Commit 06ba5d2e authored by SeongJae Park's avatar SeongJae Park Committed by Juergen Gross
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xen-blkback: Advertise feature-persistent as user requested 



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
aac8a70d ("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: aac8a70d ("xen-blkback: add a parameter for disabling of persistent grants")
Cc: <stable@vger.kernel.org> # 5.10.x
Suggested-by: default avatarJuergen Gross <jgross@suse.com>
Signed-off-by: default avatarSeongJae Park <sj@kernel.org>
Tested-by: default avatarMarek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Reviewed-by: default avatarJuergen Gross <jgross@suse.com>
Link: https://lore.kernel.org/r/20220831165824.94815-2-sj@kernel.org


Signed-off-by: default avatarJuergen Gross <jgross@suse.com>
parent c5deb278

drivers/block/xen-blkback/common.h

+3 −0
Original line number Diff line number Diff line
@@ -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;

};

drivers/block/xen-blkback/xenbus.c

+4 −2
Original line number Diff line number Diff line
@@ -907,7 +907,7 @@ static void connect(struct backend_info *be) 
	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_info *be) 
		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;