[PATCH 1/2] node_device_udev: handle move events

Michal Privoznik mprivozn at redhat.com
Mon Apr 20 10:11:24 UTC 2020

On 4/18/20 3:25 PM, Martin Kletzander wrote:
> On Thu, Apr 16, 2020 at 11:57:45AM -0400, Mark Asselstine wrote:
>> It is possible and common to rename some devices, this is especially
>> true for ethernet devices such as veth pairs.
>> In the udevEventHandleThread() we will be notified of this change but
>> currently we only process "add", "change" and "remove"
>> events. Renaming a device such as above results in a "move" event, not
>> a "remove" followed by and "add" or vise versa. This change will add
>> the new/destination device to our records but unfortunately there is
>> no usable mechanism to identify the old/source device to remove it
>> from the records. So this is admittedly only a partial fix.
> There is, but it is only internal.  We should ask for the function
> `udev_device_get_devpath_old()` to be publicized, if possible.  That 
> should give
> us the old name.

I know we talked about this during weekend and I've found a way. I will 
post the patches once these are merged.

> When I checked this using `udevadm monitor --property` I got two events 
> for each
> rename, one kernel event (where the old path pointed to the previous 
> name) and
> one udev event where the old path referred to the original name the 
> device was
> created with.
> For example when I created a virtual network device with the name 
> "fdsa", then
> renamed it bunch of times, started udev monitoring and then renamed it from
> "first" to "second" this was the output of udevadm for that one 
> particular rename:
> monitor will print the received events for:
> UDEV - the event which udev sends out after rule processing
> KERNEL - the kernel uevent
> KERNEL[36343.246068] move     /devices/virtual/net/second (net)
> ACTION=move
> DEVPATH=/devices/virtual/net/second
> DEVPATH_OLD=/devices/virtual/net/first
> INTERFACE=second
> SEQNUM=4609
> UDEV  [36343.246785] move     /devices/virtual/net/fdsa (net)
> ACTION=move
> DEVPATH=/devices/virtual/net/fdsa
> DEVPATH_OLD=/devices/virtual/net/first
> SEQNUM=4609

Problem is, UDEV doesn't update INTERFACE (which is where libvirt gets 
the ifname from) when net.ifnames is present. This then leads to all 
kinds of subsequent troubles like inability to query the interface 
address, etc.  But if we'd use KERNEL as the source then we would see 
updated ifnames.

Reviewed-by: Michal Privoznik <mprivozn at redhat.com>


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