 	 * the hypercall to unmap the grants - that is all done in
 	 * xen_blkbk_unmap.
 	 */
-	if (xen_blkbk_map(req, pending_req, seg))
+	if (operation != BLKIF_OP_DISCARD &&
+			xen_blkbk_map(req, pending_req, seg))
 		goto fail_flush;
 
-	/* This corresponding xen_blkif_put is done in __end_block_io_op */
+	/*
+	 * This corresponding xen_blkif_put is done in __end_block_io_op, or
+	 * below (in "!bio") if we are handling a BLKIF_OP_DISCARD.
+	 */
 	xen_blkif_get(blkif);
 
 	for (i = 0; i < nseg; i++) {
@@ -654,18 +705,25 @@ static int dispatch_rw_block_io(struct xen_blkif *blkif,
 		preq.sector_number += seg[i].nsec;
 	}
 
-	/* This will be hit if the operation was a flush. */
+	/* This will be hit if the operation was a flush or discard. */
 	if (!bio) {
-		BUG_ON(operation != WRITE_FLUSH);
+		BUG_ON(operation != WRITE_FLUSH && operation != REQ_DISCARD);
 
-		bio = bio_alloc(GFP_KERNEL, 0);
-		if (unlikely(bio == NULL))
-			goto fail_put_bio;
+		if (operation == WRITE_FLUSH) {
+			bio = bio_alloc(GFP_KERNEL, 0);
+			if (unlikely(bio == NULL))
+				goto fail_put_bio;
 
-		biolist[nbio++] = bio;
-		bio->bi_bdev    = preq.bdev;
-		bio->bi_private = pending_req;
-		bio->bi_end_io  = end_block_io_op;
+			biolist[nbio++] = bio;
+			bio->bi_bdev    = preq.bdev;
+			bio->bi_private = pending_req;
+			bio->bi_end_io  = end_block_io_op;
+		} else if (operation == REQ_DISCARD) {
+			xen_blk_discard(blkif, req);
+			xen_blkif_put(blkif);
+			free_req(pending_req);
+			return 0;
+		}
 	}
 
 	/*