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

On 18.01.21 16:15, Roger Pau Monne wrote:
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

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,

This would mean that "discard-secure" will be evaluated only if the
other two items are set in Xenstore. From blkif.h I can't see this is
required, and your patch is modifying today's behavior in this regard.

You might want to have three xenbus_read_unsigned() calls instead.


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