xen-blkfront: Advertise feature-persistent as user requested

stable inclusion
from stable-v5.10.142
commit f210912d1aa91e7c16f9dab7b2a43f1134db23da
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I6CSFH

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f210912d1aa91e7c16f9dab7b2a43f1134db23da



--------------------------------

commit 9f5e0fe5 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
74a85247 ("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: 74a85247 ("xen-blkfront: 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/20220831165824.94815-3-sj@kernel.org


Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jialin Zhang <zhangjialin11@huawei.com>
Reviewed-by: Zheng Zengkai <zhengzengkai@huawei.com>