[PATCH 5.19 102/155] xen-blkback: Advertise feature-persistent as user requested

Greg Kroah-Hartman
2022-09-06T14:13:12Z

From: SeongJae Park <sj@kernel.org>

commit 06ba5d2e943e97bb66e75c152e87f1d2c7027a67 upstream.

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
aac8a70db24b ("xen-blkback: add a parameter for disabling of persistent
grants") made a field of blkback, 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 blkback saves the
parameter value in a separate place and advertises the support based on
only the saved value.

Fixes: aac8a70db24b ("xen-blkback: add a parameter for disabling of persistent grants")
Cc: <stable@vger.kernel.org> # 5.10.x
Suggested-by: Juergen Gross <jgross@suse.com>
Signed-off-by: SeongJae Park <sj@kernel.org>
Tested-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Link: https://lore.kernel.org/r/20220831165824.94815-2-sj@kernel.org
Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/block/xen-blkback/common.h | 3 +++
drivers/block/xen-blkback/xenbus.c | 6 ++++--
2 files changed, 7 insertions(+), 2 deletions(-)

--- a/drivers/block/xen-blkback/common.h
+++ b/drivers/block/xen-blkback/common.h
@@ -226,6 +226,9 @@ struct xen_vbd {
sector_t size;
unsigned int flush_support:1;
unsigned int discard_secure:1;
+ /* Connect-time cached feature_persistent parameter value */
+ unsigned int feature_gnt_persistent_parm:1;
+ /* Persistent grants feature negotiation result */
unsigned int feature_gnt_persistent:1;
unsigned int overflow_max_grants:1;
};
--- a/drivers/block/xen-blkback/xenbus.c
+++ b/drivers/block/xen-blkback/xenbus.c
@@ -907,7 +907,7 @@ again:
xen_blkbk_barrier(xbt, be, be->blkif->vbd.flush_support);

err = xenbus_printf(xbt, dev->nodename, "feature-persistent", "%u",
- be->blkif->vbd.feature_gnt_persistent);
+ be->blkif->vbd.feature_gnt_persistent_parm);
if (err) {
xenbus_dev_fatal(dev, err, "writing %s/feature-persistent",
dev->nodename);
@@ -1085,7 +1085,9 @@ static int connect_ring(struct backend_i
return -ENOSYS;
}

- blkif->vbd.feature_gnt_persistent = feature_persistent &&
+ blkif->vbd.feature_gnt_persistent_parm = feature_persistent;
+ blkif->vbd.feature_gnt_persistent =
+ blkif->vbd.feature_gnt_persistent_parm &&
xenbus_read_unsigned(dev->otherend, "feature-persistent", 0);

blkif->vbd.overflow_max_grants = 0;