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

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Date:   Mon, 18 Jan 2021 16:15:28 +0100
From:   Roger Pau Monne <roger.pau@...rix.com>
To:     <linux-kernel@...r.kernel.org>
CC:     Roger Pau Monne <roger.pau@...rix.com>,
        Arthur Borsboom <arthurborsboom@...il.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Jens Axboe <axboe@...nel.dk>, <xen-devel@...ts.xenproject.org>,
        <linux-block@...r.kernel.org>
Subject: [PATCH] xen-blkfront: don't make discard-alignment mandatory

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@...il.com>
Signed-off-by: Roger Pau Monné <roger.pau@...rix.com>
---
Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc: Juergen Gross <jgross@...e.com>
Cc: Stefano Stabellini <sstabellini@...nel.org>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc: "Roger Pau Monné" <roger.pau@...rix.com>
Cc: Jens Axboe <axboe@...nel.dk>
Cc: xen-devel@...ts.xenproject.org
Cc: linux-block@...r.kernel.org
Cc: Arthur Borsboom <arthurborsboom@...il.com>
---
 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