[PATCH v2 2/3] xen-blkfront: Advertise feature-persistent as user requested

[SeongJae Park <sj@xxxxxxxxxx>]

The advertisement of the persistent grants feature (writing
'feature-persistent' to xenbus) should mean not the decision for using
the feature but only the availability of the feature.  However, commit
74a852479c68 ("xen-blkfront: add a parameter for disabling of persistent
grants") made a field of blkfront, which was a place for saving only the
negotiation result, to be used for yet another purpose: caching of the
'feature_persistent' parameter value.  As a result, the advertisement,
which should follow only the parameter value, becomes inconsistent.

This commit fixes the misuse of the semantic by making blkfront saves
the parameter value in a separate place and advertises the support based
on only the saved value.

Fixes: 74a852479c68 ("xen-blkfront: add a parameter for disabling of persistent 
grants")
Cc: <stable@xxxxxxxxxxxxxxx> # 5.10.x
Suggested-by: Juergen Gross <jgross@xxxxxxxx>
Signed-off-by: SeongJae Park <sj@xxxxxxxxxx>
---
 drivers/block/xen-blkfront.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 8e56e69fb4c4..dfae08115450 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -213,6 +213,9 @@ struct blkfront_info
        unsigned int feature_fua:1;
        unsigned int feature_discard:1;
        unsigned int feature_secdiscard:1;
+       /* Connect-time cached feature_persistent parameter */
+       unsigned int feature_persistent_parm:1;
+       /* Persistent grants feature negotiation result */
        unsigned int feature_persistent:1;
        unsigned int bounce:1;
        unsigned int discard_granularity;
@@ -1848,7 +1851,7 @@ static int talk_to_blkback(struct xenbus_device *dev,
                goto abort_transaction;
        }
        err = xenbus_printf(xbt, dev->nodename, "feature-persistent", "%u",
-                       info->feature_persistent);
+                       info->feature_persistent_parm);
        if (err)
                dev_warn(&dev->dev,
                         "writing persistent grants feature to xenbus");
@@ -2281,7 +2284,8 @@ static void blkfront_gather_backend_features(struct 
blkfront_info *info)
        if (xenbus_read_unsigned(info->xbdev->otherend, "feature-discard", 0))
                blkfront_setup_discard(info);
 
-       if (feature_persistent)
+       info->feature_persistent_parm = feature_persistent;
+       if (info->feature_persistent_parm)
                info->feature_persistent =
                        !!xenbus_read_unsigned(info->xbdev->otherend,
                                               "feature-persistent", 0);
-- 
2.25.1