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 <[email protected]>
---
This is a follow-up to my Xen toolstack patch:
https://lists.xenproject.org/archives/html/xen-devel/2018-09/msg00266.html
without it we're seeing -EPERM on write and the issue I'm trying to address
here stays hidden.
---
drivers/xen/manage.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/drivers/xen/manage.c b/drivers/xen/manage.c
index c93d8ef8df34..5bb01a62f214 100644
--- a/drivers/xen/manage.c
+++ b/drivers/xen/manage.c
@@ -280,9 +280,11 @@ static void sysrq_handler(struct xenbus_watch *watch, const char *path,
/*
* 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);
--
2.14.4
On Thu, Sep 06, 2018 at 01:26:08PM +0200, Vitaly Kuznetsov wrote:
> 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 <[email protected]>
Reviewed-by: Wei Liu <[email protected]>
On 09/06/2018 07:26 AM, Vitaly Kuznetsov wrote:
> 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 <[email protected]>
>
Applied to for-linus-19b.
-boris