[PATCH] xen-blkfront: don't make discard-alignment mandatory

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

Don't require the discard-alignment xenstore node to be present in
order to correctly setup the feature. This can happen with versions of
QEMU that only write the discard-granularity but not the
discard-alignment node.

Assume discard-alignment is 0 if not present. While there also fix the
logic to not enable the discard feature if discard-granularity is not
present.

Reported-by: Arthur Borsboom <arthurborsboom@xxxxxxxxx>
Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Cc: Juergen Gross <jgross@xxxxxxxx>
Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Cc: "Roger Pau Monné" <roger.pau@xxxxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx
Cc: linux-block@xxxxxxxxxxxxxxx
Cc: Arthur Borsboom <arthurborsboom@xxxxxxxxx>
---
 drivers/block/xen-blkfront.c | 25 +++++++++++++------------
 1 file changed, 13 insertions(+), 12 deletions(-)

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 5265975b3fba..5a93f7cc2939 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -2179,22 +2179,23 @@ static void blkfront_closing(struct blkfront_info *info)
 
 static void blkfront_setup_discard(struct blkfront_info *info)
 {
-       int err;
-       unsigned int discard_granularity;
-       unsigned int discard_alignment;
+       unsigned int discard_granularity = 0;
+       unsigned int discard_alignment = 0;
+       unsigned int discard_secure = 0;
 
-       info->feature_discard = 1;
-       err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
+       xenbus_gather(XBT_NIL, info->xbdev->otherend,
                "discard-granularity", "%u", &discard_granularity,
                "discard-alignment", "%u", &discard_alignment,
+               "discard-secure", "%u", &discard_secure,
                NULL);
-       if (!err) {
-               info->discard_granularity = discard_granularity;
-               info->discard_alignment = discard_alignment;
-       }
-       info->feature_secdiscard =
-               !!xenbus_read_unsigned(info->xbdev->otherend, "discard-secure",
-                                      0);
+
+       if (!discard_granularity)
+               return;
+
+       info->feature_discard = 1;
+       info->discard_granularity = discard_granularity;
+       info->discard_alignment = discard_alignment;
+       info->feature_secdiscard = !!discard_secure;
 }
 
 static int blkfront_setup_indirect(struct blkfront_ring_info *rinfo)
-- 
2.29.2