[PATCH v2] drivers/base: add sysfs entries for suppliers and consumers

[Ioana Ciornei]

Instead of scraping dmesg for messages such as 'Linked as a consumer to'
or 'Dropping the link to' export two new sysfs entries in the device
folder that list the consumer and supplier devices.

Signed-off-by: Ioana Ciornei <ioana.ciornei@xxxxxxx>
---
Changes in v2:
  - add documentation entries for the new sysfs files

 Documentation/ABI/testing/sysfs-devices-links | 13 +++++++++
 drivers/base/core.c                           | 42 +++++++++++++++++++++++++++
 2 files changed, 55 insertions(+)
 create mode 100644 Documentation/ABI/testing/sysfs-devices-links

diff --git a/Documentation/ABI/testing/sysfs-devices-links b/Documentation/ABI/testing/sysfs-devices-links
new file mode 100644
index 0000000..0c73ef5
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-devices-links
@@ -0,0 +1,13 @@
+What:		/sys/devices/.../consumers
+Date:		July 2018
+Contact:	Ioana Ciornei <ioana.ciornei@xxxxxxx>
+Description:
+		Read-only attribute that lists the devices that have a device
+		link which denodes a consumer relationship to this device.
+
+What:		/sys/devices/.../suppliers
+Date:		July 2018
+Contact:	Ioana Ciornei <ioana.ciornei@xxxxxxx>
+Description:
+		Read-only attribute that lists the devices that have a device
+		link which denodes a supplier relationship to this device.
diff --git a/drivers/base/core.c b/drivers/base/core.c
index df3e1a4..6d245f7 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -1055,6 +1055,34 @@ static ssize_t online_store(struct device *dev, struct device_attribute *attr,
 }
 static DEVICE_ATTR_RW(online);
 
+static ssize_t suppliers_show(struct device *dev, struct device_attribute *attr,
+			      char *buf)
+{
+	struct device_link *link;
+	size_t count = 0;
+
+	list_for_each_entry(link, &dev->links.suppliers, c_node)
+		count += scnprintf(buf + count, PAGE_SIZE - count, "%s\n",
+				   dev_name(link->supplier));
+
+	return count;
+}
+static DEVICE_ATTR_RO(suppliers);
+
+static ssize_t consumers_show(struct device *dev, struct device_attribute *attr,
+			      char *buf)
+{
+	struct device_link *link;
+	size_t count = 0;
+
+	list_for_each_entry(link, &dev->links.consumers, s_node)
+		count += scnprintf(buf + count, PAGE_SIZE - count, "%s\n",
+				   dev_name(link->consumer));
+
+	return count;
+}
+static DEVICE_ATTR_RO(consumers);
+
 int device_add_groups(struct device *dev, const struct attribute_group **groups)
 {
 	return sysfs_create_groups(&dev->kobj, groups);
@@ -1226,8 +1254,20 @@ static int device_add_attrs(struct device *dev)
 			goto err_remove_dev_groups;
 	}
 
+	error = device_create_file(dev, &dev_attr_suppliers);
+	if (error)
+		goto err_remove_online;
+
+	error = device_create_file(dev, &dev_attr_consumers);
+	if (error)
+		goto err_remove_suppliers;
+
 	return 0;
 
+ err_remove_suppliers:
+	device_remove_file(dev, &dev_attr_suppliers);
+ err_remove_online:
+	device_remove_file(dev, &dev_attr_online);
  err_remove_dev_groups:
 	device_remove_groups(dev, dev->groups);
  err_remove_type_groups:
@@ -1245,6 +1285,8 @@ static void device_remove_attrs(struct device *dev)
 	struct class *class = dev->class;
 	const struct device_type *type = dev->type;
 
+	device_remove_file(dev, &dev_attr_consumers);
+	device_remove_file(dev, &dev_attr_suppliers);
 	device_remove_file(dev, &dev_attr_online);
 	device_remove_groups(dev, dev->groups);
 
-- 
1.9.1