xen/blk[front|back]: Enhance discard support with secure erasing support.

Part of the blkdev_issue_discard(xx) operation is that it can also
issue a secure discard operation that will permanantly remove the
sectors in question. We advertise that we can support that via the
'discard-secure' attribute and on the request, if the 'secure' bit
is set, we will attempt to pass in REQ_DISCARD | REQ_SECURE.

CC: Li Dongyang <lidongyang@novell.com>
[v1: Used 'flag' instead of 'secure:1' bit]
[v2: Use 'reserved' uint8_t instead of adding a new value]
[v3: Check for nseg when mapping instead of operation]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

3 files changed, 29 insertions, 8 deletions

diff --git a/drivers/block/xen-blkback/blkback.c b/drivers/block/xen-blkback/blkback.c
index d7104abc8b7..9d2261b02f2 100644
--- a/drivers/block/xen-blkback/blkback.c
+++ b/drivers/block/xen-blkback/blkback.c
@@ -422,13 +422,16 @@ static void xen_blk_discard(struct xen_blkif *blkif, struct blkif_request *req)
 	int status = BLKIF_RSP_OKAY;
 	struct block_device *bdev = blkif->vbd.bdev;
 
-	if (blkif->blk_backend_type == BLKIF_BACKEND_PHY)
+	if (blkif->blk_backend_type == BLKIF_BACKEND_PHY) {
+		unsigned long secure = (blkif->vbd.discard_secure &&
+			(req->u.discard.flag & BLKIF_DISCARD_SECURE)) ?
+			BLKDEV_DISCARD_SECURE : 0;
 		/* 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) {
+				GFP_KERNEL, secure);
+	} 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;
@@ -643,8 +646,11 @@ static int dispatch_rw_block_io(struct xen_blkif *blkif,
 		break;
 	}
 
-	/* Check that the number of segments is sane. */
-	nseg = req->u.rw.nr_segments;
+	if (unlikely(operation == REQ_DISCARD))
+		nseg = 0;
+	else
+		/* Check that the number of segments is sane. */
+		nseg = req->u.rw.nr_segments;
 
 	if (unlikely(nseg == 0 && operation != WRITE_FLUSH &&
 				operation != REQ_DISCARD) ||
@@ -708,7 +714,7 @@ 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 (operation != REQ_DISCARD && xen_blkbk_map(req, pending_req, seg))
+	if (nseg && xen_blkbk_map(req, pending_req, seg))
 		goto fail_flush;
 
 	/*
diff --git a/drivers/block/xen-blkback/common.h b/drivers/block/xen-blkback/common.h
index dbfe7b3b073..d0ee7edc9be 100644
--- a/drivers/block/xen-blkback/common.h
+++ b/drivers/block/xen-blkback/common.h
@@ -69,7 +69,7 @@ struct blkif_x86_32_request_rw {
 } __attribute__((__packed__));
 
 struct blkif_x86_32_request_discard {
-	uint8_t        nr_segments;  /* number of segments                   */
+	uint8_t        flag;         /* BLKIF_DISCARD_SECURE or zero         */
 	blkif_vdev_t   _pad1;        /* was "handle" for read/write requests */
 	uint64_t       id;           /* private guest value, echoed in resp  */
 	blkif_sector_t sector_number;/* start sector idx on disk (r/w only)  */
@@ -104,7 +104,7 @@ struct blkif_x86_64_request_rw {
 } __attribute__((__packed__));
 
 struct blkif_x86_64_request_discard {
-	uint8_t        nr_segments;  /* number of segments                   */
+	uint8_t        flag;         /* BLKIF_DISCARD_SECURE or zero         */
 	blkif_vdev_t   _pad1;        /* was "handle" for read/write requests */
         uint32_t       _pad2;        /* offsetof(blkif_..,u.discard.id)==8   */
 	uint64_t       id;
@@ -164,6 +164,7 @@ struct xen_vbd {
 	/* Cached size parameter. */
 	sector_t		size;
 	bool			flush_support;
+	bool			discard_secure;
 };
 
 struct backend_info;
@@ -261,6 +262,7 @@ static inline void blkif_get_x86_32_req(struct blkif_request *dst,
 			dst->u.rw.seg[i] = src->u.rw.seg[i];
 		break;
 	case BLKIF_OP_DISCARD:
+		dst->u.discard.flag = src->u.discard.flag;
 		dst->u.discard.sector_number = src->u.discard.sector_number;
 		dst->u.discard.nr_sectors = src->u.discard.nr_sectors;
 		break;
@@ -290,6 +292,7 @@ static inline void blkif_get_x86_64_req(struct blkif_request *dst,
 			dst->u.rw.seg[i] = src->u.rw.seg[i];
 		break;
 	case BLKIF_OP_DISCARD:
+		dst->u.discard.flag = src->u.discard.flag;
 		dst->u.discard.sector_number = src->u.discard.sector_number;
 		dst->u.discard.nr_sectors = src->u.discard.nr_sectors;
 		break;
diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
index f759ad4584c..187fd2c1a15 100644
--- a/drivers/block/xen-blkback/xenbus.c
+++ b/drivers/block/xen-blkback/xenbus.c
@@ -338,6 +338,9 @@ static int xen_vbd_create(struct xen_blkif *blkif, blkif_vdev_t handle,
 	if (q && q->flush_flags)
 		vbd->flush_support = true;
 
+	if (q && blk_queue_secdiscard(q))
+		vbd->discard_secure = true;
+
 	DPRINTK("Successful creation of handle=%04x (dom=%u)\n",
 		handle, blkif->domid);
 	return 0;
@@ -420,6 +423,15 @@ int xen_blkbk_discard(struct xenbus_transaction xbt, struct backend_info *be)
 				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,
+					"writting discard-secure");
+				goto kfree;
+			}
 		}
 	} else {
 		err = PTR_ERR(type);