[RFC net-next] ptp: add clock_index as a device attribute

The PTP clock associated with a networking device is reported by the
ETHTOOL_GET_TS_INFO ioctl, by using the ptp->index clock index variable.

In order to associate this clock index with the proper device,
userspace applications make the assumption that /dev/ptpX has a clock
index of X. If this assumption is wrong, such as if user space renames
a device, then there isn't a mechanism to associate the clock index with
the device.

Add a new device attribute to the device sysfs folder, clock_index,
which will report the exact clock index of the device. This enables
userspace applications to determine the clock_index of the PTP devices
in a more robust way.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
---
 drivers/ptp/ptp_sysfs.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/ptp/ptp_sysfs.c b/drivers/ptp/ptp_sysfs.c
index be076a91e20e..8ba9556c939a 100644
--- a/drivers/ptp/ptp_sysfs.c
+++ b/drivers/ptp/ptp_sysfs.c

@@ -17,6 +17,14 @@ static ssize_t clock_name_show(struct device *dev,
 }
 static DEVICE_ATTR_RO(clock_name);
 
+static ssize_t clock_index_show(struct device *dev,
+				struct device_attribute *attr, char *page)
+{
+	struct ptp_clock *ptp = dev_get_drvdata(dev);
+	return snprintf(page, PAGE_SIZE-1, "%d\n", ptp->index);
+}
+static DEVICE_ATTR_RO(clock_index);
+
 #define PTP_SHOW_INT(name, var)						\
 static ssize_t var##_show(struct device *dev,				\
 			   struct device_attribute *attr, char *page)	\

@@ -150,6 +158,7 @@ static DEVICE_ATTR(pps_enable, 0220, NULL, pps_enable_store);
 
 static struct attribute *ptp_attrs[] = {
 	&dev_attr_clock_name.attr,
+	&dev_attr_clock_index.attr,
 
 	&dev_attr_max_adjustment.attr,
 	&dev_attr_n_alarms.attr,

base-commit: 0c2a01dc27f68024108b7303002678bd72446a4e
-- 
2.28.0.497.g54e85e7af1ac