[PATCH 0/3] xen-block: changes for discard support

[PATCH 0/3] xen-block: changes for discard support

[Olaf Hering]

Fix blkfront to handle all sorts of backends.

Also let blkback recognize a xenstore property to disable discard for a
given device. It requires upcoming libxl changes ("discard-enable"):
http://lists.xenproject.org/archives/html/xen-devel/2014-01/msg02632.html

Olaf Hering (3):
  xen-blkfront: remove type check from blkfront_setup_discard
  xen blkif.h: fix comment typo in discard-alignment
  xen/blkback: disable discard feature if requested by toolstack

 drivers/block/xen-blkback/xenbus.c |  7 ++++++-
 drivers/block/xen-blkfront.c       | 40 +++++++++++++-------------------------
 include/xen/interface/io/blkif.h   |  2 +-
 3 files changed, 21 insertions(+), 28 deletions(-)

[PATCH 1/3] xen-blkfront: remove type check from blkfront_setup_discard

[Olaf Hering]

In its initial implementation a check for "type" was added, but only phy
and file are handled. This breaks advertised discard support for other
type values such as qdisk.

Fix and simplify this function: If the backend advertises discard
support it is supposed to implement it properly, so enable
feature_discard unconditionally. If the backend advertises the need for
a certain granularity and alignment then propagate both properties to
the blocklayer. The discard-secure property is a boolean, update the code
to reflect that.

Signed-off-by: Olaf Hering <olaf@aepfle.de>
---
 drivers/block/xen-blkfront.c | 40 ++++++++++++++--------------------------
 1 file changed, 14 insertions(+), 26 deletions(-)

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 8dcfb54..4d8ddea 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -1635,36 +1635,24 @@ blkfront_closing(struct blkfront_info *info)
 static void blkfront_setup_discard(struct blkfront_info *info)
 {
 	int err;
-	char *type;
 	unsigned int discard_granularity;
 	unsigned int discard_alignment;
 	unsigned int discard_secure;
 
-	type = xenbus_read(XBT_NIL, info->xbdev->otherend, "type", NULL);
-	if (IS_ERR(type))
-		return;
-
-	info->feature_secdiscard = 0;
-	if (strncmp(type, "phy", 3) == 0) {
-		err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
-			"discard-granularity", "%u", &discard_granularity,
-			"discard-alignment", "%u", &discard_alignment,
-			NULL);
-		if (!err) {
-			info->feature_discard = 1;
-			info->discard_granularity = discard_granularity;
-			info->discard_alignment = discard_alignment;
-		}
-		err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
-			    "discard-secure", "%d", &discard_secure,
-			    NULL);
-		if (!err)
-			info->feature_secdiscard = discard_secure;
-
-	} else if (strncmp(type, "file", 4) == 0)
-		info->feature_discard = 1;
-
-	kfree(type);
+	info->feature_discard = 1;
+	err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
+		"discard-granularity", "%u", &discard_granularity,
+		"discard-alignment", "%u", &discard_alignment,
+		NULL);
+	if (!err) {
+		info->discard_granularity = discard_granularity;
+		info->discard_alignment = discard_alignment;
+	}
+	err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
+		    "discard-secure", "%d", &discard_secure,
+		    NULL);
+	if (!err)
+		info->feature_secdiscard = !!discard_secure;
 }
 
 static int blkfront_setup_indirect(struct blkfront_info *info)

[PATCH 2/3] xen blkif.h: fix comment typo in discard-alignment

[Olaf Hering]

Add the missing 'n' to discard-alignment

Signed-off-by: Olaf Hering <olaf@aepfle.de>
---
 include/xen/interface/io/blkif.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/xen/interface/io/blkif.h b/include/xen/interface/io/blkif.h
index ae665ac..19ebcc5 100644
--- a/include/xen/interface/io/blkif.h
+++ b/include/xen/interface/io/blkif.h
@@ -86,7 +86,7 @@ typedef uint64_t blkif_sector_t;
  *     Interface%20manuals/100293068c.pdf
  * The backend can optionally provide three extra XenBus attributes to
  * further optimize the discard functionality:
- * 'discard-aligment' - Devices that support discard functionality may
+ * 'discard-alignment' - Devices that support discard functionality may
  * internally allocate space in units that are bigger than the exported
  * logical block size. The discard-alignment parameter indicates how many bytes
  * the beginning of the partition is offset from the internal allocation unit's

[PATCH 3/3] xen/blkback: disable discard feature if requested by toolstack

[Olaf Hering]

Newer toolstacks may provide a boolean property "discard-enable" in the
backend node. Its purpose is to disable discard for file backed storage
to avoid fragmentation. Recognize this setting also for physical
storage.  If that property exists and is false, do not advertise
"feature-discard" to the frontend.

Signed-off-by: Olaf Hering <olaf@aepfle.de>
---
 drivers/block/xen-blkback/xenbus.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
index c2014a0..83125e2 100644
--- a/drivers/block/xen-blkback/xenbus.c
+++ b/drivers/block/xen-blkback/xenbus.c
@@ -467,10 +467,15 @@ static void xen_blkbk_discard(struct xenbus_transaction xbt, struct backend_info
 	struct xenbus_device *dev = be->dev;
 	struct xen_blkif *blkif = be->blkif;
 	int err;
-	int state = 0;
+	int state = 0, discard_enable;
 	struct block_device *bdev = be->blkif->vbd.bdev;
 	struct request_queue *q = bdev_get_queue(bdev);
 
+	err = xenbus_scanf(XBT_NIL, dev->nodename, "discard-enable", "%d",
+			   &discard_enable);
+	if (err == 1 && !discard_enable)
+		return;
+
 	if (blk_queue_discard(q)) {
 		err = xenbus_printf(xbt, dev->nodename,
 			"discard-granularity", "%u",