[PATCH 3.18 093/120] xen/manage: dont complain about an empty value in control/sysrq node

Greg Kroah-Hartman
2018-10-11T15:39:58Z

From: Vitaly Kuznetsov <vkuznets@redhat.com>

[ Upstream commit 87dffe86d406bee8782cac2db035acb9a28620a7 ]

When guest receives a sysrq request from the host it acknowledges it by
writing '\0' to control/sysrq xenstore node. This, however, make xenstore
watch fire again but xenbus_scanf() fails to parse empty value with "%c"
format string:

sysrq: SysRq : Emergency Sync
Emergency Sync complete
xen:manage: Error -34 reading sysrq code in control/sysrq

Ignore -ERANGE the same way we already ignore -ENOENT, empty value in
control/sysrq is totally legal.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/xen/manage.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

--- a/drivers/xen/manage.c
+++ b/drivers/xen/manage.c
@@ -277,9 +277,11 @@ static void sysrq_handler(struct xenbus_
/*
* The Xenstore watch fires directly after registering it and
* after a suspend/resume cycle. So ENOENT is no error but
- * might happen in those cases.
+ * might happen in those cases. ERANGE is observed when we get
+ * an empty value (''), this happens when we acknowledge the
+ * request by writing '\0' below.
*/
- if (err != -ENOENT)
+ if (err != -ENOENT && err != -ERANGE)
pr_err("Error %d reading sysrq code in control/sysrq\n",
err);
xenbus_transaction_end(xbt, 1);