[PATCH] net-sysfs: expose IRQ number

["Rafał Miłecki" <zajec5@gmail.com>]

From: Rafał Miłecki <rafal@milecki.pl>

Knowing IRQ number makes e.g. reading /proc/interrupts much simpler.
It's more reliable than guessing device name used by a driver when
calling request_irq().

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
---
I found a script parsing /proc/interrupts for a given interface name. It wasn't
working for me as it assumed request_irq() was called with a device name. It's
not a case for all drivers.

I also found some other people looking for a proper solution for that:
https://unix.stackexchange.com/questions/275075/programmatically-determine-the-irqs-associated-with-a-network-interface
https://stackoverflow.com/questions/7516984/retrieving-irq-number-of-a-nic

Let me know if this solution makes sense. I can say it works for me ;)
---
 Documentation/ABI/testing/sysfs-class-net |  7 +++++++
 net/core/net-sysfs.c                      | 16 ++++++++++++++++
 2 files changed, 23 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-class-net b/Documentation/ABI/testing/sysfs-class-net
index 664a8f6a634f..33440fe77ca7 100644
--- a/Documentation/ABI/testing/sysfs-class-net
+++ b/Documentation/ABI/testing/sysfs-class-net
@@ -301,3 +301,10 @@ Contact:	netdev@vger.kernel.org
 Description:
 		32-bit unsigned integer counting the number of times the link has
 		been down
+
+What:		/sys/class/net/<iface>/irq
+Date:		April 2019
+KernelVersion:	5.2
+Contact:	netdev@vger.kernel.org
+Description:
+		IRQ number used by device
diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index e4fd68389d6f..a3eb7c3f1f37 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -512,6 +512,21 @@ static ssize_t phys_switch_id_show(struct device *dev,
 }
 static DEVICE_ATTR_RO(phys_switch_id);
 
+static ssize_t irq_show(struct device *dev, struct device_attribute *attr,
+			char *buf)
+{
+	const struct net_device *netdev = to_net_dev(dev);
+	ssize_t ret;
+
+	if (!rtnl_trylock())
+		return restart_syscall();
+	ret = sprintf(buf, "%d\n", netdev->irq);
+	rtnl_unlock();
+
+	return ret;
+}
+static DEVICE_ATTR_RO(irq);
+
 static struct attribute *net_class_attrs[] __ro_after_init = {
 	&dev_attr_netdev_group.attr,
 	&dev_attr_type.attr,
@@ -542,6 +557,7 @@ static struct attribute *net_class_attrs[] __ro_after_init = {
 	&dev_attr_proto_down.attr,
 	&dev_attr_carrier_up_count.attr,
 	&dev_attr_carrier_down_count.attr,
+	&dev_attr_irq.attr,
 	NULL,
 };
 ATTRIBUTE_GROUPS(net_class);
-- 
2.21.0