macvtap.patch

Workaround for macvtap bug where associated tap device is created on host as
/dev/tap<ifindex> with ifindex coming from container namespace, causing clashes
with existing host interfaces and/or tap devices.

Manifests as:

[123733.628877] ------------[ cut here ]------------
[123733.628884] WARNING: CPU: 3 PID: 13569 at fs/sysfs/dir.c:31 sysfs_warn_dup+0x63/0x80()
[123733.628886] sysfs: cannot create duplicate filename '/class/macvtap/tap2'

The workaround creates the associated tap device as /dev/<name> where name is
the interface name specified at macvtap creation time.

Patch is against latest LTS kernel (4.1.13)

WARNING WARNING WARNING

This is only a tentative workaround and may have unexpected consequences. The
impact of creating a macvtap interface with the same name as an existing device
is unknown. I tried e.g. 'sdb' and nothing bad happened, as in existing
/dev/sdb did not get trashed.

Use at your own risk!

WARNING WARNING WARNING

Author: Martin Lucina <mato@unikernel.com>

--- a/drivers/net/macvtap.c	2015-11-12 12:32:14.094900977 +0100
+++ b/drivers/net/macvtap.c	2015-11-12 10:51:01.196721284 +0100
@@ -1198,7 +1198,7 @@
 
 		devt = MKDEV(MAJOR(macvtap_major), vlan->minor);
 		classdev = device_create(macvtap_class, &dev->dev, devt,
-					 dev, "tap%d", dev->ifindex);
+					 dev, dev->name);
 		if (IS_ERR(classdev)) {
 			macvtap_free_minor(vlan);
 			return notifier_from_errno(PTR_ERR(classdev));