atm: expose ATM device index in sysfs

It's currently exposed only through /proc which, besides requiring
screen-scraping, doesn't allow userspace to distinguish between two
identical ATM adapters with different ATM indexes.  The ATM device index
is required when using PPPoATM on a system with multiple ATM adapters.
Signed-off-by: Dan Williams <dcbw@redhat.com>
Reviewed-by: Eric Dumazet <eric.dumazet@gmail.com>
Tested-by: David Woodhouse <dwmw2@infradead.org>
Cc: stable@kernel.org
Signed-off-by: David S. Miller <davem@davemloft.net>

net/atm/atm_sysfs.c

@@ -59,6 +59,14 @@ static ssize_t show_atmaddress(struct device *cdev,
 	return pos - buf;
 }
 
+static ssize_t show_atmindex(struct device *cdev,
+			     struct device_attribute *attr, char *buf)
+{
+	struct atm_dev *adev = to_atm_dev(cdev);
+
+	return sprintf(buf, "%d\n", adev->number);
+}
+
 static ssize_t show_carrier(struct device *cdev,
 			    struct device_attribute *attr, char *buf)
 {
@@ -99,6 +107,7 @@ static ssize_t show_link_rate(struct device *cdev,
 
 static DEVICE_ATTR(address, S_IRUGO, show_address, NULL);
 static DEVICE_ATTR(atmaddress, S_IRUGO, show_atmaddress, NULL);
+static DEVICE_ATTR(atmindex, S_IRUGO, show_atmindex, NULL);
 static DEVICE_ATTR(carrier, S_IRUGO, show_carrier, NULL);
 static DEVICE_ATTR(type, S_IRUGO, show_type, NULL);
 static DEVICE_ATTR(link_rate, S_IRUGO, show_link_rate, NULL);
@@ -106,6 +115,7 @@ static DEVICE_ATTR(link_rate, S_IRUGO, show_link_rate, NULL);
 static struct device_attribute *atm_attrs[] = {
 	&dev_attr_atmaddress,
 	&dev_attr_address,
+	&dev_attr_atmindex,
 	&dev_attr_carrier,
 	&dev_attr_type,
 	&dev_attr_link_rate,