[PATCH] node_device: Use "udev" monitor source

[Daniel P. Berrangé]

On Tue, Nov 17, 2020 at 02:29:27PM +0100, Michal Privoznik wrote:
> On 11/17/20 1:51 PM, Daniel P. Berrangé wrote:
> > On Tue, Nov 17, 2020 at 01:29:47PM +0100, Michal Privoznik wrote:
> > > In v6.3.0-rc1~67 I've made a switch: instead of listening on udev
> > > events the nodedev driver started listening for kernel events.
> > > This was because when a device changes its name (e.g. NICs) we
> > > will get "move" event with DEVPATH_OLD property set, which we can
> > > then use to remove the old device and thus keep our internal list
> > > up to date. The switch to "kernel" source was made because if the
> > > old NICs naming (eth0, eth1, ...) is enabled (e.g. via
> > > net.ifnames=0 on the kernel cmd line) then udev overwrites the
> > > property with the new name making our internal list go out of
> > > sync. Interestingly, when the od NICs naming is not enabled then
> > > the DEVPATH_OLD contains the correct value.
> > 
> > I don't see any difference in properties regardless of net.ifnames
> > is 0 or 1. In both cases, there is DEVPATH + DEVPAT_OLD, and
> > INTERFACE has the new NIC name.  Can you actually reproduce the
> > original problem with net.ifnames=0 ?  If so, which distro ?
> 
> Have you tried renaming back and forth? for instance:
> 
> # ip link set tunl0 name tunl1
> # ip link set tunl1 name tunl0
> 
> 
> The "kernel" source yields:
> 
> KERNEL[778387.296879] move     /devices/virtual/net/tunl1 (net)
> ACTION=move
> DEVPATH=/devices/virtual/net/tunl1
> DEVPATH_OLD=/devices/virtual/net/tunl0
> IFINDEX=5
> INTERFACE=tunl1
> SEQNUM=20701
> SUBSYSTEM=net
> 
> KERNEL[778400.944769] move     /devices/virtual/net/tunl0 (net)
> ACTION=move
> DEVPATH=/devices/virtual/net/tunl0
> DEVPATH_OLD=/devices/virtual/net/tunl1
> IFINDEX=5
> INTERFACE=tunl0
> SEQNUM=20702
> SUBSYSTEM=net
> 
> 
> But "udev" gets:
> 
> UDEV  [778387.297247] move     /devices/virtual/net/tunl1 (net)
> ACTION=move
> DEVPATH=/devices/virtual/net/tunl1
> DEVPATH_OLD=/devices/virtual/net/tunl0
> IFINDEX=5
> INTERFACE=tunl1
> SEQNUM=20701
> SUBSYSTEM=net
> USEC_INITIALIZED=5901449841
> net.ifnames=0
> 
> UDEV  [778400.945195] move     /devices/virtual/net/tunl1 (net)
> ACTION=move
> DEVPATH=/devices/virtual/net/tunl1
> DEVPATH_OLD=/devices/virtual/net/tunl1
> IFINDEX=5
> INTERFACE=tunl1
> SEQNUM=20702
> SUBSYSTEM=net
> USEC_INITIALIZED=5901449841
> net.ifnames=0
>
> 
> In both cases the first rename (tunl0 -> tunl1) gets correct DEVPATH_OLD,
> but the second rename is problematic (tunl1 -> tunl0) and only "kernel" gets
> it right.

Hmm, this simply smells like a bug we should report to udev. It makes
no sense that the event is correct for the first rename, and then wrong
for the subsequent rename.


Regards,
Daniel
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