[PATCH V2] xen: export device state to sysfs

[Joe Jin <joe.jin@oracle.com>]

Export device state to sysfs to allow for easier get device state.

Signed-off-by: Joe Jin <joe.jin@oracle.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
---
 Documentation/ABI/stable/sysfs-bus-xen-backend | 9 +++++++++
 drivers/xen/xenbus/xenbus_probe.c              | 9 +++++++++
 2 files changed, 18 insertions(+)

diff --git a/Documentation/ABI/stable/sysfs-bus-xen-backend b/Documentation/ABI/stable/sysfs-bus-xen-backend
index 3d5951c8bf5f..e8b60bd766f7 100644
--- a/Documentation/ABI/stable/sysfs-bus-xen-backend
+++ b/Documentation/ABI/stable/sysfs-bus-xen-backend
@@ -73,3 +73,12 @@ KernelVersion:	3.0
 Contact:	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
 Description:
                 Number of sectors written by the frontend.
+
+What:		/sys/bus/xen-backend/devices/*/state
+Date:		August 2018
+KernelVersion:	4.19
+Contact:	Joe Jin <joe.jin@oracle.com>
+Description:
+                The state of the device. One of: 'Unknown',
+                'Initialising', 'Initialised', 'Connected', 'Closing',
+                'Closed', 'Reconfiguring', 'Reconfigured'.
diff --git a/drivers/xen/xenbus/xenbus_probe.c b/drivers/xen/xenbus/xenbus_probe.c
index f2088838f690..5b471889d723 100644
--- a/drivers/xen/xenbus/xenbus_probe.c
+++ b/drivers/xen/xenbus/xenbus_probe.c
@@ -402,10 +402,19 @@ static ssize_t modalias_show(struct device *dev,
 }
 static DEVICE_ATTR_RO(modalias);
 
+static ssize_t state_show(struct device *dev,
+			    struct device_attribute *attr, char *buf)
+{
+	return sprintf(buf, "%s\n",
+			xenbus_strstate(to_xenbus_device(dev)->state));
+}
+static DEVICE_ATTR_RO(state);
+
 static struct attribute *xenbus_dev_attrs[] = {
 	&dev_attr_nodename.attr,
 	&dev_attr_devtype.attr,
 	&dev_attr_modalias.attr,
+	&dev_attr_state.attr,
 	NULL,
 };
 
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